WO2018141114A1

WO2018141114A1 - Method and device for identifying pdn connection for ims service

Info

Publication number: WO2018141114A1
Application number: PCT/CN2017/073001
Authority: WO
Inventors: Lu Wang; Juying GAN
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2017-02-06
Filing date: 2017-02-06
Publication date: 2018-08-09
Anticipated expiration: 2019-08-06

Abstract

Embodiments of the present disclosure relate to a method and device for identifying a Packet Date Network (PDN) connection for an Internet Protocol (IP) Multimedia Subsystem (IMS) service. In example embodiments, after a serving node in a packet switched core network receives, from a terminal device, a first request for establishing a PDN connection, the serving node determines whether the PDN connection is to be established for an IMS service. If it is determined that the PDN connection is to be established for the IMS service, the serving node stores an identification of the IMS service for the PDN connection for a restoration of the PDN connection at a later instant. Accordingly, in a restoration of the PDN connection at a later instant, the serving node may facilitate only the PDN identified for the IMS service. In this way, the restoration of the PDN connection is more effective and efficiently.

Description

METHOD AND DEVICE FOR IDENTIFYING PDN CONNECTION FOR IMS SERVICE

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to the field of telecommunications， and in particular， to a method and device for identifying a Packet Date Network (PDN) connection for an Internet Protocol (IP) Multimedia Subsystem (IMS) service.

BACKGROUND

An IP Multimedia Subsystem (IMS) voice service refers to a voice service based on an IMS core network which typically includes a Proxy-Call Session Control Session Function (P-CSCF) and a Service-Call Session Control Session Function (S-CSCF) . Technologies for the IMS voice service， for example， include Voice over Long-Term Evolution (VoLTE) ， Voice over Wireless Fidelity (VoWiFi) ， and the like.

In standardization of Global System for Mobile Communications Alliance (GSMA) ， a common Access Point Name (APN) has been defined for an IMS voice service over Packet Switching (PS) sessions. In particular， the common APN has been proposed for use in a Local Breakout (LBO) architecture. For example， in the LBO architecture， when a terminal device is roaming in a Visited Public Land Mobile Network (VPLMN) ， the terminal device may use the common APN to select a Packet Data Network Gateway (P-GW or PGW) in the VPLMN to initiate the IMS voice service.

Due to a challenge of deployments of the LBO architecture， an S8 Home Routed (S8HR) architecture has been presented. In the S8HR architecture， individual operators may define operator-specific APNs. With the specific APN of an operator serving a Home Public Land Mobile Network (HPLMN) ， the terminal device may select the P-GW of the HPLMN in roaming in the VPLMN. The same specific APN may be specified by an operator for use in VoLTE， VoWiFi， and other IMS services such as Rich Communication Services (RCS) .

With the VoLTE technology in a Long-Term Evolution (LTE) network， a failed IMS service due to a failure of a P-CSCF in the IMS core network may be restored. For example， when a S-CSCF in the IMS core network detects the failure of the P-CSCF， the S-CSCF may inform a Home Subscriber Server (HSS) of the terminal device of the failure. The HSS then may request a Mobility Management Entity (MME) in an Evolved Packet Core (EPC) network to initiate a P-CSCF restoration procedure. During this procedure， a new P-CSCF may be selected to continue the IMS service.

According to the third Generation Partnership Project (3GPP) standards， during the initiation of the P-CSCF restoration procedure in the LTE network， the MME needs to identify a PDN connection for the IMS service and facilitate the P-CSCF restoration related to the PDN connection. If the common APN has been used by the terminal device， the MME may identify the PDN connection for the IMS service， for example， by checking an APN Network Identifier (APN-NI) . However， if an operator-specific APN is used， the MME is unable to distinguish the PDN connection for the IMS service due to unawareness of definitions of APNs specified by the respective operators.

SUMMARY

In general， example embodiments of the present disclosure provide a method and device for identifying a PDN connection for an IMS service.

In a first aspect， a method implemented at a serving node in a packet switched core network is provided. According to the method， after the serving node receives， from a terminal device， a first request for establishing a PDN connection， the serving node determines whether the PDN connection is to be established for an IMS service. If it is determined that the PDN connection is to be established for the IMS service， the serving node stores an identification of the IMS service for the PDN connection for a restoration of the PDN connection at a later instant.

In some embodiments， the serving node may receive， from a home subscriber database associated with the terminal device and during an attachment of the terminal device to the serving node， a first indication that an APN associated with the PDN connection is used for the IMS service.

In some embodiments， the serving node may determine whether the first indication has been received. If it is determined that the first indication has been received， the serving node may determine that the PDN connection is to be established for the IMS service.

In some embodiments， the serving node may receive， from the home subscriber database and during the attachment， an APN configuration of the terminal device including the first indication.

In some embodiments， the serving node may receive， from the terminal device， a second indication that the PDN connection is to be established for the IMS service. In response to receiving the second indication， the serving node may determine that the PDN connection is to be established for the IMS service.

In some embodiments， the serving node may send， to a gateway in the first packet switched core network， a second request for creating a session on the PDN connection. Then， the serving node may receive， from the gateway， a response to the second request. In response to the response indicating that the PDN connection is to be used for the IMS service， the serving node may determine that the PDN connection is to be established for the IMS service.

In some embodiments， the serving node may be a source serving node of the terminal device. The serving node may send， to a target serving node in a second packet switched core network toward which the terminal device is moving， a third indication that the PDN connection is established for the IMS service.

In some embodiments， the serving node may receive， from an IMS core network， a notification that the IMS service associated with the terminal device fails. In response to the receipt of the notification， the serving node may facilitate the restoration of the PDN connection based on the stored IMS identification of the IMS service.

In a second aspect， there is provided a device implemented at a serving node. The device comprises a processor and a memory. The memory contains instructions executable by the processor， whereby the device is operative to perform the method according to the first aspect.

In a third aspect， there is provided a computer program product that is tangibly stored on a computer readable storage medium. The computer program product includes instructions which， when executed on at least one processor， cause the at least one processor to carry out the method according to the first aspect.

Through the following description， it would be appreciated that according to embodiments of the present disclosure， the serving node identifies a PDN connection for an IMS service when the terminal device requests an establishment of the PDN connection. Accordingly， in a restoration of the PDN connection at a later instant， the serving node may facilitate only the PDN identified for the IMS service. In this way， the restoration of the PDN connection is more effective and efficiently.

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 an example P-CSCF restoration in the case that Protocol Configuration Options (PCO) -based optional extension is not supported according to 3GPP specifications；

Fig. 2 is another example P-CSCF restoration in the case that the PCO-based optional extension is supported according to 3GPP specifications；

Fig. 3 is an example wireless communication network in which embodiments of the present disclosure can be implemented；

Fig. 4 is an example procedure of communications and operations in the wireless communication network according to some embodiments of the present disclosure；

Fig. 5 is an example procedure of communications and operations in the wireless communication network in accordance with some other embodiments of the present disclosure；

Fig. 6 is an example procedure of communications and operations in the wireless communication network in accordance with yet other embodiments of the present disclosure；

Fig. 7 is a flowchart of an example method in accordance with some other embodiments of the present disclosure；

Fig. 8 is a block diagram of a serving node in accordance with some embodiments of the present disclosure； and

Fig. 9 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 limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims， unless defined otherwise， all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

As used herein， the term “terminal device” refers to a device capable of， configured for， arranged for， and/or operable for communications in a wireless communication network. The communications may involve transmitting and/or receiving wireless signals using electromagnetic signals， radio waves， infrared signals， and/or other types of signals suitable for conveying information through air. In particular embodiments， the terminal device may be configured to transmit and/or receive information without direct human interaction. For instance， the terminal device may be designed to transmit information to a network side on predetermined schedules， when triggered by an internal or external event， or in response to requests from the network side.

The terminal device may refer to the endpoint of a wireless connection. Accordingly， the terminal device may be referred to as a wireless terminal. Furthermore， the terminal device may be mobile and， accordingly， referred to as a mobile device or a mobile terminal. Examples of the terminal device include， but are not limited to， user equipment (UE) such as smart phones. Further examples of the terminal device include wireless-enabled tablet computers， laptop-embedded equipment (LEE) ， laptop-mounted equipment (LME) ， and/or wireless customer-premises equipment (CPE) .

As one specific example， the terminal device refers to the UE configured for communication in accordance with one or more communication technologies and corresponding communication standards promulgated by the 3GPP， the Internet Engineering Task Force (IETF) ， or other standardization organizations， such as Global System for Mobile (GSM) ， Universal Mobile Telecommunications System (UMTS) ， Code Division Multiple Access (CDMA) ， Wideband Code Division Multiple Access (WCDMA) ， High-Speed Packet Access (HSPA) ， Long Term Evolution (LTE) ， LTE-Advanced (LTE-A) ， Orthogonal Frequency Division Multiplexing (OFDM) ， the fifth generation (5G) standards， wireless local area network (WLAN) ， Worldwide Interoperability for Microwave Access (WiMAX) ， Bluetooth， ZigBee， and/or any other technologies either currently known or to be developed in the future.

As used herein， the term “user equipment” or “UE” may not necessarily have a “user” in the sense of a human user who owns and/or operates the relevant device. Instead， the UE refers to a device that is intended for sale to， or operation by， a human user but that may not initially be associated with a specific human user. For the purpose of discussion， in the following， some embodiments will be described with reference to UEs as examples of the terminal devices， and the terms “terminal device” and “user equipment” (UE) may be used interchangeably in the context of the present disclosure.

As used herein， the term “packet switched core network” refers to a packet domain core of the wireless communication network. The packet switched core network may be capable of， configured for， arranged for， and/or operable for forwarding or switching information in the wireless communication network on the basis of a packet. The packet switched core network may include at least a serving node and a gateway. Examples of the packet switched core network include， but are not limited to， an EPC network， a General Packet Radio Service (GPRS) core network， and the like.

As used herein， the term “serving node” refers to a central node that serves the terminal device in the packet switched core network. Examples of the serving node include， but are not limited to， a MME in the EPC network， a Serving GPRS Support Node (SGSN) in the GPRS core network， an Evolved Packet Date Gateway (ePDG) /Trusted WLAN Access Gateway (TWAG) in a WLAN， and the like.

As used herein， the term “gateway” refers to an edge node of the packet switched core network. Examples of the gateway include， but are not limited to， a PDN Gateway (P-GW) in the EPC network， a Gateway GPRS Support Node (GGSN) in the GPRS core network， and the like.

As used herein， the term “home subscriber database” refers to a subscriber database in a home location of the terminal device， which contains subscription data and/or user profiles associated with the terminal device. Examples of the home subscriber database include， but are not limited to， a Home Subscriber Server (HSS) ， a Home Location Register (HLR) ， and the like.

As used herein， the term “IMS service” refers to a service that involves an IMS core network. Examples of the IMS service include， but are not limited to， VoLTE services， VoWiFi services， RCS， and the like.

As used herein， the singular forms “a” ， “an” and “the” are intended to include the plural forms as well， unless the context clearly indicates otherwise. 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.

As described above， a P-CSCF restoration procedure has been proposed for the VoLTE service. Example P-CSCF restoration procedures will be discussed below with reference to Figs. 1 and 2. Fig. 1 shows an example P-CSCF restoration in the case that PCO-based optional extension is not supported according to 3GPP specifications. As shown， after an S-CSCF receives (1) a Session Initiation Protocol (SIP) message， the S-CSCF sends (2) a SIP message to a P-CSCF. If the P-CSCF is failed， the S-CSCF may receive (3) a SIP Error message， or a lack of a response from the P-CSCF may be occurred. Accordingly， the S-CSCF may detect the failure of the P-CSCF.

Then， the S-CSCF sends (4) ， to the HSS， a Cx Server-Assignment-Request (SAR) ， which includes a P-CSCF restoration indication， to inform the HSS of the failure of the P-CSCF. After receiving the indication from the S-CSCF， the HSS sends (5b) ， to a MME/SGSN， an S6a/S6d message Insert Subscriber Data Request (IDR) /Insert Subscriber Data Answer (IDA) ， which includes a P-CSCF restoration indication， to request the MME/SGSN to perform the P-CSCF restoration procedure. As shown， the P-CSCF restoration indication included in the IDR/IDA may be implemented in a “P-CSCF Restoration Request” bit set in the IDR/IDA， for example.

If the PCO-based optional extension is not supported， the MME/SGSN causes (7) an IMS PDN release. In the context of the present disclosure， the IMS PDN refers to a PDN connection used for the IMS service. Then， user equipment (UE) may initiate (105) an IMS PDN re-establishment. For example， the UE may perform SIP REGISTER via a new P-CSCF.

Fig. 2 shows another example P-CSCF restoration in the case that the PCO-based optional extension is supported according to 3GPP specifications. As shown， after a MME/S4-SGSN decides to perform the P-CSCF restoration procedure， the MME/S4-SGSN sends (7a) ， to a P-GW via a Serving Gateway (S-GW) ， a Modify Bearer Request/Response if the PCO-based optional extension is supported. The Modify Bearer Request/Response may include a P-CSCF restoration indication. In this way， the MME/S4-SGSN may inform the P-GW of the P-CSCF restoration. Further， the P-GW may cause to update (9) an Evolved Packet Switched (EPS) bearer of the UE if the UE supports the P-CSCF restoration. If the UE does not support the P-CSCF restoration， the P-GW may cause to delete (9) the EPS bearer of the UE. Then， the UE may initiate (205) an IMS PDN re-establishment.

As described above， during the initiation of the P-CSCF restoration with the LTE network， if the MME knows which PDN connection is used for the IMS voice service， the MME may release the corresponding PDN connection or inform the P-GW of the related P-SCSF restoration. If the common APN has been used by the UE， the MME may determine the PDN connection for the IMS service by checking the APN-NI. However， if the specific APN has been used， the MME will be unable to distinguish the PDN connection for the IMS service. Accordingly， the MME may choose not to initiate the related P-CSCF restoration procedure， or choose to initiate the related P-CSCF restoration procedures for all the existing PDN connections， including PDN connection for IMS service， and PDN connections for non-IMS services， which is superfluous and may unnecessarily result in interruption of non-IMS services.

A similar problem exists in a WLAN. For example， if the UE uses the specific APN to access the WLAN， an ePDG/TWAG may not be able to determine which PDN connection is established for the IMS service. Further， the ePDG/TWAG is unable to initiate the related P-CSCF restoration procedure.

In order to at least in part solve the above and other potential problems， embodiments of the present disclosure allow a serving node in a packet switched core network to determine whether a PDN connection is to be established for an IMS service after receiving from a terminal device a request (referred to as “first request” ) for establishing the PDN connection. If the PDN connection is determined to be established for the IMS service， the serving node stores an identification of the IMS service for the PDN connection for use in a restoration of the PDN connection at a later instant. In this way， the serving node may identify the PDN connection for the IMS service. Accordingly， if the IMS service is failed， the serving node may facilitate a restoration of the PDN connection based on the stored identification of the IMS service. In this way， the restoration of the PDN connection is more effective and efficiently.

Fig. 3 shows an example wireless communication network 300 in which embodiments of the present disclosure can be implemented. The wireless communication network 300 includes a packet switched core network 305 which is a packet domain core of the wireless communication network 300. The network 300 also includes a terminal device 310 which may communicate with a serving node 320 of the packet switched core network 305， for example， via a base station or an access node (not shown) . The communications in the network 300 may conform to any suitable standard and using any suitable communication technologies such as LTE， LTE-A， OFDM， HSPA， WCDMA， CDMA， GSM， WLAN， WiMAX， Bluetooth， Zigbee， and/or any other technologies either currently known or to be developed in the future.

It is to be understood that the numbers of terminal devices and packet switched core networks in the network 300 are only for the purpose of illustration without suggesting any limitation. The network 300 may include any suitable number of terminal devices and packet switched core networks adapted for implementing embodiments of the present disclosure.

It is also to be understood that the network 300 may include any other suitable devices or entities at the network side. For example， the network 300 may also include a gateway of the packet switched core network 305， a home subscriber database associated with the terminal device 310， an IMS core network， and the like. Embodiments in this regard will be described in the following paragraphs.

As described above， according to embodiments of the present disclosure， if the terminal device 310 requests a PDN connection establishment， the serving node 320 may identify the PDN connection to be established for an IMS service. In particular， as shown in Fig. 3， the serving node 320 receives (325) from the terminal device 310 the first request for establishing a PDN connection. The first request may be sent by the terminal device 310 in any suitable timing. For example， the terminal device 310 may send the first request during or after an attachment of the terminal device 310 to the serving node 320. Detailed examples will be described in the following paragraphs.

After receiving (325) the first request from the terminal device 310， the serving node 320 determines (330) whether the PDN connection is to be established for an IMS service. The determination of the PDN may be implemented in any suitable approaches. In some embodiments， the serving node 320 may receive， from a home subscriber database associated with the terminal device 310 and during the attachment of the terminal device 310 to the serving node 320， an indication (referred to as “first indication” ) that an APN associated with the PDN connection is used for the IMS service.

The pre-defined association between the APN and the PDN connection may be acquired by the serving node 320 in any suitable approach. For example， the first request from the terminal device 310 may indicate the APN associated with the PDN connection. It is also possible that the serving node 320 acquires the associated APN from other devices or entities in the network 300.

The first indication related to the associated APN may be implemented in any suitable form. In some embodiments， the first indication may be a separate indication sent by the home subscriber database. In order to further facilitate backward compatibility， in some other embodiments， the first indication may be sent by the home subscriber database as part of APN configuration in subscription data of the terminal device 310. For example， the home subscriber database may set a flag for a certain APN to indicate that this APN is used for the IMS service.

Based on the first indication， the serving node 320 may determine that the associated PDN connection is to be used for the IMS service. For example， the serving node 320 may determine that the PDN connection is to be established for the IMS service if the first indication of the associated APN has been received.

As described above， the serving node 320 may receive the first request from the terminal device 310 in any suitable timing. As an example， the first request may be received by the serving node 320 during the attachment of the terminal device 310. In this scenario， upon the reception of the first indication of the associated APN， the serving node 320 may determine that the PDN connection is to be established for the IMS service.

As another example， the first request may be received by the serving node 320 after the attachment of the terminal device 310. In this scenario， the serving node 320 may likewise determine that the PDN connection is to be used for the IMS service if it is determine that the first indication has been received.

In some embodiments， upon the reception of the first indication from the home subscriber database during the attachment of the terminal device 310， the serving node 320 may store the first indication for later use. In this example， if the serving node 320 receives the first request from the terminal device 310 after the attachment， the serving node 320 may determine， based on the stored first indication， that the PDN connection is to be established for the IMS service.

In addition to the first indication of the associated APN received from the home subscriber database， in some embodiments， the serving node 320 may determine the PDN connection to be established for the IMS service based on an explicit indication from the terminal device 310. For example， the terminal device 310 may send an indication (referred to as “second indication” ) that the PDN connection is to be established for the IMS service.

The second indication may be implemented in any suitable form. For example， in some embodiments， the second indication may be a separate indication sent by the terminal device 310 to the serving node 320. In order to further facilitate the backward compatibility， in some other embodiments， the second indication may be included in the first request from the terminal device 310. Accordingly， upon the reception of the second indication， the serving node 320 may determine that the PDN connection is to be established for the IMS service.

In certain network deployments， the gateway of the packet switched core network 305 may mark a PDN connection for the IMS service during an establishment of the PDN connection. Accordingly， in some embodiments， the gateway may indicate to the serving node 320 that the established PDN connection is used for the IMS service.

The indication from the gateway to the serving node 320 may be implemented in any suitable way. In some embodiments， the serving node 320 may send to the gateway a request (referred to as “second request” ) for creating a session on the PDN connection. Then， the gateway may send a response to the second request to the serving node 320. If the response indicates that the PDN connection is to be established for the IMS service， the serving node 320 may determine the PDN connection to be established for the IMS service.

Still with reference to Fig. 3， if the PDN connection is determined (330) to be established for the IMS service， the serving node 320 stores (335) an identification of the IMS service for the PDN connection for use in a restoration of the PDN connection at a later instant. For example， if the serving node 320 receives， from the IMS core network， a notification that the IMS service is failed， the serving node 320 may only facilitate the restoration of the PDN connection for the IMS service based on the stored identification.

Example communications and operations in the wireless communication network 300 according to some embodiments of the present disclosure will be described below with reference to Figs. 4-6. Fig. 4 shows an example procedure 400 of communications and operations in the wireless communication network 300 in accordance with some embodiments of the present disclosure， where the serving node determines the PDN connection to be established for the IMS service based on the first indication of the associated APN received from the HSS during the attachment of the terminal device to the serving node.

In this example， the IMS service is implemented as an IMS voice service. Furthermore， the packet switched core network 305 as shown in Fig. 3 is implemented as an EPC network， and the serving node 320 as shown in Fig. 3 is implemented as a MME 405 in the EPC network. The EPC network also includes a PGW 410 functioning as the gateway of the packet switched core network 310. In addition to the EPC network， as shown， the wireless communication network 300 also includes an IMS core network 415 which includes at least a P-CSCF 420 and a S-CSCF 425. In particular， the network 300 additionally includes the HSS 430 associated with the terminal device 310.

As shown in Fig. 4， in Scenario 1 of a PDN setup for the IMS voice service during the attachment of the terminal device 310 to the MME 405， the MME 405 may receive (435) ， from the terminal device 310， an attach request including a PDN connectivity request which functions as the first request for establishing the PDN connection. In this example， the attach request from the terminal device 310 may include an APN associated with the PDN connection.

In response to the reception of the attach request， the MME 405 may send (440) an update-location-request to the HSS 415 and then receive (445) an update-location-answer from the HSS 415. The update-location-answer may include the APN configurations in the subscription data of the terminal device 310. The APN configurations may include the associated APN with a flag that indicates that the APN is used for the IMS voice service.

Upon the reception of the first indication of the associated APN， the MME 405 stores (450) the first indication in the subscription data for later use. For example， if the MME 405 receives a further PDN connection associated with the APN after the attachment， the MME 405 may determine， based on the stored indication of the APN， that the further PDN connection is to be established for the IMS service. Detailed examples will be described in the following paragraphs.

As shown in Fig. 4， after determining that the PDN connection is to be established for the IMS service， the MME 405 stores (455) an IMS identification (also referred to as an identification of the IMS service) for the PDN connection. Accordingly， if the IMS voice service is failed at a later instant， the MME 405 may facilitate only the restoration of the PDN connection for the IMS service based on the stored identification. Detailed procedure of the restoration will be described in the following paragraphs.

In Scenario 2 of a PDN setup for the IMS voice service after the attachment of the terminal device 310， as shown， the MME 405 may receive (460) from the terminal device 310 a PDN connectivity request which may include the associated APN. In this scenario， since the first indication of the associated APN has been stored (455) ， the MME 405 may determine that the PDN connection is to be established for the IMS service. Further， the MME 405 may store (460) an IMS identification for the PDN connection.

Subsequently， if the S-CSCF 435 detects (470) a P-CSCF failure， such as a failure of the P-CSCF 430， the S-CSCF 435 may send (475) ， to the HSS 430， a SAR including a P-CSCF restoration indication to inform the HSS of the P-CSCF failure. Further， the MME 405 may receive (480) an IDR including the P-CSCF restoration indication. Then， based on the stored IMS identification， the MME 405 may only initiate (485) the restoration of the PDN connection for the IMS service. As shown， the MME 405 may release only the PDN connection for the IMS service， or inform the PGW 410 with the P-CSCF restoration only for the PDN connection for the IMS service.

In addition to the facilitation of the PDN connection restoration， in some embodiments， the MME 405 may determine， based on the stored IMS identification， whether to set a Voice over PS session (VoPS) bit in an Attach Accept or a Tracking Area Update Accept to the terminal device 310

Fig. 5 shows an example procedure 500 of communications and operations in the wireless communication network 300 in accordance with some other embodiments of the present disclosure， where the serving node determines the PDN connection to be established for the IMS service based on the second indication received from the terminal device. In this example， the wireless communication network 300 is implemented as a LTE network， and the IMS service is implemented as a VoLTE service.

Furthermore， similar to the implementations as shown in Fig. 4， the packet switched core network 305 as shown in Fig. 3 is implemented as an EPC network， which includes the MME 405 functioning as the serving node 320， and the PGW 410 functioning as the gateway of the packet switched core network 310. As shown in Fig. 5， the wireless communication network 300 also includes the IMS core network 415 which includes the P-CSCF 420 and the S-CSCF 425， and the HSS 430.

As shown in Fig. 5， in Scenario 1 of a PDN setup for a VoLTE service during the attachment of the terminal device 310 to the MME 405， the MME 405 may receive (505) ， from the terminal device 310， an attach request including a PDN connectivity request. In this example， the attach request may also include an indicator (also referred to as the second indication) that the PDN connection is established for the IMS voice service. Upon the reception of the indicator， the MME 405 may store (510) an IMS identification for the PDN connection.

In Scenario 2 of a PDN setup for a VoLTE service after the attachment， as shown， the MME 405 may receive (515) a PDN connectivity request from the terminal device 310. The PDN connectivity request may include the indicator that the PDN connection is established for the VoLTE service. Then， the MME 405 stores (520) an IMS identification for the PDN connection. Subsequently， if the P-CSCF 420 is failed， the MME 405 may facilitate only the restoration of the PDN connection for the IMS service based on the stored IMS identification. The procedures of the restoration are similar to those described above with reference to Fig. 4， and details thereof will be omitted.

Fig. 6 shows an example procedure 600 of communications and operations in the wireless communication network 300 in accordance with yet other embodiments of the present disclosure， where the serving node determines the PDN connection to be established for the IMS service based on the indication from the gateway. The example implementations related to devices， entities， or functions in the wireless communication network 300 is similar to those as shown in Fig. 4， and details thereof will be omitted.

As shown in Fig. 6， in Scenario 1 of a PDN setup for the IMS voice service during the attachment of the terminal device 310 to the MME 405， the MME 405 may receive (605) ， from the terminal device 310， an attach request including a PDN connectivity request. If the terminal device 310 requests a P-CSCF server address along with the PDN connectivity， the MME 405 may send (610) a Create Session Request (also referred to as the second request for creating a session on the PDN connection) to the PGW 410. The PGW 410 may determine whether PCO in the received request includes a P-CSCF server request. If the P-CSCF server request is included， the PGW 410 may include (615) ， in a Create Session Response， an indication that the PDN connection is established for the IMS service. Then， the MME 405 may receive (620) from the PGW 410 the Create Session Response that includes the indication.

If the terminal device 310 has a pre-configured P-CSCF server address and does not request the P-CSCF server address， the MME 405 may not include the P-CSCF server request into the Create Session Request sent (610) to the PGW 410. Accordingly， the PGW 410 will neither distinguish the PDN for the IMS service nor send the corresponding indication.

In Scenario 2 of a PDN setup for the IMS voice service after the attachment of the terminal device 310， as shown， the MME 405 may receive (625) a PDN connectivity request from the terminal device 310. The PDN connectivity request may include a P-CSCF server address request. Then， the MME 405 may send (630) ， to the PGW 410， a Create Session Request including P-CSCF server address request. If the PGW 410 determines that the PCO in the received request includes the P-CSCF server request， the PGW 410 may include (635) ， in a Create Session Response， an indication that the PDN connection is established for the IMS voice service. Further， the MME 405 may receive (640) from the PGW 410 the Create Session Response including the indication.

Accordingly， the MME 405 may determine that the PDN connection is to be established for the IMS service. Then， the MME 405 may store (645) an IMS identification for the PDN connection. If the P-CSCF 430 is failed at a later instant， the MME 405 may only facilitate the restoration of the PDN connection for the IMS service. The procedures of the restoration are also similar to those described above with reference to Fig. 4， and details thereof will be omitted.

It is to be understood that the example implementations of the wireless communication network 300 as shown in Figs. 4-6 are only for the purpose of illustration， without suggesting any limitation. The embodiments of the present disclosure may be applied in any suitable network and any suitable device or entity within the network. In some implementations， the wireless communication network 300 may be implemented as a 2G or 3G network， and the packet switched core network 310 may be implemented as a GPRS core network.

Accordingly， the serving node 320 may be implemented as a SGSN. In some embodiments， the SGSN may use an S4 interface and interwork with a HSS functioning as the home subscriber database. In some other embodiments， the SGSN may use a Gn interface and interwork with a HLR functioning as the home subscriber database.

In addition to the implementations of the 2G or 3G network as described above， in some other implementations， the wireless communication network 300 may implemented as an untrusted or trusted WLAN. Accordingly， the serving node 320 may be implemented as an ePDG/TWAG. In the embodiments where the ePDG/TWAG receives， from the HSS， the first indication of the APN associated with the PDN connection， the ePDG/TWAG may receive the subscriber data from the HSS via an Authentication， Authorization， and Accounting (AAA) server.

In the embodiments where the ePDG/TWAG receives the second indication from the terminal device， in the untrusted WLAN， the second indication may be carried in an Internet Protocol Security (IPsec) protocol message. In the trusted WLAN， the second indication may be carried in a WLAN Control Protocol (WLCP) message.

In some embodiments， the stored identification of the IMS service for the PDN connection may be transferred during inter-MME mobility or Inter-Radio Access Technology (IRAT) mobility. Such mobility may include a location update， such as Tracking Area Update (TAU) /Route Area Update (RAU) ， handover， and the like. For example， if the serving node 320 is a source serving node during the mobility， the serving node 320 may send， to a target serving node， an indication (referred to as “third indication” ) that the PDN connection is established for the IMS service in order to transfer the identification of the IMS service for the PDN connection to the target serving node. The source and target serving nodes may or may not be located in the same packet switched core network.

The transfer of the identification for the PDN connection may be implemented in any suitable way. In some embodiments， the source serving node may transfer all the PDN connections associated with the terminal device to the target serving node， for example， through a (SGSN) Context Response or Forward Relocation Request message which may contain an indication of an active PDN connection for the IMS service.

Fig. 7 shows a flowchart of an example method 700 inaccordance with some other embodiments of the present disclosure. The method 700 can be implemented at the serving node 320 as shown in Fig. 3. For the purpose of discussion， the method 700 will be described with reference to Fig. 3.

At block 705， the serving node 320 receives， from the terminal device 310， a first request for establishing a PDN connection. At block 710， the serving node 320 determines whether the PDN connection is to be established for an IMS service. At block 715， in response to determining that the PDN connection is to be established for the IMS service， the serving node 320 stores an identification of the IMS service for the PDN connection for a restoration of the PDN connection at a later instant.

In some embodiments， at block 720， the serving node 320 may receive， from a home subscriber database associated with the terminal device 310 and during an attachment of the terminal device 310 to the serving node 320， a first indication that an APN associated with the PDN connection is used for the IMS service.

In some embodiments， at block 725， the serving node 320 may send， to a target serving node in a second packet switched core network toward which the terminal device 310 is moving， a third indication that the PDN connection is established for the IMS service.

In some embodiments， at block 730， the serving node 320 may receive， from an IMS core network， a notification that the IMS service associated with the terminal device 310 fails. At block 735， in response to the receipt of the notification， the serving node 320 may facilitate the restoration of the PDN connection based on the stored IMS identification of the IMS service.

It is to be understood that all operations and features related to the serving node 320 described above with reference to Figs. 3-6 are likewise applicable to the method 700 and have similar effects. For the purpose of simplification， the details will be omitted.

Fig. 8 shows a block diagram of a serving node 800 in accordance with some embodiments of the present disclosure. The serving node 800 can be considered as an example implementation of the serving node 320 as shown in Fig. 3.

As shown， the serving node 800 comprises： a first receiving unit 805 configured to receive， from the terminal device 310， a first request for establishing a PDN connection； a determining unit 810 configured to determine whether the PDN connection is to be established for an IMS service； and a storing unit 815 configured to in response to determine that the PDN connection is to be established for the IMS service， store an identification of the IMS service for the PDN connection for a restoration of the PDN connection at a later instant.

In some embodiments， the serving node 800 may comprise a second receiving unit 820 configured to receive， from a home subscriber database associated with the terminal device 310 and during an attachment of the terminal device 310 to the serving node 800， a first indication that an APN associated with the PDN connection is used for the IMS service.

In some embodiments， the serving node 800 may comprise a sending unit 825 configured to send， to a target serving node in a second packet switched core network toward which the terminal device 310 is moving， a third indication that the PDN connection is established for the IMS service.

In some embodiments， the serving node 800 may comprise a third receiving unit 830 configured to receive， from an IMS core network， a notification that the IMS service associated with the terminal device 310 fails； and a facilitating unit 835 configured to in response to the receipt of the notification， facilitate the restoration of the PDN connection based on the stored IMS identification of the IMS service.

It should be appreciated that units included in the apparatus 800 correspond to the blocks of the method 700. Therefore， all operations and features described above with reference to Figs. 3 to 7 are likewise applicable to the units included in the apparatus 800 and have similar effects. For the purpose of simplification， the details will be omitted.

The units included in the apparatus 800 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 terminal device 500 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. 9 is a simplified block diagram of a device 900 that is suitable for implementing embodiments of the present disclosure. The device 900 can be considered as a further example implementation of the serving node 320 as shown in Fig. 3. Accordingly， the device 900 can be implemented at or as at least a part of the serving node 320.

As shown， the device 900 includes a processor 910， a memory 920 coupled to the processor 910， and a communication module 940 coupled to the processor 910. The memory 910 stores at least a part of a program 930. The communication module 940 has a communication interface which may represent any interface that is necessary for communication with other devices or entities in the network， such as an S1 interface for communication between a MME/S-GW and an eNB， an S4 interface for communication between an SGSN and an SGW， an S6d interface for communication between an SGSN using S4 interface and a HSS， and the like.

The program 930 is assumed to include program instructions that， when executed by the associated processor 910， enable the device 900 to operate in accordance with the embodiments of the present disclosure， as discussed herein with reference to Figs. 3 to 7. The embodiments herein may be implemented by computer software executable by the processor 910 of the device 900， or by hardware， or by a combination of software and hardware. The processor 910 may be configured to implement various embodiments of the present disclosure. Furthermore， a combination of the processor 910 and memory 910 may form processing means 950 adapted to implement various embodiments of the present disclosure.

The memory 910 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology， such as a non-transitory computer readable storage medium， 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 910 is shown in the device 900， there may be several physically distinct memory modules in the device 900. The processor 910 may be of any type suitable to the local technical network， 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 900 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， techniques 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.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions， such as those included in program modules， being executed in a device on a target real or virtual processor， to carry out the method as described above with reference to any of Figs. 3-8. 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.

The above program code may be embodied on a machine readable medium， which 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 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 (700) implemented at a serving node (320， 800) in a first packet switched core network (305) ， comprising：

receiving (705) ， from a terminal device (310) ， a first request for establishing a Packet Data Network， PDN， connection；

determining (710) whether the PDN connection is to be established for an Internet Protocol Multimedia Subsystem， IMS， service； and

in response to determining (710) that the PDN connection is to be established for the IMS service， storing (715) an identification of the IMS service for the PDN connection for a restoration of the PDN connection at a later instant.
The method (700) of claim 1， further comprising：

receiving (720) ， from a home subscriber database associated with the terminal device (310) and during an attachment of the terminal device (310) to the serving node (320， 800) ， a first indication that an Access Point Name， APN， associated with the PDN connection is used for the IMS service.
The method (700) of claim 2， wherein determining (710) whether the PDN connection is to be established for the IMS service comprises：

determining whether the first indication has been received； and

in response to determining that the first indication has been received， determining that the PDN connection is to be established for the IMS service.
The method (700) of claim 2 or 3， wherein receiving the first indication comprises：

receiving， from the home subscriber database and during the attachment， an APN configuration of the terminal device (310) including the first indication.
The method (700) of claim 1， wherein determining (710) whether the PDN connection is to be established for the IMS service comprises：

receiving， from the terminal device (310) ， a second indication that the PDN connection is to be established for the IMS service； and

in response to receiving the second indication， determining that the PDN connection is to be established for the IMS service.
The method (700) of claim 1， wherein determining (710) whether the PDN connection is to be established for the IMS service comprises：

sending， to a gateway in the first packet switched core network (305) ， a second request for creating a session on the PDN connection；

receiving， from the gateway， a response to the second request； and

in response to the response indicating that the PDN connection is to be used for the IMS service， determining that the PDN connection is to be established for the IMS service.
The method (700) of any of claims 1-6， wherein the serving node (320， 800) is a source serving node of the terminal device (310) ， and the method (700) further comprises：

sending (725) ， to a target serving node (320， 800) in a second packet switched core network toward which the terminal device (310) is moving， a third indication that the PDN connection is established for the IMS service.
The method (700) of any of claims 1-7， further comprising：

receiving (730) ， from an IMS core network， a notification that the IMS service associated with the terminal device (310) fails； and

in response to the receipt of the notification， facilitating (735) the restoration of the PDN connection based on the stored IMS identification of the IMS service.
A device (900) implemented at a serving node (320， 800) ， comprising：

a processor (910) and a memory (920) ， the memory (920) containing instructions executable by the processor (910) whereby the device (900) is operative to：

receive (705) ， from a terminal device (310) ， a first request for establishing a Packet Data Network， PDN， connection；

determine (710) whether the PDN connection is to be established for an Internet Protocol Multimedia Subsystem， IMS， service； and

in response to determining (710) that the PDN connection is to be established for the IMS service， store (715) an identification of the IMS service for the PDN connection for a restoration of the PDN connection at a later instant.
The device (900) of claim 9， wherein the memory (920) further contains instructions executable by the processor (910) whereby the device (900) is operative to：

receive (720) ， from a home subscriber database associated with the terminal device (310) and during an attachment of the terminal device (310) to the serving node (320， 800) ， a first indication that an Access Point Name， APN， associated with the PDN connection is used for the IMS service.
The device (900) of claim 10， wherein the memory (920) further contains instructions executable by the processor (910) whereby the device (900) is operative to：

determine whether the first indication has been received； and

in response to determining that the first indication has been received， determine that the PDN connection is to be established for the IMS service.
The device (900) of claim 10 or 11， wherein the memory (920) further contains instructions executable by the processor (910) whereby the device (900) is operative to：

receive， from the home subscriber database and during the attachment， an APN configuration of the terminal device (310) including the first indication.
The device (900) of claim 9， wherein the memory (920) further contains instructions executable by the processor (910) whereby the device (900) is operative to：

receive， from the terminal device (310) ， a second indication that the PDN connection is to be established for the IMS service； and

in response to receiving the second indication， determine that the PDN connection is to be established for the IMS service.
The device (900) of claim 9， wherein the memory (920) further contains instructions executable by the processor (910) whereby the device (900) is operative to：

send， to a gateway in the first packet switched core network (305) ， a second request for creating a session on the PDN connection；

receive， from the gateway， a response to the second request； and

in response to the response indicating that the PDN connection is to be used for the IMS service， determining that the PDN connection is to be established for the IMS service.
The device (900) of any of claims 9-14， wherein the serving node (320， 800) is a source serving node of the terminal device (310) ， and the memory (920) further contains instructions executable by the processor (910) whereby the device (900) is operative to：

send (725) ， to a target serving node (320， 800) in a second packet switched core network toward which the terminal device (310) is moving， a third indication that the PDN connection is established for the IMS service.
The device (900) of any of claims 9-15， wherein the memory (920) further contains instructions executable by the processor (910) whereby the device (900) is operative to：

receive (730) ， from an IMS core network， a notification that the IMS service associated with the terminal device (310) fails； and

in response to the receipt of the notification， facilitate (735) the restoration of the PDN connection based on the stored IMS identification of the IMS service.
A computer program product being tangibly stored on a computer readable storage medium and including instructions which， when executed on at least one processor， cause the at least one processor to carry out the method according to any of claims 1-8.