Indian Patents. 263950:OPERATING AND SUPPORTING DUAL MODE USER EQUIPMENT

Title of Invention	OPERATING AND SUPPORTING DUAL MODE USER EQUIPMENT
Abstract	The invention relates to methods and devices for enabling the handling of terminating speech calls to a dual mode user equipment by using a further access network for transmitting said data.

Full Text	[technical field] The present invention relates to methods and devices for enabling the access to a cellular telecommunications network via a further access network. [related art] In recent years the percentage of household having a broadband connection at home was increasing. Today 11% of the households in Germany are equipped with a broadband connection (mainly ADSL). In Sweden the percentage is already 22% (50% ADSL, 50 % other technologies). It is expected that these percentages will increase significantly over the next years. Many of these users will install private WLAN(Wireless Local Area Network- access points to connect their PCs (Personal Computers), PDA (Personal Digital Assistants), mobile phones etc. to their fixed broadband connection. Furthermore, it is expected that the number of public WLAN-hot spots in Europe will increase from approx. 18.000 (2003) to 36.000 (2009). Parallel, to the increased number of broadband connections the users are starting to use IP (Internet Protocol) telephony over their WLAN-broadband connection via PCs and PDAs. In the next years mobile phone vendors will launch so-called GSM/WLAN dual mode phones (e.g. Nokia 2005). For these users of the GSM/WLAN dual mode phones it will be quite easy to originate calls via the SIP-client over the WLAN-radio interface towards other SIP-clients connected to the same network or even to the internet. However, and unsolved matter is the reception of incoming calls at the dual mode devices. Today several architectures are proposed how to integrate cellular networks with WLAN- access points. The main focus is the integration of the WLAN-access point towards the packet switching network. For example Mobile @home proposes an architecture where the WLAN-access point is connected via a broadband connection to the BSC. The disadvantage of this solution is that 2 the same operator has to supply the cellular mobile network and the broadband connection. Furthermore, Mobile @home proposes a solution based on the ADSL (Asymmetric Digital Subscriber Line) technology. US 2003/026245 Al discloses a communication system including an interworking mobile switching centre for call termination. However, the document does not relate to an architecture involving different access networks. US 2003/134636 Al discloses methods and apparatus for a mobile station to sense and select a wireless local area network or a wide area mobile wireless network. However, the document does not disclose the handling of incoming calls. It is a shortcoming of the state of the art that solutions designed for speech connections lack flexibility. Therefore it is object of the invention to provide methods and devices for enabling the access for speech connections to a cellular telecommunications network via a further access network with an improved flexibility. [summary] This will be solved advantageously by the methods of claims 1 and 11, the control node of claim 12 and the user equipment of claim 19. Further advantageous embodiments can be derived from the dependent claims. One advantage of the invented method, control node and user equipment is that it requires modifications in the control node and the user equipment. Thus the invention can be implemented without major modifications of the existing networks. The invention introduces a method for handling an incoming call to a user equipment by a control node of a cellular telecommunication network. Said method comprises the steps of receiving an indication of an incoming call to the user equipment in the control node, determining that the called user equipment can be reached via a device operating according to a session initiation protocol, initiating the linking in on a route towards the device operating 3 according to a session initiation protocol, of a device that transforms messages sent according to a call control signalling protocol used in the cellular telecommunications network into messages according to the session initiation protocol and vice versa, and initiating the linking in on a route towards the device operating according to a session initiation protocol, of a device that transforms user plane transmitted according to a protocol used in the cellular telecommunications network into user plane transmitted according to an internet protocol and vice versa. This enables the use of a further access network for transmitting payload at a terminating call. In most cases the further access network is cheaper for the transmission of data that the scarce radio resources of the 2G or 3G radio network. In an embodiment of the invention, the method comprises the steps of receiving in the control node an indication that the user equipment can be reached via a device operating according to a session initiation protocol, determining an address of the device operating according to a session initiation protocol, and sending an indication that the user equipment can be reached via a device operating according to a session initiation protocol to a storage connected to the control node. The method can further comprise the additional step of sending a message comprising an indication that the user equipment can be reached via a device operating according to a session initiation protocol is sent to a database for storing subscriber data. The indication that the user equipment can be reached via a device operating according to a session initiation protocol can be received in a location area update message sent by the user equipment. In a further embodiment of the invention, the step of determining comprises the steps of interrogating a database for storing subscriber data for routing information for reaching the called user equipment, receiving a response from said database and determining from analysing the response that the user equipment can be reached via a device operating according to a session initiation protocol. 4 The database can be an AAA server, a home location register or a home subscriber server. The control node can be a mobile services switching centre., and the device that transforms messages sent according to a call control signalling protocol used in the cellular telecommunications network into messages according to the session initiation protocol and vice versa transforms messages can be a media gateway control function. In an embodiment of the invention, the device that transforms user plane transmitted according to a protocol used in the cellular telecommunications network into user plane transmitted according to an internet protocol is a media gateway or is located in a media gateway. The device operating according to a session initiation protocol can be for example a service initiation protocol proximity server or an interrogating call session control function. The invention further introduces a method for operating a user equipment that comprises a first transmission unit for communicating with a cellular telecommunications access network and a second transmission unit for communicating with a further access network. The method comprises the steps of attaching to the cellular telecommunications network, determining that the user equipment is currently located in an area that is covered by the further access network, sending a session initiation protocol message for registering the user equipment at a server of the further access network, receiving a session initiation protocol message confirming that the user equipment has been registered, sending a message comprising an indication that the user equipment can be reached via a device operating according to the session initiation protocol to a control node of the cellular telecommunications network via the cellular telecommunications access network. A control node for a cellular telecommunication network according to the invention comprises in input unit, an output unit, a control unit, wherein the control unit is adapted to determine that a user equipment can be reached via a device operating according to a session initiation protocol. The control unit is further adapted to initiate the linking in on a route towards the device operating according to a session initiation protocol, of a device that transforms messages sent according to a call control signalling protocol used in the cellular telecommunications network into messages according to the session initiation protocol and 5 vice versa, and to initiate the linking in on a route towards the device operating according to a session initiation protocol, of a device that transforms user plane transmitted according to a protocol used in the cellular telecommunications network into user plane transmitted according to an internet protocol and vice versa. In an embodiment of the invention, the control node is connected to a storage for storing subscriber data, and the input unit is adapted to receive an indication that a user equipment can be reached via a device operating according to a session initiation protocol and to signal it to the control unit, and that the control unit is adapted to initiate the sending of an indication that the user equipment can be reached via a device operating according to a session initiation protocol to the storage for storing subscriber data and to determine an address for sending data towards the user equipment. In an embodiment of the invention the indication sent to the storage for string subscriber data comprises an address of the device operating according to a session initiation protocol. The control node can be implemented by means of a mobile services switching centre or a mobile services switching centre server. The storage can be a visitor location register. In an embodiment of the invention, the control node is adapted to initiate the sending of a message to a database for storing subscriber data, wherein the message comprises an indication that the user equipment can be reached via a device that operates according to a session initiation protocol. The control node can comprise a media gateway control function. The invention further introduces a user equipment comprising a first transmission unit for communicating with a first access network of a telecommunications network, a second transmission unit for communicating with a further access network, and a control unit. The control unit is adapted to receive an indication from the second transmission unit that the user equipment is currently located in an area covered by the further access network, and in response thereto to initiate the registration of the user equipment at a server of the further 6 access network via the second transmission unit, to receive a confirmation that the registration was successful via the second transmission unit, and to send an indication that the user equipment can be reached via a device operating according to a session initiation protocol to the telecommunications network via the first transmission unit. In an embodiment of the invention the user equipment comprises a first transmission unit that is adapted to operate according to at least one of a Global System for Mobile Telecommunication, Code Division Multiple Access, Wideband Code Division Multiple Access, American Mobile Phone System, Digital- American Mobile Phone System, or Pacific Digital Cellular standards. The user equipment can further comprise a second transmission unit that is adapted to operate according to at least one of Bluetooth, ISDN, or Wireless Local Area Network recommendations. [brief description of the drawings] The following figures show: Fig. 1 depicts an architecture for enabling a user equipment to access a telecommunications network via a further access network, Fig.1a depicts a registration of a dual mode user equipment with a SIP proxy, (state of the art) and the indicating of this to the telecommunications network Fig. 2 depicts signal flow for an incoming call according to the invention, Fig. 3 depicts an alternative architecture for enabling a user equipment to access a telecommunications network via a further access network, Fig. 4 depicts an alternative signal flow for an incoming call according to the invention, Fig. 5 depicts a control node according to the invention, and Fig. 6 depicts a user equipment according to the invention. [detailed description] In the following the invention will be further described by means of examples and by means of figures. 7 It should be noted that the WLAN access is just an exemplary embodiment and could be replaced by any other access technology as for example Bluetooth, optical connection or fixed line connection. In particular access technology with lower costs on transmission resources like bandwidth than the GSM or WCDMA technology can be used advantageously for the further access. It should be further noted that for an implementation of the invented methods, the access point adapted to communicate over a radio, fixed or optical connection to user equipment, may be connected by any means to a domain operating according to a session initiation protocol and transmitting data according to an internet protocol. Figure 1 depicts an architecture for enabling a user equipment to access a telecommunications network via a further access network, comprising an home location register 101, a gateway mobile services switching centre, a combined mobile services switching centre/media gateway control function 103 which are connected to each other. In another embodiment of the invention the mobile services switching centre and the media gateway control function are not combined but just interconnected. The combined mobile services switching centre/media gateway control function 103 is further connected to an internet domain 104 comprising a first SIP (Session Initiation Protocol) proxy (proximity server) 105 and a second SIP proxy 106 that is connected to telephone 107 adapted to send signals according to SIP. The internet domain is connected via an ISP (Internet Service Provider) 108 and a DSLAM (Digital Subscriber Line Access Multiplexer) 109 to a local exchange 110 which is connected to a public switched telephony network 111. The local exchange is further connected via a DSL (Digital Subscriber Line) modem 112 to a WLAN-access Point 113. A user equipment 116 is connected via a WLAN radio connection 114 to the WLAN Access Point and via a GSM or WCDMA radio connection 115 to the mobile services switching centre/media gateway control function. According to the invention, the user equipment 116 can use the WLAN radio connection 114 to register in the first SIP proxyl05. The details of the registration will be explained in figure 8 la. Figure la depicts a registration of the mode user equipment 116 with the first SIP proxy 105. This is state of the art. To that end the user equipment 106 sends a SIP register message towards the SIP proxy 105 via the WLAN radio connection 114. After successful registration the SIP proxy returns a 200 OK message to the user equipment. After receiving this confirmation that the registration has been successful the user equipment sends an indication that it can be reached via the SIP proxy to the mobile services switching centre via the GSM or WCDMA connection 115 by sending a location update message. The mobile services switching centre stores the indication in a visitor location register. It returns an accepted message to indicate the reception of the location update. The sending of the indication can be implemented in several ways. It can be sent for example in a USSD (Unstructured Supplementary Service Data) message or any other signalling means between user equipment and mobile services switching centre. In the preferred embodiment it is included in a location update message. Independent from the means used for transporting the information from user equipment to mobile services switching centre, the information can be sent as a simple indication, for example a flag, indicating that an alternative access technology is available. In that case one can always use the same predefined device for routing calls from the mobile services switching centre/media gateway control function to the user equipment. Such device can be for example an interrogating call session control function as defined in the 3GPP recommendation 29.163 version 6.2.0 of March 2004. If not always the same device is used a device must be identified. In a preferred embodiment of the invention the SIP proxy is identified by an identification of the user equipment. To that end, an identification of the user equipment, e.g. the MSISDN or the IMSI, is stored in a table or a database in association with an identification of the SIP proxy, conveniently this can be the address of the SIP proxy. In a further embodiment of the invention, the user equipment identification can be related to an operator and the operator identification can be stored in relation to the SIP proxy identification. Alternatively, a device can be identified for example by determining location information of the user equipment like a location area or geographical coordinates and using a mapping table 9 that maps said location information to an address. A further way to address the user equipment is the use of an ENUM (tElephone NUmber Mapping) database as defined in IETF (Internet Engineering Task Force) RFC 3761. The ENUM database maps the telephone number, for example the IMSI (International Mobile Subscriber Identity) of the user equipment, to an IP address. A further way is the transmission of a location area identifier in the location update message. The location area identifier carries an identification of the SIP proxy or of an access point, for example an ESSID (Extended Services Set IDentification), a domain name or a WLAN location area identification. Figure 2 depicts signal flow for an incoming call according to the invention. The architecture of figure 1 is used for receiving an incoming call at the user equipment 116 via the further access network, the WLAN access point 113. In a first step 201 a call request message, here an IAM (Initial address Message) is received at a control node, the gateway mobile services switching centre 102. The gateway mobile services switching centre analyses the received data and requests routing info from a database for storing subscriber data by sending a send routing info message 202 to the home location register 101. The home location register analyses the request and sends a request for an address of the called user equipment to a control node by sending a provide roaming number message 203 to the mobile services switching centre 103. The mobile services switching centre responds with a provide roaming number message 204 comprising a roaming number of the called user equipment. The home location register provides routing information 205 to the gateway mobile services switching centre which uses this information to forward the call request message 206 to the mobile services switching centre. The call control node mobile services switching centre receives the indication of an incoming call the IAM 206 and determines from that the call is directed to a user equipment that can be reached via a device operating according to a SIP protocol. It determines that the call can be routed via the SIP proxy 105 and links in the media gateway control function for transforming the ISUP signalling into SIP signalling. Not depicted is the linking of the media gateway for transforming payload transmitted according to a transfer mode used in the cellular core network to payload transmitted according to an IP. 10 In a next step 207 the control node mobile services switching centre 103 forwards the signalling via the media gateway control function as SIP signalling to the device operating according to a SIP, the SIP proxy 105. The SIP proxy 105 analyses the received information from the mobile services switching centre. By using the information received when registering the user equipment it initiates that the call is routed to the user equipment in a next step 209. The user equipment terminates the call in a step 210, via the further access network, implemented as the WLAN radio connection from the WLAN access point. Figure 3 depicts an alternative architecture for enabling a user equipment to access a telecommunications network via a further access network. The architecture comprises a control node implemented as a gateway mobile services switching centre 301. The gateway mobile services switching centre is collocated with a device that transforms messages sent according to a call control signalling protocol used in the cellular telecommunications network into messages according to the session initiation protocol and vice versa, in the example a media gateway control function. This collocation is optional, for the invention it is sufficient if they are connected to each other. The gateway mobile services switching centre/media gateway control function is connected to database for storing subscriber data, implemented as a home location register 303. The gateway mobile services switching centre/media gateway control function 301 is further connected to a control node 302 which is a mobile services switching centre. The home location register and mobile services switching centre are also connected to each other. The mobile services switching centre 302 is further connected to an internet domain 104 in particular to a device operating according to a session initiation protocol, implemented as a SIP proxy 105 known from figure 1. Apart from the home location register 303, the mobile services switching centre 302 and the gateway mobile services switching centre/media gateway control function 301, the architecture is similar to the architecture of figure 1. Also similar are the actions of the user equipment 116 that registers itself with a server of the further access network, that is with the SIP server 105 and sends an indication that it can be reached via a device operating according to a SIP, that is again SIP server 105, to the control node 302 of the cellular telecommunications network. However, the mobile services switching centre will perform one additional step compared to the architecture of figure 1, it sends an indication that the user equipment can be reached via a device operating according to a SIP to the home location register 303. The home location register stores said indication related to the user equipment or related to the subscriber or user 11 of the user equipment. In a preferred embodiment of the invention, the indication comprises an address of the device operating according to a SIP. Figure 4 depicts an alternative signal flow for an incoming call according to the invention, in the architecture of figure 3. In a first step 401 the gateway mobile services switching centre/media gateway control function 301 receives an indication of an incoming call to the user equipment by means of an IAM. It analyses the IAM and requests routing information of the home location register 303 by sending a send routing info message in a step 402. The home location register analyses the message and checks the appropriate subscriber data. Said data comprise an indication that the user equipment can be reached via device operating according to a SIP. The home location register returns an address of the device or information that enables the determination of the device in a send routing info message in a step 403. The gateway mobile services switching centre determines that the called user equipment can be reached via a device operating according to a session initiation protocol. It initiates the linking in on a route towards the device operating according to a session initiation protocol, i.e. the SIP server, of a device that transforms messages sent according to a call control signalling protocol used in the cellular telecommunications network into messages according to the session initiation protocol and vice versa, i.e. the gateway mobile services switching centre. The gateway mobile services switching centre further initiates the linking in on a route towards the device operating according to a session initiation protocol, of a device that transforms user plane transmitted according to a protocol used in the cellular telecommunications network into user plane transmitted according to an internet protocol and vice versa, which is a media gateway or a device connected to or comprised in a media gateway. After initiating the linking in at least on the signalling path, the gateway mobile services switching centre forwards the call request to the SIP proxy in a step 404. the further steps are the same as described by means of figure 2, i.e. the SIP proxy 105 analyses the received information from the mobile services switching centre. By using the information received when registering the user equipment it initiates that the call is routed to the user equipment in a next step 405. 12 Figure 5 depicts a control node CN5 according to the invention, comprising an input unit IU5, an output unit OU5, and a control unit CU5. The control node can be operating for example as a mobile services switching centre or a gateway mobile services switching centre. Figure 6 depicts a user equipment UE6 according to the invention, comprising a first transmission unit TU61 for communicating with a first access network of a telecommunications network, a second transmission unit TU62 for communicating with a further access network, and a control unit CU6. The user equipment first attaches to a first cellular telecommunications access network like a so-called 2G or 3G network via the first transmission unit TU61.When the user equipment enters a coverage area for the second transmission unit TU62, the second transmission unit sends an indication to the control unit indicating that. The control unit receives an indication from the second transmission unit that the user equipment is currently located in an area covered by the further access network, and in response thereto to initiate the registration of the user equipment at a server of the further access network via the second transmission unit. After successful registration the second transmission unit receives a confirmation that the registration was successful and forwards it to the control unit. The control unit sends an indication that the user equipment can be reached via a device operating according to a session initiation protocol to the telecommunications network via the first transmission unit. 13 We Claim : 1. Method for handling an incoming call to a user equipment (116, UE6) by a control node (CN5, 102, 103, 301, 302) of a cellular telecommunication network, said method comprising the following steps: • receiving an indication of an incoming call to the user equipment in the control node, • determining that the called user equipment can be reached via a device of a further access network operating according to a session initiation protocol (105), • initiating the linking in on a route towards the device operating according to a session initiation protocol, of a device (103, 301) that transforms messages sent according to a call control signaling protocol used in the cellular telecommunications network into messages according to the session initiation protocol and vice versa, and • initiating the linking in on a route towards the device operating according to a session initiation protocol, of a device that transforms user plane transmitted according to a protocol used in the cellular telecommunications network into user plane transmitted according to an internet protocol and vice versa. 2. Method according to claim 1, with the steps of: • receiving in the control node an indication that the user equipment can be reached via a device operating according to a session initiation protocol, • determining an address of the device operating according to a session initiation protocol, and • sending an indication that the user equipment can be reached via a device operating according to a session initiation protocol to a storage connected to the control node. 3. Method according to any of the preceding claims, with the additional step of • sending a message comprising an indication that the user equipment can be reached via a device operating according to a session initiation protocol is sent to a database for storing subscriber data. 14 4. Method according to any of the preceding claims, wherein the indication that the user equipment can be reached via a device operating according to a session initiation protocol, is received in a location area update message sent by the user equipment. 5. Method according to claim 1, wherein the step of determining comprises the steps of • interrogating a database for storing subscriber data (101) for routing information for reaching the called user equipment, • receiving a response from said database and • determining from analysing the response that the user equipment can be reached via a device operating according to a session initiation protocol. 6. Method according to claim 3 or 4, wherein the database is an AAA server, a home location register or a home subscriber server. 7. Method according to any of the preceding claims wherein the control node is a mobile services switching centre. 8. Method according to any of the preceding claims wherein the device that transforms messages sent according to a call control signaling protocol used in the cellular telecommunications network into messages according to the session initiation protocol and vice versa transforms messages is a media gateway control function. 9. Method according to any of the preceding claims, wherein the device that transforms user plane transmitted according to a protocol used in the cellular telecommunications network into user plane transmitted according to an internet protocol is a media gateway or is located in a media gateway. 10. Method according to any of the preceding claims wherein the device operating according to a session initiation protocol is a service initiation protocol proximity server or an interrogating call session control function. 15 11. Method for operating a user equipment (UE6, 116) that comprises a first transmission unit (TU61) for communicating with a cellular telecommunications access network and a second transmission unit (TU62) for communicating with a further access network (113, 112, 110, 109) the method comprising the steps of: • attaching to the cellular telecommunications network, • determining that the user equipment is currently located in an area that is covered by the further access network, • sending a session initiation protocol message for registering the user equipment at a server of the further access network, • receiving a session initiation protocol message confirming that the user equipment has been registered, • sending a message comprising an indication that the user equipment can be reached via a device operating according to the session initiation protocol to a control node of the cellular telecommunications network via the cellular telecommunications access network. 12. Control node (CN6, 102, 103, 301, 302) for a cellular telecommunication network comprising in input unit (IU5), an output unit (OU5), and a control unit (CU5), characterised by that the control unit is adapted • to determine that a user equipment can be reached via a device of a further access network operating according to a session initiation protocol, • to initiate the linking in on a route towards the device operating according to a session initiation protocol, of a device that transforms messages sent according to a call control signaling protocol used in the cellular telecommunications network into messages according to the session initiation protocol and vice versa, and • to initiate the linking in on a route towards the device operating according to a session initiation protocol, of a device that transforms user plane transmitted according to a protocol used in the cellular telecommunications network into user plane transmitted according to an internet protocol and vice versa. 13. Control node according to claim 12, wherein the control node is connected to a storage for storing subscriber data, characterised by 16 that the input unit is adapted to receive an indication that a user equipment can be reached via a device operating according to a session initiation protocol and to signal it to the control unit, and that the control unit is adapted to initiate the sending of an indication that the user equipment can be reached via a device operating according to a session initiation protocol to the storage for storing subscriber data and to determine an address for sending data towards the user equipment. 14. Control node according to claim 13, wherein the indication sent to the storage for storing subscriber data comprises an address of the device operating according to a session initiation protocol. 15. Control node according to any of the claims 12, 13 or 14, that is implemented by means of a mobile services switching centre or a gateway mobile services switching centre server. 16. Control node according to claim 13, 14 or 15, wherein the storage is a visitor location register. 17. Control node according to any of the claims 12 to 16, wherein the control node is adapted to initiate the sending of a message to a database for storing subscriber data, the message comprising an indication that the user equipment can be reached via a device that operates according to a session initiation protocol. 18. Control node according to any of the preceding claims, wherein the control node comprises a media gateway control function. 19. User equipment (UE6, 116) comprising a first transmission unit (TU61) for communicating with a first access network of a telecommunications network, a second transmission unit (TU62) for communicating with a further access network (113, 112, 110, 109), and a control unit (CU6), characterised by that the control unit is adapted to receive an indication from the second transmission unit that the user equipment is currently located in an area covered by the 17 further access network, and in response thereto to initiate the registration of the user equipment at a server of the further access network via the second transmission unit, to receive a confirmation that the registration was successful via the second transmission unit, and to send an indication that the user equipment can be reached via a device operating according to a session initiation protocol to the telecommunications network via the first transmission unit. 18 20. User equipment according to claim 19, wherein the first transmission unit is adapted to operate according to at least one of a Global System for Mobile Telecommunication, Code Division Multiple Access, Wideband Code Division Multiple Access, American Mobile Phone System, Digital- American Mobile Phone System, or Pacific Digital Cellular standards. 21. User equipment according to claim 19 or 20 wherein the second transmission unit is adapted to operate according to at least one of Bluetooth, ISDN, or Wireless Local Area Network recommendations. The invention relates to methods and devices for enabling the handling of terminating speech calls to a dual mode user equipment by using a further access network for transmitting said data.

Full Text

[technical field]
The present invention relates to methods and devices for enabling the access to a cellular
telecommunications network via a further access network.
[related art]
In recent years the percentage of household having a broadband connection at home was
increasing. Today 11% of the households in Germany are equipped with a broadband
connection (mainly ADSL). In Sweden the percentage is already 22% (50% ADSL, 50 %
other technologies). It is expected that these percentages will increase significantly over the
next years. Many of these users will install private WLAN(Wireless Local Area Network-
access points to connect their PCs (Personal Computers), PDA (Personal Digital Assistants),
mobile phones etc. to their fixed broadband connection.
Furthermore, it is expected that the number of public WLAN-hot spots in Europe will increase
from approx. 18.000 (2003) to 36.000 (2009).
Parallel, to the increased number of broadband connections the users are starting to use IP
(Internet Protocol) telephony over their WLAN-broadband connection via PCs and PDAs. In
the next years mobile phone vendors will launch so-called GSM/WLAN dual mode phones
(e.g. Nokia 2005).
For these users of the GSM/WLAN dual mode phones it will be quite easy to originate calls
via the SIP-client over the WLAN-radio interface towards other SIP-clients connected to the
same network or even to the internet.
However, and unsolved matter is the reception of incoming calls at the dual mode devices.
Today several architectures are proposed how to integrate cellular networks with WLAN-
access points. The main focus is the integration of the WLAN-access point towards the packet
switching network.
For example Mobile @home proposes an architecture where the WLAN-access point is
connected via a broadband connection to the BSC. The disadvantage of this solution is that
2

the same operator has to supply the cellular mobile network and the broadband connection.
Furthermore, Mobile @home proposes a solution based on the ADSL (Asymmetric Digital
Subscriber Line) technology.
US 2003/026245 Al discloses a communication system including an interworking mobile
switching centre for call termination. However, the document does not relate to an
architecture involving different access networks.
US 2003/134636 Al discloses methods and apparatus for a mobile station to sense and select
a wireless local area network or a wide area mobile wireless network. However, the document
does not disclose the handling of incoming calls.
It is a shortcoming of the state of the art that solutions designed for speech connections lack
flexibility.
Therefore it is object of the invention to provide methods and devices for enabling the access
for speech connections to a cellular telecommunications network via a further access network
with an improved flexibility.
[summary]
This will be solved advantageously by the methods of claims 1 and 11, the control node of
claim 12 and the user equipment of claim 19. Further advantageous embodiments can be
derived from the dependent claims.
One advantage of the invented method, control node and user equipment is that it requires
modifications in the control node and the user equipment. Thus the invention can be
implemented without major modifications of the existing networks.
The invention introduces a method for handling an incoming call to a user equipment by a
control node of a cellular telecommunication network. Said method comprises the steps of
receiving an indication of an incoming call to the user equipment in the control node,
determining that the called user equipment can be reached via a device operating according to
a session initiation protocol, initiating the linking in on a route towards the device operating
3

according to a session initiation protocol, of a device that transforms messages sent according
to a call control signalling protocol used in the cellular telecommunications network into
messages according to the session initiation protocol and vice versa, and initiating the linking
in on a route towards the device operating according to a session initiation protocol, of a
device that transforms user plane transmitted according to a protocol used in the cellular
telecommunications network into user plane transmitted according to an internet protocol and
vice versa.
This enables the use of a further access network for transmitting payload at a terminating call.
In most cases the further access network is cheaper for the transmission of data that the scarce
radio resources of the 2G or 3G radio network.
In an embodiment of the invention, the method comprises the steps of receiving in the control
node an indication that the user equipment can be reached via a device operating according to
a session initiation protocol, determining an address of the device operating according to a
session initiation protocol, and sending an indication that the user equipment can be reached
via a device operating according to a session initiation protocol to a storage connected to the
control node.
The method can further comprise the additional step of sending a message comprising an
indication that the user equipment can be reached via a device operating according to a
session initiation protocol is sent to a database for storing subscriber data.
The indication that the user equipment can be reached via a device operating according to a
session initiation protocol can be received in a location area update message sent by the user
equipment.
In a further embodiment of the invention, the step of determining comprises the steps of
interrogating a database for storing subscriber data for routing information for reaching the
called user equipment, receiving a response from said database and determining from
analysing the response that the user equipment can be reached via a device operating
according to a session initiation protocol.
4

The database can be an AAA server, a home location register or a home subscriber server.
The control node can be a mobile services switching centre., and the device that transforms
messages sent according to a call control signalling protocol used in the cellular
telecommunications network into messages according to the session initiation protocol and
vice versa transforms messages can be a media gateway control function.
In an embodiment of the invention, the device that transforms user plane transmitted
according to a protocol used in the cellular telecommunications network into user plane
transmitted according to an internet protocol is a media gateway or is located in a media
gateway.
The device operating according to a session initiation protocol can be for example a service
initiation protocol proximity server or an interrogating call session control function.
The invention further introduces a method for operating a user equipment that comprises a
first transmission unit for communicating with a cellular telecommunications access network
and a second transmission unit for communicating with a further access network. The method
comprises the steps of attaching to the cellular telecommunications network, determining that
the user equipment is currently located in an area that is covered by the further access
network, sending a session initiation protocol message for registering the user equipment at a
server of the further access network, receiving a session initiation protocol message
confirming that the user equipment has been registered, sending a message comprising an
indication that the user equipment can be reached via a device operating according to the
session initiation protocol to a control node of the cellular telecommunications network via
the cellular telecommunications access network.
A control node for a cellular telecommunication network according to the invention
comprises in input unit, an output unit, a control unit, wherein the control unit is adapted to
determine that a user equipment can be reached via a device operating according to a session
initiation protocol. The control unit is further adapted to initiate the linking in on a route
towards the device operating according to a session initiation protocol, of a device that
transforms messages sent according to a call control signalling protocol used in the cellular
telecommunications network into messages according to the session initiation protocol and
5

vice versa, and to initiate the linking in on a route towards the device operating according to a
session initiation protocol, of a device that transforms user plane transmitted according to a
protocol used in the cellular telecommunications network into user plane transmitted
according to an internet protocol and vice versa.
In an embodiment of the invention, the control node is connected to a storage for storing
subscriber data, and the input unit is adapted to receive an indication that a user equipment
can be reached via a device operating according to a session initiation protocol and to signal it
to the control unit, and that the control unit is adapted to initiate the sending of an indication
that the user equipment can be reached via a device operating according to a session initiation
protocol to the storage for storing subscriber data and to determine an address for sending data
towards the user equipment.
In an embodiment of the invention the indication sent to the storage for string subscriber data
comprises an address of the device operating according to a session initiation protocol.
The control node can be implemented by means of a mobile services switching centre or a
mobile services switching centre server.
The storage can be a visitor location register.
In an embodiment of the invention, the control node is adapted to initiate the sending of a
message to a database for storing subscriber data, wherein the message comprises an
indication that the user equipment can be reached via a device that operates according to a
session initiation protocol.
The control node can comprise a media gateway control function.
The invention further introduces a user equipment comprising a first transmission unit for
communicating with a first access network of a telecommunications network, a second
transmission unit for communicating with a further access network, and a control unit. The
control unit is adapted to receive an indication from the second transmission unit that the user
equipment is currently located in an area covered by the further access network, and in
response thereto to initiate the registration of the user equipment at a server of the further
6

access network via the second transmission unit, to receive a confirmation that the registration
was successful via the second transmission unit, and to send an indication that the user
equipment can be reached via a device operating according to a session initiation protocol to
the telecommunications network via the first transmission unit.
In an embodiment of the invention the user equipment comprises a first transmission unit that
is adapted to operate according to at least one of a Global System for Mobile
Telecommunication, Code Division Multiple Access, Wideband Code Division Multiple
Access, American Mobile Phone System, Digital- American Mobile Phone System, or Pacific
Digital Cellular standards.
The user equipment can further comprise a second transmission unit that is adapted to operate
according to at least one of Bluetooth, ISDN, or Wireless Local Area Network
recommendations.
[brief description of the drawings]
The following figures show:
Fig. 1 depicts an architecture for enabling a user equipment to access a telecommunications
network via a further access network,
Fig.1a depicts a registration of a dual mode user equipment with a SIP proxy, (state of the art)
and the indicating of this to the telecommunications network
Fig. 2 depicts signal flow for an incoming call according to the invention,
Fig. 3 depicts an alternative architecture for enabling a user equipment to access a
telecommunications network via a further access network,
Fig. 4 depicts an alternative signal flow for an incoming call according to the invention,
Fig. 5 depicts a control node according to the invention, and
Fig. 6 depicts a user equipment according to the invention.
[detailed description]
In the following the invention will be further described by means of examples and by means
of figures.
7

It should be noted that the WLAN access is just an exemplary embodiment and could be
replaced by any other access technology as for example Bluetooth, optical connection or fixed
line connection. In particular access technology with lower costs on transmission resources
like bandwidth than the GSM or WCDMA technology can be used advantageously for the
further access.
It should be further noted that for an implementation of the invented methods, the access point
adapted to communicate over a radio, fixed or optical connection to user equipment, may be
connected by any means to a domain operating according to a session initiation protocol and
transmitting data according to an internet protocol.
Figure 1 depicts an architecture for enabling a user equipment to access a telecommunications
network via a further access network, comprising an home location register 101, a gateway
mobile services switching centre, a combined mobile services switching centre/media
gateway control function 103 which are connected to each other. In another embodiment of
the invention the mobile services switching centre and the media gateway control function are
not combined but just interconnected. The combined mobile services switching centre/media
gateway control function 103 is further connected to an internet domain 104 comprising a first
SIP (Session Initiation Protocol) proxy (proximity server) 105 and a second SIP proxy 106
that is connected to telephone 107 adapted to send signals according to SIP. The internet
domain is connected via an ISP (Internet Service Provider) 108 and a DSLAM (Digital
Subscriber Line Access Multiplexer) 109 to a local exchange 110 which is connected to a
public switched telephony network 111.
The local exchange is further connected via a DSL (Digital Subscriber Line) modem 112 to a
WLAN-access Point 113.
A user equipment 116 is connected via a WLAN radio connection 114 to the WLAN Access
Point and via a GSM or WCDMA radio connection 115 to the mobile services switching
centre/media gateway control function.
According to the invention, the user equipment 116 can use the WLAN radio connection 114
to register in the first SIP proxyl05. The details of the registration will be explained in figure
8

la. Figure la depicts a registration of the mode user equipment 116 with the first SIP proxy
105. This is state of the art. To that end the user equipment 106 sends a SIP register message
towards the SIP proxy 105 via the WLAN radio connection 114. After successful registration
the SIP proxy returns a 200 OK message to the user equipment. After receiving this
confirmation that the registration has been successful the user equipment sends an indication
that it can be reached via the SIP proxy to the mobile services switching centre via the GSM
or WCDMA connection 115 by sending a location update message. The mobile services
switching centre stores the indication in a visitor location register. It returns an accepted
message to indicate the reception of the location update.
The sending of the indication can be implemented in several ways. It can be sent for example
in a USSD (Unstructured Supplementary Service Data) message or any other signalling
means between user equipment and mobile services switching centre. In the preferred
embodiment it is included in a location update message.
Independent from the means used for transporting the information from user equipment to
mobile services switching centre, the information can be sent as a simple indication, for
example a flag, indicating that an alternative access technology is available. In that case one
can always use the same predefined device for routing calls from the mobile services
switching centre/media gateway control function to the user equipment. Such device can be
for example an interrogating call session control function as defined in the 3GPP
recommendation 29.163 version 6.2.0 of March 2004. If not always the same device is used a
device must be identified.
In a preferred embodiment of the invention the SIP proxy is identified by an identification of
the user equipment. To that end, an identification of the user equipment, e.g. the MSISDN or
the IMSI, is stored in a table or a database in association with an identification of the SIP
proxy, conveniently this can be the address of the SIP proxy. In a further embodiment of the
invention, the user equipment identification can be related to an operator and the operator
identification can be stored in relation to the SIP proxy identification.
Alternatively, a device can be identified for example by determining location information of
the user equipment like a location area or geographical coordinates and using a mapping table
9

that maps said location information to an address. A further way to address the user
equipment is the use of an ENUM (tElephone NUmber Mapping) database as defined in IETF
(Internet Engineering Task Force) RFC 3761. The ENUM database maps the telephone
number, for example the IMSI (International Mobile Subscriber Identity) of the user
equipment, to an IP address. A further way is the transmission of a location area identifier in
the location update message. The location area identifier carries an identification of the SIP
proxy or of an access point, for example an ESSID (Extended Services Set IDentification), a
domain name or a WLAN location area identification.
Figure 2 depicts signal flow for an incoming call according to the invention. The architecture
of figure 1 is used for receiving an incoming call at the user equipment 116 via the further
access network, the WLAN access point 113.
In a first step 201 a call request message, here an IAM (Initial address Message) is received at
a control node, the gateway mobile services switching centre 102. The gateway mobile
services switching centre analyses the received data and requests routing info from a database
for storing subscriber data by sending a send routing info message 202 to the home location
register 101. The home location register analyses the request and sends a request for an
address of the called user equipment to a control node by sending a provide roaming number
message 203 to the mobile services switching centre 103. The mobile services switching
centre responds with a provide roaming number message 204 comprising a roaming number
of the called user equipment. The home location register provides routing information 205 to
the gateway mobile services switching centre which uses this information to forward the call
request message 206 to the mobile services switching centre.
The call control node mobile services switching centre receives the indication of an incoming
call the IAM 206 and determines from that the call is directed to a user equipment that can be
reached via a device operating according to a SIP protocol. It determines that the call can be
routed via the SIP proxy 105 and links in the media gateway control function for transforming
the ISUP signalling into SIP signalling. Not depicted is the linking of the media gateway for
transforming payload transmitted according to a transfer mode used in the cellular core
network to payload transmitted according to an IP.
10

In a next step 207 the control node mobile services switching centre 103 forwards the
signalling via the media gateway control function as SIP signalling to the device operating
according to a SIP, the SIP proxy 105. The SIP proxy 105 analyses the received information
from the mobile services switching centre. By using the information received when
registering the user equipment it initiates that the call is routed to the user equipment in a next
step 209. The user equipment terminates the call in a step 210, via the further access network,
implemented as the WLAN radio connection from the WLAN access point.
Figure 3 depicts an alternative architecture for enabling a user equipment to access a
telecommunications network via a further access network. The architecture comprises a
control node implemented as a gateway mobile services switching centre 301. The gateway
mobile services switching centre is collocated with a device that transforms messages sent
according to a call control signalling protocol used in the cellular telecommunications
network into messages according to the session initiation protocol and vice versa, in the
example a media gateway control function. This collocation is optional, for the invention it is
sufficient if they are connected to each other. The gateway mobile services switching
centre/media gateway control function is connected to database for storing subscriber data,
implemented as a home location register 303. The gateway mobile services switching
centre/media gateway control function 301 is further connected to a control node 302 which is
a mobile services switching centre. The home location register and mobile services switching
centre are also connected to each other. The mobile services switching centre 302 is further
connected to an internet domain 104 in particular to a device operating according to a session
initiation protocol, implemented as a SIP proxy 105 known from figure 1. Apart from the
home location register 303, the mobile services switching centre 302 and the gateway mobile
services switching centre/media gateway control function 301, the architecture is similar to
the architecture of figure 1. Also similar are the actions of the user equipment 116 that
registers itself with a server of the further access network, that is with the SIP server 105 and
sends an indication that it can be reached via a device operating according to a SIP, that is
again SIP server 105, to the control node 302 of the cellular telecommunications network.
However, the mobile services switching centre will perform one additional step compared to
the architecture of figure 1, it sends an indication that the user equipment can be reached via a
device operating according to a SIP to the home location register 303. The home location
register stores said indication related to the user equipment or related to the subscriber or user
11

of the user equipment. In a preferred embodiment of the invention, the indication comprises
an address of the device operating according to a SIP.
Figure 4 depicts an alternative signal flow for an incoming call according to the invention, in
the architecture of figure 3. In a first step 401 the gateway mobile services switching
centre/media gateway control function 301 receives an indication of an incoming call to the
user equipment by means of an IAM. It analyses the IAM and requests routing information of
the home location register 303 by sending a send routing info message in a step 402. The
home location register analyses the message and checks the appropriate subscriber data. Said
data comprise an indication that the user equipment can be reached via device operating
according to a SIP. The home location register returns an address of the device or information
that enables the determination of the device in a send routing info message in a step 403.
The gateway mobile services switching centre determines that the called user equipment can
be reached via a device operating according to a session initiation protocol. It initiates the
linking in on a route towards the device operating according to a session initiation protocol,
i.e. the SIP server, of a device that transforms messages sent according to a call control
signalling protocol used in the cellular telecommunications network into messages according
to the session initiation protocol and vice versa, i.e. the gateway mobile services switching
centre.
The gateway mobile services switching centre further initiates the linking in on a route
towards the device operating according to a session initiation protocol, of a device that
transforms user plane transmitted according to a protocol used in the cellular
telecommunications network into user plane transmitted according to an internet protocol and
vice versa, which is a media gateway or a device connected to or comprised in a media
gateway.
After initiating the linking in at least on the signalling path, the gateway mobile services
switching centre forwards the call request to the SIP proxy in a step 404. the further steps are
the same as described by means of figure 2, i.e. the SIP proxy 105 analyses the received
information from the mobile services switching centre. By using the information received
when registering the user equipment it initiates that the call is routed to the user equipment in
a next step 405.
12

Figure 5 depicts a control node CN5 according to the invention, comprising an input unit IU5,
an output unit OU5, and a control unit CU5.
The control node can be operating for example as a mobile services switching centre or a
gateway mobile services switching centre.
Figure 6 depicts a user equipment UE6 according to the invention, comprising a first
transmission unit TU61 for communicating with a first access network of a
telecommunications network, a second transmission unit TU62 for communicating with a
further access network, and a control unit CU6. The user equipment first attaches to a first
cellular telecommunications access network like a so-called 2G or 3G network via the first
transmission unit TU61.When the user equipment enters a coverage area for the second
transmission unit TU62, the second transmission unit sends an indication to the control unit
indicating that.
The control unit receives an indication from the second transmission unit that the user
equipment is currently located in an area covered by the further access network, and in
response thereto to initiate the registration of the user equipment at a server of the further
access network via the second transmission unit.
After successful registration the second transmission unit receives a confirmation that the
registration was successful and forwards it to the control unit. The control unit sends an
indication that the user equipment can be reached via a device operating according to a
session initiation protocol to the telecommunications network via the first transmission unit.
13

We Claim :
1. Method for handling an incoming call to a user equipment (116, UE6) by a control node
(CN5, 102, 103, 301, 302) of a cellular telecommunication network, said method
comprising the following steps:
• receiving an indication of an incoming call to the user equipment in the control
node,
• determining that the called user equipment can be reached via a device of a further
access network operating according to a session initiation protocol (105),
• initiating the linking in on a route towards the device operating according to a
session initiation protocol, of a device (103, 301) that transforms messages sent
according to a call control signaling protocol used in the cellular
telecommunications network into messages according to the session initiation
protocol and vice versa, and
• initiating the linking in on a route towards the device operating according to a
session initiation protocol, of a device that transforms user plane transmitted
according to a protocol used in the cellular telecommunications network into user
plane transmitted according to an internet protocol and vice versa.
2. Method according to claim 1, with the steps of:
• receiving in the control node an indication that the user equipment can be reached
via a device operating according to a session initiation protocol,
• determining an address of the device operating according to a session initiation
protocol, and
• sending an indication that the user equipment can be reached via a device
operating according to a session initiation protocol to a storage connected to the
control node.
3. Method according to any of the preceding claims, with the additional step of
• sending a message comprising an indication that the user equipment can be
reached via a device operating according to a session initiation protocol is sent to
a database for storing subscriber data.
14

4. Method according to any of the preceding claims, wherein the indication that the user
equipment can be reached via a device operating according to a session initiation
protocol, is received in a location area update message sent by the user equipment.
5. Method according to claim 1, wherein the step of determining comprises the steps of
• interrogating a database for storing subscriber data (101) for routing information
for reaching the called user equipment,
• receiving a response from said database and
• determining from analysing the response that the user equipment can be reached
via a device operating according to a session initiation protocol.
6. Method according to claim 3 or 4, wherein the database is an AAA server, a home
location register or a home subscriber server.
7. Method according to any of the preceding claims wherein the control node is a mobile
services switching centre.
8. Method according to any of the preceding claims wherein the device that transforms
messages sent according to a call control signaling protocol used in the cellular
telecommunications network into messages according to the session initiation protocol
and vice versa transforms messages is a media gateway control function.
9. Method according to any of the preceding claims, wherein the device that transforms
user plane transmitted according to a protocol used in the cellular telecommunications
network into user plane transmitted according to an internet protocol is a media gateway
or is located in a media gateway.
10. Method according to any of the preceding claims wherein the device operating
according to a session initiation protocol is a service initiation protocol proximity server
or an interrogating call session control function.
15

11. Method for operating a user equipment (UE6, 116) that comprises a first transmission
unit (TU61) for communicating with a cellular telecommunications access network and
a second transmission unit (TU62) for communicating with a further access network
(113, 112, 110, 109) the method comprising the steps of:
• attaching to the cellular telecommunications network,
• determining that the user equipment is currently located in an area that is covered
by the further access network,
• sending a session initiation protocol message for registering the user equipment at
a server of the further access network,
• receiving a session initiation protocol message confirming that the user equipment
has been registered,
• sending a message comprising an indication that the user equipment can be
reached via a device operating according to the session initiation protocol to a
control node of the cellular telecommunications network via the cellular
telecommunications access network.
12. Control node (CN6, 102, 103, 301, 302) for a cellular telecommunication network
comprising in input unit (IU5), an output unit (OU5), and a control unit (CU5),
characterised by that the control unit is adapted
• to determine that a user equipment can be reached via a device of a further access
network operating according to a session initiation protocol,
• to initiate the linking in on a route towards the device operating according to a
session initiation protocol, of a device that transforms messages sent according to
a call control signaling protocol used in the cellular telecommunications network
into messages according to the session initiation protocol and vice versa, and
• to initiate the linking in on a route towards the device operating according to a
session initiation protocol, of a device that transforms user plane transmitted
according to a protocol used in the cellular telecommunications network into user
plane transmitted according to an internet protocol and vice versa.
13. Control node according to claim 12, wherein the control node is connected to a storage
for storing subscriber data,
characterised by
16

that the input unit is adapted to receive an indication that a user equipment can be
reached via a device operating according to a session initiation protocol and to signal it
to the control unit, and
that the control unit is adapted to initiate the sending of an indication that the user
equipment can be reached via a device operating according to a session initiation
protocol to the storage for storing subscriber data and to determine an address for
sending data towards the user equipment.
14. Control node according to claim 13, wherein the indication sent to the storage for
storing subscriber data comprises an address of the device operating according to a
session initiation protocol.
15. Control node according to any of the claims 12, 13 or 14, that is implemented by means
of a mobile services switching centre or a gateway mobile services switching centre
server.
16. Control node according to claim 13, 14 or 15, wherein the storage is a visitor location
register.
17. Control node according to any of the claims 12 to 16, wherein the control node is
adapted to initiate the sending of a message to a database for storing subscriber data, the
message comprising an indication that the user equipment can be reached via a device
that operates according to a session initiation protocol.
18. Control node according to any of the preceding claims, wherein the control node
comprises a media gateway control function.
19. User equipment (UE6, 116) comprising a first transmission unit (TU61) for
communicating with a first access network of a telecommunications network, a second
transmission unit (TU62) for communicating with a further access network (113, 112,
110, 109), and a control unit (CU6),
characterised by that the control unit is adapted to receive an indication from the second
transmission unit that the user equipment is currently located in an area covered by the
17

further access network, and in response thereto to initiate the registration of the user
equipment at a server of the further access network via the second transmission unit, to
receive a confirmation that the registration was successful via the second transmission
unit, and to send an indication that the user equipment can be reached via a device
operating according to a session initiation protocol to the telecommunications network
via the first transmission unit.
18
20. User equipment according to claim 19, wherein the first transmission unit is adapted to
operate according to at least one of a Global System for Mobile Telecommunication,
Code Division Multiple Access, Wideband Code Division Multiple Access, American
Mobile Phone System, Digital- American Mobile Phone System, or Pacific Digital
Cellular standards.
21. User equipment according to claim 19 or 20 wherein the second transmission unit is
adapted to operate according to at least one of Bluetooth, ISDN, or Wireless Local Area
Network recommendations.

The invention relates to methods and devices for enabling the handling of terminating speech
calls to a dual mode user equipment by using a further access network for transmitting said
data.

OPERATING AND SUPPORTING DUAL MODE USER EQUIPMENT

Documents:

Inventors:

PCT Conventions: