WO2017124218A1

WO2017124218A1 - Method, apparatus and device for transfer between different networks

Info

Publication number: WO2017124218A1
Application number: PCT/CN2016/071179
Authority: WO
Inventors: Qi XIA; Chunbo Wang
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2016-01-18
Filing date: 2016-01-18
Publication date: 2017-07-27

Abstract

Embodiments of the present disclosure relate to a method, apparatus and device for transfer between different networks. In example embodiments, a request is received, at a core network associated with a mobile communication network, to transfer an ongoing call originated by a terminal device. In response to determining that a current access network serving the terminal device is a wireless local network (WLAN) and a destination access network to serve the terminal device is a cellular access network associated with a different mobile communication network, it is determined whether the transfer is allowed based on a policy. Such determination based on the policy of whether to allow the transfer from the WLAN to the cellular access network is more adaptive and flexible.

Description

METHOD， APPARATUS AND DEVICE FOR TRANSFER BETWEEN DIFFERENT NETWORKS

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to the field of telecommunication， and in particular， to a method， apparatus， and device for transfer between different networks.

BACKGROUND

Due to wide deployment of Wireless Fidelity (Wi-Fi) networks， a Voice over Wi-Fi (VoWi-Fi) call has become an effective complement to a cellular call in third Generation Partnership Project (3GPP) networks especially in the case where coverage of the 3GPP networks is poor. Furthermore， a terminal device may prefer the VoWi-Fi call due to low cost when roaming aboard. The coverage of a Wi-Fi network is generally local， and， accordingly， when the terminal device in the VoWi-Fi call is moving out of the coverage of the Wi-Fi network， the VoWi-Fi call may be handed over to a cellular network， such as a Long Term Evolution (LTE) network， a second generation (2G) /third generation (3G) network and the like， so as to enable seamless call continuity.

A Dual Radio Voice Call Continuity (DRVCC) technology is an accepted solution of a call handover from the Wi-Fi network to the cellular network. Based on the DRVCC technology， when the handover is needed， the terminal device may initiate a call transfer by calling a Session Transfer Number (STN) directed to an Internet Protocol (IP) Multimedia Subsystem (IMS) network which is deployed in a heterogeneous network composed of the Wi-Fi network， the cellular network and the like. In the IMS network， the Wi-Fi call leg may be replaced by a cellular call leg， and therefore the call may be continued.

During roaming， the terminal device in the VoWi-Fi call is served by Home Public Land Mobile Network (HPLMN) Evolved Packet Data Gateway (ePDG) /Packet Gateway (PGW) /IMS， and the call is charged as a local call. If the DRVCC based handover is performed， and the terminal device continues the call in the LTE network or a 2G/3G Circuit Switching (CS) domain， the terminal device will be served instead by a Visited Public Land Mobile Network (VPLMN) Mobile Switching Center (MSC) server， and the call will be charged as an international call which is extremely expensive. Conventionally， the handover is automatically triggered and unknown by a user of the terminal device， which might be undesirable. As a result， there is a need to limit such an international roaming call caused by the DRVCC based handover so as to reduce unexpected call expenses.

SUMMARY

In general， example embodiments of the present disclosure provide a method， apparatus， and device for transfer between different networks.

In a first aspect， a method implemented at a core network associated with a first mobile communication network is provided. According to the method， a request is received to transfer an ongoing call originated by a terminal device. A current access network serving the terminal device and a destination access network to serve the terminal device are determined. In response to determining that the current access network is a wireless local network (WLAN) and the destination access network is a cellular access network associated with a second mobile communication network different from the first mobile communication network， it is determined whether the transfer is allowed based on a policy. In response to determining that the transfer is allowed， the ongoing call is transferred from the WLAN to the cellular access network. A computer program product for carry out this method is also provided.

In some embodiments， determining whether the transfer is allowed comprises： in response to determining that the second mobile communication network is a visited mobile network of the terminal device， determining whether the policy allows roaming； and in response to determining that the policy allows the roaming， determining that the transfer is allowed.

In some embodiments， determining the current access network comprises： obtaining subscriber information of the terminal device from the request； retrieving， from a record maintained at the core network， setup information on the ongoing call based on the subscriber information； and determining the current access network of the ongoing call based on the setup information.

In some embodiments， determining the destination access network comprises： obtaining， from the request， an identification of a country and network； and determining the destination access network based on the identification of the country and network.

In some embodiments， the method further comprises： disconnecting the ongoing call in response to determining， based on the policy， that the transfer is disallowed.

In some embodiments， the core network is an Internet Protocol (IP) Multimedia Subsystem (IMS) network， and the request is received at a Proxy Call Session Control Function (P-CSCF) of the IMS network. Furthermore， the method further comprises： receiving， at the P-CSCF， the policy from a policy and charging rules function (PCRF) of an evolved packet core network (EPC) during an initial setup of the ongoing call； and storing the policy at the P-CSCF.

In some embodiments， the policy is specified by a user. The request is a session initiation protocol (SIP) Invite message.

In a second aspect， an apparatus implemented at a core network associated with a first mobile communication network is provided. The apparatus comprises： a request receiving unit configured to receive a request to transfer an ongoing call originated by a terminal device； a network determining unit configured to determine a current access network serving the terminal device and a destination access network to serve the terminal device； a transfer determining unit configured to， in response to determining that the current access network is a wireless local network (WLAN) and the destination access network is a cellular access network associated with a second mobile communication network different from the first mobile communication network， determining whether the transfer is allowed based on a policy； and a transferring unit configured to， in response to determining that the transfer is allowed， transfer the ongoing call from the WLAN to the cellular access network.

In a third aspect， a device implemented at a core network associated with a first mobile communication network is provided. The device comprises a receiver configured to receive a request to transfer an ongoing call originated by a terminal device； a processor； and a memory containing instructions which， when executed by the processor， cause the processor to： determine a current access network serving the terminal device and a destination access network to serve the terminal device； in response to determining that the current access network is a wireless local network (WLAN) and the destination access network is a cellular access network associated with a second mobile communication network different from the first mobile communication network， determine whether the transfer is allowed based on a policy； and in response to determining that the transfer is allowed， transfer the ongoing call from the WLAN to the cellular access network.

In a fourth aspect， a device implemented at a core network associated with a first mobile communication network is provided. The terminal comprises means operative to： receive a request to transfer an ongoing call originated by a terminal device； determine a current access network serving the terminal device and a destination access network to serve the terminal device； in response to determining that the current access network is a wireless local network (WLAN) and the destination access network is a cellular access network associated with a second mobile communication network different from the first mobile communication network， determine whether the transfer is allowed based on a policy； and in response to determining that the transfer is allowed， transfer the ongoing call from the WLAN to the cellular access network.

Through the following description， it would be appreciated that according to embodiments of the present disclosure， whether to allow the transfer from the WLAN to the cellular access network may be determined based on a specified policy instead of being totally denied. Such determination based on the policy of whether to allow the transfer is more adaptive and flexible.

It is to be understood that the summary section is not intended to identify key or essential features of embodiments of the present disclosure， nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the more detailed description of some embodiments of the present disclosure in the accompanying drawings， the above and other objects， features and advantages of the present disclosure will become more apparent， wherein：

Fig. 1 is a block diagram of an environment in which embodiments of the present disclosure can be implemented；

Fig. 2 is a flowchart of a method of transferring from the WLAN to the cellular access network in accordance with an embodiment of the present disclosure；

Fig. 3 is a flowchart of a method of transferring from the WLAN to the cellular access network in accordance with another embodiment of the present disclosure；

Fig. 4 is a simplified block diagram of an apparatus of transferring from the WLAN to the cellular access network in accordance with embodiments of the present disclosure； and

Fig. 5 is a simplified block diagram of a device that is suitable for implementing embodiments of the present disclosure.

Throughout the drawings， the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure， without suggesting any limitations as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones describe below.

As used herein， the term “terminal device” or “terminal” refers to any device having wireless communication capabilities， including， but not limited to， mobile phones， cellular phones， smart phones， personal digital assistants (PDAs) ， portable computers， image capture devices such as digital cameras， gaming devices， music storage and playback appliances， any portable units or terminals that have wireless communication capabilities， or Internet appliances enabling wireless Internet access and browsing and the like.

In addition， in the context of the present disclosure， the terms “terminal device” or “user equipment” (UE) can be used interchangeably for ease of discussion. Examples of a UE in a telecommunication system include， but are not limited to， a Mobile Terminal (MT) ， a Subscriber Station (SS) ， a Portable Subscriber Station (PSS) ， a Mobile Station (MS) ， or an Access Terminal (AT) .

As used herein， the term “base station” (BS) refers to a device which is capable of providing or hosting a cell to which one or more terminal devices can access. Examples of a BS include， but are not limited to， a Node B (NodeB or NB) ， an Evolved NodeB (eNodeB or eNB) ， a Remote Radio Unit (RRU) ， a radio header (RH) ， a remote radio head (RRH) ， a relay， a low power node such as a femto， a pico， and the like. The term “base station” (BS) refers to a device which is capable of providing or hosting an area to which one or more terminal devices can access. An access node may be implemented， for example， as a wireless router and the like.

As used herein， the term “includes” and its variants are to be read as open terms that mean “includes， but is not limited to. ” The term “based on” is to be read as “based at least in part on. ” The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment. ” The term “another embodiment” is to be read as “at least one other embodiment. ” Other definitions， explicit and implicit， may be included below.

Fig. 1 shows a block diagram of an environment 100 in which embodiments of the present disclosure can be implemented. In this example， a WLAN 110 is a Wi-Fi network， through which a terminal device 140 may initiate a VoIP call. The WLAN 110 may communicate with a core network 130 which may be an IMS network in this example. As shown， the IMS network may comprise a proxy call session control function (P-CSCF) or access transfer control function (ATCF) 131， and a service centralization and continuity-application server (SCC-AS) 132. In this way， the terminal device 140 can make a call through its own HPLMN 150 even if the terminal device 140 is now located in a VPLMN 160. In the context of the present disclosure， the term “P-CSCF (ATCF) ” refers to a P-CSCF enabling the ATCF.

Specifically， when the terminal device 140 is roaming to the VPLMN 160， if the terminal device 140 is located within coverage area of the WLAN 110， the terminal device 140 may establish a VoIP call， for example， by sending a session initiation protocol (SIP) Invite message to the P-CSCF (ATCF) 131 via an evolved packet date gateway (ePDG) 170 and a packet data network gateway (PGW) 180. In this way， the VoIP call of the terminal device 140 roaming to the VPLMN 160 is charged as a local call.

In this example， the terminal device 140 may also camp on a cellular access network 120， which may be a 3GPP network， for example， associated with the VPLMN 160 through which the terminal device 140 may make a cellular call. While the user is making a VoIP call， if the terminal device 140 moves out of the coverage area of the WLAN 110， the terminal device 140 may trigger DRVCC to a Mobile Switching Center 190 of the cellular access network 120. Then the call can be transferred from the WLAN 110 to the cellular access network 120 to continue. However， the transfer might be undesirable. For example， when the VPLMN 160 and HPLMN 150 are in different countries， the transferred cellular call will be charged as an international call which is very expensive. To address this problem， a conventional way is to prevent the call from being transferred from the WLAN 110 to the cellular access network 120 even if a user expects such transfer， which might degrade user experiences.

It is to be understood that although some specific implementations are described above with reference to Fig. 1， this is merely for the purpose of illustration. For example， the WLAN 110 does not necessarily be implemented as a Wi-Fi network. The WLAN 110 may conform to any suitable WLAN standards including， but not limited to， Institute of Electrical and Electronics Engineers (IEEE) 802.11x， IEEE 802.16x， and the like. Furthermore， the VoIP call is only an example implementation of the call over the WLAN 110， without suggesting any limitation as to the scope of the present disclosure. Any other suitable implementations are possible as well.

Additionally， the communication of the terminal device 140 through the cellular access network 120 may conform to any suitable cellular communication standards including， but not limited to， LTE-Advanced (LTE-A) ， LTE， Wideband Code Division Multiple Access (WCDMA) ， Code Division Multiple Access (CDMA) and Global System for Mobile Communications (GSM) and the like. Furthermore， the communications may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include， but are not limited to， the first generation (1G) ， the second generation (2G) ， 2.5G， 2.75G， the third generation (3G) ， the fourth generation (4G) ， 4.5G， the future fifth generation (5G) communication protocols.

As another example， the HPLMN 150 and the VPLMN 160 are only examples of a mobile communication network， and the IMS network is only an example of the core network 130. Furthermore， the components of the IMS network are also example implementations. Any other suitable implementations of the mobile communication network and the core network 130 are possible as well. In addition， depending on specific implementations， some components as shown may be removed， and some components may be added to the environment 100.

In order to solve the above and other potential problems， embodiments of the present disclosure allow adaptively and flexibly triggering the call transfer based on a policy indicating whether the transfer from a WLAN to a cellular access network is permitted. In general， in accordance with embodiments of the present disclosure， when the P-CSCF 131 of the core network (such as an IMS network) 130 receives a request to transfer an ongoing call， it determines whether request is concerning a transfer from a WLAN to a cellular access network， for example， of a VPLMN. If so， P-CSCF 131 may decide whether to allow the transfer based on the predefined policy.

Fig. 2 shows a high-level diagram of transferring a call from the WLAN to the cellular access network in accordance with one embodiment of the present disclosure. As shown， in this example， the terminal device 140 is roaming to the VPLMN 160. When the terminal device 140 is located within the coverage of the WLAN 110 which may be a Wi-Fi network， the terminal device 140 may carry out a VoWi-Fi call. To this end， the terminal device 140 may send (201) a SIP Invite message to the P-CSCF (ATCF) 131 via the ePDG 170 and the PGW 180， for example.

The P-CSCF (ATCF) 131 may send (202) a SIP Invite message to the SCC-AS 132. If a “200 OK” message is received (203) from the SCC-AS 132， the P-CSCF (ATCF) 131 sends (204) to a policy and charging rules function (PCRF) 220 an AAR (AUTH_APPLICATION_REQUEST) for a policy of DRVCC restriction. Then， the PCRF 220 returns (205) to the P-CSCF (ATCF) 131 “AAA (AUTH_APPLICATION_ANSWER) ” containing the policy. After receiving the policy for DRVCC restriction， the P-CSCF (ATCF) 131 stores (206) the policy， and returns (207) “200 OK” to the terminal device 140. In this example， the P-CSCF (ATCF) 131 may record information on the current access network of the call which may indicate that the ongoing call is a VoWi-Fi call and/or the current access network complies a specific protocol， for example. The P-CSCF (ATCF) 131 may also return a session transfer number (STN) directed to the P-CSCF (ATCF) such that the terminal device 140 may use the STN to trigger the DRVCC.

When the terminal device 140 moves out of the coverage area of the Wi-Fi network， the terminal device 140 may trigger the DRVCC in order to maintain the call. Specifically， the terminal device 140 may send (208) a call setup message to the MSC 190 of the VPLMN 160 if the terminal device 140 is camping on the cellular access network 120 associated with the MSC 190. The call setup message may contain the STN. Upon receipt of the call setup message， the MSC 190 may send (209) a SIP Invite message to the P-CSCF (ATCF) 131. In some embodiments， the SIP Invite message contains the identification of a country and network of the VPLMN 160 as well as the STN. Furthermore， the SIP Invite message may contain the identification of the MSC 190 to notify the P-CSCF (ATCF) 131 that the SIP Invite message is sent from the MSC 190.

Based on the STN contained in the received SIP Invite message， the P-CSCF (ATCF) 131 knows that the DRVCC is triggered. Then， the P-CSCF (ATCF) 131 determines (210) whether the DRVCC is allowed. Specifically， the P-CSCF (ATCF) 131 may determine whether the current access network is a WLAN and the destination access network is a cellular access network of a different mobile communication network such as the VPLMN 160. In this example， the P-CSCF (ATCF) 131 may retrieve a record related to the ongoing call and determines， based on the record， whether the call is a VoWi-Fi call and the current access network complies with， for example， IEEE 802.11. The P-CSCF (ATCF) 131 also determines that the SIP Invite message is received from the MSC 190 of the VPLMN 150. If it is determined that the current access network is a WLAN and the destination access network is a cellular access network of a different mobile communication network， the P-CSCF (ATCF) 131 determines whether the DRVCC is allowed based on a stored policy for the DRVCC restriction.

If the policy indicates that the DRVCC is allowed， the P-CSCF (ATCF) 131 will transfer the ongoing call from the WLAN 110 to the cellular access network 120. In the example as shown in Fig. 2， the policy specifies that the DRVCC is not allowed. In this case， the P-CSCF (ATCF) 131 sends (211) to the MSC 190 4XX to indicate that the DRVCC is not allowed. Accordingly， the MSC 190 sends (212) a call disconnect message to the terminal device 140. Then， the ongoing call is disconnected.

It is to be understood the processes and elements as described above are only example implementations， without suggesting any limitations as to the scope of the present disclosure. Embodiments of the present disclosure may be implemented in any other suitable environments with alternative and/or additional elements， protocols， standards and the like.

Fig. 3 shows a flowchart of a method 300 of transfer from the WLAN to the cellular access network in accordance with another embodiment of the present disclosure. The method 300 can be implemented at the core network 130， such as the IMS network， associated with the HPLMN 150 in the environment 100 as shown in Fig. 1， for example. More specifically， the method 300 may be implemented at the P-CSCF (ATCF) 131. For the purpose of illustration， the method 300 will be described below with reference to Fig. 1. It is to be understood that any other suitable implementations of the core network is possible. For example， the core network may be associated with any suitable mobile communication network and comprise any suitable components， which may enable the transfer from the WLAN 110 to the cellular network 120.

As shown， the method 300 is entered in step 310， where a request is received to transfer an ongoing call originated by the terminal device 140. After the request is received， a current access network serving the terminal device and a destination access network to serve the terminal device 140 are determined in step 320.

In accordance with embodiments of the present disclosure， the current access network may be determined in any suitable ways. In one embodiment， information on the current access network may be recorded at the core network 130 when the ongoing call is set up. For example， when the ongoing call is initiated by the terminal device 140， the setup information is recorded at core IMS network 130 in association with subscriber information of the terminal device 140. The setup information may include the information on the current access network. In this example， the request for the transfer includes the subscriber information of the terminal device 140. In response to receiving the request， the subscriber information of the terminal device 140 is obtained from the request. Then， the setup information on the ongoing call is retrieved from a record maintained at the core network 130. Accordingly， the current access network may be determined based on the setup information.

The core network 130， such as the IMS network， as shown in Fig. 1 includes the P-CSCF (ATCF) 131 and the SCC-AS 132. The method 300 may be implemented by the P-CSCF (ATCF) 131， for example. It is to be understood that the P-CSCF (ATCF) 131 is only an example implementation of the function enabling the method 300. The IMS network may comprise any other suitable functions that may implement the method 200. For example， such a function may be a general P-CSCF without the ATCF.

In one embodiment， the record related to the setup information of the ongoing call may be maintained in the P-CSCF (ATCF) 131. By way of example， if the ongoing call is a VoIP call， when the call is initiated by the terminal device 140， the P-CSCF (ATCF) 131 records the setup information including a call indication that the ongoing call is a call over a WLAN. After the P-CSCF (ATCF) 131 receives the request for the transfer of the ongoing call， the P-CSCF (ATCF) 131 retrieves the related record and then determines， based on the call indication， that the current access network of the ongoing call is the WLAN 110.

P-CSCF (ATCF) In accordance with embodiments of the present disclosure， the destination access network may also be determined in any suitable ways. In one embodiment， the P-CSCF (ATCF) 131 may obtain， from the request， an identification of a country and network. Then， the P-CSCF (ATCF) 131 may determine the destination access network based on the obtained identifications.

For example， in the case that the terminal device 140 is in a VoIP call over the WLAN 110， when the terminal device 140 moves out of the coverage WLAN 110， the terminal device 140 may trigger a transfer to the cellular access network 120 that the terminal device 140 is camping on. In order to trigger the transfer， the terminal device 140 sends a call setup request to the cellular access network 120， for example， to the MSC 190 associated with the cellular access network 120. Then， the MSC 190 sends a request for the transfer to the P-CSCF (ATCF) 131 of the IMS network， wherein the request includes the identification of the country and network associated with the cellular access network 120. Based on the identifications， the P-CSCF (ATCF) 131 may determine the request is received from a further mobile communication network， such as the VPLMN 160. At the same time， the P-CSCF (ATCF) 131 may also determine that the request is sent from the cellular access network 120.

It is to be understood that the VPLMN is only an example implementation of the further mobile communication network， without suggesting any limitation as to the scope of the present disclosure. Any other suitable implementations of the further mobile communication network are possible as well.

If it is determined in step 320 that the current destination access network is the WLAN 110， and that the destination access network is the cellular access network 120 associated with the VPLMN 160， the method 300 proceeds to step 330， where the P-CSCF (ATCF) 131 determines whether the transfer is allowed based on a policy. If the transfer is allowed， in step 340， the P-CSCF (ATCF) 131 transfers the ongoing call from the WLAN 110 to the cellular access network 120.

The policy may be any suitable policy that may be specified by an operator of the HPLMN 150 or a user of the terminal device 140. For example， the operator of the HPLMN 150 may specify for the terminal device 140 in advance that roaming is not allowed. In this case， if the transferred destination is the VPLMN 160， the P-CSCF (ATCF) 131 of the IMS network of the HPLMN 150 determines that the transfer to the cellular access network 120 of the VPLMN 160 is not allowed. As an alternative example， the user may specify in advance that the roaming is expected. Accordingly， the P-CSCF (ATCF) 131 determines that the transfer is allowed.

In this way， whether to allow the transfer from the WLAN 110 to the cellular access network 120 may be determined based on a specified policy. Compared with the conventional solution of totally barring the transfer from the WLAN 110 to the cellular access network 120 when the terminal device 140 is roaming， the determination based on the policy of whether to allow the transfer is more flexible and effective.

In accordance with embodiments of the present disclosure， the P-CSCF (ATCF) 131 may use any suitable approach to obtain the policy. In one embodiment， the policy may be stored in the PCRF 220 as shown in Fig. 2 before the ongoing call is setup. Accordingly， the P-CSCF (ATCF) 131 may obtain the policy from the PCRF 120 at any suitable timing.

For example， the P-CSCF (ATCF) 131 may obtain the policy when receiving the request for the transfer. As another example， the P-CSCF (ATCF) 131 may obtain and store the policy locally when the ongoing call is setup. The pre-storage of the policy in the P-CSCF (ATCF) 131 enables the P-CSCF (ATCF) 131 to be aware of the policy in real time upon the receipt of the request and to make a timely decision on the transfer to the cellular access network of the VPLMN 160 if the transfer is allowed by the policy.

Fig. 4 shows a block diagram of an apparatus 400 for transferring from the WLAN to the cellular access network in accordance with one embodiment of the present disclosure. The apparatus 400 can be implemented at the core network 130， such as the IMS network associated with the PLMN， in the environment 100 as shown in Fig. 1， for example.

As shown， the apparatus 400 comprises a request receiving unit 410， a network determining unit 420， a transfer determining unit 430， and a transferring unit 440. The request receiving unit 410 is configured to receive a request to transfer an ongoing call originated by a terminal device. The network determining unit 420 is configured to determine a current access network serving the terminal device and a destination access network to serve the terminal device. The transfer determining unit 430 is configured to， in response to determining that the current access network is a wireless local network (WLAN) and the destination access network is a cellular access network associated with a second mobile communication network different from the first mobile communication network， determining whether the transfer is allowed based on a policy. Furthermore， the transferring unit 440 is configured to， in response to determining that the transfer is allowed， transfer the ongoing call from the WLAN to the cellular access network.

In one embodiment， the transfer determining unit 430 may comprise a roaming determining unit which is configured to， in response to determining that the second mobile communication network is a visited mobile network of the terminal device， determine whether the policy allows roaming. The transfer determining unit 430 may further comprise a first transfer determining unit which is configured to， in response to determining that the policy allows the roaming， determine that the transfer is allowed.

In one embodiment， the network determining unit 420 may comprise an information obtaining unit， an information retrieving unit， and a current access network determining unit. The information obtaining unit may be configured to obtain subscriber information of the terminal device from the request. The information retrieving unit may be configured to retrieve， from a record maintained at the core network， setup information on the ongoing call based on the subscriber information. The current access network determining unit may be configured to determine the current access network of the ongoing call based on the setup information.

In one embodiment， the network determining unit 420 may further comprises an identification obtaining unit and a destination network determining unit. The identification obtaining unit may be configured to obtain， from the request， an identification of a country and network. The destination network determining unit may be configured to determine the destination access network based on the identification of the country and network.

In one embodiment， the apparatus 400 may further comprise a disconnecting unit. The disconnecting unit may be configured to disconnect the ongoing call in response to determining， based on the policy， that the transfer is disallowed.

In one embodiment， the core network is an Internet Protocol (IP) Multimedia Subsystem (IMS) network， and the apparatus is implemented at a Proxy Call Session Control Function (P-CSCF) of the IMS network. In this example， the apparatus 400 may further comprise： a policy receiving unit configured to receive the policy from a policy and charging rules function (PCRF) of an evolved packet core network (EPC) during an initial setup of the ongoing call； and a storing unit configured to store the policy. In one embodiment， the policy may be specified by a user. In one embodiment， the request may a session initiation protocol (SIP) Invite message.

It should be appreciated that units included in the apparatus 400 correspond to the steps of the methods 200 and 300. Therefore， all operations and features described above with reference to Figs. 2 and 3 are likewise applicable to the units included in the apparatus 400 and have similar effects. For the purpose of simplification， the details will be omitted.

The units included in the apparatus 400 may be implemented in various manners， including software， hardware， firmware， or any combination thereof. In one embodiment， one or more units may be implemented using software and/or firmware， for example， machine-executable instructions stored on the storage medium. In addition to or instead of machine-executable instructions， parts or all of the units in the apparatus 400 may be implemented， at least in part， by one or more hardware logic components. For example， and without limitation， illustrative types of hardware logic components that can be used include Field-programmable Gate Arrays (FPGAs) ， Application-specific Integrated Circuits (ASICs) ， Application-specific Standard Products (ASSPs) ， System-on-a-chip systems (SOCs) ， Complex Programmable Logic Devices (CPLDs) ， and the like.

Fig. 5 is a simplified block diagram of a device 500 that is suitable for implementing embodiments of the present disclosure. The device 500 can be implemented at the core network 130， such as the IMS network associated with the PLMN， in the environment 100 as shown in Fig. 1， for example.

As shown， the device 500 includes a processor 510， a memory 520 coupled to the processor 510， a suitable transmitter (TX) and receiver (RX) 540 coupled to the processor 510， and a communication interface 550 coupled to the processor 510. The memory 510 stores at least a part of a program 530. The TX/RX 540 is for bidirectional wireless communications. The TX/RX 540 has at least one antenna to facilitate communication， though in practice an Access Node mentioned in this application may have several ones. The cormnunication interface 550 may represent any interface that is necessary for communication with other network elements， such as X2 interface for bidirectional communications between eNBs， S1 interface for communication between a Mobility Management Entity (MME) /Serving Gateway (S-GW) and the eNB， Un interface for communication between the eNB and a relay node (RN) ， or Uu interface for communication between the eNB and a terminal device.

The program 530 is assumed to include program instructions that， when executed by the associated processor 510， enable the device 500 to operate in accordance with the embodiments of the present disclosure， as discussed herein with reference to Figs. 2 and 3. The embodiments herein may be implemented by computer software executable by the processor 510 of the device 500， or by hardware， or by a combination of software and hardware. A combination of the processor 510 and memory 510 may form processing means adapted to implement various embodiments of the present disclosure.

The memory 510 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology， such as semiconductor based memory devices， magnetic memory devices and systems， optical memory devices and systems， fixed memory and removable memory， as non-limiting examples. While only one memory 510 is shown in the device 500， there may be several physically distinct memory modules in the device 500. The processor 510 may be of any type suitable to the local technical environment， and may include one or more of general purpose computers， special purpose computers， microprocessors， digital signal processors (DSPs) and processors based on multicore processor architecture， as non-limiting examples. The device 500 may have multiple processors， such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

Generally， various embodiments of the present disclosure may be implemented in hardware or special purpose circuits， software， logic or any combination thereof. Some aspects may be implemented in hardware， while other aspects may be implemented in firmware or software which may be executed by a controller， microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams， flowcharts， or using some other pictorial representation， it will be appreciated that the blocks， apparatus， systems， teclmiques or methods described herein may be implemented in， as non-limiting examples， hardware， software， firmware， special purpose circuits or logic， general purpose hardware or controller or other computing devices， or some combination thereof.

By way of example， embodiments of the present disclosure can be described in the general context of machine-executable instructions， such as those included in program modules， being executed in a device on a target real or virtual processor. Generally， program modules include routines， programs， libraries， objects， classes， components， data structures， or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device， program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer， special purpose computer， or other programmable data processing apparatus， such that the program codes， when executed by the processor or controller， cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine， partly on the machine， as a stand-alone software package， partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of this disclosure， a machine readable medium may be any tangible medium that may contain， or store a program for use by or in connection with an instruction execution system， apparatus， or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but not limited to an electronic， magnetic， optical， electromagnetic， infrared， or semiconductor system， apparatus， or device， or any suitable combination of the foregoing. More specific examples of the machine readable storage medium would include an electrical connection having one or more wires， a portable computer diskette， a hard disk， a random access memory (RAM) ， a read-only memory (ROM) ， an erasable programmable read-only memory (EPROM or Flash memory) ， an optical fiber， a portable compact disc read-only memory (CD-ROM) ， an optical storage device， a magnetic storage device， or any suitable combination of the foregoing.

Further， while operations are depicted in a particular order， this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order， or that all illustrated operations be performed， to achieve desirable results. In certain circumstances， multitasking and parallel processing may be advantageous. Likewise， while several specific implementation details are contained in the above discussions， these should not be construed as limitations on the scope of the present disclosure， but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely， various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in language specific to structural features and/or methodological acts， it is to be understood that the present disclosure defined in the appended claims network is not necessarily limited to the specific features or acts described above. Rather， the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A method (300) implemented at a core network (130) associated with a first mobile communication network (150) ， the method (300) comprising：

receiving (310) a request to transfer an ongoing call originated by a terminal device (140) ；

determining (320) a current access network serving the terminal device (140) and a destination access network to serve the terminal device (140) ；

in response to determining that the current access network is a wireless local network (WLAN) (110) and the destination access network is a cellular access network (120) associated with a second mobile communication network (160) different from the first mobile communication network (150) ， determining (330) whether the transfer is allowed based on a policy； and

in response to determining that the transfer is allowed， transferring (340) the ongoing call from the WLAN (110) to the cellular access network (120) .
The method (300) of clam 1， wherein the first mobile communication network (150) is a home network of the terminal device (140) ， and

wherein determining (330) whether the transfer is allowed comprises：

in response to determining that the second mobile communication network (160) is a visited network of the terminal device (140) ， determining whether the policy allows roaming； and

in response to determining that the policy allows the roaming， determining that the transfer is allowed.
The method (300) of claim 1， wherein determining (320) the current access network comprises：

obtaining subscriber information of the terminal device (140) from the request；

retrieving， from a record maintained at the core network (130) ， setup information on the ongoing call based on the subscriber information； and

determining the current access network of the ongoing call based on the setup information.
The method (300) of claim 1， wherein determining (320) the destination access network comprises：

obtaining， from the request， an identification of a country and network； and

determining the destination access network based on the identification of the country and network.
The method (300) of claim 1， further comprising：

disconnecting the ongoing call in response to determining， based on the policy， that the transfer is disallowed.
The method (300) of claim 1， wherein the core network (130) is an Intemet Protocol (IP) Multimedia Subsystem (IMS) network， and the request is received at a Proxy Call Session Control Function (P-CSCF) of the IMS network， and wherein the method (300) further comprises：

receiving， at the P-CSCF， the policy from a policy and charging rules function (PCRF) (220) during an initial setup of the ongoing call； and

storing the policy at the P-CSCF (220) .
The method (300) of claim 1， wherein the policy is specified by a user.
The method (300) of claim 1， wherein the request is a session initiation protocol (SIP) Invite message.
An apparatus (400) implemented at a core network (130) associated with a first mobile communication network (150) ， the apparatus (400) comprising：

a request receiving unit (410) configured to receive a request to transfer an ongoing call originated by a terminal device (140) ；

a network determining unit (420) configured to determine a current access network serving the terminal device (140) and a destination access network to serve the terminal device (140) ；

a transfer determining unit (430) configured to， in response to determining that the current access network is a wireless local network (WLAN) (110) and the destination access network is a cellular access network (120) associated with a second mobile communication network (160) different from the first mobile communication network (150) ， determining whether the transfer is allowed based on a policy； and

a transferring unit (440) configured to， in response to determining that the transfer is allowed， transfer the ongoing call from the WLAN (110) to the cellular access network (120) .
The apparatus (400) of claim 9， wherein the first mobile communication network (150) is a home network of the terminal device (140) ， and wherein the transfer determining unit (430) comprises：

a roaming determining unit configured to， in response to determining that the second mobile communication network (160) is a visited network of the terminal device (140) ， determine whether the policy allows roaming； and

a first transfer determining unit configured to， in response to determining that the policy allows the roaming， determine that the transfer is allowed.
The apparatus (400) of claim 9， wherein the network determining unit (420) comprises：

an information obtaining unit configured to obtain subscriber information of the terminal device (140) from the request；

an information retrieving unit configured to retrieve， from a record maintained at the core network (130) ， setup information on the ongoing call based on the subscriber information； and

a current access network determining unit configured to determine the current access network of the ongoing call based on the setup information.
The apparatus (400) of claim 9， wherein the network determining unit (420) comprises：

an identification obtaining unit configured to obtain， from the request， an identification of a country and network； and

a destination network determining unit configured to determine the destination access network based on the identification of the country and network.
The apparatus (400) of claim 9， further comprising：

a disconnecting unit configured to disconnect the ongoing call in response to determining， based on the policy， that the transfer is disallowed.
The apparatus (400) of claim 9， wherein the core network (130) is an Intemet Protocol (IP) Multimedia Subsystem (IMS) network， and the apparatus is implemented at a Proxy Call Session Control Function (P-CSCF) of the IMS network， and wherein the apparatus (140) further comprises：

a policy receiving unit configured to receive the policy from a policy and charging rules function (PCRF) (220) during an initial setup of the ongoing call； and

a storing unit configured to store the policy.
The apparatus (400) of claim 9， wherein the policy is specified by a user.
The apparatus (400) of claim 9， wherein the request is a session initiation protocol (SIP) Invite message.
A device (500) implemented at a core network (130) associated with a first mobile communication network (150) ， comprising：

a receiver (540) configured to receive (310) a request to transfer an ongoing call originated by a terminal device (140) ；

a processor (510) ； and

a memory (520) containing instructions (530) which， when executed by the processor (510) ， cause the processor (510) to：

determine (320) a current access network serving the terminal device (140) and a destination access network to serve the terminal device (140) ；

in response to determining that the current access network is a wireless local network (WLAN) (110) and the destination access network is a cellular access network (120) associated with a second mobile communication network (160) different from the first mobile communication network (150) ， determine (330) whether the transfer is allowed based on a policy； and

in response to determining that the transfer is allowed， transfer the ongoing call from the WLAN (110) to the cellular access network (120) .
A device (500) implemented at a core network (130) associated with a first mobile communication network (150) ， comprising means operative to：

receive (310) a request to transfer an ongoing call originated by a terminal device (140) ；

determine (320) a current access network serving the terminal device (140) and a destination access network to serve the terminal device (140) ；

in response to determining that the current access network is a wireless local network (WLAN) (110) and the destination access network is a cellular access network (120) associated with a second mobile communication network (160) different from the first mobile communication network (150) ， determine (330) whether the transfer is allowed based on a policy； and

in response to determining that the transfer is allowed， transfer (340) the ongoing call from the WLAN (110) to the cellular access network (120) .
A computer program product being tangibly stored on a computer readable storage medium and including instructions which， when executed on at least one processor (510) ， cause the at least one processor (510) to carry out the method (200) according to any of Claims 1 to 8.