Title of Invention	DUAL MODE MOBILE TERMINAL AND OPERATING METHOD THEREOF
Abstract	A Dual mode mobile terminal (MT2) comprising a WLAN interface (WLAN_NIC) and a cellular radio interface (GSM_NIC) has been described wherein when receiving a Page Request (6) message over the cellular radio interface (GSM_NIC), indicating an incoming voice call over the cellular radio interface, or upon receiving an indication from the user of the dual mode terminal to perform an outgoing voice call, performing a determination (7) as to whether a WLAN coverage is possible from an AP providing WLAN telephony calls, and if so responding, by issuing a WLAN call message (8) to a WLAN AP over the WLAN interface to an interworking node (IWFN). There is moreover provided an Interworking node (IWFN) comprising a cellular control unit (CTRL_SIP), a cellular unit (GSM_U), a voice over IP unit (VO_IP) and a router (R), which upon receiving a WLAN call (9) from a dual mode terminal via a WLAN AP, is establishing a connection against a serving mobile switching centre (S_MSC/VLR) (10, 10a, 10b), is performing a call initiation procedure (12-15), a assign traffic channel procedure (16 - 20) and a call confirmation and call accepted procedure (22- 27) between the dual mode terminal (MT2) and the serving switching mode centre (S_MSC/VLR), is initiating duplex GSM/IP translation (29) and is routing the cellular call between the AP and the serving mobile switching centre (S_MSC).

Title of Invention

DUAL MODE MOBILE TERMINAL AND OPERATING METHOD THEREOF

Abstract

A Dual mode mobile terminal (MT2) comprising a WLAN interface (WLAN_NIC) and a cellular radio interface (GSM_NIC) has been described wherein when receiving a Page Request (6) message over the cellular radio interface (GSM_NIC), indicating an incoming voice call over the cellular radio interface, or upon receiving an indication from the user of the dual mode terminal to perform an outgoing voice call, performing a determination (7) as to whether a WLAN coverage is possible from an AP providing WLAN telephony calls, and if so responding, by issuing a WLAN call message (8) to a WLAN AP over the WLAN interface to an interworking node (IWFN). There is moreover provided an Interworking node (IWFN) comprising a cellular control unit (CTRL_SIP), a cellular unit (GSM_U), a voice over IP unit (VO_IP) and a router (R), which upon receiving a WLAN call (9) from a dual mode terminal via a WLAN AP, is establishing a connection against a serving mobile switching centre (S_MSC/VLR) (10, 10a, 10b), is performing a call initiation procedure (12-15), a assign traffic channel procedure (16 - 20) and a call confirmation and call accepted procedure (22- 27) between the dual mode terminal (MT2) and the serving switching mode centre (S_MSC/VLR), is initiating duplex GSM/IP translation (29) and is routing the cellular call between the AP and the serving mobile switching centre (S_MSC).

Full Text	Field of the invention The present invention relates to dual mode systems and nodes. In particular, the present invention relates to the area of WLAN - mobile telephony integration of voice services. Background of the invention The current GSM/3G and WLAN technologies constitute two separate radio network technologies. They operate at different frequencies and make use of separate desig- nated protocols. Currently standardization work is ongoing on integrating data and other services of WLAN and GSM/3G in the forums of 3GPP, 3GPP2 and IEEE. Six scenarios dealing with various degrees of integration have been sketched in the third generation partnership project, 3GPP. Scenarios 1, 2 and 3 have been defined so far. However, the work for scenario 6, i.e. WLAN GSM/3G integration of telephony (Circuit Switched voice services) has not yet started. A desirable concept known as "always best connected" aims to ensure that the best and cheapest service connection is rendered available to the user at all times and performing handover in such a way that the user hardly notices the underlying access technology. Currently, dual mode mobile phones integrating different kinds of radio access tech- niques, such as WLAN and GSM/3G, providing prior art access on the choice of the user by means of one apparatus have been rendered available on the marketplace. However, Cellular systems and WLAN systems are currently not interoperable on the network side. A further problem for the integration of WLAN and GSM/3G services is the pico-cell character of the WLAN radio network. The WLAN radio network consists of a flat struc- ture of pico-cells, not at all suitable for typical mobile user behavior. A telephony call would be difficult to maintain in a WLAN network when a user moves with high speed as he is used to in a cellular network. Prior art document GB2336069 shows a dual use mobile station (10, 21,41) having a GSM interface (451) and a local area interface, such as a RS-232 interface, W-LAN, USB or an IR interface (52) for connecting to a personal base unit (PBU) which com- prises a (virtual) base transceiver station (BTS) emulator or virtual base station, which may be implemented by means of a personal computer (PC). The PBU has a LAN inter- face for connecting to an Interworking Unit (IWU). The interworking unit (IWU) is having on one hand connectivity for the PBU and a GMS base station transceiver and on the other hand connectivity to a Home Location Register (HLR), a Mobile Station Switching Centre (MSC) and an IP Plane. This allows cellular users to utilize private intranets to carry the cellular services within the intranet coverage area. Access to public GSM net- work is offered by introducing a transparent location management method, which allows terminals connected to the intranet to be reached from the GSM network in a normal manner. The Interworking Unit comprises among others an Intranet Location Register (ILR). The function of the Intranet Location Register is to store mobility management in- formation and call statistics of the subscribers configured into the Wireless Intranet Of- fice system. Roaming of visitors is controlled by the mobile switching centre. For visitors, only temporary information will be stored into the Intranet Location Register. When a mobile station is connected to the PBU, for example over the RS-232 cable or RF inter- face, information such as voice data, Fax SMS (Short Message Service) is transmitted over the local area network. The information and GSM layer 3 (i.e. Mobility management messaging, paging, page response, routing area updates etc.) signalling messages are re-directed to the RF interface branch. When the mobile station and the PBU are linked, the "field strength" of the virtual BTS will be (rendered) greater than that of other BTS's in the GSM network. Consequently, handover is made to the virtual BTS. Prior art document US6119003 shows a multimode cellular telephone capable of bi- directionally exchanging control messages and status messages with primary and sec- ondary system controllers, such as a of a D-AMPS (Digital-Advanced Mobile Phone Ser- vice) and an AMPS network, for automatically switching the state of the terminal be- tween primary and secondary systems. If the terminal is using its preferred network, then it stays connected to the primary network until the network is no longer available. If the latter applies the terminal begins scanning for the second network in an ordered priority list. Prior art document US2004/0105434showsa WLAN base station emulating the func- —tic^^a^ity^fa-BT5^ase^«nseeive^Stafo _.... Multiplex Access) protocols. D3 bridges the gap between in-building WLAN network en- vironment and the external cellular environment to ensure that a data link exists between the wide area network across the WLAN air interface provided a WLAN access point. Once an interworking node (Ethercell) is aware that a dual mode cellular phone has been authenticated, it will assign a service point Identification value to the dual-mode cellular phone. Such assignment will be used for future communications with the dual mode cellular phone. According to D3 a mapping of IEEE 802.11 WLAN specific values are mapped to traditional cellular hand-over parameters for enabling seamless hand- over's between these heterogeneous networks. Throughout any call set-up processes, all communications between the dual mode cellular phone and the interworking node take place via a LAPDm (Link Access Protocol in the D channel - mobile) data link using previously assigned SAPI values during the registration process. All signalling messages (either GSM (Global System for Mobile Communications), TDMA (Time Division Multi- plex Access), or CDMA (Code Division Multiplex Access)) exchanged between the dual mode cellular phone and the interworking node are formatted into LAPDm message frames. The LAPDm message frames are further encapsulated in IEEE 802.11 MAC (Medium Access Control) headers and transmitted across the WLAN air link. Although it is not specifically stated how paging is carried out in D3 it appears inherently disclosed that even paging messages are sent through the WLAN interface. Prior art document "Interworking Between WLAN's and Third generation Cellular Data Networks", A. K. Salkintzis, 2003, IEEE, pp 1803-1806 discloses a WLAN adaptation function (WAF) that supports interworking functions between GPRS (General Packet Data Radio System) signalling and data over 802.11 WLAN's. The system is intended for data services and no special means for voice services are defined. Brief description of the drawings Fig. 1 shows a first preferred embodiment of a system architecture according the in- vention comprising an InterWorking Forwarding Node (IWFN), Fig. 2 shows a schematic representation of a dual mode terminal according to the in- vention having both GMS and WLAN capabilities and corresponding network in- " ; terface cards, - - - - - - Fig. 3 shows an Interworking Forwarding Node according to the invention, and Fig. 4 and 5 shows, among other, a handshaking diagram for a telephone call originating from a mobile telephone system being acknowledged via the GSM network in- terface card of a dual mode terminal and subsequently being handed over to the WLAN network interface card, and Fig. 6 shows a state diagram for the dual mode terminal according to the invention. Summary of the invention It is a first object to set forth a method or an apparatus for integration of telephony be- tween WLAN and GSM/3G and which provides mobility and paging efficiency while re- quiring minimum adaptation of existing legacy cellular systems. This object has been accomplished by the method defined in claim 1. This object has moreover been accomplished by the apparatus defined in claim 8. Further advantages will appear from the following detailed description of the invention. Detailed description of preferred embodiments of the invention The present invention proposes a method for integrating the telephony service of WLAN and GSM/3G. The integrated architecture according to a first embodiment of the invention is shown in figure 1. A GSM/3G network is shown, comprising prior art elements: base station set, BSS, Serving Mobile Node, also denoted Mobile Switching Center / Visiting Location Register, S_MSC/VLR, (also partly referred to as Serving GPRS Support Node), G_MSC/VLR, Gateway Node Mobile Switching Centre / Visiting Location Register, S;_MSCA/tR7(also partly referred to as Gateway —regjster;iHt^Ae7lherplatrrot^^ mobile terminalra The WLAN AP node may be coupled to the interworking and forwarding node IWFN ei- ther through an appropriate network such as an Ethernet LAN or via another network such as an ADSL modem and suitable backbone network, BKBN. In fig. 2, a logic diagram pertaining to the dual mode WLAN-GSM/3G mobile, MT2, ac- cording to a preferred embodiment of the present invention is shown. The dual mode terminal comprises two radio network interfaces - one for GSM/ 3G transmission / recep- tion, GSM_NIC, and one for WLAN transmission / reception, WLAN_NIC, whereby both interfaces may be in operation simultaneously. The dual mode mobile terminal moreover comprises a conventional sound card, SND_C, offering connections to loudspeaker / amplifier and microphone. The dual mode terminal may consist of a standard processing platform, such as a laptop or personal digital assistant (PDA), controlled by a usual common operating system. The network interface cards may be off-the-shelf components, while the functionality of the call selection processor and the various logic functions may be performed by a software application running on the standard processing platform, such as a common laptop com- puter or PDA. According to a preferred embodiment of the invention, the dual mode platform comprises a software application, D_APP, which comprises the following logic functions: apparatus control and call selection, CTRL_CALL_SELCTION, SIP/H323 logic and signal process- ing, SIP/H323J_OGIC, voice over IP coding/ decoding, VOJP, GSM logic and signal processing, GSM_LOGIC and GSM voice coding / decoding, GSM_CODEC. Finally there is provided a camp logic function, CMPJ-OGIC, for controlling whether the dual mode mobile terminal shall operate over the GSM or WLAN network interface cards. In the following, a preferred embodiment for the handshaking between the dual mode mo- bile terminal and the exterior (cf. fig. 4 and 5) is illustrated using SIP protocol signaling. As an alternative, the H323 protocol may be used. For the WLAN network interface card, signal streams are communicated over a user plane, UP, bearing voice over IP packets and a H323 / SIP control plane, CP. For the GSM network interface card signals are transmitted over GSM-codec, UP, and GSM control signaling plane, CP. In a manner, which shall be disclosed in the following, voice signals may selectively be transferred between the sound card, SND_C, and the WLAN network interface card, WLAN_NIC or the GSM network Interface card, GSM_NIC. The control plane signaling issued on the respective Interface cards shall be explained later with reference to fig. 4 and 5. It should be noticed that, the principles of the present invention also applies to a 3G/WLAN equipped dual mode terminal although the exem- plary embodiment has been shown for GSM/WLAN dual mode terminal. It should be fur- ther noticed that the term dual mode terminal does not exclude more than two access technologies being provided in the terminal. According to the invention a WLAN-GSM/3G Interworking, IWFN, has been provided between the WLAN AP and the S_MSCA/LR. The IWFN is responsible for "translat ing" a voice call between GSM voice and IP telephony, that is, translate the GSM audio codec format to voice over IP audio codec and performing signaling for enabling the call to be made via standard nodes. In fig. 3, a preferred embodiment of the IWFN has been shown. It comprises an A-GSM interface for connection to a mobile switching center, MSC, and an Ethernet interface for coupling to a WLAN access point AP. It moreover comprises an GSM codec coder and decoding unit, GSMJJ, as well as a voice over IP coding and decoding unit, VOJP, for translating a GSM codec stream into voice over IP stream and vice versa. Moreover, the unit comprises a SIP signaling protocol control unit, CTRL_SIP, for transmitting for sig- naling to a GSM interface card. It moreover contains a H.323 service. The functionality of the IWFN shall be dealt with in more detail later. As mentioned above, the WLAN AP node may be coupled to the interworking and for- warding node IWFN either through an appropriate network such as an Ethernet LAN or via another network such as an ADSL modem and suitable backbone network, BKBN. According to the invention, The Serving MSC is configured such that it can hand over a voice call from the Base station to the new IWF node. However, the IWF node preferably "appears like* an ordinary base station system, BSS, to the MSC and normal HO is done between WLAN and GSM/3G from the MSC point of view. Advantageously, the dual mode mobile terminal MT2 may identify the IWF node by an IP address that is preconfigured In the dual mode mobile terminal, MT2. According to the invention as exemplary system is envisaged where many AP's are pro- vided In different locations so as to provide so-called "hot-spof access to prescription users. The system according to the invention may moreover comprise predetermined lhr^n,^H"tP?hVide? in hTB and °ffiCe environments. Common for these AP's are that they are coupled to the mterworking node, IWFN, according to the invention, alternatively, that there are provided several interworklng nodes to which respective the AP's are cou- pled. A preferred embodiment of the invention shall now be explained with reference to fig 4 and 5. I. - Signaling method for incoming voice calls from the GSM/3G system and hand-over to the WLAN radio interface of a dual mode terminal Figure 4 and 5 shows the signaling sequence according to the invention where a voice call is received tn the cellular network and handed over to the WLAN network interface card of the dual mode terminal. In the present embodiment the dual mode terminal is active and is attached to both the GSM network as well as a WLAN network. It should be understood that the network pro- vider both supports both the GSM facilities as well as the WLAN facilities to the dual user subscriber. 1. An Incoming Voice Call to Gateway G-MSC (GSM Mobile Switching Center) /VLR Is detected 2. the G-MSC Initiates a HLR Location Request to find the S-MSC to which the ad- dressed terminal Is attached, the HLR responds 3. the G-MSC signals a Call Arrived message to the S-MSC 4. a Complete Call instruction is sent from the G-MSC to the S-MSC, the voice Call forwarded to S-MSC 5. a Page Request Is sent from the S-MSC to BaseStatlon (BSS) 6. the Pag© Request is forwarded to the dual mode mobile terminal on the Air Inter- face 7. the dual mode mobile terminal performs a determination as to whether WLAN access is possible from an AP providing WLAN telephony calls, and if so, de- cides to proceed further over the WLAN radio interface (by the mechanism pro- posed below in connection with fig. 8) 8. a Page Response is sent from MT2 to WLAN AP (the IWF is addressed an IP address pre-conflgured by the dual mode mobile terminal) 9. - which is forwarded to the IWFN, 10. -and further to the S-MSC 11. security functions are carried out in order to authenticate the MT 12. setup; initiate call setup 13. Invite (SIP); Initiate call setup (translated to SIP) 14. Offer Response (SIP); Initiation confirmed (translated to SIP) 15. Call Conference (SIP); Initiation confirmed 16. Allocate; Request reservation of resources for call 17. Reservation (SIP); request reservation of resources for call (translated to SIP) 18. Alert User (SIP); terminal is prepared for call reception 19. Reservation Conference; resource reservation confirmed (translated to SIP) 20. Allocation Complete; resource reservation confirmed 21. Ringing (SIP); ring tone generated at B-party (translated to SIP) 22. Alert; ring tone generated at B-party 23.200 OK (SIP); answer indication i.e. B-party answers (translated to SIP) 24. Connect; answer indication i.e. B-party answers 25. Connect Acknowledge; when answer indication is received an acknowledge is sent to terminal 26. Start Media (SIP); when terminal has sent the answer indication (200 OK) it starts to send the media stream i.e. VoIP payload 27. Acknowledge (SIP); when answer indication Is received an acknowledge is sent to terminal (translated to SIP) 28. Complete Call; serving MSC acknowledges back to gateway MSC that call has been established. 29,GSM„P translation 29; the IWFN does any necessary coding/decoding or other translation between VoIP payload and GSM coded payload 30. caiTln progress The SIP signals comparative to the SIP protocol have been indicated in brackets above. It Is seen that in. relatjpp to a prior art GSM call, the voice call according to the Invention Is routed to the IWFN instead of to the Base station (BSS) in the serving MSC. II. - Signaling method for making outgoing voice calls from a WLAN radio Interface to a GSM/3G system A method is also set forth involving a user of the dual mode terminal Initiating a phone call. This procedure shall also be explained with respect to fig. 4 and 5, using the follow- ing steps: -.' The user of the dual mode terminal, MT2, wants to make an outgoing telephone call 7. The dual mode mobile terminal decides to make the call over the WLAN network interface card (by the mechanism proposed below as explained in connection with fig. 6) 8.- 30 A voice call setup signal is sent via WLAN AP IWFN to S-MSC (the IWF is addressed by a MT preconfigured IP address) as explained according to steps 8 - 30 above The voice call is handled as usual in the GSM/3G network and is setup towards the fixed end user, The call is made and when completed the dual mode mobile terminal goes back to camp on the GSM/3G channel. III. - Signaling method for handing over a voice call from the WLAN radio interface to the GSM/3G interface of the dual mode terminal If during a voice call in WLAN radio access, the dual mode mobile terminal moves out of reach for the WLAN AP, a handover to GSM/3G is triggered. The action taken in the dual mode mobile tormina) is as follows: As mentioned above, when a particular predefined AP is discovered ("home AP"), 103, WLAN access may be selected, MS3, without any timer being set. WLAN is installed in many homes today, and a given Home AP may be set as preferred access. Alternatively, a typical preferred AP may be the WLAN in the office, hence more than one pre-defined "home AP" may be provided. In any case, when the selection mechanism enters the state "WLAN Access Allowed", MS3, the behavior of the dual mode mobile terminal can be such that the dual mode mobile terminal by itself always access through the WLAN or alternatively it can be indi- cated to the user that this state has been entered, so that the user can chose to do ac- cess by WLAN. Preferable, the actual state is notified to the user when the state is en- tered or left or when an automatic transition between the WLAN system and the GSM/3G system occurs. This notification can be a noise signal, a light signal, a buzz signal, a message or an icon on the display or any other type of signal. The above mechanism secures that if the user of the dual mode terminal is on the move and is passing through a given area in which WLAN access is available, the readiness for responding, making and keeping GSM/3g phone calls, including during GSM/3G handover, is prioritised and secured. On the other hand, if the user is within a "station- ary" reach of a "home AP", calls are enabled over the WLAN interface. If the user remains within coverage of the predetermined home AP, but is not using the dual mode mobile terminal actively, the dual mode terminal may enter a power save mode in which the WLAN network interface card is set to sleep after a suitable period of inactivity, 106. If activity is again encountered involving attempting to use the WLAN network interface or an activity on the GSM interface is encountered, a wake-up request 107, places the terminal back in the WLAN access allowed state, MS4. In this instance the user may or may not have moved out of WLAN coverage, in the former case, the dual mode mobile terminal entering state MS1. This mechanism may work as exemplified by the states of the dual mode mobile terminal MS1, MS2 and MS3 and the corresponding change state conditions that are shown in figure 6. There is moreover provided an optional power save mode MS4, in view of the relatively high power consumption of current WLAN network interface cards. The selec- tion mechanism may be implemented in the application, D-APP, in the logic function camping logic, CMPJJDGIC, shown in fig. 2. The mobile terminal initially adopts a WLAN access disallowed state, MS1, searching for WLAN AP's, 101. if a WLAN AP is identified offering access, state MS2 js adopted. One way of determining whether the found AP is offering connection to an JWFN is that the terminal tries to communicate with the IWFN, sending a WLAN Call message (cf. fig. 4) step 8-WLAN Call (Page Response)) and await an Invite, (cf. fig. 4, step 13, Invite) or some other message, such as Pinging the IWFN. In state MS2 a timer value T1 is defined such that, if the dual mode mobile terminal has heard the same WLAN AP for a time longer than given by the timer, MS2 - "WLAN ac- cess disallowed wait for T1", then the dual mode mobile terminal is set in a state, MS3, allowing voice calls to be handed over to WLAN, "WLAN access allowed", since the dual mode mobile terminal is probably not moving, if the signal is lost the mobile terminal goes back to MS1,102. When, in MS3, the dual mode mobile terminal cannot hear the WLAN AP anymore -104, WLAN lost - the dual mode mobile terminal is set to state "WLAN access disallowed", MS1. WLAN access may also be allowed when one of a set of pre-defined AP's, such as a "home AP" is found, 103. In other instances, when the AP Is lost, the WLAN access disallowed state MS1 is chosen. In MS3 the WLAN Interface card is powered on and will remain so if the WLAN card is used for transmission or access to the WLAN AP is not lost. However, if no transmission takes place while the AP Is being present, the dual mode mobile terminal may enter a power save mode switching off the WLAN network interface card, WLAN_NIC. According to a further embodiment, the user may also actively select or overrule WLAN access by giving a command to the dual mode mobile terminal that WLAN access is pre- ferred. This selection can be based on a presentation of available radio access networks as sensed by the dual mode mobile terminals, e.g. WLAN AP's that are within reach. As mentioned above, when a particular predefined AP is discovered ("home AP"), 103, WLAN access may be selected, MS3, without any timer being set. WLAN is installed in many homes today, and a given Home AP may be set as preferred access. Alternatively, a typical preferred AP may be the WLAN in the office, hence more than one pre-defined "home AP" may be provided. In any case, when the selection mechanism enters the state "WLAN Access Allowed", MS3, the behavior of the dual mode mobile terminal can be such that the dual mode mobile terminal by itself always access through the WLAN or alternatively it can be indi- cated to the user that this state has been entered, so that the user can chose to do ac- cess by WLAN. Preferable, the actual state is notified to the user when the state is en- tered or left or when an automatic transition between the WLAN system and the GSM/3G system occurs. This notification can be a noise signal, a light signal, a buzz signal, a message or an icon on the display or any other type of signal. The above mechanism secures that if the user of the dual mode terminal is on the move and is passing through a given area in which WLAN access is available, the readiness for responding, making and keeping GSM/3g phone calls, including during GSM/3G handover, is prioritised and secured. On the other hand, if the user is within a "station- ary" reach of a "home AP", calls are enabled over the WLAN interface. If the user remains within coverage of the predetermined home AP, but is not using the dual mode mobile terminal actively, the dual mode terminal may enter a power save mode in which the WLAN network interface card is set to sleep after a suitable period of inactivity, 106. If activity is again encountered involving attempting to use the WLAN network interface or an activity on the GSM interface is encountered, a wake-up request 107, places the terminal back in the WLAN access allowed state, MS4. In this instance the user may or may hot have moved out of WLAN coverage, in the former case, the dual mode mobile terminal entering state MS1. WE CLAIM 1. Method of operating a dual mode mobile terminal (MT2) comprising a wireless local area network interface (WLAN_NIC) and a cellular radio interface (GSM_NIC), wherein the following steps are carried out the dual mode mobile terminal camping on the cellular radio interface when idle, characterized by when receiving a Page Request (6) message over the cellular radio interface (GSM_NIC) indicating an incoming voice call over the cellular radio interface, performing a determination (7) as to whether wireless local area network cover- age is possible from an access point (WLAN-AP) providing wireless local area network telephony calls, and if so responding, by issuing a wireless local area network call message (8) to the wire-less local area network access point (WLAN-AP) thus determined over the wire-less local area network interface (WLAN-NIC) to an interworking node (IWFN), subsequently engaging in a call initiation procedure (12-15), an assign traffic channel procedure (16 - 20) and a call confirmation and call accepted procedure (21- 27) with the interworking node (IWFN), and processing the incoming voice call as a voice over IP telephony call over the wireless local area network interface (29, 30) towards another party, wherein when the call is ended, the dual mode mobile terminal (MT2) going back to camp on the cellular channel. 2. Method as claimed in claim 1, wherein the call initiation procedure comprises the interworking node (IWFN) issuing an Invite signal (13) to the dual mode mobile terminal (MT2) upon receiving a setup (12) from the mobile serving node (S- MSC/VLR), and issuing a call confirm signal (15), upon receiving an offer response signal (14) from the dual mode mobile terminal. 3. Method as claimed in claims 1-2, wherein the assign traffic channel procedure comprises the interworking node (IWFN) issuing a reservation confirm signal (17) to the dual mode mobile terminal (MT2) upon receiving an allocate signal (16) from the mobile serving node (S-MSC/VLR), and issuing an allocation complete signal (20), upon receiving a reservation confirm signal (19) from the mobile serving node (S-MSCNLR). 4. Method as claimed in claims 1-3, wherein the call confirmation and call accepted procedure comprises the interworking node (IWFN) issuing alert (22) and connect (24) signals (17) to the mobile serving node (S-MSC/VLR), upon receiving ringing and 200-OK signals (21, 23) from the dual mode mobile terminal (MT2), the interworking node (IWFN) issuing an acknowledgement signal (27) to the dual mode mobile terminal (MT2) upon receiving a connection acknowledged signal (25) from the mobile serving node (S-MSC/VLR). 5. Method as claimed in claims 1-4, further comprising a step of selecting to receive or make voice calls over the cellular interface or over the wireless local area network interface, by performing the steps of initially adopting a state (MSI) in which voice calls over wireless local area net- work access are disallowed, searching for a wireless local area network access point (AP) offering connection to voice calls, when identifying a predetermined wireless local area network access point (AP) offering connection to voice calls, starting a timer (T1, MS2), upon the timer (T1) expiring, allowing voice calls to be performed over the predetermined wireless local area network access point (AP, MS3). 6. Method as claimed in claim 5, wherein when entering a wireless local area net- work access allowed state, but the user not using the wireless local area network access for a given period, entering a power save mode (MS4), in which wireless local area network access is not allowed. 7. Method as claimed in claim 5, wherein if in the power save mode (MS4) obtaining a page request signal (6) or if necessitated by the user actively seeking to use the wireless local area network interface or wishing to make a phone call, entering the wireless local area network allowed state (MS3). 8. Dual mode mobile terminal (MT2) comprising a wireless local area network inter- face (WLAN_NIC) and a cellular radio interface (GSM_NIC), means for executing a software application, (D_APP) comprising apparatus control and call selection (CTRL_CALL_SELCTION), SIP/H323-logic and signal processing (SIP/H323-LOGIC), voice over IP coding/ decoding (VO_IP), GSM-logic and signal processing (GSM LOGIC) and cellular voice coding / decoding (GSM_CODEC) and a camp logic function (CMP_LOGIC) for controlling whether the dual mode mobile terminal shall operate over the cellular or the wireless local area network interfaces (WLAN_NIC, GSM_IMIC), the dual mobile mode terminal further comprising: means for camping on the cellular radio interface when idle, characterized by the dual mode mobile terminal (MT2) further comprising: means for indicating an incoming voice call over the cellular radio interface, when receiving a Page Request (6) message over the cellular radio interface (GSM_NIC), and for performing a determination (7) as to whether wireless local area network coverage is possible from an access point (WLAN-AP) providing wireless local area network telephony calls means for responding to a positive determination (7) by issuing a wireless local area network call message (8) to the wireless local area network access point (WLAN-AP) thus determined over the wireless local area network interface (WLAN-NIC) to an interworking node (IWFN) means for subsequently engaging in a call initiation procedure (12-15), an assign traffic channel procedure (16 - 20) and a call confirmation and call accepted procedure (21- 27) with the interworking node (IWFN), and means for processing the incoming voice call as a voice over IP telephony call over the wireless local area network interface(29, 30) towards another party, wherein said means for camping are arranged to go back to camp on the cellular channel when the call is ended. 9. Dual mode mobile terminal (MT2) as claimed in claim 8, further comprising means for selecting to receive or make voice calls over the cellular interface or over the wireless local area network interface which comprise means for initially adopting a state (MSI) in which voice calls over wireless local area network access is disallowed, and for searching for a wireless local area network access point (AP) offering connection to voice calls, means , responsive to identifying a predetermined wireless local area network access point (AP), for offering connection to voice calls, and for starting a timer (T1, MS2), means for, upon the timer (T1) expiring, allowing voice calls to be performed over the predetermined wireless local area network access point (AP, MS3). 10. Dual mode mobile terminal (MT2) as claimed in claim 9, comprising means, responsive to entering a wireless local area network access allowed state, and to the user not using the wireless local area network access for a given period, for entering a power save mode (MS4), in which wireless local area network access is not allowed. 11. Dual mode mobile terminal (MT2) as claimed in claim 9, comprising means for obtaining a page request signal (6) if in the power save mode (MS4) or for entering the wireless local area network allowed state (MS3), if necessitated by the user actively seeking to use the wireless local area network interface or wishing to make a phone call. ABSTRACT DUAL MODE MOBILE TERMINAL AND OPERATING METHOD THEREOF A Dual mode mobile terminal (MT2) comprising a WLAN interface (WLAN_NIC) and a cellular radio interface (GSM_NIC) has been described wherein when receiving a Page Request (6) message over the cellular radio interface (GSM_NIC), indicating an incoming voice call over the cellular radio interface, or upon receiving an indication from the user of the dual mode terminal to perform an outgoing voice call, performing a determination (7) as to whether a WLAN coverage is possible from an AP providing WLAN telephony calls, and if so responding, by issuing a WLAN call message (8) to a WLAN AP over the WLAN interface to an interworking node (IWFN). There is moreover provided an Interworking node (IWFN) comprising a cellular control unit (CTRL_SIP), a cellular unit (GSM_U), a voice over IP unit (VO_IP) and a router (R), which upon receiving a WLAN call (9) from a dual mode terminal via a WLAN AP, is establishing a connection against a serving mobile switching centre (S_MSC/VLR) (10, 10a, 10b), is performing a call initiation procedure (12-15), a assign traffic channel procedure (16 - 20) and a call confirmation and call accepted procedure (22- 27) between the dual mode terminal (MT2) and the serving switching mode centre (S_MSC/VLR), is initiating duplex GSM/IP translation (29) and is routing the cellular call between the AP and the serving mobile switching centre (S_MSC).

Full Text

Field of the invention
The present invention relates to dual mode systems and nodes. In particular, the present
invention relates to the area of WLAN - mobile telephony integration of voice services.
Background of the invention
The current GSM/3G and WLAN technologies constitute two separate radio network
technologies. They operate at different frequencies and make use of separate desig-
nated protocols. Currently standardization work is ongoing on integrating data and other
services of WLAN and GSM/3G in the forums of 3GPP, 3GPP2 and IEEE.
Six scenarios dealing with various degrees of integration have been sketched in the third
generation partnership project, 3GPP. Scenarios 1, 2 and 3 have been defined so far.
However, the work for scenario 6, i.e. WLAN GSM/3G integration of telephony (Circuit
Switched voice services) has not yet started.
A desirable concept known as "always best connected" aims to ensure that the best and
cheapest service connection is rendered available to the user at all times and performing
handover in such a way that the user hardly notices the underlying access technology.
Currently, dual mode mobile phones integrating different kinds of radio access tech-
niques, such as WLAN and GSM/3G, providing prior art access on the choice of the user
by means of one apparatus have been rendered available on the marketplace. However,
Cellular systems and WLAN systems are currently not interoperable on the network side.
A further problem for the integration of WLAN and GSM/3G services is the pico-cell
character of the WLAN radio network. The WLAN radio network consists of a flat struc-
ture of pico-cells, not at all suitable for typical mobile user behavior. A telephony call
would be difficult to maintain in a WLAN network when a user moves with high speed as
he is used to in a cellular network.
Prior art document GB2336069 shows a dual use mobile station (10, 21,41) having a
GSM interface (451) and a local area interface, such as a RS-232 interface, W-LAN,

USB or an IR interface (52) for connecting to a personal base unit (PBU) which com-
prises a (virtual) base transceiver station (BTS) emulator or virtual base station, which
may be implemented by means of a personal computer (PC). The PBU has a LAN inter-
face for connecting to an Interworking Unit (IWU). The interworking unit (IWU) is having
on one hand connectivity for the PBU and a GMS base station transceiver and on the
other hand connectivity to a Home Location Register (HLR), a Mobile Station Switching
Centre (MSC) and an IP Plane. This allows cellular users to utilize private intranets to
carry the cellular services within the intranet coverage area. Access to public GSM net-
work is offered by introducing a transparent location management method, which allows
terminals connected to the intranet to be reached from the GSM network in a normal
manner. The Interworking Unit comprises among others an Intranet Location Register
(ILR). The function of the Intranet Location Register is to store mobility management in-
formation and call statistics of the subscribers configured into the Wireless Intranet Of-
fice system. Roaming of visitors is controlled by the mobile switching centre. For visitors,
only temporary information will be stored into the Intranet Location Register. When a
mobile station is connected to the PBU, for example over the RS-232 cable or RF inter-
face, information such as voice data, Fax SMS (Short Message Service) is transmitted
over the local area network. The information and GSM layer 3 (i.e. Mobility management
messaging, paging, page response, routing area updates etc.) signalling messages are
re-directed to the RF interface branch. When the mobile station and the PBU are linked,
the "field strength" of the virtual BTS will be (rendered) greater than that of other BTS's
in the GSM network. Consequently, handover is made to the virtual BTS.
Prior art document US6119003 shows a multimode cellular telephone capable of bi-
directionally exchanging control messages and status messages with primary and sec-
ondary system controllers, such as a of a D-AMPS (Digital-Advanced Mobile Phone Ser-
vice) and an AMPS network, for automatically switching the state of the terminal be-
tween primary and secondary systems. If the terminal is using its preferred network, then
it stays connected to the primary network until the network is no longer available. If the
latter applies the terminal begins scanning for the second network in an ordered priority
list.
Prior art document US2004/0105434showsa WLAN base station emulating the func-
—tic^^a^ity^fa-BT5^ase^«nseeive^Stafo _....
Multiplex Access) protocols. D3 bridges the gap between in-building WLAN network en-
vironment and the external cellular environment to ensure that a data link exists between
the wide area network across the WLAN air interface provided a WLAN access point.

Once an interworking node (Ethercell) is aware that a dual mode cellular phone has
been authenticated, it will assign a service point Identification value to the dual-mode
cellular phone. Such assignment will be used for future communications with the dual
mode cellular phone. According to D3 a mapping of IEEE 802.11 WLAN specific values
are mapped to traditional cellular hand-over parameters for enabling seamless hand-
over's between these heterogeneous networks. Throughout any call set-up processes,
all communications between the dual mode cellular phone and the interworking node
take place via a LAPDm (Link Access Protocol in the D channel - mobile) data link using
previously assigned SAPI values during the registration process. All signalling messages
(either GSM (Global System for Mobile Communications), TDMA (Time Division Multi-
plex Access), or CDMA (Code Division Multiplex Access)) exchanged between the dual
mode cellular phone and the interworking node are formatted into LAPDm message
frames. The LAPDm message frames are further encapsulated in IEEE 802.11 MAC
(Medium Access Control) headers and transmitted across the WLAN air link. Although it
is not specifically stated how paging is carried out in D3 it appears inherently disclosed
that even paging messages are sent through the WLAN interface.
Prior art document "Interworking Between WLAN's and Third generation Cellular Data
Networks", A. K. Salkintzis, 2003, IEEE, pp 1803-1806 discloses a WLAN adaptation
function (WAF) that supports interworking functions between GPRS (General Packet
Data Radio System) signalling and data over 802.11 WLAN's. The system is intended
for data services and no special means for voice services are defined.
Brief description of the drawings
Fig. 1 shows a first preferred embodiment of a system architecture according the in-
vention comprising an InterWorking Forwarding Node (IWFN),
Fig. 2 shows a schematic representation of a dual mode terminal according to the in-
vention having both GMS and WLAN capabilities and corresponding network in-
" ; terface cards, - - - - - -
Fig. 3 shows an Interworking Forwarding Node according to the invention, and

Fig. 4 and 5 shows, among other, a handshaking diagram for a telephone call originating
from a mobile telephone system being acknowledged via the GSM network in-
terface card of a dual mode terminal and subsequently being handed over to
the WLAN network interface card, and
Fig. 6 shows a state diagram for the dual mode terminal according to the invention.
Summary of the invention
It is a first object to set forth a method or an apparatus for integration of telephony be-
tween WLAN and GSM/3G and which provides mobility and paging efficiency while re-
quiring minimum adaptation of existing legacy cellular systems.
This object has been accomplished by the method defined in claim 1.
This object has moreover been accomplished by the apparatus defined in claim 8.
Further advantages will appear from the following detailed description of the invention.
Detailed description of preferred embodiments of the invention
The present invention proposes a method for integrating the telephony service of WLAN
and GSM/3G.
The integrated architecture according to a first embodiment of the invention is shown in
figure 1. A GSM/3G network is shown, comprising prior art elements: base station set,
BSS, Serving Mobile Node, also denoted Mobile Switching Center / Visiting Location
Register, S_MSC/VLR, (also partly referred to as Serving GPRS Support Node),
G_MSC/VLR, Gateway Node Mobile Switching Centre / Visiting Location Register,
S;_MSCA/tR7(also partly referred to as Gateway
—regjster;iHt^Ae7lherplatrrot^^ mobile terminalra

The WLAN AP node may be coupled to the interworking and forwarding node IWFN ei-
ther through an appropriate network such as an Ethernet LAN or via another network
such as an ADSL modem and suitable backbone network, BKBN.
In fig. 2, a logic diagram pertaining to the dual mode WLAN-GSM/3G mobile, MT2, ac-
cording to a preferred embodiment of the present invention is shown. The dual mode
terminal comprises two radio network interfaces - one for GSM/ 3G transmission / recep-
tion, GSM_NIC, and one for WLAN transmission / reception, WLAN_NIC, whereby both
interfaces may be in operation simultaneously. The dual mode mobile terminal moreover
comprises a conventional sound card, SND_C, offering connections to loudspeaker /
amplifier and microphone.
The dual mode terminal may consist of a standard processing platform, such as a laptop
or personal digital assistant (PDA), controlled by a usual common operating system. The
network interface cards may be off-the-shelf components, while the functionality of the
call selection processor and the various logic functions may be performed by a software
application running on the standard processing platform, such as a common laptop com-
puter or PDA.
According to a preferred embodiment of the invention, the dual mode platform comprises
a software application, D_APP, which comprises the following logic functions: apparatus
control and call selection, CTRL_CALL_SELCTION, SIP/H323 logic and signal process-
ing, SIP/H323J_OGIC, voice over IP coding/ decoding, VOJP, GSM logic and signal
processing, GSM_LOGIC and GSM voice coding / decoding, GSM_CODEC. Finally
there is provided a camp logic function, CMPJ-OGIC, for controlling whether the dual
mode mobile terminal shall operate over the GSM or WLAN network interface cards. In
the following, a preferred embodiment for the handshaking between the dual mode mo-
bile terminal and the exterior (cf. fig. 4 and 5) is illustrated using SIP protocol signaling.
As an alternative, the H323 protocol may be used.
For the WLAN network interface card, signal streams are communicated over a user
plane, UP, bearing voice over IP packets and a H323 / SIP control plane, CP. For the

GSM network interface card signals are transmitted over GSM-codec, UP, and GSM
control signaling plane, CP. In a manner, which shall be disclosed in the following, voice
signals may selectively be transferred between the sound card, SND_C, and the WLAN
network interface card, WLAN_NIC or the GSM network Interface card, GSM_NIC.
The control plane signaling issued on the respective Interface cards shall be explained
later with reference to fig. 4 and 5. It should be noticed that, the principles of the present
invention also applies to a 3G/WLAN equipped dual mode terminal although the exem-
plary embodiment has been shown for GSM/WLAN dual mode terminal. It should be fur-
ther noticed that the term dual mode terminal does not exclude more than two access
technologies being provided in the terminal.
According to the invention a WLAN-GSM/3G Interworking, IWFN, has been provided
between the WLAN AP and the S_MSCA/LR. The IWFN is responsible for "translat
ing" a voice call between GSM voice and IP telephony, that is, translate the GSM audio
codec format to voice over IP audio codec and performing signaling for enabling the call
to be made via standard nodes.
In fig. 3, a preferred embodiment of the IWFN has been shown. It comprises an A-GSM
interface for connection to a mobile switching center, MSC, and an Ethernet interface for
coupling to a WLAN access point AP. It moreover comprises an GSM codec coder and
decoding unit, GSMJJ, as well as a voice over IP coding and decoding unit, VOJP, for
translating a GSM codec stream into voice over IP stream and vice versa. Moreover, the
unit comprises a SIP signaling protocol control unit, CTRL_SIP, for transmitting for sig-
naling to a GSM interface card. It moreover contains a H.323 service. The functionality
of the IWFN shall be dealt with in more detail later.
As mentioned above, the WLAN AP node may be coupled to the interworking and for-
warding node IWFN either through an appropriate network such as an Ethernet LAN or
via another network such as an ADSL modem and suitable backbone network, BKBN.
According to the invention, The Serving MSC is configured such that it can hand over a
voice call from the Base station to the new IWF node. However, the IWF node preferably
"appears like* an ordinary base station system, BSS, to the MSC and normal HO is done
between WLAN and GSM/3G from the MSC point of view.

Advantageously, the dual mode mobile terminal MT2 may identify the IWF node by an IP
address that is preconfigured In the dual mode mobile terminal, MT2.
According to the invention as exemplary system is envisaged where many AP's are pro-
vided In different locations so as to provide so-called "hot-spof access to prescription
users. The system according to the invention may moreover comprise predetermined
lhr^n,^H"tP?hVide? in hTB and °ffiCe environments. Common for these AP's are that they
are coupled to the mterworking node, IWFN, according to the invention, alternatively,
that there are provided several interworklng nodes to which respective the AP's are cou-
pled.
A preferred embodiment of the invention shall now be explained with reference to fig 4
and 5.
I. - Signaling method for incoming voice calls from the GSM/3G system and hand-over to
the WLAN radio interface of a dual mode terminal
Figure 4 and 5 shows the signaling sequence according to the invention where a voice
call is received tn the cellular network and handed over to the WLAN network interface
card of the dual mode terminal.
In the present embodiment the dual mode terminal is active and is attached to both the
GSM network as well as a WLAN network. It should be understood that the network pro-
vider both supports both the GSM facilities as well as the WLAN facilities to the dual
user subscriber.
1. An Incoming Voice Call to Gateway G-MSC (GSM Mobile Switching Center)
/VLR Is detected
2. the G-MSC Initiates a HLR Location Request to find the S-MSC to which the ad-
dressed terminal Is attached, the HLR responds
3. the G-MSC signals a Call Arrived message to the S-MSC
4. a Complete Call instruction is sent from the G-MSC to the S-MSC, the voice Call
forwarded to S-MSC
5. a Page Request Is sent from the S-MSC to BaseStatlon (BSS)

6. the Pag© Request is forwarded to the dual mode mobile terminal on the Air Inter-
face
7. the dual mode mobile terminal performs a determination as to whether WLAN
access is possible from an AP providing WLAN telephony calls, and if so, de-
cides to proceed further over the WLAN radio interface (by the mechanism pro-
posed below in connection with fig. 8)
8. a Page Response is sent from MT2 to WLAN AP (the IWF is addressed an IP
address pre-conflgured by the dual mode mobile terminal)
9. - which is forwarded to the IWFN,
10. -and further to the S-MSC
11. security functions are carried out in order to authenticate the MT
12. setup; initiate call setup
13. Invite (SIP); Initiate call setup (translated to SIP)
14. Offer Response (SIP); Initiation confirmed (translated to SIP)
15. Call Conference (SIP); Initiation confirmed
16. Allocate; Request reservation of resources for call
17. Reservation (SIP); request reservation of resources for call (translated to SIP)
18. Alert User (SIP); terminal is prepared for call reception
19. Reservation Conference; resource reservation confirmed (translated to SIP)
20. Allocation Complete; resource reservation confirmed
21. Ringing (SIP); ring tone generated at B-party (translated to SIP)
22. Alert; ring tone generated at B-party
23.200 OK (SIP); answer indication i.e. B-party answers (translated to SIP)
24. Connect; answer indication i.e. B-party answers
25. Connect Acknowledge; when answer indication is received an acknowledge is
sent to terminal
26. Start Media (SIP); when terminal has sent the answer indication (200 OK) it
starts to send the media stream i.e. VoIP payload
27. Acknowledge (SIP); when answer indication Is received an acknowledge is sent
to terminal (translated to SIP)
28. Complete Call; serving MSC acknowledges back to gateway MSC that call has
been established.
29,GSM„P translation 29; the IWFN does any necessary coding/decoding or other
translation between VoIP payload and GSM coded payload
30. caiTln progress

The SIP signals comparative to the SIP protocol have been indicated in brackets above.
It Is seen that in. relatjpp to a prior art GSM call, the voice call according to the Invention
Is routed to the IWFN instead of to the Base station (BSS) in the serving MSC.
II. - Signaling method for making outgoing voice calls from a WLAN radio Interface to a
GSM/3G system
A method is also set forth involving a user of the dual mode terminal Initiating a phone
call. This procedure shall also be explained with respect to fig. 4 and 5, using the follow-
ing steps:
-.' The user of the dual mode terminal, MT2, wants to make an outgoing telephone
call
7. The dual mode mobile terminal decides to make the call over the WLAN network
interface card (by the mechanism proposed below as explained in connection with
fig. 6)
8.- 30 A voice call setup signal is sent via WLAN AP IWFN to S-MSC (the IWF is
addressed by a MT preconfigured IP address) as explained according to steps 8 -
30 above
The voice call is handled as usual in the GSM/3G network and is setup towards the fixed
end user, The call is made and when completed the dual mode mobile terminal goes
back to camp on the GSM/3G channel.
III. - Signaling method for handing over a voice call from the WLAN radio interface to the
GSM/3G interface of the dual mode terminal
If during a voice call in WLAN radio access, the dual mode mobile terminal moves out of
reach for the WLAN AP, a handover to GSM/3G is triggered. The action taken in the
dual mode mobile tormina) is as follows:

As mentioned above, when a particular predefined AP is discovered ("home AP"), 103,
WLAN access may be selected, MS3, without any timer being set. WLAN is installed in
many homes today, and a given Home AP may be set as preferred access. Alternatively,
a typical preferred AP may be the WLAN in the office, hence more than one pre-defined
"home AP" may be provided.
In any case, when the selection mechanism enters the state "WLAN Access Allowed",
MS3, the behavior of the dual mode mobile terminal can be such that the dual mode
mobile terminal by itself always access through the WLAN or alternatively it can be indi-
cated to the user that this state has been entered, so that the user can chose to do ac-
cess by WLAN. Preferable, the actual state is notified to the user when the state is en-
tered or left or when an automatic transition between the WLAN system and the
GSM/3G system occurs. This notification can be a noise signal, a light signal, a buzz
signal, a message or an icon on the display or any other type of signal.
The above mechanism secures that if the user of the dual mode terminal is on the move
and is passing through a given area in which WLAN access is available, the readiness
for responding, making and keeping GSM/3g phone calls, including during GSM/3G
handover, is prioritised and secured. On the other hand, if the user is within a "station-
ary" reach of a "home AP", calls are enabled over the WLAN interface.
If the user remains within coverage of the predetermined home AP, but is not using the
dual mode mobile terminal actively, the dual mode terminal may enter a power save
mode in which the WLAN network interface card is set to sleep after a suitable period of
inactivity, 106. If activity is again encountered involving attempting to use the WLAN
network interface or an activity on the GSM interface is encountered, a wake-up request
107, places the terminal back in the WLAN access allowed state, MS4. In this instance
the user may or may not have moved out of WLAN coverage, in the former case, the
dual mode mobile terminal entering state MS1.

This mechanism may work as exemplified by the states of the dual mode mobile terminal
MS1, MS2 and MS3 and the corresponding change state conditions that are shown in
figure 6. There is moreover provided an optional power save mode MS4, in view of the
relatively high power consumption of current WLAN network interface cards. The selec-
tion mechanism may be implemented in the application, D-APP, in the logic function
camping logic, CMPJJDGIC, shown in fig. 2.
The mobile terminal initially adopts a WLAN access disallowed state, MS1, searching for
WLAN AP's, 101. if a WLAN AP is identified offering access, state MS2 js adopted. One
way of determining whether the found AP is offering connection to an JWFN is that the
terminal tries to communicate with the IWFN, sending a WLAN Call message (cf. fig. 4)
step 8-WLAN Call (Page Response)) and await an Invite, (cf. fig. 4, step 13, Invite) or
some other message, such as Pinging the IWFN.
In state MS2 a timer value T1 is defined such that, if the dual mode mobile terminal has
heard the same WLAN AP for a time longer than given by the timer, MS2 - "WLAN ac-
cess disallowed wait for T1", then the dual mode mobile terminal is set in a state, MS3,
allowing voice calls to be handed over to WLAN, "WLAN access allowed", since the dual
mode mobile terminal is probably not moving, if the signal is lost the mobile terminal
goes back to MS1,102. When, in MS3, the dual mode mobile terminal cannot hear the
WLAN AP anymore -104, WLAN lost - the dual mode mobile terminal is set to state
"WLAN access disallowed", MS1. WLAN access may also be allowed when one of a set
of pre-defined AP's, such as a "home AP" is found, 103. In other instances, when the AP
Is lost, the WLAN access disallowed state MS1 is chosen.
In MS3 the WLAN Interface card is powered on and will remain so if the WLAN card is
used for transmission or access to the WLAN AP is not lost. However, if no transmission
takes place while the AP Is being present, the dual mode mobile terminal may enter a
power save mode switching off the WLAN network interface card, WLAN_NIC.
According to a further embodiment, the user may also actively select or overrule WLAN
access by giving a command to the dual mode mobile terminal that WLAN access is pre-
ferred. This selection can be based on a presentation of available radio access networks
as sensed by the dual mode mobile terminals, e.g. WLAN AP's that are within reach.

As mentioned above, when a particular predefined AP is discovered ("home AP"), 103,
WLAN access may be selected, MS3, without any timer being set. WLAN is installed in
many homes today, and a given Home AP may be set as preferred access. Alternatively,
a typical preferred AP may be the WLAN in the office, hence more than one pre-defined
"home AP" may be provided.
In any case, when the selection mechanism enters the state "WLAN Access Allowed",
MS3, the behavior of the dual mode mobile terminal can be such that the dual mode
mobile terminal by itself always access through the WLAN or alternatively it can be indi-
cated to the user that this state has been entered, so that the user can chose to do ac-
cess by WLAN. Preferable, the actual state is notified to the user when the state is en-
tered or left or when an automatic transition between the WLAN system and the
GSM/3G system occurs. This notification can be a noise signal, a light signal, a buzz
signal, a message or an icon on the display or any other type of signal.
The above mechanism secures that if the user of the dual mode terminal is on the move
and is passing through a given area in which WLAN access is available, the readiness
for responding, making and keeping GSM/3g phone calls, including during GSM/3G
handover, is prioritised and secured. On the other hand, if the user is within a "station-
ary" reach of a "home AP", calls are enabled over the WLAN interface.
If the user remains within coverage of the predetermined home AP, but is not using the
dual mode mobile terminal actively, the dual mode terminal may enter a power save
mode in which the WLAN network interface card is set to sleep after a suitable period of
inactivity, 106. If activity is again encountered involving attempting to use the WLAN
network interface or an activity on the GSM interface is encountered, a wake-up request
107, places the terminal back in the WLAN access allowed state, MS4. In this instance
the user may or may hot have moved out of WLAN coverage, in the former case, the
dual mode mobile terminal entering state MS1.

WE CLAIM
1. Method of operating a dual mode mobile terminal (MT2) comprising a wireless
local area network interface (WLAN_NIC) and a cellular radio interface
(GSM_NIC), wherein the following steps are carried out
the dual mode mobile terminal camping on the cellular radio interface when idle,
characterized by
when receiving a Page Request (6) message over the cellular radio interface
(GSM_NIC) indicating an incoming voice call over the cellular radio interface,
performing a determination (7) as to whether wireless local area network cover-
age is possible from an access point (WLAN-AP) providing wireless local area
network telephony calls, and if so
responding, by issuing a wireless local area network call message (8) to the wire-less
local area network access point (WLAN-AP) thus determined over the wire-less local
area network interface (WLAN-NIC) to an interworking node (IWFN), subsequently
engaging in a call initiation procedure (12-15), an assign traffic channel procedure (16 -
20) and a call confirmation and call accepted procedure (21- 27) with the interworking
node (IWFN), and
processing the incoming voice call as a voice over IP telephony call over the wireless
local area network interface (29, 30) towards another party, wherein
when the call is ended, the dual mode mobile terminal (MT2) going back to camp
on the cellular channel.
2. Method as claimed in claim 1, wherein the call initiation procedure comprises
the interworking node (IWFN) issuing an Invite signal (13) to the dual mode mobile
terminal (MT2) upon receiving a setup (12) from the mobile serving node (S-
MSC/VLR), and issuing a call confirm signal (15), upon receiving an offer response signal
(14) from the dual mode mobile terminal.

3. Method as claimed in claims 1-2, wherein the assign traffic channel
procedure comprises
the interworking node (IWFN) issuing a reservation confirm signal (17) to the dual
mode mobile terminal (MT2) upon receiving an allocate signal (16) from the mobile
serving node (S-MSC/VLR), and issuing an allocation complete signal (20), upon
receiving a reservation confirm signal (19) from the mobile serving node (S-MSCNLR).
4. Method as claimed in claims 1-3, wherein the call confirmation and call accepted
procedure comprises
the interworking node (IWFN) issuing alert (22) and connect (24) signals (17) to
the mobile serving node (S-MSC/VLR), upon receiving ringing and 200-OK signals (21,
23) from the dual mode mobile terminal (MT2),
the interworking node (IWFN) issuing an acknowledgement signal (27) to the
dual mode mobile terminal (MT2) upon receiving a connection acknowledged signal (25)
from the mobile serving node (S-MSC/VLR).
5. Method as claimed in claims 1-4, further comprising a step of selecting to receive or
make voice calls over the cellular interface or over the wireless local area network
interface, by performing the steps of
initially adopting a state (MSI) in which voice calls over wireless local area net-
work access are disallowed, searching for a wireless local area network access
point (AP) offering connection to voice calls, when identifying a predetermined wireless
local area network access point (AP) offering connection to voice calls, starting a timer
(T1, MS2),

upon the timer (T1) expiring, allowing voice calls to be performed over the
predetermined wireless local area network access point (AP, MS3).
6. Method as claimed in claim 5, wherein when entering a wireless local area net-
work access allowed state, but the user not using the wireless local area network
access for a given period, entering a power save mode (MS4), in which wireless
local area network access is not allowed.
7. Method as claimed in claim 5, wherein if in the power save mode (MS4) obtaining
a page request signal (6) or if necessitated by the user actively seeking to use
the wireless local area network interface or wishing to make a phone call, entering the
wireless local area network allowed state (MS3).
8. Dual mode mobile terminal (MT2) comprising a wireless local area network inter-
face (WLAN_NIC) and a cellular radio interface (GSM_NIC), means for executing a
software application, (D_APP) comprising apparatus control and call selection
(CTRL_CALL_SELCTION), SIP/H323-logic and signal processing
(SIP/H323-LOGIC), voice over IP coding/ decoding (VO_IP), GSM-logic and signal
processing (GSM LOGIC) and cellular voice coding / decoding
(GSM_CODEC) and a camp logic function (CMP_LOGIC) for controlling whether the
dual mode mobile terminal shall operate over the cellular or the wireless local area
network interfaces (WLAN_NIC, GSM_IMIC), the dual mobile mode terminal further
comprising:
means for camping on the cellular radio interface when idle,
characterized by the dual mode mobile terminal (MT2) further comprising:
means for indicating an incoming voice call over the cellular radio interface, when
receiving a Page Request (6) message over the cellular radio interface
(GSM_NIC), and for performing a determination (7) as to whether wireless local area

network coverage is possible from an access point (WLAN-AP) providing wireless local
area network telephony calls
means for responding to a positive determination (7) by issuing a wireless local area
network call message (8) to the wireless local area network access point (WLAN-AP)
thus determined over the wireless local area network interface (WLAN-NIC) to an
interworking node (IWFN)
means for subsequently engaging in a call initiation procedure (12-15), an assign traffic
channel procedure (16 - 20) and a call confirmation and call accepted procedure (21-
27) with the interworking node (IWFN), and
means for processing the incoming voice call as a voice over IP telephony call over the
wireless local area network interface(29, 30) towards another party, wherein said
means for camping are arranged to go back to camp on the cellular channel when the
call is ended.
9. Dual mode mobile terminal (MT2) as claimed in claim 8, further comprising means for
selecting to receive or make voice calls over the cellular interface or over the wireless
local area network interface which comprise
means for initially adopting a state (MSI) in which voice calls over wireless local area
network access is disallowed, and for searching for a wireless local area network access
point (AP) offering connection to voice calls,
means , responsive to identifying a predetermined wireless local area network access
point (AP), for offering connection to voice calls, and for starting a timer (T1, MS2),
means for, upon the timer (T1) expiring, allowing voice calls to be performed over the
predetermined wireless local area network access point (AP, MS3).

10. Dual mode mobile terminal (MT2) as claimed in claim 9, comprising means,
responsive to entering a wireless local area network access allowed state, and to the
user not using the wireless local area network access for a given period, for entering a
power save mode (MS4), in which wireless local area network access is not allowed.
11. Dual mode mobile terminal (MT2) as claimed in claim 9, comprising means for
obtaining a page request signal (6) if in the power save mode (MS4) or for entering the
wireless local area network allowed state (MS3), if necessitated by the user actively
seeking to use the wireless local area network interface or wishing to make a phone call.

ABSTRACT

DUAL MODE MOBILE TERMINAL AND OPERATING METHOD THEREOF
A Dual mode mobile terminal (MT2) comprising a WLAN interface (WLAN_NIC) and a cellular
radio interface (GSM_NIC) has been described wherein when receiving a Page Request (6)
message over the cellular radio interface (GSM_NIC), indicating an incoming voice call over the
cellular radio interface, or upon receiving an indication from the user of the dual mode terminal
to perform an outgoing voice call, performing a determination (7) as to whether a WLAN
coverage is possible from an AP providing WLAN telephony calls, and if so responding, by
issuing a WLAN call message (8) to a WLAN AP over the WLAN interface to an interworking
node (IWFN). There is moreover provided an Interworking node (IWFN) comprising a cellular
control unit (CTRL_SIP), a cellular unit (GSM_U), a voice over IP unit (VO_IP) and a router (R),
which upon receiving a WLAN call (9) from a dual mode terminal via a WLAN AP, is establishing
a connection against a serving mobile switching centre (S_MSC/VLR) (10, 10a, 10b), is
performing a call initiation procedure (12-15), a assign traffic channel procedure (16 - 20) and a
call confirmation and call accepted procedure (22- 27) between the dual mode terminal (MT2)
and the serving switching mode centre (S_MSC/VLR), is initiating duplex GSM/IP translation
(29) and is routing the cellular call between the AP and the serving mobile switching centre
(S_MSC).

DUAL MODE MOBILE TERMINAL AND OPERATING METHOD THEREOF

Documents:

Inventors:

PCT Conventions: