WO2018053691A1

WO2018053691A1 - Method and apparatus for service restoration in a wireless communication system

Info

Publication number: WO2018053691A1
Application number: PCT/CN2016/099486
Authority: WO
Inventors: Xiaotang XIE; Lihong Zhang; Weixing Wang; Pengle WANG
Original assignee: Nokia Technologies Oy; Nokia Technologies (Beijing) Co., Ltd.
Priority date: 2016-09-20
Filing date: 2016-09-20
Publication date: 2018-03-29

Abstract

Embodiments of the present disclosure provide methods, apparatuses and computer program for service restoration in a wireless communication system. A method implemented at a first core network device comprises; receiving, from a second core network device, a notification of data arrival; in response to the received notification, transmitting a paging message to a target terminal device of the data via a plurality of base stations including a last serving base station of the target terminal device, wherein the target terminal device is in an idle state; if no paging response is received from the target terminal device, checking a state of a path between the first core network device and the last serving base station; and in response to a checking result indicating failure of the path, transmitting, to the second core network device, a message indicating failure of the path and absence of the paging response from the target terminal device. By virtue of the method, availability of service may be improved and restoration latency can be reduced.

Description

METHOD AND APPARATUS FOR SERVICE RESTORATION IN A WIRELESS COMMUNICATION SYSTEM

TECHNICAL FIELD

The non-limiting and example embodiments of the present disclosure generally relate to a technical field of wireless communications， and specifically to methods， apparatuses and computer programs for service restoration in a wireless communication.

BACKGROUND

This section introduces aspects that may facilitate a better understanding of the disclosure. Accordingly， the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.

Some of the abbreviations used in the disclosure are listed in the following：

3GPP Third generation Partnership Project

LTE Long Term Evolution

VoLTE Voice over LTE

IMS Internet protocol multimedia subsystem

APN Access Point Name

RAN Radio access network

CN Core network

MME Mobility management entity

S-GW Serving gateway

eNB Evolved Node B

DDN Downlink Data Notification

TA Tracking area

UE User Equipment

IMSI International Mobile Subscriber Identity

GPRS General Packet Radio Service

GTP GPRS tunnel protocol

GBR Guaranteed bit rate

With development of wireless communications， more and more services are provided to users， and at the same time some conventional services are enhanced or upgraded. For example， more and more Long Term Evolution (LTE) subscribers will be upgraded to Voice over LTE (VoLTE) subscribers with network enhancement.

Requirement for quality of service (QoS) may vary from one service to another. For example， video content downloading requires a high data rate， while a VoLTE service requires high availability. These requirements for QoS have to be met by operators.

SUMMARY

For some services， such as voice services (e.g.， VoLTE) ， high availability is important to individual users and operators， which means that service recovery duration should be kept as short as possible.

In the present disclosure， methods， apparatuses and computer programs are provided to improve service restoration procedure and thereby improving user experience. It can be appreciated that embodiments of the present disclosure are not limited to service restoration of VoLTE， but could be more widely applied to any service restoration where similar problems exist.

In a first aspect of the disclosure， there is provided a method implemented at a first network device. The method includes： receiving， from a second core network device， a notification of data arrival； in response to the received notification， transmitting a paging message to a target terminal device of the data via a plurality of base stations including a last serving base station of the target terminal device， wherein the target terminal device is in an idle state； if no paging response is received from the target terminal device， checking a state of a path between the first core network device and the last serving base station； and in response to a checking result indicating failure of the path， transmitting， to the second core network device， a message indicating failure of the path and absence of the paging response from the target terminal device.

In one embodiment， the plurality of base stations may include base stations included in a tracking area list. In another embodiment， transmitting a paging message to a target terminal device of the data may include transmitting a plurality of paging messages to the target terminal device of the data.

In one embodiment， the message indicating failure of the path and absence of the paging response from the target terminal device may be a downlink data notification failure indication message with a cause field indicating the failure of the path and absence of the paging response from the target terminal device.

In some embodiments， the first core network device maybe a mobile management entity MME， the second core network device maybe a serving gateway S-GW， and the path maybe a S1-AP path.

In a second aspect of the disclosure， there is provided a method implemented at a second network device. The method includes： transmitting， to a first core network device， a notification of data arrival； receiving， from the first core network device， a message indicating absence of a paging response from a target terminal device of the data and failure of a path between the first network node and a last serving base station of the target terminal device， wherein the target terminal device is in an idle state； determining a service type associated with the target terminal device； and starting a network triggered service restoration procedure if the service type is determined to be a predefined service type.

In one embodiment， the message indicating absence of a paging response from a target terminal device of the data and failure of a path may be a downlink data notification failure indication message with a cause field indicating the failure of the path and absence of the paging response from the target terminal device.

In another embodiment， the predefined service type may include an internet protocol multimedia subsystem (IMS) service. In still another embodiment， the predefined service type may include a Voice over Long Term Evolution (VoLTE) service.

In still another embodiment， determining a service type associated with the terminal device may comprise determining the service type by determining an access point name associated with the target terminal device.

In some embodiments， starting a network triggered service restoration procedure may comprise transmitting the notification of data arrival with an International Mobile Subscriber Identity (IMSI) of the target terminal device to a further third core network device linked with the last serving base station. In one embodiment， the method may further comprise： receiving a message from the third core network device indicating no response from the target terminal device； and stopping the network triggered service restoration procedure in response to the received message from the third core network device.

In some embodiments， the first core network device may be a MME， the second core network device may be a serving gateway S-GW， and the path may be a S1-AP path. In one embodiment， the third core network device may be selected from a MME pool including the first core network device.

In a third aspect of the disclosure， there is provided a first network device. The first network device includes a receiving unit， configured to receive， from a second core network device， a notification of data arrival； a paging unit， configured to transmit a paging message， in response to the received notification， to a target terminal device of the data via a plurality of base stations including a last serving base station of the target terminal device， wherein the target terminal device is in an idle state； a checking unit， configured to check a state of a path between the first core network device and the last serving base station if no paging response is received from the target terminal device； and a notifying unit， configured to transmit， to the second core network device， a message indicating failure of the path and absence of the paging response from the target terminal device in response to a checking result indicating failure of the path.

In a fourth aspect of the disclosure， there is provided a second network device. The second network device includes a transmitting unit， configured to transmit， to a first core network device， a notification of data arrival； a receiving unit， configured to receive， from the first core network device， a message indicating absence of a paging response from a target terminal device of the data and failure of a path between the first network node and a last serving base station of the target terminal device， wherein the target terminal device is in an idle state； a determining unit， configured to determine a service type associated with the target terminal device； and a restoring unit， configured to start a network triggered service restoration procedure if the service type is determined to be a predefined service type by the determining unit.

In a fifth aspect of the disclosure， there is provided a first network device. The first network device includes a processor and a memory， said memory containing instructions executable by said processor， and said processor being configured to cause the network device to perform a method according the first aspect of the present disclosure.

In a sixth aspect of the disclosure， there is provided a second network device. The second network device includes a processor and a memory， said memory containing instructions executable by said processor and said processor being configured to cause the terminal device to perform a method according the second aspect of the present disclosure.

In a seventh aspect of the disclosure， there is provided a computer program， comprising instructions which， when executed on at least one processor， cause the at least one processor to carry out a method according to the first aspect of the present disclosure.

In an eighth aspect of the disclosure， there is provided a computer program， comprising instructions which， when executed on at least one processor， cause the at least one processor to carry out a method according to the second aspect of the present disclosure.

According to the various aspects and embodiments as mentioned above， latency for service restoration can be shortened and user experience can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects， features， and benefits of various embodiments of the present disclosure will become more fully apparent， by way of example， from the following detailed description with reference to the accompanying drawings， in which like reference numerals or letters are used to designate like or equivalent elements. The drawings are illustrated for facilitating better understanding of the embodiments of the disclosure and not necessarily drawn to scale， in which：

FIG. 1A illustrates an example wireless communication network in which embodiments of the disclosure may be implemented；

FIG. 1B illustrates an example of signaling diagram for providing mobile terminated (MT) service in the wireless communication network of FIG. 1A；

FIG. 2 illustrates a flowchart of a method implemented at a first core network device according to an embodiment of the present disclosure；

FIG. 3 illustrates a flowchart of a method implemented at a second core network device according to an embodiment of the present disclosure；

FIG. 4 illustrates a signaling diagram for restoring MT call according to an embodiment of the present disclosure when S1-AP path failure occurs；

FIG. 5 illustrates a schematic block diagram of an apparatus implemented as/in a first core network device according to an embodiment of the present disclosure；

FIG. 6 illustrates a schematic block diagram of an apparatus implemented as/in a second core network device according to an embodiment of the present disclosure； and

FIG. 7 illustrates a simplified block diagram of an apparatus that may be embodied as/in a first core network device， and another apparatus that may be embodied as/in a second core network device.

DETAILED DESCRIPTION

Hereinafter， the principle and spirit of the present disclosure will be described with reference to illustrative embodiments. It should be understood， all these embodiments are given merely for one skilled in the art to better understand and further practice the present disclosure， but not for limiting the scope of the present disclosure. For example， features illustrated or described as part of one embodiment may be used with another embodiment to yield still a further embodiment. In the interest of clarity， not all features of an actual implementation are described in this specification.

References in the specification to “one embodiment， ” “an embodiment， ” “an example embodiment， ” etc. indicate that the embodiment described may include a particular feature， structure， or characteristic， but it is not necessary that every embodiment includes the particular feature， structure， or characteristic. Moreover， such phrases are not necessarily referring to the same embodiment. Further， when a particular feature， structure， or characteristic is described in connection with an embodiment， it is submitted that it is within the knowledge of one skilled in the art to affect such feature， structure， or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that， although the terms “first” and “second” etc. may be used herein to describe various elements， these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example， a first element could be termed a second element， and similarly， a second element could be termed a first element， without departing from the scope of example embodiments. As used herein， the term “and/or” includes any and all combinations of one or more of the associated listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be liming of example embodiments. 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. It will be further understood that the terms “comprises” ， “comprising” ， “has” ， “having” ， “includes” and/or “including” ， when used herein， specify the presence of stated features， elements， and/or components etc.， but do not preclude the presence or addition of one or more other features， elements， components and/or combinations thereof.

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 “wireless communication network” refers to a network following any suitable wireless communication standards， such as LTE-Advanced (LTE-A) ， LTE， Wideband Code Division Multiple Access (WCDMA) ， High-Speed Packet Access (HSPA) ， and so on. Furthermore， the communications between network devices in the wireless communication network may be performed according to any suitable generation communication protocols， including， but 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， and/or any other protocols either currently known or to be developed in the future.

The wireless communication network includes a radio access network (RAN) part and a core network (CN) part connected with the RAN. As used herein， the term “core network device” refers to a device in a CN via which a terminal device receives services. The core network device may refer to， for example， a mobility management entity (MME) ， a gateway (GW) ， or any suitable network node， depending on terminology and technique being used.

The term “terminal device” refers to any end device that can access a wireless communication network and receive services therefrom. By way of example and not limitation， a terminal device may be a user equipment (UE) ， which may be a Subscriber Station (SS) ， a Portable Subscriber Station， a Mobile Station (MS) ， or an Access Terminal (AT) . The terminal device may include， but not limited to， a mobile phone， a cellular phone， a smart phone， a tablet， a wearable device， a personal digital assistant (PDA) ， portable computers， image capture terminal devices such as digital cameras， gaming terminal devices， music storage and playback appliances， wearable terminal devices， vehicle-mounted wireless terminal devices and the like. In the following description， the terms “terminal device” ， “terminal” ， “user equipment” and “UE” may be used interchangeably.

FIG. 1A illustrates an example wireless communication network 100 in which embodiments of the disclosure may be implemented. As shown in FIG. 1， the wireless communication network 100 may include one or more RAN 110 and a CN 120. The RAN 110 further includes one or more base stations， for

example base stations

111 and 112， which may be in a form of an Node B (NB) ， evolved NB (eNB) ， Base Transceiver Station (BTS) ， and/or Base Station Subsystem (BSS) ， access point (AP) and the like. Each of the

base stations

111 and 112 may provide radio connectivity to a set of terminal devices within its coverage， for example UEs 113-114 and 115-116 shown in FIG. 1. The CN 120 may include one or more MMEs (e.g.， MMEs 121 and 122) and one or more GWs (e.g.， GW 123) .

In FIG. 1B， an example of signaling diagram 130 for providing mobile terminated (MT) service is illustrated. As shown in FIG. 1B， at 131， a serving GW， e.g.， the GW 123 shown in FIG. 1A， may receive user plane data for UE 113. At 132， the S-GW 123 notifies the data arrival to the MME 121 to which the UE is registered. For example， the S-GW may send a downlink data notification (DDN) message to the MME 121 by following a generic DDN procedure specified in the technical specification TS29.274 V.13.6.0 developed by the third generation partnership project (3GPP) . As a response， at 133， the MME 121 may send a DDN acknowledgement (ACK) to the S-GW 123. In this example， it is assumed that the UE 113 is in an idle state， and the MME is only aware of last serving eNB (e.g.， base station 111 shown in FIGs. 1A and 1 B) of the UE 113， but unaware of its current position. As a result， at 134， the MME 121 sends a paging message to a plurality of base stations， for example， to all base stations included in a tracking area (TA) list. Though only eNB-1 111 and eNB-2 112 are shown in FIG. 1B as examples， it can be appreciated that the TA list may include more base stations. Then the base station which receives the paging message broadcasts a paging message to UEs within its coverage at 135. If the last serving base station 111 receives the paging message from the MME 121 and UE 112 is still in its coverage， the paging message will reach the UE 113 at 135. In response， at 136， the UE 113 initiates a service request procedure.

Authors of the present disclosure have observed that failure of a path (e.g.， S 1-AP path) between a base station (e.g.， the base station 111 shown in FIGs. 1A and 1B) and a MME (e.g.， the MME 121 shown in FIGs. 1A and 1B) often occurs in operators’ live network due to transmission failure (e.g. for a Packet Transport Network (PTN) backhaul network， both working and protection transmission paths failed) ， and a recovery duration is longer than expected. In such a case， the base station 111 will not receive the paging message from the MME 121 via the signaling 134 shown in FIG. 1B， and any idle UE (e.g.， UE 113) within coverage of this base station will not receive any MT call paging during failure of the S 1-AP path. The worst case is that UE 113 only re-connects to the network after expiry of a timer T3412 (i.e.， the PTAU timer defined in 3GPP TS24.301 V13.6.1， Table 10.2.1 which is 54 minutes long by default) . Such a long latency for service restoration is unacceptable and therefore method and apparatus for reducing the latency are required.

In 3GPP， some solutions for improving network reliability and call successful rate have been specified. For example， 3GPP TS23.007 v13.5.0， “Restoration procedures” ， clause 15A. 2 has specified a solution for S1-AP path failure as below：

15A. 2 S1-AP path failure

Upon detection of an S1-AP path failure (i.e. no more SCTP association in service) ，

- the eNodeB shall release the RRC connection of the affected UEs；

-the MME shall proceed as specified for the eNodeB failure in subclause 15A. 1.

The eNodeB shall continue to broadcast warning messages， if any， during an S1AP path failure. Upon recovery of the S1AP path， the eNodeB shall proceed as if no S1AP path failure had occurred.

15A. 1 eNodeB Failure

15A. 1.1General

。。。。。。

An MME that recognises unavailability of an eNodeB (e.g. no more SCTP association in service) or receives a Reset from an eNodeB， shall locally delete the eNodeB related information ( ″eNodeB Address in Use for S1-MME″ and ″eNodeB UE S1AP ID″ ) . The MME initiates release of all S1 bearers towards the Serving GW by sending a Release Access Bearer Request message as defined in the S1 Release procedure in 3GPP TS 23.401 [15] . The MME shall initiate the Dedicated Bearer Deactivation procedure to deactivate the GBR bearers in the packet core.

If the Serving GW receives Release Access Bearers Request message， the Serving GW shall release all eNodeB related information (address and TEIDs) for the UE， but other elements of the UE′s Serving GW context shall not be affected. Any Bearer contexts affected by eNodeB failure that have no valid S1-U tunnel in Serving GW are recovered during the UE Triggered Service Request or during the Network Triggered Service Request procedure as specified in 3GPP TS 23.401 [15] .

According to 3GPP TS23.007 v13.5.0， when S1-AP path failure occurs， an eNB is requested to release a corresponding RRC connection. However， when UE is in an IDLE state， even after a RRC disconnection with the eNB， UE may not attach to an EPC immediately. As a result， before recovery of the S1-AP path， MME still sends a Paging message to all eNBs in the TA list in response to receiving a DDN (for example dedicated for VoLTE) from the S-GW； however， both the eNB with a broken S1-AP interface with the MME and UEs in its coverage cannot receive the paging message. It leads to a failure of MT service (e.g.， a MT VoLTE service) ， and it may take a long time for the UE to recover from the service failure.

In order to solve at least part of the above problems， methods， apparatuses and computer programs have been proposed herein. It should be appreciated that embodiments of the disclosure are not limited to a wireless system operating according to a 3GPP specification， but could be more widely used to any wireless communication systems where a similar problem exists. Likewise， though for simplicity， some embodiments will be described with VoLTE service as an example， embodiments of the present disclosure are not limited to restoration of the VoLTE service， but could be more widely applied.

Reference is now made to FIG. 2， which illustrates a flowchart of a method 200 implemented at a first core network device side according to an embodiment of the present disclosure. For simplicity， the method 200 will be described below with reference to the MME 121 shown in FIGs. 1A and 1B； however， it can be appreciated that， the method 200 may also be implemented by other suitable core network devices in another wireless communication network.

As illustrated in FIG. 2， at block 210， the MME 121 receives， from a second core network device， a notification of data arrival. In one embodiment， the second core network device may be， but is not limited to， a serving gateway， for example， the S-GW 123 shown in FIG. 1A and 1B.

At block 220， in response to the received notification at block 210， the MME 121 transmits a paging message to a target terminal device of the data via a plurality of base stations including the last serving base station of the target terminal device. In one embodiment， the target terminal device may be one of UEs 113-116 shown in FIG. 1A and may be in an idle state. In the following， description will be provided with reference to UE 113 for simplicity.

In another embodiment， the MME 121 may transmit a paging message to a subset or all base stations in a tracking area (TA) list. The base stations will in turn transmit a paging message to UEs within their coverage， for example， following a normal paging procedure specified in 3GPP LTE.

Depending on a configuration of the MME 121， in still another embodiment， the MME 121 may carry out several paging attempts， i.e.， the MME 121 may transmit a plurality of paging messages before determining that no paging response from UE is received. The exact number of paging attempts may be configurable.

At block 230， if no paging response is received from the target terminal device， the MME 121 checks a state of a path with the last serving base station of the target terminal device. The path may be a S1-AP path specified in 3GPP TS23.401 V13.7.0 Section 5.1.1； in some embodiments， however， those skilled in the art can appreciate that， depending on networking technology/infrastructure being used， a different path may be involved instead.

In response to a checking result indicating failure of the path， at block 240， the MME 121 transmits， to the second core network device， e.g.， the S-GW 123 shown in FIG. 1A and 1B， a message indicating failure of the path and absence of a paging response from the target terminal device 113. The message transmitted by the MME 121 will cause the S-GW 123 to start a network triggered service restoration (NTSR) procedure and thereby service for the terminal device 113 will be restored with low latency.

In one embodiment， at block 240， the MME 121 may transmit a DDN Failure Indication message to the S-GW 123. The failure of the path and absence of the paging response from the target terminal device may be indicated in the message via a new cause field. However， embodiments of the present disclosure are not limited to any specific message or message format for transmitting the indication of path failure and absence of the paging response.

The method 200 enables the first core network device to inform failure of the S1-AP path and the fact of no paging response to the second network device， and thereby enables the second network device to initiate a network triggered service restoration (NTSR) procedure based on need. As a result， service for the target terminal device may be restored faster compared with an conventional method.

Though for simplicity purpose， some embodiments are described with reference to MME 121， S-GW 123， a S1-AP path between the MME 121 and an eNB 111 and VoLTE service， it can be appreciated by those skilled in the art that embodiments of the method 200 may be applied in other scenarios.

Reference is now made to FIG. 3， which illustrates a flowchart of a method 300 implemented at a second core network device side according to an embodiment of the present disclosure. For simplicity， the method 300 will be described below with reference to the S-GW 123 shown in FIGs. 1A and 1B； however， it can be appreciated that the method 300 may also be implemented by other suitable core network devices， depending on network technique/infrastructure being used.

As illustrated in FIG. 3， at block 310， the S-GW 123 transmits， to a first core network device， a notification of data arrival. In one embodiment， the first network device may be a MME， for example， the MME 121 shown in FIGs. 1A and 1B which may perform the method 200.

At block 320， the S-GW 123 receives， from the first core network device， a message indicating absence of a paging response from a target terminal device of the data and failure of a path between the first network node and the last serving base station of the target terminal device. In one embodiment， the target terminal device is in an idle state. In another embodiment， the message may be a DDN failure indication message， and a cause field of the message indicates the failure of the path and absence of the paging response from the target terminal device. The message may be the same as that transmitted by the MME 121 at block 240 as described with reference to FIG. 2.

At block 330， the S-GW 123 determines a service type associated with the target terminal device. In one embodiment， the S-GW 123 may determine the service type of the terminal device by determining an access point name (APN) associated with the target terminal device. For example， the S-GW 123 may maintain an EPS Bearer table locally which includes APN information (maybe together with other information， such as IMSI， S-GW TEID-C， RAT type， etc. . ) of each bearer of the subscriber. When the MME 121 sends， to S-GW 123， the DDN Failure Indication message with the new cause value indicating S1-AP failure event on the last serving eNB， it may include the TEID-C of this subscriber according to General Packet Radio Service (GPRS) tunnel protocol (GTP) . The TEID-C represents the subscriber according to GTP protocol， for example 3GPP TS 29.274 V13.6.0 Section 4.1. Then the S-GW may search the EPS Bearer table of this subscriber based on TEID-C to check the APN. However， those skilled in the art can appreciate that， this is just provided as an example， and embodiments are not limited to determining the service type or the APN in any specific way. For example， instead of determining the service type or the APN based information stored locally， the S-GW may acquire the information from a further network device.

At block 340， the S-GW starts a network triggered service restoration (NTSR) procedure if the service type is determined to be a predefined service type. In one embodiment， the predefined service type may include an internet protocol multimedia subsystem (IMS) service. In another embodiment， the predefined service type may include a VoLTE service. For example， at block 340， if the S-GW 123 determines that APN＝IMS， it will trigger the NTSR procedure.

The method 300 enables the S-GW 123 to initiate an NTSR procedure based on needs. For example， if the service of the target terminal device has a low latency and/or high availability requirement， or， the service is important， the S-GW may initiate the NTSR procedure to restore the service upon receiving the message indicating path failure from the MME 121； otherwise， the S-GW 123 may not initiate the NTSR procedure.

In some embodiment， at block 340， the S-GW may start the network triggered service restoration procedure by transmitting the notification of data arrival with an International Mobile Subscriber Identity (IMSI) of the target terminal device to a further third core network device (e.g.， another MME 122 shown in FIG. 1A) linked with the last serving base station. The MME 122 can page the target terminal device and then the target terminal device can attach to the network to receive the service.

In one embodiment， the third core network device (e.g.， the MME 122) may be selected from a MME pool which includes the old MME (i.e.， MME 121 in this example) and the new MME (i.e.， MME 122) and maybe also other MMEs. In this embodiment， upon receiving the DDN failure indication message with the new cause value， the S-GW 123 may start network triggered service restoration (NTSR) by selecting an alternative MME (e.g.， MME 122 shown in FIG. 1A) and sending DDN with International Mobile Subscriber Identity (IMSI) of the target terminal device to it. The last serving base station may have an S1-AP path with each of the MME 121 and MME 122 in the MME pool， and when the S1-AP path with MME 121 MME is broken， the S1-AP path with the MME 122 may still work. Then the selected MME 122 will send IMSI paging towards the target terminal device 113 with retrieved TA list information， via a plurality of base stations including the last serving eNB. If the UE receives the paging message， it will respond to the paging and re-attaches to the network. Afterwards， the UE can receive service (e.g.， VoLTE call) by following a generic/normal mechanism.

Though for simplicity purpose， some embodiments are described with reference to MME 121， MME 122， S-GW 123， a S1-AP path and VoLTE service， it can be appreciated by those skilled in the art that embodiments of the method 300 may be applied in other scenarios.

Reference is now made to FIG. 4， which shows an example signaling diagram 400 for restoring MT VoLTE call according to an embodiment of the present disclosure when S1-AP path failure occurs. As shown in FIG. 4， in this example， during the period of S1-AP path failure， ifno paging response is received， an old MME (i.e.， the MME associated with the broken S1-AP path) will inform S-GW about the failure of S1-AP path with last serving eNB of the UE， for example according to an embodiment of method 200， then the S-GW will trigger an NTSR procedure if it determines that a specific service type is involved， (e.g.， when APN＝IMS (VoLTE) ) ， for example according to an embodiment of method 300.

In particular， the signaling 410-440 shown in FIG. 4 may be the same as signaling 131-134 described with reference to FIG. 1B. In other words， the procedure may be the same as that in a generic DDN handling mechanism. That is， when a DDN message arrives at the MME 121， the MME 121 may start paging UE via (some or) all eNBs in the TA list of the UE. In this example， an eNB-1 111， an eNB-2 112 and an eNB-N 11N are shown as examples of the base stations in the TA list. In one embodiment of the present disclosure， at 440， the MME 121 may carry out several paging attempts.

Then at 450， upon determining that there is no paging response received from the target UE (e.g.， UE 113 shown in FIGs. 1A and 1B) ， the MME 121 may check a state of the S1-AP path with last serving NB of the UE； and ifthe S1-AP path fails， at 460， the MME 121 sends a DDN Failure Indication to the S-GW 123 with a new cause value indicating “S1-AP path with the last serving eNB fails and no response from UE” .

At 470， upon receiving the DDN Failure Indication with the new cause value from the MME 121， the S-GW 123 determines whether service type of the target terminal device is a predefined service type， e.g.， whether APN of the UE 113 is IMS. In response to a positive determination， the S-GW123 may choose an alternative MME， for example from a MME pool 140， for service restoration. Though only MME 121 and MME 122 are shown in FIG. 4， it can be appreciated that the MME pool 140 may include more MMEs.

At 480， the S-GW 123 sends a DDN to the selected MME (e.g.， MME 122 shown in FIG. iA) ， together with an IMSI of the target terminal device. Afterwards， signaling 490-493 will be transmitted as shown in FIG. 4. In one embodiment， signaling 490-493 may be the same as that defined in a normal ‘Network triggered service restoration procedure’ ， where the MME 122 may initiate an IMSI paging towards the UE 113， then the UE 113 send a paging response and re-attaches to EPC successfully.

In the example of FIG. 4， it is assumed that UE 113 is within coverage of eNB-1 111 and registered in MME 121. Further， the UE 113 is in an idle state and eNB-1 111 is the last serving eNB of the UE 113 recorded in MME 121. In this example， both MME 121 and MME 122 belong to a same MME pool 140， and when the S1-AP path between eNB-1 11 land MME 121 is down， the S1-AP path between eNB-1 111 and the MME 122 still works well. Then service can be restored when the S-GW selects the MME 122 and transmits the DDN to it.

In one embodiment， in an abnormal scenario where the selected MME 122 can’t get any UE responding for the IMSI Paging after signaling 491， the MME 122 may send a message， e.g.， a DDN Failure Indication message， to the S-GW 123 to indicate that no response from the target terminal device is received. Here， the DDN Failure Indication message may be a conventional/normal DDN Failure Indication message， i.e.， this message may not include information indicating S1-AP failure but only include a normal cause value showing ‘UE not responding’ . That is， the new cause value included in the signaling 460 of FIG. 4 may not be incorporated in the DDN Failure Indication message transmitted by the MME 122 to the S-GW 123. It can be appreciated that embodiments are not limited to any specific message for indicating the information of ‘UE not responding’ . In response to the DDN Failure Indication message from the MME 122， the S-GW 123 may stop the network triggered service restoration procedure. For example， the S-GW 123 may clear ‘Network triggered service restoration procedure’ flag， and still send DDN to the original MME 121 if any subsequent downlink data receives for that UE 113. However， this is just an example for services with very low restoration latency requirement.

Reference is now made to FIG. 5， which illustrates a schematic block diagram of an apparatus 500 in a wireless communication network (e.g.， the wireless communication network 100 shown in FIG. 1) . The apparatus may be implemented as/in a first core network device， e.g.， the MME 121 shown in FIGs. 1A and 1B. The apparatus 500 is operable to carry out the example method 200 described with reference to FIG. 2 and possibly any other processes or methods. It is also to be understood that the method 200 is not necessarily carried out by the apparatus 500. At least some steps of the method 200 can be performed by one or more other entities.

As illustrated in FIG. 5， the apparatus 500 includes a receiving unit 501， a paging unit 502， a checking unit 503 and a notifying unit 504. The receiving unit is configured to receive， from a second core network device， a notification of data arrival； and the paging unit 502 is configured to transmit a paging message， in response to the notification of data arrival received by the receiving unit 501， to a target terminal device of the data via a plurality of base stations including a last serving base station of the target terminal device， wherein the target terminal device is in an idle state. The checking unit 503 is configured to check a state of a path (e.g.， S1-AP path) between the first core network device and the last serving base station if no paging response is received from the target terminal device； and the notifying unit 504 is configured to transmit， to the second core network device， a message indicating failure of the path and absence of the paging response from the target terminal device in response to a checking result indicating failure of the path.

In one embodiment， in response to the notification of data arrival received by the receiving unit 501， the paging unit 502 may transmit a paging message to some or all base stations included in a TA list of the target terminal device. Alternatively or additionally， the paging unit 502 may be configured to transmit a plurality of paging messages to the target terminal device.

In another embodiment， the notifying unit 504 may be configured to transmit a DDN failure indication message to the second core network device (e.g.， the S-GW 123 shown in FIGs. 1A and 1B) ， and a cause field of the DDN failure message may be set to a value indicating the failure of the path and absence of the paging response from the target terminal device.

In some embodiments， the receiving unit 501， the paging unit 502， the checking unit 503 and the notifying unit 504 may be configured to perform respectively the operations of blocks 210-240 of method 200 described with reference to FIG. 2. Therefore， descriptions with respect to blocks 210-240 provided with reference to FIG. 2 also apply to the units 501-504， and details will not be repeated for simplicity.

FIG. 6 illustrates a schematic block diagram of an apparatus 600 in a wireless communication network (e.g.， the wireless communication network 100 shown in FIG. 1) . The apparatus 600 may be implemented as/in a second core network device， e.g.， the S-GW 123 shown in FIGs. 1A and 1B in communication with the first core network device (e.g.， the MME 121 shown in FIGs. 1A and 1B) or the apparatus 500. The apparatus 600 is operable to carry out the example method 300 described with reference to FIG. 3 and possibly any other processes or methods. It is also to be understood that the method 300 is not necessarily carried out by the apparatus 600. At least some steps of the method 300 can be performed by one or more other entities.

As illustrated， the apparatus 600 includes a transmitting unit 601， a receiving unit 602， a determining unit 603 and a restoring unit 604. The transmitting unit 601 is configured to transmit， to a first core network device (e.g.， the MME121 shown in FIGs. 1A and 1B) ， a notification of data arrival. The receiving unit 602 is configured to receive， from the first core network device， a message indicating absence of a paging response from a target terminal device of the data and failure of a path (e.g.， an S1-AP path) between the first network node and a last serving base station of the target terminal device， wherein the target terminal device is in an idle state. The determining unit 603 is configured to determine a service type associated with the target terminal device； and the restoring unit 604 is configured to start a network triggered service restoration procedure if the service type is determined to be a predefined service type by the determining unit.

In one embodiment， the message received by the receiving unit 602 is a DDN failure indication message with a cause field indicating the failure of the path and absence of the paging response from the target terminal device.

In another embodiment， upon receiving the message indicating path failure， the determining unit 603 may be configured to determine a service type associated with the terminal device by determining an APN associated with the target terminal device.

In still another embodiment， if the service type or APN is determined to be IMS or VoLTE by the determining unit 603， the restoring unit 604 may be configured to start a network triggered service restoration procedure.

As one example， the restoring unit 604 may be configured to start the network triggered service restoration procedure by transmitting the notification of data arrival with an IMSI of the target terminal device to a further third core network device linked with the last serving base station. The third core network device may be， e.g.， the MME 122 shown in FIG. 1A. In one embodiment， the third core network device may be selected from a MME pool including the first core network device.

Optionally， in another embodiment， the restoring unit 604 may be further configured to： receive a message from the third core network device indicating no response from the target terminal device； and stop the network triggered service restoration procedure in response to the received message from the third core network device.

In some embodiments， the transmitting unit 601， the receiving unit 602， the determining unit 603 and the restoring unit 604 may be configured to perform respectively the operations of blocks 310-340 of method 300 described with reference to FIG. 3 and FIG. 4. Therefore， descriptions with respect to blocks 310-340 provided with reference to FIG. 3 also apply to the units 601-604， and details will not be repeated for simplicity.

Furthermore， it would be appreciated that apparatuses 500 -600 may comprise other units not shown in FIGs. 5-6. In addition， some units or modules in the apparatus 500-600 can be combined in an implementation， or may be omitted in another embodiment. For example， in one embodiment， functions/operations of the determining unit 603 and the restoring unit 604 may be performed by a single unit.

FIG. 7 illustrates a simplified block diagram of an apparatus 710 that may be embodied in/as a first core network device， e.g.， the MME 121 or MME 122 shown in FIG. 1A， and an apparatus 220 that may be embodied in/as a second core network device， e.g.， the S-GW 123 shown in FIG. 1A.

The apparatus 710 may include at least one processor 711， such as a data processor (DP) and at least one memory (MEM) 712 coupled to the processor 711. The apparatus 710 may further include a transmitter TX and receiver RX 1113 coupled to the processor 711. The MEM 712 may be non-transitory machine readable storage medium and it may store a program (PROG) 714. The PROG 714 may include instructions that， when executed on the associated processor 711， enable the apparatus 710 to operate in accordance with the embodiments of the present disclosure， for example to perform the method 200. A combination of the at least one processor 711 and the at least one MEM 712 may form processing means 715 adapted to implement various embodiments of the present disclosure.

The apparatus 720 includes at least one processor 721， such as a DP， and at least one MEM 722 coupled to the processor 721. The apparatus 720 may further include a suitable TX/RX 723 coupled to the processor 721. The MEM 722 may be non-transitory machine readable storage medium and it may store a PROG 724. The PROG 724 may include instructions that， when executed on the associated processor 721， enable the apparatus 720 to operate in accordance with the embodiments of the present disclosure， for example to perform the method 300. A combination of the at least one processor 721 and the at least one MEM 722 may form processing means 725 adapted to implement various embodiments of the present disclosure.

Various embodiments of the present disclosure may be implemented by computer program executable by one or more of the

processors

711 and 721， software， firmware， hardware or in a combination thereof.

The

MEMs

712 and 722 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 terminal devices， magnetic memory terminal devices and systems， optical memory terminal devices and systems， fixed memory and removable memory， as non-limiting examples.

The

processors

711 and 721 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.

Compared with conventional service restoration solution， e.g.， the solution specified in TS23.007 (v13.5.0) clause 15A. 2 S1-AP failure solution， embodiments of the present disclosure has at least one of the following advantages：

(1) No special action is required on eNB side.

(2) Only the UE who has downlink data under path failure (e.g.， S1-AP failure) will be triggered with this solution， other reachable UEs will not be affected， which results in less signaling to network and radio side.

(3) Introducing of new interface or new message can be avoided， and some embodiments may be implemented with only a small extension in existing GTP ‘Downlink Data Notification Failure Indication’ message， by adding a new cause value.

(4) MT call (e.g.， a MT VoLTE call) successful rate can be improved.

Although some of the above description is made in the context of a wireless system with an example structure shown in FIG. 1A， it should not be construed as limiting the spirit and scope of the present disclosure. The principle and concept of the present disclosure may be more generally applicable to other network deployment scenarios and structures， and correspondingly network devices involved in the embodiments may vary depending on the exact network structure and technique being used.

In addition， the present disclosure may also provide a memory containing the computer program as mentioned above， which includes machine-readable media and machine-readable transmission media. The machine-readable media may also be called computer-readable media， and may include machine-readable storage media， for example， magnetic disks， magnetic tape， optical disks， phase change memory， or an electronic memory terminal device like a random access memory (RAM) ， read only memory (ROM) ， flash memory devices， CD-ROM， DVD， Blue-ray disc and the like. The machine-readable transmission media may also be called a carrier， and may include， for example， electrical， optical， radio， acoustical or other form of propagated signals -such as carrier waves， infrared signals， and the like.

The techniques described herein may be implemented by various means so that an apparatus implementing one or more functions of a corresponding apparatus described with an embodiment includes not only prior art means， but also means for implementing the one or more functions of the corresponding apparatus described with the embodiment and it may include separate means for each separate function， or means that may be configured to perform two or more functions. For example， these techniques may be implemented in hardware (one or more apparatuses) ， firmware (one or more apparatuses) ， software (one or more modules) ， or combinations thereof. For a firmware or software， implementation may be made through modules (e.g.， procedures， functions， and so on) that perform the functions described herein.

Example embodiments herein have been described above with reference to block diagrams and flowchart illustrations of methods and apparatuses. It will be understood that each block of the block diagrams and flowchart illustrations， and combinations of blocks in the block diagrams and flowchart illustrations， respectively， can be implemented by various means including computer program instructions. These computer program instructions may be loaded onto a general purpose computer， special purpose computer， or other programmable data processing apparatus to produce a machine， such that the instructions which execute on the computer or other programmable data processing apparatus create means for implementing the functions specified in the flowchart block or blocks.

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 subject matter described herein， but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely， various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover， although features may be described above as acting in certain combinations and even initially claimed as such， one or more features from a claimed combination can in some cases be excised from the combination， and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

It will be obvious to a person skilled in the art that， as the technology advances， the inventive concept can be implemented in various ways. The above described embodiments are given for describing rather than limiting the disclosure， and it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the disclosure as those skilled in the art readily understand. Such modifications and variations are considered to be within the scope of the disclosure and the appended claims. The protection scope of the disclosure is defined by the accompanying claims.

Claims

A method implemented at a first core network device, comprising：

receiving, from a second core network device, a notification of data arrival；

in response to the received notification, transmitting a paging message to a target terminal device of the data via a plurality of base stations including a last serving base station of the target terminal device, wherein the target terminal device is in an idle state；

if no paging response is received from the target terminal device, checking a state of a path between the first core network device and the last serving base station； and

in response to a checking result indicating failure of the path, transmitting, to the second core network device, a message indicating failure of the path and absence of the paging response from the target terminal device.
The method according to Claim 1, wherein the plurality of base stations comprise base stations included in a tracking area list.
The method according to Claim 1, wherein transmitting a paging message to a target terminal device of the data comprises：

transmitting a plurality of paging messages to the target terminal device of the data.
The method according to Claim 1, wherein the message is a downlink data notification failure indication message with a cause field indicating the failure of the path and absence of the paging response from the target terminal device.
The method according to any of Claims 1 to 4, wherein the first core network device is a mobile management entity, wherein the second core network device is a serving gateway S-GW, and wherein the path is a S1-AP path.
A method implemented at a second core network device, comprising：

transmitting, to a first core network device, a notification of data arrival；

receiving, from the first core network device, a message indicating absence of a paging response from a target terminal device of the data and failure of a path between the first network node and a last serving base station of the target terminal device, wherein the target terminal device is in an idle state；

determining a service type associated with the target terminal device； and

starting a network triggered service restoration procedure if the service type is determined to be a predefined service type.
The method according to Claim 6, wherein the message is a downlink data notification failure indication message with a cause field indicating the failure of the path and absence of the paging response from the target terminal device.
The method according to Claim 6, wherein the predefined service type includes an internet protocol multimedia subsystem IMS service.
The method according to Claim 6, wherein the predefined service type includes a Voice over Long Term Evolution service.
The method according to Claim 6, wherein determining a service type associated with the terminal device comprises：

determining the service type by determining an access point name associated with the target terminal device.
The method according to Claim 6, wherein starting a network triggered service restoration procedure comprises：

transmitting the notification of data arrival with an International Mobile Subscriber Identity of the target terminal device to a further third core network device linked with the last serving base station.
The method according to Claim 11, further comprising：

receiving a message from the third core network device indicating no response from the target terminal device； and

stopping the network triggered service restoration procedure in response to the received message from the third core network device.
The method according to any of Claims 6 to 12, wherein the first core network device is a mobile management entity MME, wherein the second core network device is a serving gateway S-GW, and wherein the path is a S1-AP path.
The method according to Claim 13 wherein the third core network device is selected from a MME pool including the first core network device.
A first core network device, comprising：

a receiving unit, configured to receive, from a second core network device, a notification of data arrival；

a paging unit, configured to transmit a paging message, in response to the received notification, to a target terminal device of the data via a plurality of base stations including a last serving base station of the target terminal device, wherein the target terminal device is in an idle state；

a checking unit, configured to check a state of a path between the first core network device and the last serving base station if no paging response is received from the target terminal device； and

a notifying unit, configured to transmit, to the second core network device, a message indicating failure of the path and absence of the paging response from the target terminal device in response to a checking result indicating failure of the path.
The first core network device according to Claim 15, wherein the plurality of base stations comprise base stations included in a tracking area list.
The first core network device according to Claim 15, wherein the paging unit is configured to transmit a plurality of paging messages to the target terminal device.
The first core network device according to Claim 15, wherein the message is a downlink data notification failure indication message with a cause field indicating the failure of the path and absence of the paging response from the target terminal device.
The first core network device according to any of Claims 15 to 18, wherein the first core network device is a mobile management entity, wherein the second core network device is a serving gateway S-GW, and wherein the path is a S1-AP path.
A second core network device, comprising：

a transmitting unit, configured to transmit, to a first core network device, a notification of data arrival；

a receiving unit, configured to receive, from the first core network device, a message indicating absence of a paging response from a target terminal device of the data and failure of a path between the first network node and a last serving base station of the target terminal device, wherein the target terminal device is in an idle state；

a determining unit, configured to determine a service type associated with the target terminal device； and

a restoring unit, configured to start a network triggered service restoration procedure if the service type is determined to be a predefined service type by the determining unit.
The second core network device according to Claim 20, wherein the message is a downlink data notification failure indication message with a cause field indicating the failure of the path and absence of the paging response from the target terminal device.
The second core network device according to Claim 20, wherein the predefined service type includes an internet protocol multimedia subsystem IMS service.
The second core network device according to Claim 20, wherein the predefined service type includes a Voice over Long Term Evolution service.
The second core network device according to Claim 20, wherein the determining unit is configured to determine a service type associated with the terminal device by determining an access point name associated with the target terminal device.
The second core network device according to Claim 20, wherein the restoring unit is configured to start a network triggered service restoration procedure by transmitting the notification of data arrival with an International Mobile Subscriber Identity of the target terminal device to a further third core network device linked with the last serving base station.
The second core network device according to Claim 25, wherein the restoring unit is further configured to：

receive a message from the third core network device indicating no response from the target terminal device； and

stop the network triggered service restoration procedure in response to the received message from the third core network device.
The second core network device according to any of Claims 20 to 26, wherein the first core network device is a mobile management entity MME, wherein the second core network device is a serving gateway S-GW, and wherein the path is a S1-AP path.
The second core network device according to Claim 27 wherein the third core network device is selected from a MME pool including the first core network device.
An apparatus implemented at a first core network node, the apparatus comprising：

at least one processor； and

at least one memory including computer program code；

the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to：

receive, from a second core network device, a notification of data arrival；

in response to the received notification, transmit a paging message to a target terminal device of the data via a plurality of base stations including a last serving base station of the target terminal device, wherein the target terminal device is in an idle state；

if no paging response is received from the target terminal device, check a state of a path between the first core network device and the last serving base station； and

in response to a checking result indicating failure of the path, transmit, to the second core network device, a message indicating failure of the path and absence of the paging response from the target terminal device.
An apparatus implemented at a second core network node, the apparatus comprising：

at least one processor； and

at least one memory including computer program code；

the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to perform：

transmit, to a first core network device, a notification of data arrival；

receive, from the first core network device, a message indicating absence of a paging response from a target terminal device of the data and failure of a path between the first network node and a last serving base station of the target terminal device, wherein the target terminal device is in an idle state；

determine a service type associated with the target terminal device； and

start a network triggered service restoration procedure if the service type is determined to be a predefined service type.
An apparatus comprising means for performing a method according to any of claims 1 to 5.
An apparatus comprising means for performing a method according to any of claims 6 to 14.
A computer program product comprising at least one computer readable non-transitory memory medium having program code stored thereon, the program code which, when executed by an apparatus, causes the apparatus to perform a method according to any of claims 1 to 14.