WO2011124760A1

WO2011124760A1 - Call control for mobile station in ip environment

Info

Publication number: WO2011124760A1
Application number: PCT/FI2011/050294
Authority: WO
Inventors: Mikko Elo
Original assignee: Fujitsu Finland Oy
Current assignee: Fujitsu Finland Oy
Priority date: 2010-04-07
Filing date: 2011-04-06
Publication date: 2011-10-13
Anticipated expiration: 2012-10-07
Also published as: FI20105355A0; FI20105355L; FI20105355A7

Abstract

A client application installed in a mobile station (MS1) monitors broadband networks (WLAN) available in the area. When a call is set up from the mobile station (MS1), the application intervenes in all outgoing calls and if a broad¬ band network (WLAN) is available, it enquires a voice server (2) whether a called subscriber (MS2) is reachable by a VoIP call over the broadband net¬ work. If the called subscriber (MS2) is reachable by a VoIP call and a VoIP call over the broadband network is economically and technically reasonable, the voice server (2) controls the mobile station (MS1) to set up a VoIP call. If the called subscriber (MS1) is not reachable by a VoIP call or not in a network rea¬ sonable for a VoIP call, the voice server (2) controls the calling mobile station (MS1) to set up a normal circuit-switched mobile call (CS).

Description

Call control for mobile station in IP environment

The invention relates to mobile communications and particularly controlling the calls of a mobile station in an IP environment.

Speech is still our most important communications application. Transfer of speech over an IP (Internet Protocol) presents specific challenges. One of these is integration, because a speech system is no longer a separate entity but integrated into office applications and to instant messaging and presence functions. An intelligent mobile phone is also capable of operating in a broadband IP network, for example in a wireless local area network (WLAN) and it may be provided with IP voice application programs.

VoIP (Voice over Internet Protocol), or IP speech, is an umbrella term for a method that allows voice and video image to be transferred in real time as packet data streams in data networks. VoIP generally comprises standards H.323 and SIP. The most important advantage of IP calls is that they are inexpensive compared with ordinary calls transferred over conventional circuit-switched systems. For the user, the most interesting VoIP application is bypassing the conventional public switched telephone network (PSTN) or public land mobile network (PLMN) through the IP network, which provides savings in the long-distance and local call charges. A telecommunications op- erator is only needed for calls made to the conventional telephone network. VoIP technology can be used on trunk connections of a telecommunications network for interconnecting switches or other network elements to save on transfer charges. The same technical solution has been employed also on private branch exchanges (PBX) and company networks for example to intercon- nect office sites that are geographically apart from one another, to implement call centre services. Conventionally, a PBX (Private Branch Exchange) refers to a non-public telephone network used inside a company to interconnect the internal extensions of the company and to connect them to the public telephone network. In the PBX telephone system the users have common lines for external calls. Telephone exchange systems supporting VoIP and IP protocols are often known as VolP-PBX or IP-PBX. A mobile PBX extends a fixed line PBX functionality to mobile stations by provisioning them for use as PBX extensions. In addition, VoIP speech transfer has been applied in mobile communications as an alternative to circuit-switched calls. The principal existing solutions for using mobile phones in a broadband IP network are the following:

1) A mobile phone integration built in a private branch exchange en- vironment (PBX), with numbering from the branch exchange environment

(fixed network numbering) and the calls being always routed through the branch exchange environment. A separate mobile phone application employs the IP network for call whenever it is available. If necessary, a seamless handover of a VoIP call between networks (e.g. IP <-> GSM) is in some cases pos- sible.

2) An implementation integrated into a mobile services switching centre, where the numbering may be from a fixed network or from a mobile communications network, and the calls are always routed through the mobile services switching centre. This solution is based on a mobile phone application conforming to the 3GPP or a corresponding standard, where the IP network is always used if it is available. If necessary, a seamless handover of the VoIP call between networks (e.g. IP <-> GSM) is possible.

For the user, these prior art implementations are all complicated, heavy and expensive to provide, and they are strongly dependent on a mobile communications network or a telephone exchange system.

Brief description of the invention

It is therefore an object of the invention to provide a solution for mobile station call control in an IP environment to allow at least some of the above problems to be overcome or alleviated. The object of the invention is achieved by the characteristics disclosed in the accompanying independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.

A first aspect of the invention is a call control method in a mobile station having capability for both voice calls switched over a mobile communications network and Internet Protocol (IP) voice calls over an IP network, in which method

a client application executed in the mobile station intervenes in an outgoing voice call of a mobile communication network initiated from a user interface and, if an IP network is available, enquires over the IP network an IP voice server of whether the outgoing call is to be set up as an IP voice call over the IP network; the client application, in response to a reply received from the IP voice server, controls the mobile station to set up the outgoing call as a circuit- switched voice call over the mobile communications network or as an IP voice call over the IP network; and,

if the IP network is not available, the client application controls the mobile station to set up the outgoing call as a circuit-switched voice call over the mobile communications network without making an enquiry.

According to an embodiment of the invention

the client application registers itself with the voice server when the IP network is available and, optionally, registers its status regularly with the voice server; and

the client application performs said enquiry to the IP server, if/when the IP network is available and the client application is registered with the IP server.

According to an embodiment of the invention

the client application is deactivated from the user interface by a predetermined key or key combination for a predetermined period of time and, optionally, the IP voice server is informed of the deactivation;

when the client application is deactivated, an outgoing call is always set up as a circuit-switched voice call over a mobile communications network; and

the client application is reactivated after the predetermined period of time.

According to an embodiment of the invention, the user may reacti- vate the client application from his/her user interface before the deactivation period expires.

According to an embodiment of the invention, if an IP voice call attempt is not successful within a predetermined time, the client application interrupts the IP voice call attempt and changes the outgoing call to a circuit- switched voice call over a mobile communications network.

According to an embodiment of the invention, the IP network is a wireless broadband network, a packet-switched mobile communications network or a wireless local area network.

A second aspect of the invention is a call control method in an IP voice server, where the IP voice server receives over the IP network an enquiry from a client application executed on a calling subscriber's mobile station of whether an outgoing voice call from the mobile station is to be set up as an IP voice call over the IP network;

the IP voice server checks whether the called subscriber is reachable by an IP voice call and, optionally, whether an IP voice call is economically and/or technically reasonable;

the IP voice server sends the client application a response to the enquiry over the IP network and commands it to set up the outgoing call as an IP voice call if the called subscriber is reachable by an IP voice call and, optionally, if an IP voice call is economically and/or technically reasonable; and, the IP voice server sends the client application a response to the enquiry over the IP network and commands it to set up the outgoing call as a voice call switched over a mobile communications network if the called sub- scriber is not reachable by an IP voice call and, optionally, if an IP voice call is not economically and/or technically reasonable.

According to an embodiment of the invention

the IP voice server maintains a register of the reachability of the mobile station subscribers within its IP voice service on the basis of registra- tions sent by their client applications;

the IP voice server checks from the register whether a called subscriber is reachable by an IP voice call;

the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to set up the outgoing call as an IP voice call if the called subscriber is reachable by an IP voice call and, optionally, if an IP voice call is economically and/or technically reasonable; and,

the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to set up the outgoing call as a circuit-switched voice call over a mobile communications network if according to the register the called subscriber is not reachable by an IP voice call or, optionally, if an IP voice call is not economically and/or technically reasonable.

According to an embodiment of the invention

the IP voice server checks whether the called subscriber is reachable by an IP voice call by attempting an IP connection to the called subscriber; the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to set up the outgoing call as an IP voice call if the IP call attempt to the called subscriber is successful and, optionally, if an IP voice call is economically and/or technically reasonable; and,

the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to set up the outgoing call as a circuit-switched voice call over a mobile communications network if the IP connection attempt to the called subscriber fails or, op- tionally, if an IP voice call is not economically and/or technically reasonable.

According to an embodiment of the invention

the IP voice server maintains a register of the reachability of the mobile station subscribers within its IP voice service on the basis of registrations sent by their client applications;

if according to the register the called subscriber is not reachable by an IP voice call, the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to set up the outgoing call as a circuit-switched voice call over a mobile communications network;

if according to the register the called subscriber is reachable by an IP voice call, the IP voice server verifies the reachability by attempting an IP connection to the called subscriber;

the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to set up the outgoing call as an IP voice call if the IP connection attempt to the called subscriber is successful and, optionally, if an IP voice call is economically and/or technically reasonable; and

the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to set up the outgoing call as a circuit-switched voice call over a mobile communications network if the IP connection attempt to the called subscriber fails or, optionally, if an IP voice call is economically and/or technically not reasonable. According to an embodiment of the invention, the IP voice server is independent of the branch exchange system or mobile communications network where the mobile station is operating.

A third aspect of the invention is software which, when installed into a mobile station and executed there, implements an embodiment of the call control method according to the first aspect.

A fourth aspect of the invention is a computer program which, when executed in a computer, implements an embodiment of the method according to the second aspect of the invention.

A fifth aspect of the invention is a mobile station provided with means for an embodiment of the call control method according to the first aspect.

A sixth aspect of the invention is a server system provided with means for implementing an embodiment of the method according to the se- cond aspect.

A seventh aspect of the invention is a client-server system provided with at least one mobile station according to the fifth aspect and at least one server system according to the sixth aspect.

Brief description of the figures

In the following the invention will be disclosed in greater detail with reference to exemplary embodiments and the accompanying drawings, in which

Figure 1 illustrates an example of a communications system environment where the embodiments of the invention are applicable;

Figure 2 is a flow chart illustrating the operation of a client application according to an exemplary embodiment of the invention;

Figure 3A is a flow chart illustrating the operation of an IP voice server according to an exemplary embodiment of the invention;

Figure 3B is a flow chart illustrating the operation of an IP voice server according to an exemplary embodiment of the invention;

Figure 4 is a diagram illustrating an example of the setting up of an outgoing call in accordance with an exemplary embodiment of the invention;

Figure 5 is a diagram illustrating a second example of the setting up of an outgoing call in accordance with an exemplary embodiment of the inven- tion; Figure 6 is a diagram illustrating a third example of the setting up of an outgoing call in accordance with an exemplary embodiment of the invention; and

Figure 7 is a diagram illustrating a fourth example of the setting up of an outgoing call in accordance with an exemplary embodiment of the invention.

Description of exemplary embodiment of the invention

Figure 1 illustrates an example of a communications system environment where the embodiments of the invention are applicable. Figure 1 shows a wireless circuit-switched network 6 serving a mobile station MS1 , such as a mobile communications network (PLMN, Public Land Mobile Network) and/or a mobile private branch exchange system (PBX), a wireless circuit-switched network 7 serving a mobile station MS2, a public switched telephone network (PSTN) 8, which may also be an integrated services digital network (ISDN). Transfer connections 9 between the wireless circuit-switched networks 6 and 7 may be implemented by any transfer technology or system, including the public switched telephone network PSTN. The present invention is independent of a wireless circuit-switched network serving a mobile station, and the implementation or type of the wireless circuit-switched network has no relevance to the invention. Examples of possible wireless circuit-switched networks include the GSM, other similar second generation (2G) mobile communications systems, and WCDMA (Wideband Code Division Multiple Access) and other similar third generation (3G) mobile communications systems. In circuit-switched technology an end-to-end connection or channel is set up or allo- cated for a connection between two terminals, such as MS1 and MS2, for the entire duration of a call, information from one terminal to another being transferred over this circuit-switched connection without address information. The switched connection or channel may also be a logical or virtual connection set up between the devices, call data being transferred over the connection ac- cording to connection parameters. In this specification this type of call is referred to as a circuit-switched (CS) call. Examples of circuit-switched calls include a call between two mobile stations over a mobile communications network and a call between a mobile station and a line telephone over a mobile communications network and a public switched telephone network.

Figure 1 further shows a wireless broadband packet-switched network 3, such as a wireless local area network (WLAN), serving the mobile sta- tion MS1 , a wireless broadband packet-switched network 4 serving the mobile station MS2 and the Internet 5. In this specification a wireless broadband circuit-switched network refers to any wireless network providing a mobile station with a broadband packet-switched connection suitable for speech transfer. The most typical network may be a wireless local area network WLAN based on the IEEE 802.11b-g technology, for example. In that case the mobile station has to be equipped also with a WLAN adapter which is in fact integrated in most of today's smart mobile stations. Examples of these mobile stations include Nokia E71 and Nokia E72. The wireless broadband packet-switched connection may also be implemented through a packet-switched mobile communications network service, such as the GPRS (General Packet Radio Service), although usually this does not provide any advantage in costs compared to a circuit- switched connection. Most mobile stations, such as Nokia E71 and Nokia E72 also support a packet-switched mobile communications network service, such as the GPRS. Nevertheless, the primary field of application of the invention is the use of broadband connections, such as WLAN, independent of a mobile communications network.

A packet-switched connection allows speech to be transferred over an IP (Internet Protocol) in voice packets. In this specification this type of call is referred to as an IP voice call. In packet-switched technology the band is occupied by one packet a time, i.e. a continuous connection for an IP call is not set up. An analog speech signal from a microphone is converted into digital speech information which is divided into packets that travel to the destination over different routes in the network. The packets are typically forwarded through a local area network to the Internet. If the transmitted packets contain the recipient's IP address, they can be routed directly to the recipient. Typically, particularly if the recipient is identified by his/her telephone number or an alias, the packets can be routed over the Internet to the IP address of the voice service provider. The service provider preferably has a voice server that for- wards the IP calls, i.e. the data packets. In Figure 1 this type of voice server is represented by a server 2. The databases of the voice server may contain the information on the associations between the IP addresses and telephone numbers of users, for example. This information enables the data packets to be routed to the correct recipient. When a packet arrives at its destination, the receiving end puts the packets in the correct order to compile the transmitted digital information, which is then converted into an analog speech signal for the earpiece. A weakness in comparison with the analog network is that packets may be lost, which most often appears as interruptions in the speech at the receiving end. VoIP (Voice over Internet Protocol) is an umbrella term for a technology that allows voice and video image to be transferred in real time as packet data streams in data networks. VoIP generally comprises standards H.323 and SIP.

According to the embodiments of the invention, the integration of VoIP calls to the conventional circuit-switched mobile communications technology is fully transparent for the users, and calls may be routed in a manner that is optimal as regards both the user and the costs, i.e. either as a VoIP call over a broadband network or as a circuit-switched (CS) call over a mobile communications network.

According to the embodiment examples of the invention, this is carried out by two components that together form a client-server system: (i) by a client application 1 installed to a mobile station and (ii) an IP voice server 2 in an IP network. As illustrated in Figure 1 , the IP voice server 2 may be connected to any IP network, such as to the Internet 5 in general, to a wireless broadband network 3 or 5 (broken lines 15 and 16) or to some other local area network or a private company network. The voice server 2 may also have the possibility to route the call to the mobile communication networks 6, 7 or to the public switched telephone network 8 through voice gateways, which are depicted by broken lines 10, 11 , 12, 13 and 14 in Figure 1.

According to the exemplary embodiments of the invention, the mobile subscriber and the mobile station number may be provisioned by a short message or a web interface, for example, to be suitable for the IP voice service. Also the downloading of the client application 1 to a mobile station and its configuring may be carried out in manners known per se. Confidential data, such as identifiers and encryption keys, may preferably be exchanged between the client application 1 and the IP speech server 2 by a secured handshake procedure. These confidential data may then be used for securing the speech and the control data. However, the manner in which the client application 1 is downloaded, installed, configured, data is exchanged or a subscriber is provisioned is not relevant to the invention and is not disclosed in greater detail here. The mobile station is preferably what is known as a smart telephone in which the client application 1 may be executed on top of an operation system specifically designed for mobile stations, such as Symbian S60. Examples of these smart telephones include Nokia E71 and Nokia E72. Through application programming interfaces (API) of the operation system the client application 1 may utilize the different functionalities, software and hardware of the mobile station, such as a broadband network adapter, display, keyboard, the radio transmitter of the mobile station, etc. Alternatively, the client application 1 may be a native program of the mobile station.

In accordance with the exemplary embodiments of the invention, an active client application 1 installed in a mobile station monitors through a broadband network adapter the broadband networks available in the area. When the client application 1 detects a broadband network suitable for IP voice service in its neighbourhood, it registers with the voice server 2 through this broadband network. The voice server 2 records the reachability of the client application 1 (mobile station) and its current IP address in its register. According to an embodiment of the invention, the client application updates its status on the IP voice server 2 at short intervals, the server 2 thus knowing that the client application is reachable through the IP network. Any number of mobile stations may be provisioned and registered for the IP voice server 2 in this manner. For the sake of clarity, Figure 1 only shows two mobile stations MS1 and MS2 provided with the client application 1 according to the embodiments of the invention. The invention is particularly advantageous when both the calling and the called mobile station are provisioned for the same voice service 2, although this is not necessary. The voice server 2 may relay the IP call to the recipient also through another similar voice service or to subscribers of another public VoIP service, for example.

According to the exemplary embodiments of the invention, the user may set up a call through the user interface (display and/or keyboard) of a mobile station similarly as a conventional mobile phone call; the functionality of the invention is substantially invisible to the user. For example, the user may initiate an outgoing call by keying in the recipient's telephone number, by se- lecting the recipient's name and telephone number from the address book of the mobile station, by selecting the connection link from a received message or site, by selecting the recipient by voice control, etc. In other words, the user does not need to pay attention to whether s/he is making a circuit-switched mobile call or an IP voice call or to make any difference between these two - s/he acts as if s/he was setting up a conventional mobile call. In accordance with the exemplary embodiments of the invention, the client application 1 of the mobile station MS1 monitors the user interface (step 20 in Figure 2) and when a call from a mobile phone (step 21) is set up, it intervenes either in all calls or in those of a predetermined type and interrupts the setting up of a conventional circuit-switched mobile call. If the broadband IP network 3 is available and the client application 1 is registered to the IP voice server 2 (step 22), the client application 1 enquires over the IP network 3 the IP voice server 2 of whether the outgoing call is to be set up as an IP voice call over the IP network 3 (step 23). If a broadband IP network is not currently available, the client application 1 controls the mobile station MS1 to perform an outgoing circuit-switched call over the mobile communications network 6 without making an enquiry to the IP server (phase 25). The IP voice server 2 receives from the client application 1 the enquiry (step 30 in Figures 3A and 3B) over the IP network 3 (and typically over the Internet 5) and checks whether the called subscriber (the number that is being called, for example the telephone number of the mobile station MS2) is reachable by an IP voice call (step 31) and, optionally, whether an IP voice call is economically and/or technically reasonable (step 33). The IP voice server 2 sends the client application 1 a response to the enquiry over the IP network 3 and commands it to set up the outgoing call as an IP voice call (step 34), if the called subscriber is reachable by an IP voice call and, optionally, if an IP voice call is economically and/or technically reasonable. If the called subscriber is not reachable by an IP voice call or, optionally, if an IP voice call is not economically and/or technically reasonable, the IP voice server 2 sends the client application 1 a response to the enquiry over the IP network 3 and commands it to set up an outgoing circuit-switched call over the mobile com- munications network 6 (step 32).

On the basis of the response received from the IP voice server 2 (step 24 in Figure 2) the client application 1 controls the mobile station MS1 to set up the outgoing call either as a circuit-switched voice call over the mobile communications network 6 (step 25) or as an IP voice call over the IP network (step 26). Consequently, in accordance with the exemplary embodiments of the invention the voice server 2 provides routing decisions regarding the networks to be used for outgoing calls and the client application 1 performs the local control (routing) of the outgoing calls of the mobile station MS1 to a circuit- switched or packet-switched network on the basis of the commands received from the voice server 2. In other words, both the client application 1 installed to the mobile station and the voice server 2 contain part of the logic used for the routing.

The routing decision of the voice server may be determined to be based on any criteria. The criteria may be determined subscriber-specifically (according to subscriber preferences, for example), subscriber-group- specifically (employers of a company, for example) and/or in a general manner.

According to an embodiment of the invention, the reachability of a recipient, for example, may be checked from a register that the IP application server 2 maintains on the reachability of the mobile stations of subscribers belonging to its IP voice service on the basis of registrations sent by their client applications. This situation is possible for example when all employers of a company have been connected to this service. If the service provider offers the service to a number of different companies, it may use the reachability infor- mation in the registers also for checking intercompany reachability. The more subscribers there are within the service, the more efficient becomes the decision-making.

According to an embodiment of the invention, the voice server 2 may check the reachability from another IP voice service.

Even if the reachability data showed the recipient to be reachable, this is not necessarily correct. According to some exemplary embodiments of the invention, the IP voice server 2 checks whether the called subscriber is reachable by an IP voice call by attempting an IP connection to the called subscriber (step 35 in Figure 3B). This may take place in addition to or instead of a check based on the registration data. Connection may be attempted by any IP message, such as an IP call. If the recipient responds by an appropriate IP message, the connection attempt has been successful and the reachability of the recipient has been confirmed. Further operation of the server depends on whether the connection attempt succeeds (step 36). If the recipient does not respond, the connection attempt has failed and the recipient is not reachable by an IP call request. The IP voice server 2 sends the client application 1 of the calling subscriber a response to the enquiry over the IP network 3 and commands it to set up the outgoing call as an IP voice call (step 34) if the IP connection attempt is successful and, optionally, if an IP voice call is economically and/or technically reasonable (step 33). The IP voice server 2 sends the client application 1 of the mobile station MS1 a response to the enquiry over the IP network 2 and commands it to set up the outgoing call as a circuit-switched voice call over the mobile communications network 6 (step 32) if the IP connection attempt to the client application of the called subscriber fails or, optionally, if an IP voice call is not economically and/or technically reasonable (step 33). An attempt to reach a called subscriber over the IP network ensures that an IP call is really possible and the mobile station MS1 is not controlled to make an IP call in vain but may be controlled to set up a circuit-switched call instead. Compared with an ordinary outgoing circuit-switched mobile call, the additional delay caused by a call intervention according to the invention, i.e. enquiry, connection attempt and receiving a reply, is small, only 2 to 3 seconds, for example. This is not much in comparison with common delays in call set up in mobile communications networks, which are manifold. On the other hand, a successful IP connection attempt from the IP server 2 also activates the called subscriber's IP application and its connection to the IP network and may even initiate IP call set-up at the receiving end, thus speeding up the establishment of an end-to-end IP call. It is to be noted that the voice server 2 may perform the IP connection attempt and/or relay the IP call to the recipient also through another similar voice service or to subscribers of another public VoIP service, for example.

According to the embodiment examples of the invention, the IP voice server 2 is capable of estimating whether an IP voice call is economically and/or technically reasonable. For example, the IP voice server 2 enables to obtain information about the costs of different networks, connection alternatives and/or connection combinations. If an outgoing call is to be set up for ex- ample to a recipient who is for example in the same mobile communications network or the same country as the calling subscriber, the IP voice server 2 may estimate the possible cost savings obtained by an IP call to be less significant than the advantage gained from the reliability and quality of a circuit- switched mobile call. The voice server 2 may thus command the client applica- tion 1 to establish a circuit-switched outgoing call, although the called subscriber would be reachable also by an IP call. On the other hand, if the called subscriber is in a different country and reachable by an IP call, the voice server 2 probably commands the client application 1 to set up an outgoing IP call which is then routed at a low cost to the other country. This basic idea will make it obvious for a skilled person that different decision-making algorithms and criteria may be applied to obtain an economically and/or technically sound routing decision in each particular case.

According to some embodiments of the invention, the IP voice server 2 may command the client application 1 to set up an outgoing IP call, even if the IP voice server 2 had no knowledge about the reachability of the called subscriber by an IP call or even if it knew that the called subscriber is not reachable by an IP call. In that case the IP call may be routed from the mobile station MS1 through the IP network to the IP voice server 2, which further routes the IP call to a gateway that is most advantageous from the point of view of the telephone network (e.g. PLMN or PSTN) used by the called subscriber and from which the call may continue as a circuit-switched call to the called subscriber. This routing decision may be possible for example when the user of the mobile station MS1 calls a foreign country telephone number, or a home country number when roaming abroad. Also in these embodiments the decision on whether a circuit-switched call or an IP call is chosen and on the routing of the call is taken automatically, independently of the circuit-switched network and in a manner which is invisible to the user.

According to an embodiment of the invention, the user may deactivate the client application for a predetermined period by one key or a key com- bination. In this context pushing a key refers to a pushing a keyboard or a touch screen or a similar operation performed on the user interface. A particularly suitable free key for this purpose is the backspace key. During the period in question all outgoing calls set up by the user are circuit-switched calls through a mobile communications network. The user may apply this function- ality for example when s/he is moving away from the coverage area of a wireless broadband, for example when entering a lift, exiting an office, getting into a car, etc., or when s/he for some other reason wants to make sure that the call is not disconnected. Preferably, the client application resumes an active state automatically after the predetermined time. According to an embodiment of the invention, also the IP voice server 2 is informed of the deactivation and may thus register the client application 1 as non-reachable for the period in question. Thanks to this, no attempts are made to connect incoming IP calls to the user either. According to an embodiment of the invention, the user may reactivate the client application from his/her user interface before the deactiva- tion period expires. Figure 4 shows an example illustrating the setting up of an outgoing call in accordance with an exemplary embodiment of the invention. In this example user Alice of the mobile station MS1 selects an outgoing mobile call to Bob, who is the user of the mobile station MS2. The client application 1 of the mobile station MS1 monitors the user interface and intervenes in the outgoing call to interrupt the setting up of a conventional circuit-switched mobile call. The client application 1 detects that a broadband WLAN network is available and as the client application 1 is registered to the IP voice server 2, it enquires over the WLAN network the IP voice server 2 of whether the outgoing call is to be set up as an IP voice call over the WLAN network 3. On the basis of the telephone number of the mobile station MS2 the IP voice server 2 checks from its register whether Bob is reachable by an IP voice call. The register check shows Bob to be reachable, but to ensure his reachability the IP voice server 2 makes a connection attempt to the mobile station MS2. The attempted connec- tion over the WLAN network is successful and since an IP voice call is economically and/or technically reasonable, the IP voice server 2 sends the client application 1 of the mobile station MS1 a command over the WLAN network to set up an IP voice call. As a result, an IP call is set up between the mobile stations MS1 and MS2 over WLAN networks.

Figure 5 shows a second example illustrating the setting up of an outgoing call in accordance with an exemplary embodiment of the invention. Again user Alice of the mobile station MS1 selects an outgoing mobile call to Bob, the user of the mobile station MS2. The client application 1 of the mobile station MS1 monitors the user interface and intervenes in the outgoing call to interrupt the setting up of a conventional circuit-switched mobile call. The client application 1 detects that a broadband WLAN network is available and as the client application 1 is registered to the IP voice server 2, it enquires over the WLAN network the IP voice server 2 of whether the outgoing call is to be set up as an IP voice call over the WLAN network 3. On the basis of the telephone number of the mobile station MS2 the IP voice server 2 checks from its register whether Bob is reachable by an IP voice call. According to the register Bob is not reachable and, moreover, the IP server 2 may perform a connection attempt, which fails. As a result, the IP voice server 2 sends the client application 1 of the mobile station MS1 a command over the WLAN network to set up a circuit-switched call through the GSM mobile communications network. Con- sequently, a conventional mobile call over the GSM network is set up between the mobile stations MS1 and MS2.

Figure 6 shows a third example illustrating the setting up of an outgoing call in accordance with an exemplary embodiment of the invention. In this example user Alice of the mobile station MS1 selects an outgoing call to a number in an IP-PBX or a similar communications system to Bob, who is the user of the mobile station MS2 and a computer PC. The client application 1 of the mobile station MS1 monitors the user interface, intervenes in the outgoing call and performs an enquiry to the IP voice server 2 over a WLAN network. On the basis of Bob's IP-PBX number the IP voice server 2 checks from its database whether Bob is reachable by an IP voice call. The check shows Bob to be reachable and the IP voice server 2 thus controls the mobile station MS1 , in accordance with the example of Figure 4, for example, to set up an IP call that is routed to Bob's IP-PBX system and to the application on the computer PC.

Figure 7 shows a fourth example illustrating the setting up of an outgoing call in accordance with an exemplary embodiment of the invention. In this example user Alice of the mobile station MS1 selects an outgoing call to a number in an IP-PBX or a similar communications system to Bob, the user of the mobile station MS2 and the computer PC. The client application 1 of the mobile station MS1 monitors the user interface, intervenes in the outgoing call and performs an enquiry to the IP voice server 2 over a WLAN network. On the basis of Bob's IP-PBX number the IP voice server 2 checks from its data base whether Bob is reachable by an IP voice call. The check shows Bob to be reachable and the IP voice server 2 thus controls the mobile station MS1 , in accordance with the example of Figure 4, for example, to set up an IP call that is routed to Bob's IP-PBX system. Alternatively, the IP voice server 2 may perform a connection attempt. However, Bob has call forwarding to his IP-PBX system activated on his mobile station MS2. Bob's IP-PBX system informs the IP voice server 2 about the call forwarding, and the server routes the IP call forward according to the logic of Figures 4 and 5, for example, but because of the call forwarding, the caller is not Alice's MS1 but Bob's IP-PBX system. In that case there is still an IP call between the client application 1 of the mobile station MS1 and the IP voice server 2, and the IP voice server 2 is in charge of optimizing Bob's reachability between the IP and the GSM mobile communica- tions networks. If Bob's MS2 is reached by the IP call, the call forwarding does not cause any costs (the routing of the call may continue as shown in Figure 4, where the IP voice server 2 detects that according to its register the application 1 of Bob's mobile station MS2 is reachable). If Bob is not reachable by the IP voice call (e.g. Bob's application 1 is not reachable according to the register of the IP voice server 2), the IP voice server 2 may transfer the call to a gateway from where it continues as a circuit-switched call (such as a GSM call) to Bob's mobile station MS2.

The methods described here may be implemented by various means so that a device implementing one or more mobile station or server functionalities described in connection with an embodiment, may comprise separate means for each functionality, or the means may be configured to carry out two or more functionalities. The methods in question may be implemented e.g. by hardware (one or more devices), firmware (one or more devices), software (one or more devices) or by combinations of these. Server functions, for example, may be implemented by a server system of one or more servers. The program code may be stored in any suitable (one or more) data storage media that are readable by a processor/computer or (one or more) memory units or (one or more) products and it may be executed by one or more processors/computers. The data storage medium or memory unit may be inside the processor/computer or an external unit, and in the latter case it may be in communication connection with the processor/computer through different media, as is known in the art.

A skilled person will find it obvious that, as technology advances, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not restricted to the above examples but may vary within the scope of the claims.

Claims

1. A call control method in a mobile station having capability for both voice calls switched over a mobile communications network and Internet Protocol (IP) voice calls switched over an IP network, in which method

a client application executed in the mobile station intervenes in an outgoing voice call of a mobile communication network initiated from a user interface and, if an IP network is available, enquires over the IP network an IP voice server of whether the outgoing call is to be set up as an IP voice call oyer the IP network;

the client application, in response to a reply received from the IP voice server, controls the mobile station to set up the outgoing call as a circuit- switched voice call over the mobile communications network or as an IP voice call over the IP network; and

the client application controls the mobile station to set up the out- going call as a circuit-switched voice call over the mobile communications network without making an enquiry if the IP network is not available.

2. A method according to claim 1 , wherein

the client application performs said enquiry to the IP server if/when the IP network is available and the client application is registered with the IP server.

3. A method according to claim 1 or 2, wherein

the client application is reactivated after the predetermined period.

4. A method according to any one of claims 1 to 3, wherein the client application interrupts the IP voice call attempt and changes the outgoing call to a circuit-switched voice call over a mobile communica- tions network if an IP voice call attempt is not successful within the predetermined period of time.

5. A method according to any one of claims 1 to 4, wherein the IP network is a wireless broadband network, a packet-switched mobile communications network or a wireless local area network.

6. A call control method in an IP voice server, where

the IP voice server receives over the IP network an enquiry from a client application executed on a calling subscriber's mobile station of whether an outgoing voice call from the mobile station is to be set up as an IP voice call over the IP network;

the IP voice server checks whether the called subscriber is reacha- ble by an IP voice call and, optionally, whether an IP voice call is economically and/or technically reasonable;

the IP voice server sends the client application a response to the enquiry over the IP network and commands it to set up the outgoing call as an IP voice call, if the called subscriber is reachable by an IP voice call and, op- tionally, if an IP voice call is economically and/or technically reasonable; and the IP voice server sends the client application a response to the enquiry over the IP network and commands it to set up the outgoing call as a voice call switched over a mobile communications network if the called subscriber is not reachable by an IP voice call or, optionally, if an IP voice call is not economically and/or technically reasonable.

7. A method according to claim 6, wherein

the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to set up the outgoing call as an IP voice call if according to the register the called subscriber is reachable by an IP voice call and, optionally, if an IP voice call is economically and/or technically reasonable; and

the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to set up the outgoing call as a circuit-switched voice call over a mobile communica- tions network if according to the register the called subscriber is not reachable by an IP voice call or, optionally, if an IP voice call is not economically and/or technically reasonable.

8. A method according to claim 6 or 7, wherein

the IP voice server checks whether the called subscriber is reacha- ble by an IP voice call by attempting an IP connection to the called subscriber;

the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to set up the outgoing call as an IP voice call if the IP call attempt to the called subscriber is successful and, optionally, if an IP voice call is economically and/or technically reasonable; and

9. A method according to claim 6, 7 or 8, wherein

the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to generate the outgoing call as an IP voice call if the IP connection attempt to the called subscriber is successful and, optionally, if an IP voice call is economically and/or technically reasonable; and

the IP voice server sends the client application of the calling subscriber a response to the enquiry over the IP network and commands it to set up the outgoing call as a circuit-switched voice call over a mobile communications network if the IP connection attempt to the called subscriber fails or, optionally, if an IP voice call is not economically and/or technically reasonable.

10. A method according to any one of claims 6 to 9, wherein the IP voice server is independent of the branch exchange system or mobile communications network where the mobile station is operating.

11. Software which, when installed and executed in a mobile station, implements the steps of a method according to any one of claims 1 to 5.

12. A computer program which, when executed in a computer, im- plements the steps of a method according to any one of claims 6 to 10.

13. A mobile station provided with means for implementing a method according to any one of claims 1 to 5.

14. A server system provided with means for implementing a method according to any one of claims 6 to 10.

15. A client-server system provided with at least one mobile station according to claim 13 and at least one server computer according to claim 14.