Call set-up process

The arrangement disclosed allows a user of a mobile telephone 11 to use intelligent network (IN) services specific to his home network, regardless of whether the network 12, 13, 14 to which he is currently connected can support the service. When the user makes an outgoing call attempt (step 1) the associated signalling is transmitted over a signalling channel. The mobile switching centre (MSC) 13 recognises a customer identity (encoded electronically in the call set-up signals ) and accesses the data relating to the user which is stored in a register 14. The data in the register 14 relating to the user 11 includes a marking identifying him as an IN served customer, causing the MSC 13 to halt the call process and send a signal (2), protocol, to the service control point (SCP) 15 in the user's home network. The SCP 15 then activates the user's service profile and as part of that profile recognises the need to retrieve additional information from the user 11, e.g. a PIN (personal identity number) or some other information. Having identified the information needed, the SCP initiates a message 3 to the mobile station, for example requesting an authorisation code, which is passed back to the MS 11 by way of the switching centre MSC 13 and base station BSS 12, using a signalling protocol. The user, having received the message 3, responds such that the mobile station 11 sends a second signal 4 by way of the host network back to the SCP 15. The SCP 15 acts on the message received and returns a response 5 to the MSC 13, whereby the MSC 13 will then act on that information for example to set up a call, including a full speech channel if required (6). This system allows data to be transmitted directly between the SCP 15 and the user 11, the host network not requiring to be compatible with the signalling protocols except for the initial and final states 1, 5. Moreover, since signalling channels are used, traffic (speech) channels, which have a larger bandwidth, are not used unless and until the call set-up process is completed.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to telecommunications systems. It is of particular
 application to the digital cellular radio system known as GSM (Global
 System for Mobile Communications) but is not limited thereto. The
 invention is concerned with improving the accessibility of advanced
 telecommunications services.
 2. Related Art
 Intelligent networks (IN) have been conceived and developed in order to
 allow advanced and versatile telecommunications services to be supplied
 over conventional telephone networks. Some of these services require users
 to carry out transactions, using their telephones, in addition to the
 conditional call set-up transaction, and others require modification of
 the conventional call set-up transaction. Such services include the
 routing of calls under centralised control, according to factors such as
 call diversions set up by the called party, number translation services
 (e.g. to allow connection to different local service providers using the
 same number from any point within a wide area, by routing the call
 differently according to the origin of the call) and many other
 facilities, or to allow the use of special-tariff dialling codes (free,
 local rate, or premium). Some services require the user to enter
 information, subsequent to initiating a transaction. For example certain
 premium rate services require a special user identification number
 (usually known as a PIN--Personal Identification Number) to be transmitted
 in order to allow access to the service. This prevents personnel who have
 access to the telephone from making unauthorised transactions, for example
 international calls, or calls to premium rate services, whilst still
 allowing them unhindered access for other categories of transaction such
 as local or emergency calls.
 Intelligent networks have been conceived and developed largely on the basis
 of an analogue Public Switched Telephone Network (PSTN), i.e. the
 conventional fixed telephone network. For services which require the user
 to enter information, subsequent to initiating the transaction, a special
 resource has to be switched into the connection to play a voice menu,
 receive DTMF tones, etc. In other words, an analogue-based exchange of
 information is passed between the user and the special Intelligent Network
 resource. In general terms the special resource then translates this into
 a digital signalling message to send to a intelligent network service
 control system for processing information on the system, such as
 authorising or barring the transaction attempt.
 The digital cellular radio system GSM has started to develop and introduce
 a comparable IN development under a service description known by the
 acronym CAMEL (Customer Applications for Mobile Enhanced Logic). In
 existing proposals for this intelligent Network development, standard
 analogue collection of information is required in order to control service
 requests etc. For example, if a mobile station transmits a short-code
 number using e.g. DTMF tones, the switching centre recognises this as a
 request for an IN service and transmits this code, together with the
 mobile station's user identity, to a service controller which identifies
 the line to which the transaction relates (which may depend on the user
 code), and routes the transaction appropriately (or fails the transaction
 if the user is not authorised to use the code). This raises a particular
 difficulty in that in a cellular system a full speech channel is not
 normally allocated until a call is ultimately set up. Call set-up is
 carried out using a narrow-bandwidth signalling channel. This avoids
 allocation of a speech channel to a call attempt which is not going to
 succeed.
 In the present specification, he term `signalling connection` is used to
 identify such narrow-bandwidth channels used for call set-up, et., as
 distinct from traffic channels.
 In order that the voice menu, DTMF tones, etc. can be transmitted using the
 `CAMEL` system, a speech channel is required. It is inconvenient to have
 such channels used for service requests which will not result in a
 requirement for a speech channel, (e.g. if the transaction is going to
 fail because the correct authorisation code is not sent).
 Moreover, when the mobile station is not operating on its home network, it
 requires that the current ("host") network can handle the IN service
 required. This may not be possible as different networks have different
 capabilities, or may use different signalling protocols, for example using
 the same short code to signify different services.
 The GSM system also has a capability known as the Unstructured
 Supplementary Service Data (USSD) capability. This service was introduced
 to allow supplementary service control between a terminal and its home
 network. This capability provides transmission of a "packet" of data
 between the terminal and the home network and vice versa, to enable
 operators to introduce their own special service offerings, allowing users
 to operate these special services even when not operating on their home
 network. This capability allows such services to be introduced without the
 need to modify the mobile station, provided the user is informed of the
 sequence of keystrokes required to perform it. The system can return codes
 which the mobile station will recognise, e.g. error code `10` may cause
 the mobile station to display an appropriate message in a language
 selected according to the initial programming of the mobile station.
 The USSD capability allows the transmission of data direct between the
 mobile station and the service control system, without any interaction of
 the switching centre. This is of particular advantage in the context of
 "roaming", wherein the mobile station operates with a switch belonging to
 an operator other than its home network. When a terminal is `roaming` the
 switch may only be compatible with the terminal to the extend required by
 the standardisation implicit in the GSM standard, and therefore services
 specific to the user's "home" network are not necessarily supported by the
 switch to which the user is currently connected.
 It has not so far been possible within the standard GSM protocols to
 associate the sending of such message packets with a call, to manage
 specific call-related services in real time. USSD has only been used to
 update more static customer data, such as setting up a call-forward
 arrangement representing advice of the user's own telephone number, etc.
 SUMMARY OF THE INVENTION
 According to the invention there is provided a method initiating a
 telecommunications transaction, the method comprising the steps of;
 setting up a low-bandwidth initial signalling path interconnecting a
 terminal, a switching centre, and a service control system;
 transmitting an initial signal from the terminal to the switching centre
 over the initial signalling path,
 transmitting, over the initial signalling path, a first, transaction
 request, signal from the switching centre to the service control system,
 according to a first signalling protocol;
 transmitting, over the initial signalling path, a second signal from the
 service control system to the terminal according to a signalling protocol
 different from the first signalling protocol,
 transmitting, over the initial signalling path a third signal, in reply to
 the second signal, from the terminal to the service control system, also
 according to a signalling protocol different from the first signalling
 protocol,
 in response to the third signal, generating a fourth, transaction control,
 signal for transmission from the service control system to the switching
 centre to control the transaction.
 According to a further aspect of the invention there is provided a service
 control system for a telecommunications network, the service control
 system comprising:
 means for receiving a first, transaction request, signal according to a
 first signalling protocol, the transaction request relating to a specified
 terminal,
 transmitting means for transmitting a second signal to the specified
 terminal in relation to which the transaction request is received, the
 second signal being according to a signalling protocol other than the
 first signalling protocol;
 means for receiving from the said terminal a third signal in response to
 the transmitted second signal, the third signal being according to a
 signalling protocol other tan the first signalling protocol;
 processing means for processing the third signal to generate an instruction
 to initiate the required transaction; and
 means controlled by the processing means for transmitting a fourth,
 transaction control, signal to a switching means of the telecommunications
 system instructing the switching means to initiate the transaction to be
 performed,
 the signalling protocols used for the first, second, third and fourth
 signals all being suitable for carrying over a low bandwidth initial
 signalling path.
 By use of this invention, authorisation and any other transaction-related
 messages can be transmitted directly between the terminal and the user's
 home network by way of the current "host" switch, without any data
 processing by the host switch, between establishment of a high-bandwidth
 full speech channel. The invention avoids the setting up of a high
 bandwidth connection until it is determined that such a connection is
 required for the transaction to be performed. It should be noted that the
 transaction to be performed may differ from that requested, for example if
 a transaction is requested which is barred to the user making the request.
 The service control system may, in response to the third signal, perform
 the steps of:
 determining whether the transaction to be performed requires a high
 bandwidth communications path,
 providing such a high bandwidth path only if so required, and
 initiating the transaction to be performed, the transaction using said high
 bandwidth path if provided, and using said initial signalling path if no
 high bandwidth communications path is provided. Accordingly, a speech
 channel need not be set up by the host switch unless the service control
 centre in the user's "home" network determines tat such a speech channel
 is required to support the service requested. For example, even if the
 requested transaction requires a speech channel, the intelligent network
 capability does not allocate a speech channel unless the transaction which
 is in fact to be performed also requires a speech channel.
 Services can also be requested which do not require speech channels at all,
 such as location information, for example to indicate to the user the cost
 of the current call, which depends on the tariff currently applicable to
 him (which is set by the home system, not the current `host` network, but
 may also depend on the user's present location).
 It is convenient for the second and third signals to use the same
 signalling protocol. In the preferred embodiment this protocol is the USSD
 protocol discussed above.
 It is also convenient for the fourth signal to use the same, first,
 signalling protocol sued by the initial transaction request signal. In the
 preferred embodiment this first signalling protocol may be the INAP
 (Intelligent Network Application Part).
 In the preferred embodiment to be described, the system is a cellular radio
 system, specifically according to the GSM standard. However, the system is
 applicable to other telecommunications networks, whether mobile or fixed.
 The third signal, transmitted form the switching centre to the service
 control system, may include any information necessary for setting up the
 service. This may include the identity of the terminal setting up the
 transaction, an authorisation code (entered manually by the user or
 automatically, in response to a prompt from the service control system),
 the location of the terminal, (for example an indication of the base
 station currently servicing the mobile station), and any other information
 necessary to support the required service. The location information may be
 retransmitted to the terminal as part of the exchange of the information.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
 A mobile station (MS) 11 is in radio communication with a base station
 system (BSS) 12 forming part of the fixed part of a mobile radio system.
 The base station is none of several connected to a mobile switching centre
 (MSC) 13. The switching centre 13 controls the routing of calls to and
 from mobile stations 11 by way of the base stations 12, transferring the
 fixed end of the communication link with the mobile station 11 from one
 base station 12 to another as the mobile station 11 moves. Whilst the
 mobile station 11 is connected to the switching centre 13 through one of
 its associated base stations 12, the switching centre has details of the
 user stored in an associated database known as the Visitor Location
 Register (VLR) 14. On report of a handover to a base station controlled by
 another switching centre, this record is deleted, having been added to the
 VLR associated with the new switching centre. The switching centre MSC 13
 is also in communications with an Intelligent Network Service Control
 Point (SCP) 15, which is part of the home network of the user of the
 mobile station (MS) 11. The base station BSS 12 plays no part in the
 signal processing. It is the interface between the fixed (12-15) and
 mobile 11 parts of the network, and its primary function is as a radio
 transceiver.
 The steps in the process are as follows.
 When the user of the mobile unit 11 makes an outgoing call attempt, the
 associated signalling is transmitted over a signalling channel (step 1).
 The MSC 13 recognises a customer identity (encoded electronically in the
 call set-up signals) and accesses the data relating to the user and stored
 in the VLR 14. The data in the VLR 14 relating to the user 11 includes a
 flag identifying him as an IN served customer, i.e. this is part of his
 overall service support, entered and agreed with the mobile service
 provider when the user initially takes out a contract with the mobile
 service provider. The user having been recognised as an IN user, the MSC
 13 halts the call process (as per standard CAMEL procedure) and sends an
 initial detection point message (2), according the INAP (Intelligent
 Network Application Part) protocol, to the service control point SCP 15.
 The SCP 15 then activates the user's service profile and as part of that
 profile recognises the need to retrieve additional information from the
 user 11, e.g. a PIN (personal identity number) or some other information.
 Having identified the information needed, the SCP initiates a message 3 to
 the mobile station, for example requesting an authorisation code, which is
 passed back to the MS 11 by way of the switching centre MSC 13 and base
 station BSS 12, using the USSD protocols, over the signalling channel. The
 MSC 11, having received the USSD message 3, may display the contents e.g.
 on a visual display or as an audible message. The user may then enter any
 information requested, such as the requested authorisation code, and the
 mobile station 11 sends a second USSD message 4, containing this
 information by way of the BSS 12 and MSC 13, back to the SCP 15. The SCP
 15 acts on the message received and returns the standard INAP response 5
 to the MSC 13, whereupon the MSC 13 will act on that information for
 example to set up a call, including a full speech channel if required (6).
 This system has a number of advantages. Firstly, all of the transactions
 involved in retrieving information between the MS 11 and the SCP 15 are
 passed in associated signalling links so there is not need for the
 time-consuming and difficult process of instructing the switching centre
 MSC 13 to insert special resources. Another benefit for the mobile system
 is that by the use of USSD a signalling channel can be used, instead of a
 traffic (speech) channel. A traffic channel requires eight times as much
 air interface capacity as a signalling channel. The use of a signalling
 channel is therefore a much more efficient usage of the spectrum capacity.
 The use of this approach means that operator-specific services can be
 implemented and presented to users in a simple way. As an example it is
 possible for the SCP 15 to generate a simple menu display and encapsulate
 a signal in USSD to have that menu displayed to the user, making data
 entry by the user simple and straightforward. The system only requires IN
 compatibility between the user equipment (MS) 11 and the service control
 point SCP 15, which is part of the user's `home` system (the one to which
 he pays his subscription). The user can be connected through an MSC 13 of
 a system other than his home system (a process known as "roaming") whether
 or not the other system supports the same service to its own subscribers.
 The USSD data collection process required by the "CAMEL" capability of GSM
 is completely independent of the initial call set-up 1 and response 5 from
 the SCP, so the present embodiment is fully compatible with this
 capability, and there are no additional developments needed of these
 capabilities.
 Enhancements of the invention allow for the SCP 15 to "notify" the terminal
 of an event recognised within the SCP 15. An example of tis could be a
 service wherein the SCP 15 recognises whether the user 11 is making a
 transaction in an area that is part of the local call zone, and if it is
 not in that zone a message is delivered to the terminal displaying that
 the transaction is not at cheap rate. Other service examples are possible,
 e.g. an indication of current credit available to the user in a pre-paid
 service option.
 A second enhancement makes it possible for the USSD message to be used to
 retrieve data from the user's terminal 11 at the request of the SCP 15. A
 service example of this could be the retrieval of a pre-stored PIN. This
 simplifies services for the user, allowing the user to avoid entry of data
 for service action.