APPARATUS AND METHOD FOR CALLBACK IN A MOBILE COMMUNICATION SYSTEM
Background of the Invention
This invention relates to mobile communications, and more
specifically but not exclusively to apparatus for and methods of establishing
circuit connections in a mobile communications system such as a GSM
(Global System for Mobile Communications) digital cellular radio network.
If a subscriber is outside his home network and is roaming in a visited
(foreign) network, any call initiated by the subscriber from his mobile station
is established from the visited network. International call rates charged by a
visited network for a call made to a party in the home network can be
considerably higher than that charged by the home network for a call to the
roaming subscriber established from fhe home network. It would be desirable
to provide apparatus and methods enabling, inter alia, cheaper call rates for
roaming subscribers.
In the field of telecommunications, callback methods for setting up
calls in a reverse direction are known, for example from US-A-5438616 and
US-A-5710809.
US-A-5438616 describes a fixed line telephone system comprising a
first and a second party interconnected via a controller. Initially, a first
connection is established between the first party and the controller by the first
party placing a telephone call to a telephone number associated with the
controller. Once this connection is established, the controller receives and
stores a first callback telephone number and a second callback telephone
number as provided by the first party. Then the first connection is torn down
by initiating conventional hang-up procedures. A second connection is re¬
established between the first party and the controller by operation of the
controller to initiate a telephone call to the first callback telephone number.
Then, a third connection is established between the second party and the
controller by operation of the controller to initiate a telephone call to the
second callback telephone number. Finally, the first party and the second
party are bridged to allow conversation by coupling the second connection to
the third connection.
US-A-5710809 describes a fixed line telecommunications system
comprising a telecommunications node local to a calling location, a central
switching unit associated with a called location, a conventional voice network
and a data signalling channel external to the voice network linking the
telecommunications node with the switching unit. A call from the calling
location is received by the telecommunications node which transmits caller
and called party identifications via the data signalling channel to the switching
unit. The switching unit interrogates the called location by initiating a first
call to the called location and, on answer from the called location, initiates a
second phone call to the calling location via the voice network and the
telecommunications node. Thereupon, the first and second calls are
teleconferenced.
j
These, and other known callback methods, require the calling party to
initiate a callback using a call to a network node, whether it is local or distant,
which alone or in cooperation with other network nodes arranges the callback.
Summary of the Invention
According to one aspect of the present invention, there is provided
network-side apparatus for use in a mobile communications network, the
apparatus comprising: means for receiving a callback request signal originated
from a mobile station using a non-circuit-related data transfer mechanism, and
calling means for establishing a first circuit connection with the mobile station
in response to the callback request signal.
According to another aspect of the present invention, there is provided
a method of establishing a circuit connection between network-side apparatus
in a mobile communications network and a mobile station, the method
comprising: receiving a callback request signal originated from the mobile
station using a non-circuit-related data transfer mechanism; and arranging a
circuit connection from the apparatus to the mobile station in response to
receipt of the callback request signal.
The use of a non-circuit-related data transfer mechanism has various
advantages not available with the prior art methods, in which a voice call must
be placed in order to initiate a callback request.
The procedure for setting up a call may be more convenient and
familiar to the user than that using a voice call for the callback request, since
the user may compose the message using only keyboard and graphical display
interactions, similar to the more familiar forward direction call set up
procedure, instead of participating in a preliminary call. The request may for
example be generated by interaction with a menu facility on a display of the
mobile station.
Furthermore, as the cost to the user, in particular when being served in
a visited network, of the transmission from the mobile station of signals using
a non-circuit-related data transfer mechanism is generally less than the cost of
a circuit-based voice or data call for the same purpose, the invention provides
means and methods for call establishment which are not only convenient but
also more cost-effective to the user of the mobile station than prior art
methods.
According to another aspect of the invention, there is provided a
mobile station comprising: means for recognising a predetermined command
entered by a user as a callback request command and for generating a callback
request in response thereto; means for transmitting the generated callback
request using a non-circuit-related data transfer mechanism; and means for
receiving a circuit connection establishment request signal following
transmission of the callback request.
This aspect of the invention is intended to provide further convenience
to the user in using the callback service of the present invention, insofar as the
mobile station is adapted to format information provided by the user as a
recognisable callback request when transmitted, without the need for the user
to memorise or utilise the required message format.
Brief Description of the Drawings
Embodiments of the present invention will now be described, by way
of example only, with reference to the accompanying drawings, in which:
Figure 1 is a block diagram of a mobile communications network
arranged in accordance with first and second embodiments of the invention:
Figure 2 illustrates a sendee node arranged in accordance with the first
and second embodiments of the invention;
Figure 3 is a flow diagram illustrating steps carried out by the service
node of Figure 2;
Figure 4 is a block diagram illustrating how USSD messages are
handled in a first embodiment of the invention;
Figure 5 is a block diagram illustrating the operation of the first
embodiment of the invention; and
Figure 6 is a block diagram illustrating the operation of the network in
accordance with the second embodiment of the invention.
Detailed Description of the Drawings
Referring first to Figure 1, a Mobile Switching Centre (MSC) 2 is
connected via communication links to a number of Base Station Controllers
(BSCs) 4. The BSCs 4 are dispersed geographically across areas served by
the Mobile Switching Centre 2. Each BSC 4 controls one or more Base
Transceiver Stations (BTSs) 6 located remote from, and connected by further
communication links to, the BSC 4. Each BTS 6 transmits radio signals to.
and receives signals from, mobile stations 8 which are in an area served by
that BTS 6. The area is referred to as a "cell". A GSM network is provided
with a large number of such cells, which are ideally contiguous to provide
continuous coverage over the whole network territory.
A Mobile Switching Centre 2 is also connected via communication
links to other mobile switching centres in the remainder of the mobile
communications system 10, which includes other GSM networks, in particular
GSM networks (having configurations similar to that illustrated) in other
territories having roaming agreements with the illustrated network, and to a
Public Service Telephone Network (PSTN), which is not illustrated. The
Mobile Switching Centre 2 is provided with a Home Location Register (HLR)
12 which is a database storing subscriber data including the International
Mobile Subscriber Identity (IMSI) which is unique to each mobile station 8.
The IMSI is also stored in the mobile station in a removable data store,
referred to as a Subscriber Identity Module (SIM), along with other
subscriber-specific information.
The Mobile Switching Centre 2 is also provided with a Nisitor
Location Register (NLR) 14 which is a database temporarily storing
subscriber data for mobile stations which are active in the area served by the
Mobile Switching Centre 2.
The network additionally comprises a Service Node 24 which is
connected, in a manner to be detailed below, to the MSC 2, the HLR 12 and a
Short Message Service Centre (SMSC 18).
The storing and forwarding of SMS messages in the network is
managed by a Short Message Service Centre (SMSC) 18. The SMSC 18
connected to MSC 2 is used in the second embodiment of the invention, and is
directly or indirectly connected to the service node 24. The transmission of
SMS messages from the MSC 2 to the service node 24 is relayed by the
SMSC 18. Figure 2 shows a schematic block diagram of the service node 24,
incorporating the first and second embodiments of the invention. The service
node 24 comprises a USSD Handler 71 and a Short Message Handler 72 for
receiving USSD and SMS messages, respectively. The service node 24 also
comprises a switch matrix 73. The switch matrix 73 terminates a large
number of voice circuits 74 and is capable of accepting incoming voice calls,
generating outgoing voice calls and cross-connecting different circuits. It is
also capable of connecting voice calls to an Interactive Voice Response Unit
(IVRU) 75. The IVRU 75, in turn, is capable of accepting DTMF signalling
and playing recorded announcements, to conduct interactions with service
users.
The USSD Handler 71, the Short Message Handler 72, the switch
matrix 73 and the IVRU 75 each are connected to a Service Node Control
Processor (SNCP) 76. The SNCP 76 is responsible for the processing service
logic for supported services, the control of signalling and other interfaces, and
the control of the Switch Matrix 73. The SNCP 76 illustrated is interfaced
with a database 77 which contains on-board subscriber and service data.
Alternatively, the SNCP 76 may also use the services of an external Service
Data Function.
In addition, the service node 24 also includes external interfaces 78, 79
for SS7 signalling, and Administration, Maintenance and Provisioning
(OAM&P). respectively.
The operation of the service node 24 is now described in connection
with the flow diagram of Figure 3.
At step 80, a callback request is received by either USSD Handler 71
or Short Message Handler 72. A callback request received by either of these
interfaces is passed to the appropriate application in the SNCP 76.
At step 81 , the SNCP 76 initiates a first outgoing call to the requesting
subscriber using an available port of the Switch Matrix 73.
At step 82, the SNCP 76 determines whether an identifiable recipient
exists. If no such recipient identification has been received then the SNCP 76,
at step 83, determines the required service through use of the IVRU 75. This
is achieved by connecting the voice circuit supporting a successful outgoing
call to the subscriber to a port of the IVRU 75, instructing the IVRU 75 to
play appropriate announcements, and gathering and interpreting the
subscriber's responses, which may be voiced and/or DTMF tones.
At step 84, the SNCP 76 determines whether the received service
request is a third party call request or a request for a network service provided
in the home network. In the latter case, the SNCP initiates a second outgoing
call to the required service administration interface at step 85. If the service
request is a third party call request, the SNCP 76 initiates a second outgoing
call to the required third party number at step 86, using an available port of
the switch matrix 73. On successful establishment of the second outgoing call
the SNCP 76 instructs the switch matrix 73 at step 87 to bridge the two
associated call legs together, allowing two way communication between the
subscriber and their chosen service or third party.
In the first embodiment of the invention, the GSM Unstructured
Supplementary Service Data (USSD) data transfer mechanism is used. The
USSD data transfer mechanism is defined in, wter alia, the GSM Technical
Specifications 02.90, 03.90 and 04.90 (published by the European
Telecommunications Standards Institute). The USSD data transfer
mechanism allows mobile subscribers to transmit user specified data to a
network entity on the basis of unstructured message protocols. For example, a
mobile station can transmit text messages generated by the user via the
station's man-machine interface (MMI) to a network entity to be processed by
an associated application.
The USSD signalling between the network and the mobile station is
performed in a transparent way, i.e. no review or manipulation of the user-
specified contents of the USSD request is performed during transmission
other than in the HLR application module. Using the USSD data transfer
mechanism, a mobile station can communicate with a network entity without
establishing a circuit connection and without requiring a dedicated two-way
transmission channel. Rather, the signalling is performed through a non-
circuit-related data transfer mechanism between the mobile station and the
network, using a Stand-alone Dedicated Control Channel (SDCCH) in the
radio interface.
According to the first embodiment of the invention, a subscriber who
uses his mobile station in a roamed-to network, referred to in GSM as a
Visited Public Land Mobile Network (VPLMN), can transmit a specially
formatted USSD message from his mobile station to the subscriber's home
network, referred to in GSM as the Home Public Land Mobile Network
(HPLMN). This has the effect of initiating a first call from the HPLMN to the
subscriber's mobile station, a second call from the HPLMN to a recipient
party the subscriber wishes to call, and the first and second calls to be bridged.
Figure 4 illustrates how a USSD message originated by a mobile
station 8a roaming in a VPLM is handled in accordance with this
embodiment. The message is first passed to the serving MSC 21 in the
VPLMN, on to the VLR 22 associated with that MSC, and via inter-network
links, to the subscriber's home HLR 12. The HLR passes the message to the
callback service node 24 in the HPLMN. Each of the illustrated entities, i.e.
mobile station 8a, MSC 21, VLR 22, HLR 12, and service node 24 comprises
a USSD handler 25 to 29, respectively. Mobile station 8a comprises a Man-
Machine Interface (MMI) 30 which allows the user to enter a USSD message
into MS 8a. MMI 30 in turn is linked with the station's USSD handler 25.
Each of MSC 21, VLR 22 and HLR 12 comprises an application
module 31 to 33, respectively. The application modules 31 to 33 in turn are
linked with USSD handlers 26, 27 and 28, respectively. The USSD handlers
examine a received USSD message to determine whether the message should
be processed locally, or passed on to the next USSD handler in the chain, as
defined in GSM Technical Specification 03.90, section 6. The application
modules 31 to 33 are provided for processing a USSD message locally in the
respective network entity. The location, nature and content of the USSD
application modules is determined by the service provider and/or network
operator.
The operation of the first embodiment is now described in connection
with Figure 5.
If the subscriber using mobile station 8a wishes to initiate a call in
accordance with the first embodiment, he first activates his mobile station 8a,
and enters an alphanumeric character string, having a predetermined callback
request format, by using the keys of mobile station 8a and instructs the
transmission thereof to the serving network. Alternatively, the mobile station
may be adapted such that a correctly formatted USSD message can be created
and sent by means of a dedicated callback menu facility on the mobile station.
For example, the SIM of the mobile station 8a may be provided with a
prestored application program (e.g. a SIM Application Toolkit program, see
GSM Technical Specification 11.14) which is arranged to instruct the mobile
station to provide one or more selectable menu options (e.g. "Voicemail
Callback", "Third Party Callback", etc.), to allow user interaction in a selected
menu option and to create and instruct the mobile station 8a to transmit a
USSD message which is correctly formatted in the predetermined callback
request format. The user would thus select from menu options which are
represented graphically on the display of the mobile station (e.g. "Third Party
Callback"). The user may then be prompted to select from further menu
options a desired prestored third party telephone number, or to enter the third
party telephone number by using the keyboard of mobile station 8a. The
mobile station would then convert the entered information into the
predetermined callback request format before transmission as a USSD
message.
The USSD message also contains the actual user data, e.g. the
alphanumeric character string input by the user. The user data includes a
predetermined character set and is arranged in a defined callback message
format (for example including a predetermined character set in a
predetermined part of the message) indicating that the message is to be passed
to the service node 24. It also includes the Mobile Station International
Directory Number (MSISDN, often referred to simply as the "directory
number"). The MSISDN is included because the MSISDN is required to
enable the home network to establish a return call to the calling subscriber in
the visited network. Alternatively, the MSISDN may be omitted since an
appropriate MSISDN may be retrieved, with reference to the IMSI of the
subscriber (which is generally included in the USSD signalling) of the
subscriber, from the home HLR 12 by or on behalf of the service node 24.
The user data may include data identifying the required service. This
may identify a network service to be administered, in which case a service
code unique to the service is included, or the establishment of a call to a third
party, in which case the number of the third party to be called is included.
Once the subscriber has entered the required information and the
USSD message has been transmitted from the mobile station 8a, the USSD
message is transmitted via the radio interface and network elements of the
visited network to the serving MSC 21. The MSC 21 then sets up a
transaction to its associated VLR 22 and forwards the USSD request to the
VLR 22 unchanged.
When the VLR 22 receives the USSD request, the VLR 22 checks,
using the IMSI supplied in the USSD request whether the user is not in the
HPLMN, as is the case for the scenario being considered. The VLR 22 then
sets up a transaction to the subscriber's home HLR 12 in the HPLMN and
forwards the USSD request to the HLR 12 unchanged.
The message handler 28 in the HLR 12 passes the request to the
service node 24. Finally, the service node 24 interprets the USSD request and
initiates a call to the calling subscriber (as indicated by arrow 45). Depending
on the content of the request, the service node 24 may also initiate a call to a
recipient requested to be called (as indicated by arrow 47), and bridge the first
and second calls (as indicated at 48). The recipient may be another mobile
station 8b, a fixed line terminal 40 or a further service node 42 of the
HPLMN, such as a voice mail retrieval system. Otherwise, the call may be
handled in the service node 24.
The above transmission steps between the entities of the networks are
transparent, i.e. the USSD messages are forwarded from one entity to another
unchanged. No dedicated traffic channel (TCH) needs to be used. In other
words, USSD messages do not require the end-to-end establishment of a
traffic path. Also, USSD message transmission may take place even if the
mobile station is already in full circuit communication. This aspect may be
used to transmit a connection request to the service node 24 to conference in
further parties to a call.
In the second embodiment of the invention, the Short Message Service
(SMS) data transfer mechanism is employed. The SMS data transfer
mechanism is a data transfer teleservice defined in, inter alia, GSM Technical
Specification 03.40.
The operation of the participating entities in accordance with the
second embodiment is illustrated in connection with Figure 6. Figure 6
illustrates a mobile station 8a, a VPLMN MSC 21, the HPLMN SMSC 18,
and the service node 24 in the mobile station's HPLMN. Similar to the
operation in accordance with the first embodiment, if the subscriber using
mobile station 8a wants to transmit a callback request, he activates his mobile
station 8a, enters an SMS message, having a predetermined callback request
format, by using the keys of mobile station 8a and transmits it to the unique
destination address of the service node 24 in his home network. Alternatively,
the mobile station may be adapted such that a correctly formatted SMS
message can be created and sent by means of a dedicated callback menu
facility on the mobile station. For example, the SIM of the mobile station 8a
may be provided with a stored application program (e.g. a SIM Application
Toolkit program) which is arranged to instruct the mobile station to provide
one or more selectable menu options (e.g. "Voicemail Callback", "Third Party
Callback", etc.), to allow user interaction in a selected menu option and to
create and instruct the mobile station 8a to transmit an SMS message which is
in the predetermined callback request format. The user would thus select
from the menu options on the display of mobile station 8a, as described in
connection with the first embodiment. The mobile station 8a then converts
the entered information into the predetermined callback request format, using
the address of the service node 24 as the destination address of the message,
before transmission.
The SMS message contains the subscriber's MSISDN number, to be
used for the callback, as the originating address. The contained MSISDN is
the subscriber's primary voice MSISDN; alternate line service MSISDNs are
not supported in the current protocol. IF an alternate line service MSISDN is
preferred to be used for the callback, it may be specified in the user data
content. If no MSISDN is included in the user data, the subscriber's primary
MSISDN is used as a default number for the callback.
The user data may include data identifying the required service. This
may identify a network service to be administered, in which case a service
code unique to the service is included, or the establishment of a call to a third
party, in which case the number of the third party to be called is included.
Once the subscriber has entered the required information the SMS
message is transmitted from the mobile station 8a via the radio interface and
network elements of the visited network to the serving MSC 21. The MSC 21
forwards the short message to the home network SMSC 18, which in turn
forwards it to the short message handler of the service node 24. Finally, the
service node 24 parses the callback request, initiates a first outgoing call to the
subscriber's mobile station 8a as indicated by arrow 64, and if appropriate
initiates a second outgoing call to a recipient party to be called as indicated by
arrow 65, and bridges the first and second outgoing calls as indicated at 66.
The recipient may be another mobile station 8b, a fixed line terminal 40 or a
further service node 42 of the HPLMN, such as a voice mail retrieval system.
Otherwise, the call may be handled in the service node 24.
SMS messages do not require the end-to-end establishment of a traffic
path. Also, short message transmission may take place even if the mobile
station is already in full circuit communication. This aspect allows a user to
transmit a connection request to the service node 24 to teleconference in
further parties to a call.
In the present invention, the apparatus (e.g. the service node 24) which
controls the callback function is network-side. The term "network-side" is
intended to refer to components on the network side of the cellular radio
interface between the network and the subscriber equipment. Thus, subscriber
equipment is not network-side.
It should be noted that the present invention is not limited to the
embodiments as described above.
For example, the service node 24 need not be configured to handle
callback requests in the form of both USSD and SMS message, but may
handle only one type of non-circuit-related data transfer mechanism.
The invention is not limited to the non-circuit-related data transfer
mechanisms exemplified (i.e. USSD and SMS). Indeed, the invention is not
limited to the GSM standard but may be used in other systems in which
subscribers may roam from one network to another, and in which mobile-
originated non-circuit-related data transfer mechanisms are available. The
invention is applicable to third generation systems, such as UMTS, in which
other non-circuit-related data transfer mechanisms may be available.
It is envisaged that various other modifications and variations to the
above described embodiments could be made without falling outside the
scope of the invention as determined from the claims.