WO2008087251A1

WO2008087251A1 - Control of connection to a network by a mobile subscription

Info

Publication number: WO2008087251A1
Application number: PCT/FI2008/050009
Authority: WO
Inventors: Lauri Isotalo; Kim Henriksson; Jari Jokela
Original assignee: Elisa Oyj
Priority date: 2007-01-19
Filing date: 2008-01-16
Publication date: 2008-07-24
Also published as: FI20075036A0; FI20075036A; FI121495B

Abstract

The invention is intended to create a technical solution, by means of which it will be possible to reduce the probability of a mobile station being connected to a roaming network (6) while it is in the service area of its home network. According to an embodiment of the invention, this is achieved in such a way that a first value is set for the search period of home-network searches while in the area of a roaming network (6), and a second value smaller than the first value is set for being in a frontier area (5) between a roaming network (6) and the home network (4).

Description

CONTROL OF CONNECTION TO A NETWORK BY A MOBILE SUBSCRIPTION

The invention relates to the control of a mobile subscription's connection to a network.

In particular, the invention relates to the control of the network connection of a mobile subscription in the edge areas of a home network, in which mobile subscription can also be connected to a roaming network, with which the home operator has a roaming agreement, instead of to a home network. Such areas are especially the frontier areas of a country.

For example, in Finland there is an extensive area near the Russian frontier, in which the reception (field strength) of Russian mobile networks is good on the Finnish side of the frontier too. This means that if a mobile station temporarily enters a shadow relative to its home network, the mobile subscription may connect to a Russian mobile network, even on the Finnish side of the frontier. Correspondingly, on the Russian side of the frontier, a mobile subscription can be connected to its home network or to a roaming network. A corresponding problem also appears in other frontier areas, for example, in the vicinity of the frontier between Finland and Sweden.

Sudden changes of the network serving a mobile subscription will cause significant problems for customers living or travelling in a frontier area. This is because there is a very considerable difference in price in mobile station operation between a home network and a roaming network, so that accidentally using a mobile subscription through a roaming network may lead to an excess cost of up to hundreds of euros. Though customers are shown the network serving their mobile station on the display of the mobile station, in practice however, situations arise, in which the network providing the service will not be checked, for example, when driving a car, or when answering a call quickly.

The invention is intended to create a technical solution, which can be used to reduce the probability of a mobile subscription being connected to a roaming network in the service area of its home network. The invention is based on implementing for a mobile subscription a control function for use in a frontier area, which commands home-network searches to be made more frequently than usual.

More specifically, the control method according to the invention is characterized by what is stated in Claim 1.

The subscriber identification unit according to the invention is, for its part, characterized by what is stated in Claim 15, and the computer program product is characterized by what is stated in Claim 26.

In one embodiment, the control function is implemented with the aid of the search period of home-network searches.

The home-network search period (HPLMN search period) is a parameter, which tells the mobile station how frequently it should search for the home network of the subscription that operates it, when the subscription is connected to a roaming network. In GSM- generation systems, the home operator sets the search period for the SIM card and the mobile station implements home-network searches under the control of the SIM card. Thus the home operator selects a search period that it deems suitable, within the range of variation defined by the standard.

If the search period is very short, the mobile station will consume a considerable amount of current in a roaming network, as the mobile station will have to make home-network searches at very frequent intervals. Home-network searches consume current and the mobile station's battery will rapidly empty. Thus, the value of the search period must be set to be high enough not to disturb the operation of the mobile station when it is in the area of a roaming network.

On the other hand, if the search period is very long, the current consumption of the mobile station will be low even in a roaming network, but problems may arise when returning to the home network. If the roaming network is able to serve the mobile-station subscription even in the service area of the home network, the mobile-station subscription will remain connected to the roaming network, right up until the next home- network search.

In a second embodiment, the control function is implemented by forcing the mobile station to perform the network-connection function at specific intervals. This can be implemented, for example, by altering the data in the LOCI file (Location Information File) stored on the SIM card. In other ways, this embodiment corresponds to embodiments using the search period of the home-network, so that it is possible to use the same time intervals, hand-over conditions, and other rules in the embodiments.

In a third embodiment, a longer interval is implemented with the aid of a home-network search period, and a shorter interval is implemented by compelling the mobile station to perform the network-connection function according to the said second embodiment.

In one embodiment, the arrival of the mobile subscription in a frontier area is detected on the basis of a connection to a roaming network.

In a second embodiment, the arrival of the mobile subscription in a frontier area is detected on the basis of one or more cell identifiers of one or more mobile cells in radio connection with the mobile station.

In a third embodiment, the arrival of the mobile subscription in a frontier area is detected on the basis of a control command received from the user.

In one embodiment, the location of the mobile subscription in a frontier area is evaluated on the basis of one or more cell identifiers of one or more mobile cells in radio connection with the mobile station.

In a second embodiment, the location of the mobile subscription in a frontier area is evaluated on the basis of the time passed after a connection to a roaming network. In a third embodiment, the location of the mobile subscription in a frontier area is evaluated on the basis of the number of cell changes taking place after connection to a roaming network.

In a fourth embodiment, the location of the mobile subscription in a frontier area is evaluated with the aid of a combination of the embodiments described above, in such a way that the mobile subscription is interpreted as having left the frontier area, if all the conditions selected from a group of all the aforementioned conditions are met.

In a fifth embodiment, the location of the mobile subscription in a frontier area is evaluated with the aid of a combination of the embodiment described above, in such a way that the mobile subscription is interpreted as having left the frontier area, if even one of a group of selected conditions of the aforementioned conditions is met.

In a sixth embodiment, the location of the mobile subscription in a frontier area is evaluated on the basis of a control command received from the user.

With the aid of the embodiments of the invention, the significant advantage is achieved that the search period of home-network searches can be kept on average at a relatively small value in a frontier area and on average at a relative large value in a roaming network farther away from the frontier area. This will clearly shorten the time for which the mobile subscription is connected to a roaming network in the service area of the home network, and thus reduce the probability of unnecessary costs arising. Despite this, the current consumption of a mobile station in a roaming network is kept reasonable, as in typical operation it is likely that for most of the duration of being in the roaming network the search period will be at a larger value.

In the embodiments, the values of the search periods can be selected in such a way that the smallest value is the minimum value defined by the standard, or is close to such a minimum value while the larger value is a value greater than the standard search-period value usually used. In the implementation of the embodiments, it is possible to utilize the subscriber identification unit. The subscriber identification unit is a unit, which can be connected to a mobile station in order to identify the subscriber. Usually, the identification unit comprises an electronic circuit and is fitted inside the mobile station, in a place reserved for it. The subscriber's identification unit is more usually referred to as a SIM card (Subscriber Identification Module). In a UMTS network, it is also referred to as a USIM card, but in the present publication the term SIM card will be used to refer also to such subscriber identification units, corresponding to a SIM card, used in newer networks.

It is therefore possible to implement the embodiments with the aid of a SIM card. Such embodiments have the additional advantage of not requiring new elements or investments in the mobile network.

In one embodiment, an application of the user's SIM card in the terminal device records the cell identifiers of the operators in the frontier area in its own database on the SIM card and utilizes this database when evaluating whether the terminal device is located in the frontier area.

In one embodiment, the cell IDs in the frontier area of both the home network and also of the roaming operators are gradually recorded on the SIM card. After this, the SIM card's application can 'predict' the cells of the home network, from which a hand-over to a cell of the roaming network could take place. In such an embodiment, when the terminal device arrives in such a cell of the home network, the application sets the HPLMN search-period value to be short, making the subscription more certain to remain in the home network.

A subscription is a technical and management totality, to which is typically linked a network identifier, a subscriber identifier, and the subscriber's data. When a subscription is said to be in a network, or connected to a network, it means that the terminal device using the subscription is radio-technically connected to a mobile network, and, in addition, that the terminal device has been granted access to the telecommunications services provided by the mobile network, within the scope of this subscription. A corresponding situation is also referred to in the present document, when reference is made to a terminal device or mobile station being connected to a network. The term mobile subscription is used to refer to a subscription, which can be used by a mobile station, and which provides access to a mobile network.

Reference to the location of a mobile subscription, for its part, refers to where the mobile station using the mobile subscription is located. In a GSM network, and in corresponding networks using a SIM card or another similar subscriber identification unit, the location of the mobile subscription refers to the location of the subscriber identification unit, which is associated with the mobile subscription in question.

Once the terminal device finally moves so far over the frontier that contact can no longer be made with the home network, the SIM-card application begins to record the cell IDs of the roaming networks in its database (e.g., 10 IDs). When the terminal device has moved even farther from the frontier area, the SIM-card application returns the HPLMN search period to its longer value.

Correspondingly, once the terminal device is again returning from the area of the roaming network to the area of its home network and is approaching the frontier area, the SIM-card application detects this, because it 'knows' the cell IDs of the frontier area. Thus, the SIM-card application can now set the HPLMN search-period value to short, so that the subscription can transfer to the home network as soon as this is found.

According to one embodiment, the SIM-card application returns the HPLMN search- period value to normal, once the terminal device has moved from the frontier area deeper in the home network.

According to a second embodiment, the search-period value of the home-network searches, i.e. the HPLMN search-period value, is kept at a small value, e.g., the minimum value, whenever the terminal device is not interpreted as being 'deep' inside a roaming network. Thus, in such an embodiment, the search-period value is always small when it is decided that the terminal device is in its home network, or in the frontier area. Keeping the search period small in the home network is not detrimental in terms of current consumption, as a mobile station will not make home-network searches when it is connected to its home network.

Further, according to one embodiment, a function is implemented, with the aid of which it can be ensured that the mobile station will use a specific most-favoured roaming network, at least in the case of outgoing telecommunications traffic, when it is outside the service area of its home network.

According to a second embodiment, a function is implemented; by means of which a mobile station connected to some other roaming network than the most-favoured roaming network will from time to time search for the most-favoured roaming network. This will increase the probability of using the most-favoured roaming network when outside the service area of the home network, also in the case of incoming telecommunications traffic.

Several advantages can be achieved with the aid of the embodiments described above and those described hereinafter.

With the aid of the embodiments, it will be highly probable that mobile-telephone customers will remain in their home network, even in the vicinity of the national frontier, at all times when reasonable contact can be made with the home network.

For a subscription customer this brings obvious advantages:

The customer need not make or receive calls, or send SMS messages at expensive roaming prices in a roaming-operator's network, if the home network has coverage in the frontier area. Particularly customers queuing in the customs area often spend many hours waiting, during which they need not worry when making calls, as they can be certain that they are in the cheaper network of their home operator. Once the customer returns to their own country, their home network will be available as soon as possible, generally even a good distance on the side of the foreign country. Thus, the prices and diverse services of the home network will be available for the longest possible time.

The embodiments also provide advantages for the home-network operator:

The home-network operator will receive all income from the traffic and not only a roaming commission.

Even large variations in signal in the frontier zone will not cause problems, because the SIM-card application is able to keep the subscription in the home network. Thus unnecessary signal traffic to the HLR of the home network, when the subscription switches to and from the home network, will also not be created.

Existing SIM-card technology can be exploited in the embodiments, nor will separate network investments be necessary.

In the case of the cell IDs, the embodiments also automatically update themselves, so that the SIM card updates the whole time, without active measures by the operator.

In the following, the invention is examined with the aid of examples and with reference to the accompanying drawings.

Figure 1 shows schematically one possible case of the movement of a mobile subscription from a home network to a roaming network.

Figure 2 shows a status-shift diagram according to one embodiment.

Figure 3 shows a flow diagram of the joint operation of the SIM card and terminal device in the implementation of the method according to one embodiment. Figure 4 shows a cell-change diagram in one possible hand-over situation.

The embodiment example of Figure 1 shows a case, in which a mobile subscription moves from a Finnish home network (Elisa's network) to a roaming network on the Russian side of the frontier. The figure shows several areas equipped with the ELISA mark, which depict Elisa's mobile cells in the frontier area. The figure also shows several shaded areas equipped with the RUS mark, which depict roaming-network mobile cells in the frontier area. In addition, the figure shows the national frontier 1, as well as arrows showing the route 2 of the mobile subscription.

The following describes the management of the situation of Figure 1, according to one embodiment.

During a previous visit to the frontier area, the SIM-card application has recorded the cell identifiers in the frontier area in its database. With the aid of this database, the SIM- card application is able to 'predict' the change from Elisa's network to a Russian network. Thus, when the terminal device arrives in the Elisa2 cell, the SIM-card application sets the HPLMN search-period value to short, so that the subscription will be certain to remain in Elisa's network. As the terminal device progresses along the path 2, the terminal device moves across the frontier into Russia. The SIM-card application then records in its memory the cell identifiers of the cells of the Russian network in the chain.

At some stage, contact with the home network is lost and the terminal connects to a roaming network. The SIM-card application continues to record in its memory the cell identifiers of the Russian network. Once the terminal device has recorded a sufficient number of cell identifiers, the SIM-card application terminates the recording of the cell data and returns the HPLMN search-period value to normal. This most probably corresponds to a situation in which the terminal device has moved farther from the frontier area. The sufficient number of cell identifiers can be preselected, for example, from the range 5 - 30. For example, 10 cell identifiers can be recorded even after contact with the home network has been lost. When the terminal device returns to Finland travelling along the route 2 in the opposite direction, the SIM-card application detects the mobile station to be in contact with at least one cell, the cell identifier of which has be recorded in the database of the application. Such a cell can be, for example, the cell RUS 1 of the figure. In response to this detection, the SIM-card application sets the HPLMN search-period value to be as short as possible, so that the subscription can transfer to Elisa's network, as soon as the coverage area of Elisa's network starts. As the terminal device progresses towards the home network, the subscription transfers to Elisa's network. Once the terminal device has moved deeper into Finland, the SIM-card application returns the HPLMN search- period value to normal.

The example described above can be varied in many ways.

In one variation, the recording of the cell identifiers is started only in response to the mobile subscription being detected as connecting or being connected to a roaming network. In a second variation, the recording of the cell identifiers is started again in response to the mobile subscription being detected as connecting or being connected to a roaming network.

In embodiments of this kind, the period of the home-network searches is preferably kept at a small value for the entire time that the mobile subscription is in the service area of the home network. There is then no need to detect the approach of the frontier area, because the period of the home-network searches is already at the smallest value. Thus there is also no need to record the cell identifiers of the home network.

In one variation, the recording of cell identifiers is terminated on the basis of contact with the home network not being made for a specific time.

Further, in one variation the recording of cell identifiers is terminated in response to contact with the home network not being made for a specific time and after a specific number of cell identifiers have been recorded after connection to a roaming network. In yet another variation of the example, the recording of cell identifiers is terminated in response to either of the conditions of the foregoing variation being met, i.e. contact with the home network has not been made for a specific time, or a specific number of cell identifiers has been recorded after connection to a roaming network.

The various variations of the example can be used when it is desired to respond to different customer needs.

In the GSM and 3G standards, the HPLMN (Home Public Land Mobile Network) search period can be given a value in the range 1 - 255. Each value means that the home- network search is made at predefined time intervals, in such a way that the length of the interval is obtained by multiplying the HPLMN search-period value by 6 minutes.

In connection with the embodiments, at least two different values are used for the HPLMN search period, in such a way that the smaller value is intended to be used when the mobile subscription is located in the frontier area and the larger value is intended to be used when the mobile subscription is located in a roaming network, outside the frontier area. The smaller value can be selected, for example, from the range 1 - 10, preferably 1 - 5. For greater effect, the smaller value is selected as 1, 2, or 3, which thus means that, in the frontier area, a home-network search is made at intervals of 6, 12, or 18 minutes, according to the selected value. 1 is preferably selected as the smaller value, at least for users for whom a low current consumption in the frontier area is not a critical factor. Thus the home-network search is made at intervals of 6 minutes, in which case the subscription can be connected to a roaming network for only a few minutes at a time, in a location in which the home network too would be available.

The larger value of the HPLMN search period can be selected, for example, from the range 10 - 255, typically the range 11 - 80. In the example, 20 is selected as the larger value, which means that, in the area of a roaming network, a home-network search is made at intervals of 120 minutes.

Instead of using the HPLMN search period for setting the time interval, it is also possible to use a separate timer, with the aid of which the mobile station is forced to perform the network-connection function. In one embodiment, this is implemented in such a way that, with the aid of a timer, at predefined intervals the contents of the LOCI file (Location Information File) on the SIM card are changed in a suitable manner. The LOCI file typically contains the last-detected LAC (Location Area Code), the MNC (Mobile Network Code), and the MCC (Mobile Network Country Code). In addition, the LOCI file contains status information. In the embodiment, the change to be made includes changing the status information of the LOCI file to 'not updated', in which case the mobile station must initiate the network-connection function. As the start of the network-connection function, the mobile station makes a home-network search. This procedure can also be applied in the embodiment of Figure 3, to be described later.

The forced network-connection function can also be exploited for selecting the most- favoured roaming operator in the roaming-network area. An application can be implemented for the SIM card, which acts in response to a connection-formation request while the mobile station is connected to a roaming network. Here the term connection- formation request refers to an attempt by the mobile station to initiate, for example, call formation, or the transmission of an SMS or multimedia message. In such a situation, the SIM-card application checks if the mobile station is connected to the most-favoured roaming network. If the mobile station is connected to the most-favoured roaming network, connection formation is initiated normally.

However, if the mobile station is not connected to the most-favoured roaming network, the SIM-card application commands the mobile station to display a menu to the user, in which the user is requested to confirm that they wish to continue connection formation in the roaming network that is in use at that moment, or whether they wish to search for the most-favoured roaming network. If the user wishes to continue connection formation in the present network, connection formation is continued normally. If, however, the user wishes to search for the most-favoured network, the SIM-card application forces the mobile station to first of all perform the network-connection function and to continue connection formation only after it is has performed the network-connection function. The connection is then formed through the first possible mobile network according to the favouredness order recorded for the SIM-card application, i.e. primarily through the home network and secondarily through the most-favoured roaming operator. The connection is formed through some other roaming operator only if neither of these networks is available. In this embodiment, the forced network-connection function can be implemented, for example, by altering the contents of the LOCI file on the SIM card in manner described above.

One example of the user of the embodiment described above is a situation, in which the home operator has a co-operation agreement with a specific roaming operator. In that case, the user of this specific roaming operator permits, for example, a better service totality, or more attractive pricing for a customer moving in the area of the roaming network. While being in the roaming network, the mobile station can, however, disconnect from the co-operating operator's network and lock onto some other roaming network. At present, it is not possible to disconnect from this other network, unless the telephone is switched off and on again, or the mobile station is manually directed to the network of the co-operating operator. It would therefore be advantageous if, unless the user is in the network of the co-operating operator prior to starting a call, an SMS message transmission, or opening a data connection, the user would be provided with the opportunity to select the network of the co-operating operator. In that case, the SIM application will automatically put the call initiation, or opening of the SMS transmission or data connection into a hold state and carry out the operation described above, by means of which the subscription is brought into the network of the co-operating operator. After this, the initiation of the call, or the opening of the SMS transmission or the data connection will continue automatically. This will cause a delay of 30 - 45 seconds, but the saving in cash, or the service advantage may be considerable. The operation is also easy for the user, who must only acknowledge in the menu in the display of the mobile station that they wish to form a data-transfer connection through the network of the co-operating operator - everything else is automatic. The menu can ask, for example, 'Search for network of co-operating operator?' and all that is needed is to select in reply YES or NO from the menu.

The search for the most-favoured roaming network can also be implemented periodically, for example, in the same way as described in the embodiments for the search for the home network. For such a timed roaming-operator selection function, an application can be implemented for the SIM card, which will perform the network- connection function at specific intervals, when the mobile station is connected to a roaming network. The network-connection function can be implemented, for example, in the manner described above while the timing can be implemented, for example, with the aid of the time counter described later in connection with Figure 3, or similar.

The SIM-card application can also be set to detect a situation, in which the mobile station is connected to the network of the most-favoured roaming operator, outside the frontier area, hi the said situation, the performance of the network-connection function can be omitted, or performed at longer intervals. If, on the other hand, the mobile station is connected to some other roaming network, the network-connection function can be performed at shorter intervals, in a manner corresponding to that described in the home- network embodiments to be performed in the frontier area.

A timed roaming-operator selection function can be implemented as an alternative to the function that operates in response to a connection-formation request. A timed function corresponding to a connection-formation request can also be in operation simultaneously and also programmed for the SIM card.

Figure 2 shows a status-shift diagram according to one example. According to the figure, the mobile subscription has a status Home Network 201 for being in the home network, a status Frontier Area 202 for being in the frontier area, and a status Roaming Network 203 for being in a roaming network. The following shifts between the statuses are defined:

210) Status shift 210 depicts the making of a conventional periodic location update, in a situation, in which the mobile station is connected to its home network. In that case, the status does not change, so that the mobile station continues in the status Home Network 201. 211) Status shift 211 relates to the connection of the mobile subscription from its home network to a roaming network. In the embodiment shown in the example, the HPLMN search-period is set to a smaller value in connection with the status shift 211.

212) Status shift 212 relates to the connection of the mobile subscription from a roaming network to its home network, in which case the HPLMN search period is set to the normal value in the embodiment described by this example.

213) Status shift 213 implements a transfer from the status Frontier Area 202 to the status Roaming Network 203, which is implemented when the transfer condition is met. In the embodiment of the example, the transfer condition relating to the status shift 213 is the passage of a predefined period of time. In the example, the predefined time is calculated from the moment when the mobile station transfers to the status Frontier Area 202, i.e. starting from status shift 211 or 215. Status shift 213 thus relates to a situation, in which it can be concluded on the basis of the passage of time (Timeout), that the home network no longer has coverage in the area of the location of the mobile subscription. In connection with status shift 213 the HPLMN search period is set to its normal value.

214) Status shift 214 implements a transfer from the status Frontier Area 202 to the status Roaming Network 203. In the embodiment of the example, the transfer condition relating to status shift 214 is that the mobile station has experienced a predefined number of cell changes after it has transferred to the status Frontier Area 202. Thus status shift 214 relates to a situation, in which it can be decided on the basis of the calculated cell changes that the home network can no longer have coverage in the area of the location of the mobile subscription. In connection with status shift 214, the HPLMN search period is set to its normal value.

215) Status shift 215 implements a transfer from the status Roaming Network 203 to the status Frontier Area 202. The transfer condition in the embodiment of the example is that the mobile station implements a transfer in a roaming network to a cell that is known to be in the frontier area. In connection with status shift 215, the HPLMN search period is set to a smaller value.

216) Status shift 216 implements the retention of the subscription in the frontier area in situation, in which Timeout is not realized and the number of cell changes is not exceeded.

217) Status shift 217 implements monitoring taking place in connection with a cell change, in a situation, in which a new cell of the roaming network serving the mobile subscription is not detected as being in the frontier area.

218) Status shift 218 implements a transfer directly from a roaming network to the home network. This is implemented, for example, in a situation, in which the subscription returns to the area of the home network while switched off. A typical example is travelling in an aircraft.

In addition to the status shifts described above, it is also possible to transfer directly from the home network to a roaming network. Such a situation may come into question, for example, after a long air journey.

Figure 3 shows, as a flow diagram according to one embodiment, the joint operation of the SIM card and the terminal device in the home network 311, in a frontier area 312, and in a roaming network 313, the areas of the location of which are shown in the figure with the aid of correspondingly numbered boxes drawn with broken lines.

In Block 301, the performance of the method is started.

In Block 302, a check is made as to whether the subscription is connected to its home network. If the subscription is connected to the home network, return to Block 302. However, if the subscription is not connected to the home network, continue to Block 303. In Block 303, the HPLMN Search Period is set to its lower value. In addition the time counter and the cell-change counter are reset to zero and the calculation of time and cell changes is commenced. At the same time, the recording of cell identifiers in the frontier- area database is also commenced. After this, continue to Block 304.

In Block 304, a check is made as to whether contact can be made with the home network. If contact is made with the home network, proceed to Block 310. If, on the other hand, is not available, move to Block 305.

In Block 305, a check is made as to whether the time-counter value has reached the threshold value. If the time-counter value has reached the threshold value, move to Block 307. If the time-counter value has not reached the threshold value, move to Block 306.

In Block 306, a check is made as to whether the cell-change counter value has reach the threshold value. If the cell-change counter value has reached the threshold value, move to Block 307. If the cell-change counter value has not reached the threshold value, move to Block 304.

In Block 307, the HPLMN Search Period is set to its greater value. The counting of time and cell changes can be stopped and the recording of cell identifiers in the frontier-area database interrupted. After this, move to Block 308.

In Block 308 cell changes are monitored, and always in connection with a cell change move to Block 309.

In Block 309, a check is made as to whether the cell identifier of the new serving cell is in the frontier-area database. If the cell identifier of the new cell is found in the frontier- area database, move to Block 303. If, on the other hand, the cell identifier of the new cell is not found in the frontier-area database, return to Block 308. In Block 310, the HPLMN Search Period is set to its greater value. Counting of time and cell changes can be stopper and the recording of cell identifiers in the frontier-area database interrupted. After this, move to Block 302.

In Figure 4, uses ovals to represent the cells of a mobile network and arrows to represent the cell changes of a mobile station from one cell to the next, when moving from the home network 4 to a roaming network 6. In the figure, there is a 'cell-change window' at the location of the frontier station, the cells of which thus belong to the frontier area 5, in terms of the present method. In the embodiment of Figure 4, the SIM-card application actively investigates cell changes and records the data relating to the cell-change events as a 'chain' in its memory. At some stage, the cells of the home network end and the cell changes continue in the cells of the roaming network. When the cell changes of the area shown with a broken line are recorded in the memory of the SIM card, all the cell identifiers of the cells in the frontier area are gradually collected in the frontier-area database and thus the SIM-card application learns to detect the approach of the frontier area.

In the embodiment of Figure 4, each SIM card collects independently data according to Figure 4 and thus gradually learns the frontier area or frontier areas that it visits.

A corresponding function can also be implemented, in such a way that all the operator's card that possess the SIM application regularly transmit the frontier-area data that they detect to the operator's central database. Information on frontier areas can then be distributed from this central database to all subscriptions possessing this SIM application. In this embodiment, the subscription can exploit the frontier-area data acquired by other subscriptions, already before it has itself been in the frontier area in question.

An embodiment using a central database also permits different frontier areas to be defined, if required, for different subscriptions or types of subscription. The frontier-area definitions can be made in the mobile network and delivered wirelessly to the mobile stations. Also in embodiments using a central database, the size and/or content (cell lists) of the frontier area can vary between different subscriptions. The selection criterion can be, for example, a specific subscription, a group of subscriptions, or the type of terminal device used by the subscription. The user can also be given an opportunity to define themselves the size and/or content (cell list) of the frontier area. This can be implemented, for example, by providing a definition function with the aid of a SIM Tool Kit application, or, for example, through an internet interface. A frontier area defined by the user themself can also be implemented in a corresponding manner in connection with a frontier-area database recorded on the SIM card. Correspondingly, a positive-guidance function can be programmed into the SIM-card application, with the aid of which the user themself can defined the frontier-area status of the subscription.

On the basis of the examples described above, it is indeed obvious that, within the scope of the invention, numerous solutions differing from the embodiments described above can be implemented. Thus, the invention is not intended to be restricted to concern only the examples described above, but instead the patent protection should be examined to the full extent of the accompanying Claims.

Claims

Claims:

1. Method for setting the length of the time interval passing between the consecutive home-network searches of a mobile subscription, in which method a first value is set for the length of the time interval for being in the area of a roaming network (6), characterized in that a second value smaller than the first value is set for the time interval for being in a frontier area between a roaming network and the home network.

2. Method according to Claim 1, characterized in that the length of the time interval is set with the aid of the search period of the home-network searches, in such a way that a first value is set (307) for the search period of the home-network searches for being in the area of a roaming network (6) and a second value smaller than the first value is set for the search period of the home-network searches for being in a frontier area (5) between a roaming network and the home network.

3. Method according to Claim 1, characterized in that at least the second value of the length of the time interval is set in such a way that the mobile subscription is commanded to perform a network-connection operation at specific intervals.

4. Method according to any of Claims 1-3, characterized in that cell identifiers of the cells of a mobile network located in the frontier area (5) are collected in a frontier-area database.

5. Method according to Claim 4, characterized in that the frontier-area database is maintained locally in a system used by the mobile subscription, such as the subscriber identification unit, or the mobile station.

6. Method according to Claim 4, characterized in that the frontier-area database is maintained centrally in the mobile network.

7. Method according to any of Claims 1-6, characterized in that arrival in the frontier area (5) is detected (309) on the basis of the cell identifier of the mobile-network cell serving the mobile station.

8. Method according to any of Claims 1-6, characterized in that the mobile subscription is interpreted (302) as having arrived in the frontier area (5), when the mobile subscription connects from the home network (4) to a roaming network (6).

9. Method according to any of Claims 1-8, characterized in that the mobile subscription is interpreted (305) as having left the frontier area (5) once a predefined period of time has passed since arrival in the frontier area (5).

10. Method according to any of Claims 1-8, characterized in that the mobile subscription is interpreted (306) as having left the frontier area (5), once the mobile station has made a predefined number of cell changes after arriving in the frontier area (5).

11. Method according to any of Claims 1-8, characterized in that the mobile subscription is interpreted (304) as having left the frontier area (5), once the mobile subscription is detected as being connected to the home network (4).

12. Method according to any of Claims 1-11, characterized in that the frontier area is defined on the basis of input received from the user of the mobile subscription.

13. Method according to any of Claims 1-11, characterized in that the frontier area is defined locally with the aid of a function of the mobile station using the mobile subscription.

14. Method according to any of Claims 1-11, characterized in that the frontier area is defined in the mobile network and definition information is transmitted wirelessly from the mobile network to the mobile station.

15. Subscriber identification unit for a mobile station, which is arranged to command the mobile station to perform home-network searches at first time intervals, characterized in that the subscriber identification unit is arranged to command the mobile station to perform home-network searches optionally at second, shorter time intervals.

16. Subscriber identification unit according to Claim 15, characterized in that rules are stored in the identification unit for performing a choice between the first and second time intervals.

17. Subscriber identification unit according to Claim 15 or 16, characterized in that the subscriber identification unit is arranged to implement the control command of the first time intervals with the aid of the search period of the home-network searches, and a first value for the search period of the home-network searches is recorded in the subscriber identification unit.

18. Subscriber identification unit according to Claim 17, characterized in that, in addition to the first value, a second value, which is smaller than the first value, is recorded in the subscriber identification unit, as are the rules, on the basis of which it is possible to select the first value and the second value as the value of the search period of the home-network searches to be used at the time in the mobile station.

19. Subscriber identification unit according to any of Claims 15-17, characteriz e d in that, in order to implement the second time interval that is shorter than the first, the subscriber identification unit is arranged to compel the mobile station to perform the network-connection function at the second time intervals.

20. Subscriber identification unit according to Claims 15-19, characterized in that it comprises a frontier-area database, for recording the cell identifiers of mobile- network cells located in the frontier are.

21. Subscriber identification unit according to any of Claims 15 - 20, characteriz e d in that it comprises a functionality for receiving from the user a command affecting the choice to be made between the first and second time intervals.

22. Subscriber identification unit according to any of Claims 15-21, characteriz e d in that it is arranged to control the mobile station according to at least one of Claims 1-14.

23. Subscriber identification unit according to any of Claims 15-22, characteriz e d in that it is arranged to implement the roaming-operator selection function in response to an attempt by the user to open a data-transfer connection, or to send data traffic through the network of a roaming operator.

24. Subscriber identification unit according to Claim 23, characterized in that information on the most-favoured roaming operator is recorded in the subscriber identification unit and that the roaming-operator selection function is arranged to operate in such a way that, when the mobile station is connected to the roaming network of some other roaming operator than the most-favoured roaming operator:

-the subscriber identification unit commands the mobile station to display to the user a menu and to receive input,

-on the basis of the input received, the subscriber identification unit commands the mobile station either 1) to continue direct data traffic transmission, or to open a data-traffic connection, or 2) to search first for the home network and/or the most-favoured roaming network and to continue data traffic transmission, or to continue opening the data-traffic connection only after having performed a search.

25. Subscriber identification unit according to any of Claims 15 - 24, characteriz e d in that it is arranged to implement a timed roaming-operator selection function while the mobile station is connected to the roaming network of some other roaming operator than the most-favoured roaming operator.

26. Computer program product for controlling a mobile subscription's connection to a network, characterized in that it is arranged to command the mobile station to use a first home-network search control function for when it is in the area of a roaming network (6) and a second home-network search control function for when it is in a frontier area (5) between a roaming network and the home network, in which the second function commands the mobile station to perform home-network searches more frequently than the first function.

27. Computer program product according to Claim 26, characterized in that it is arranged to command the mobile station to use the first value for the search period for when it is in the area of a roaming network (6) and a second value, which is smaller than the first value, for when it is in a frontier area (5) between a roaming network and the home network.

28. Computer program product according to Claim 26, characterized in that it is arranged to implement a method according to any of Claims 1-14.