WO2014072407A1

WO2014072407A1 - Notifying ue of a core network element failure in ims

Info

Publication number: WO2014072407A1
Application number: PCT/EP2013/073269
Authority: WO
Inventors: Zu Qiang; Yong Yang
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2012-11-09
Filing date: 2013-11-07
Publication date: 2014-05-15
Anticipated expiration: 2015-05-09

Abstract

The embodiments disclose a method performed in a CN-GW for notifying a UE of a core network element failure in an IMS, wherein the UE initially associates with a core network element based on DHCP. The method comprises: receiving a capability indication from the UE to obtain a failure indicator which will be used by the CN-GW to notify the UE of the core network element failure; acquiring a failure of a core network element; and notifying the UE of the failure of the core network element by means of the failure indicator using network signaling, wherein the indicator includes an identification of the failed core network element.

Description

NOTIFYING UE OF A CORE NETWORK ELEMENT FAILURE IN IMS

TECHNICAL FIELD

The present technology relates to the field of communication, particularly to a method of notifying a user equipment (UE) of a core network element failure in an internet protocol multimedia subsystem (IMS). The technology also relates to a core network gateway (CN- GW), a UE and a system suitable for implementing the method.

BACKGROUND

The IMS is an architectural framework for delivering internet protocol (IP) multimedia services. According to the 3rd Generation Partnership Project (3GPP), IMS is intended to aid the access of multimedia and voice applications from wireless and wireline terminals like a UE, i.e., to create a form of fixed-mobile convergence (FMC).

In the IMS, there are two ways for UE to register with the IMS. One way is Protocol Configuration Options (PCO) based, the other way is Dynamic Host Configuration Protocol (DHCP) based. For PCO bases way, the UE sends a request for a proxy call session control function (P-CSCF) to the CN-GW such as Gateway GPRS Support Node (GGSN) and Packet Data Network Gateway (PDN-GW) in the IMS via the PCO. As a response, the CN-GW informs the UE of a P-CSCF to be associated with the UE. In this case, the CN-GW knows the P-CSCF in association with the UE, thus when this P-CSCF fails, the CN-GW may easily notify the UE of such failure. However, in the case of DHCP based way, the UE will directly send a DHCP request for a P-CSCF to the DHCP server in the IMS, and the DHCP server will provide the available P-CSCF(s) to the UE for association, which don't involve the CN-GW. As a result, the CN-GW has no idea of the P-CSCF associated with the UE, thereby has no way to notify the failure of the P-CSCF to the UEs associated with this P-CSCF. SUMMARY

A first aspect of the present disclosure is a method performed in a CN-GW for notifying a UE of a core network element failure in an IMS, wherein the UE initially associates with a core network element based on DHCP. The method comprises: receiving a capability indication from the UE to obtain a failure indicator which will be used by the CN- GW to notify the UE of the core network element failure; acquiring a failure of a core network element; and notifying the UE of the failure of the core network element by means of the failure indicator using network signalling, wherein the indicator includes an identification of the failed core network element.

A second aspect of the present disclosure is a method performed in a UE for assisting a CN-GW to notify the UE of a core network element failure in an IMS, wherein the UE initially associates with a core network element based on dynamic DHCP. The method comprising: sending a capability indication to the CN-GW, the capability indication designates a failure indicator that will be used by the CN-GW to notify the UE of the core network element failure; receiving from the CN-GW a notification of the core network element failure and acknowledging the notification; and determining if a core network element failure associated with the UE has failed based on the notification.

A third aspect of the present disclosure is a CN-GW configured to notify a UE of a core network element failure in an IMS, wherein the UE initially associates with a core network element based on DHCP. The CN-GW comprises a first receiving unit, an acquiring unit and a notifying unit. The first receiving unit is adapted to receive a capability indication from the UE to obtain a failure indicator which will be used by the CN-GW to notify the UE of the core network element failure. The acquiring unit is adapted to acquire a failure of a core network element. The notifying unit is adapted to notify the UE of the failure of the core network element by means of the failure indicator using network signalling, wherein the indicator includes an identification of the failed core network element. A fourth aspect of the present disclosure is a UE configured to assist a CN-GW to notify the UE of a core network element failure in an IMS, wherein the UE initially associates with a core network element based on DHCP. The UE comprises a sending unit, a second receiving unit and a determining unit. The sending unit is adapted to send a capability indication to the CN-GW, the capability indication designates a failure indicator to be used by the CN-GW to notify the UE of the core network element failure. The second receiving unit is adapted to receive from the CN-GW a notification of the core network element failure and acknowledge the notification. The determining unit is adapted to determine if a core network element failure associated with the UE has failed based on the notification.

A fifth aspect of the present disclosure is a system configured to notify a core network element failure in an IMS. The system comprises a CN-GW and a UE as described above.

A six aspect of the present disclosure is a computer readable storage medium which stores instructions which, when run on a CN-GW, cause the CN-GW to perform the steps of the method as described in the first aspect.

A seventh aspect of the present disclosure is a computer readable storage medium which stores instructions which, when run on a UE, cause the UE to perform the steps of the method as described in the second aspect.

In the case of the core network element, such as P-CSCF, failure for DHCP based scenario, through negotiating a failure notification mechanism between the UE and the CN- GW in advance, for example during the initial registration phrase, the CN-GW can notify the UE of a core network element failure with which the UE may be concerned, by using the specific failure notification mechanism designated by this UE. As a result, the UE may timely be aware of the failure of the core network element that is associated with it, and make further actions based on the awareness, for example re-registering with the IMS. BRIEF DESCRIPTION OF THE DRAWINGS

The technology will now be described, by way of example, based on embodiments with reference to the accompanying drawings, wherein:

Fig. l schematically illustrates a P-CSCF failure for DHCP based scenario;

Fig.2 schematically illustrates a flowchart of notifying a UE of a core network element failure in an IMS in accordance with an embodiment;

Fig.3 schematically illustrates a core network element failure notification procedure between the UE and the CN-GW in a 3 GPP 4G based IMS in accordance with an embodiment;

Fig.4 schematically illustrates a core network element failure notification procedure between the UE and the CN-GW in a 3 GPP 2G/3G based IMS in accordance with an embodiment;

Fig.5 schematically illustrates a block diagram of a CN-GW configured to notify a UE of a core network element failure in the IMS and a UE configured to assist the CN-GW to notify the UE of a core network element failure, in accordance with an embodiment.

DETAILED DESCRIPTION

//non-limited description begin

Embodiments herein will be described more fully hereinafter with reference to the accompanying drawings. The embodiments herein may, however, be embodied in many different forms and should not be construed as limiting the scope of the appended claims. The elements of the drawings are not necessarily to scale relative to each other. Like numbers refer to like elements throughout.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. 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," "includes" and/or "including" when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The present technology is described below with reference to block diagrams and/or flowchart illustrations of methods, apparatus (systems) and/or computer program according to the present embodiments. It is understood that blocks of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, may be implemented by computer program instructions. These computer program instructions may be provided to a processor, controller or controlling unit of a general purpose computer, special purpose computer, and/or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer and/or other programmable data processing apparatus, create means for implementing the functions/acts specified in the block diagrams and/or flowchart block or blocks.

Accordingly, the present technology may be embodied in hardware and/or in software

(including firmware, resident software, micro-code, etc.). Furthermore, the present technology may take the form of a computer program on a computer-usable or computer-readable storage medium having computer-usable or computer-readable program code embodied in the medium for use by or in connection with an instruction execution system. In the context of this document, a computer-usable or computer-readable storage medium may be any medium that may contain, store, or is adapted to communicate the program for use by or in connection with the instruction execution system, apparatus, or device,

//non- limited description end

// description of claims 3 and 4 begin

Herein, for purpose clarity, the P-CSCF will be used as the example of core network element in the IMS to set forth the embodiments. It should be appreciated that the core network element may also refer to, but not limited to, a domain name server (DNS) or a dual stack mobile IPv6 home agent (DSMIPv6 HA) in the IMS. In addition, the CN-GW may represent the entity performing the gateway in the IMS, such as GGSN, PDN-GW, etc. In the following embodiments, the GGSN/PDN-GW may be directly used to describe the present disclosure by way of example.

// description of claims 3 and 4 end

Embodiments herein will be described below with reference to the drawings.

Fig.l schematically illustrates a P-CSCF failure for DHCP based scenario. Specifically, as shown in Fig.1 , for example, in step 1 -2, the UE initiates an IP-Connectivity Access Network (IP-CAN) session. The P-CSCF discovery is performed using DHCP based method in step 3. The GGSN/PDN-GW relays/sends the list of P-CSCF addresses in DHCP response. The DHCP response can include either a list of P-CSCF IPv4/IPv6 addresses or a list of full qualified domain names (FQDNs). In step 4, the GGSN/PDN-GW sends credit control answer (CCR) to request for policy and charging control (PCC) rules. In step 5, the policy and charging rules function (PCRF) provides PCC rules to be applied in CCA. In step 6, the UE performs an initial registration towards the P-CSCF received. In step 7, the P-CSCF sends Rx Push to provide the PCRF with the P-CSCF selected by the UE. In step 8, the PCRF sends Rx Push response. In step 9, the PCRF uses a Gx push procedure to provide the GGSN/PDN-GW with the P-CSCF address. In step 10, the GGSN/PDN-GW stores this address for the UE and sends Gx Push response. Also, the GGSN/PDN-GW starts monitoring the health of the P-CSCF. In step 11, the P-CSCF sends 200 OK to the UE. In the operation, when a failure in P-CSCF is detected via Gi/sGi by the GGSN/PDN-GW, it is desirable that the GGSN/PDN-GW can find way to informs to all UEs associated to the failed P-CSCF address that the P-CSCF is not available. This can be accomplished by the embodiments described below.

Fig.2 schematically illustrates a flowchart of notifying a UE of a core network element failure in an IMS in accordance with an embodiment. As shown in the Fig.2, the CN- GW 22 and the UE 21 interact with each other to accomplish the notification of a core network element failure. Now the process of the embodiment will be described in detail with reference to Fig.2.

//description of step 210 in claim 7, claims 2 and 5 begin

In step 210, the UE 21 sends a capability indication to the CN-GW 22. The capability indication designates a failure indicator that will be used by the CN-GW 22 to notify the UE 21 of the core network element failure. For example, the capability indication may include a failure indicator template. Alternatively, the CN-GW 22 may construct the failure indicator based on the information given in the capability indication.

Herein, the failure indicator may be represented by a new cause code, a new information element, a new parameter in the PCO information element, or the combination thereof, such as a new cause code in combination with a new information element. For example, the new cause code may indicate a failure of a core network element like P-CSCF, while the new information element indicates the IP address of the failed P-CSCF. The cause code and information element can be defined in the network signallings of the IMS as desired. For example, they may be defined in the non-access-stratum (NAS) signaling, general packet radio service tunneling protocol (GTP) signaling or proxy mobile IPv6 protocol (ΡΜΙΡνό) signaling. The UE 21 may send the capability indication during Initial Attach procedure, a PDP Context activation procedure or a UE request PDN connectivity procedure, i.e. when setting up a PDN, e.g. a IMS PDN connection. In an embodiment, the capability indication may be sent in a NAS message such as Attach Request, Activate PDP Context Request or PDN Connectivity Request. Alternatively, the capability indication may also be sent in the PCO.

//description of step 210 in claim 7, claims 2 and 5 end

//description of step 220 in claim 1 begin

In step 220, the CN-GW 22 receives the capability indication from the UE 21. After receiving the capability indication, the CN-GW 22 may obtain the failure indicator from the capability indication. The failure indicator from the UE 21 may indicate to the CN-GW 22 how the UE can be informed when for example attached P-CSCF has a failure. In an embodiment, the failure indicator may comprise a new information element defined in NAS signaling. The inclusion of this new information element may indicate that the UE can be informed about P-CSCF failure via NAS signaling using the new information element. In another embodiment, the failure indicator may comprise a new parameter in the PCO. The inclusion of this new parameter in the PCO may indicate that the UE can be informed about P-CSCF failure via PCO using the new parameter.

//^'description of step 220 in claim 1 end

//description of step 230 in claim 1 begin

In step 230, the CN-GW 22 acquires a failure of a core network element. In the operation, the CN-GW 22 may monitor the health of the core network elements. For example, the CN-GW 22 may imitatively poll the core network elements in the IMS for failure. Alternatively, the CN-GW 22 may also passively accept the report of the core network element failure.

//description of step 230 in claim 1 end

//description of step 240 in claim 1 begin In step 240, upon acquiring a failure of a core network element, the CN-GW 22 notifies the UE 21 of the failure of the core network element by means of the failure indicator using network signalling. The failure indicator includes an identification of the failed core network element, such as the IP address or identity of the failed core network element. The notification can be performed during PDN-GW Initiated bearer context modification procedure or GGSN initiated PDP context modification procedure.

For example, the failure indicator uses a new cause code and a new information element in the NAS signaling, the new cause code indicates the occurrence of a core network element failure, and the new information element stores the IP address of the failed core network element. In this case, the CN-GW 22 may send the new cause code and the new information element to UE 21 in a NAS message.

For another example, the failure indicator uses one or more new parameters in a PCO. It is the new parameters that store the failure indication and the IP address of the failed core network element. In this case, the CN-GW 22 may send the new parameters to the UE 21 using PCO via the GTPv2 message Update Bearer Request, or GTPvl message Update PDP Context Request or ΡΜΙΡνό Update Notification message, and then via NAS messages Modify EPS bearer context request or Modify PDP Context Request message.

//description of step 240 in claim 1 end

//description of step 250 in claim 7 begin

In step 250, the UE 21 receives from the CN-GW 22 the notification of the core network element failure and acknowledges the notification. For example, the UE 21 may send the acknowledgement to the CN-GW 22 via NAS message, and then via GTPvl /GTPv2/PMIPv6 message, which will be described in detail later.

//description of step 250 in claim 7 end

//^'description of step 260 in claim 7, claim 8 begin In step 260, the UE 21 determines if a core network element associated with the UE has failed based on the notification. Specifically, the UE 21 may obtain the failure indicator from the notification; obtain the identification of the failed core network element from the failure indicator, and then compare the identification of the failed core network element with the identification of the core network element failure associated with the UE 21, so as to determine if the core network element associated with the UE 21 has failed. For example, the UE 21 may obtain the IP address of the failed core network element from the notification, and then compare the IP address of the failed core network element with that of the core network element attached by the UE 21. If the IP addresses are the same address, then the UE 21 can determine that the core network element associated with the UE 21 has failed,

//description of step 250 in claim 7, claim 8 end

//technical effect of claim 1 in combination with claim 7 begin

As indicated, in the case of the core network element (e.g. P-CSCF) failure for DHCP based scenario, through negotiating a failure notification mechanism between the UE and the CN-GW in advance, for example during the initial registration phrase, the CN-GW can notify the UE of a core network element failure with which the UE may be concerned, by using the specific failure notification mechanism designated by this UE. As a result, the UE may timely be aware of the failure of the core network element that is associated with it, and make further actions based on the awareness, for example re-registering with the IMS.

//technical effect of claim 1 in combination with claim 7 end

//^'description of claim 9 begin

Optionally, as the steps 14 and 15 illustrated in Fig.l, when determining that the core network element associated with the UE has failed, the UE 21 may request to associate with another core network element via a new DHCP request and initiating a new IMS registration. For example, the UE 21 may request P-CSCF addresses via new DHCP request; select a new P-CSCF and then reinitiate an initial IMS registration. Since the IMS registration process is known in the art, thus it will not be described in more detail here,

//description of claim 9 end

//description of claim 6 begin

Note that the IMS herein can be built upon a 3 GPP radio access network such as 2G,

3G and 4G networks. And the embodiments of the present invention can be implemented in the IMS built upon these different infrastructures.

For the IMS based on 4G infrastructure, as shown in Fig.3, provided that the PDN- GW (PGW) knows that a UE can be informed about P-CSCF failure using NAS message and the failure indicator uses a new cause code or new information element in the NAS/GTPv2/PMIPv6 signaling through negotiating with the UE during the PDN connection creation procedure as described above. When detecting a P-CSCF failure, the PGW may sends an Update Bearer Request message (over GTPv2 or ΡΜΙΡνό) with the new cause code of P-CSCF failure and/or the new information element including the failed P-CSCF address message to the Serving GW in step 1. In step 2, the Serving GW may forward the Update Bearer Request message to the Mobile Management Entity (MME). If the UE is in ECM- IDLE state, the MME will trigger the Network Triggered Service Request, and in step 3 and 4, the MME may send the Modify EPS bearer context request message to the UE including the new cause code of P-CSCF failure and/or the new information element including the failed P- CSCF address. Upon receiving the failure indicator including the new cause code and/or the new information element, the UE may acknowledge the request by sending the response to the PGW in steps 5-8.

Alternatively, if the PGW knows the UE can be informed about P-CSCF failure using PCO, i.e. the UE has indicated the PGW via the PCO sent from UE during the PDN connection creation procedure, the PGW can then include failure indicator in the PCO, in other words, the failure indicator uses the new parameter in the PCO. The sending/response procedure is same as above. The only difference is the failure indicator is sent using the new parameter in the PCO instead of a new cause code or a new information element in NAS/GTP/PMIPv6 signaling.

As for the IMS based on 2G/3G infrastructure, the existing GGSN-Initiated PDP Context Modification Procedure can be reused with a new cause code and/or a new or modified existing information element. As shown in Fig.4, provided that the GGSN knows that a Mobile Station (MS) can be informed about P-CSCF failure using NAS message and the failure indicator uses a new cause code or new information element in the NAS/GTPvl signaling through negotiating with the UE during the PDN connection creation procedure as described above. When detecting a P-CSCF failure, the GGSN sends an Update PDP Context Request message including the new cause code of P-CSCF failure and/or a new information element including failed P-CSCF address to the SGSN in step 1. In step 4, the SGSN sends a Modify PDP Context Request message with the new cause code of P-CSCF failure and/or a new information element including failed P-CSCF address to the MS. Upon receiving the failure indicator including the new cause code and/or the new information element, the MS may acknowledge the request by sending the response to the GGSN in steps 5-6.

Alternatively, if the GGSN knows the MS can be informed about P-CSCF failure using PCO, i.e. the MS has indicated the GGSN via the PCO sent from MS during the PDN connection creation procedure, the GGSN can then include the failure indicator in the PCO, in other words, the failure indicator uses the new parameter in the PCO. The sending/response procedure is same as above. The only difference is the failure indicator is sent using the new parameter in the PCO instead of a new cause code or a new information element in NAS/GTP signaling.

//description of claim 6 end

//apparatus claims description begin Fig.5 schematically illustrates a block diagram of a CN-GW configured to notify a UE of a core network element failure in the IMS and a UE configured to assist the CN-GW to notify the UE of a core network element failure in accordance with an embodiment. As illustrated in Fig.5, the CN-GW 520 comprises a first receiving unit 521, an acquiring unit 522 and a notifying unit 523. The UE 510 comprises a sending unit 511, a second receiving unit 512 and a determining unit 513. It should be appreciated that the CN-GW and UE are not limited to the shown elements, and can comprise other conventional elements and the additional elements for other purposes. Here, the UE 510 and the CN-GW 520 functions as the UE 21 and CN-GW 22 in Fig.2. Now the functions of the individual units will be described in detail with reference to the Fig. 5.

The sending unit 51 lof the UE 510 sends a capability indication to the CN-GW 520. The capability indication designates a failure indicator that will be used by the CN-GW 520 to notify the UE 510 of the core network element failure. For example, the capability indication may include a failure indicator template. Alternatively, the CN-GW 520 may construct the failure indicator based on the information given in the capability indication.

Herein, the failure indicator may be represented by a new cause code, a new information element, a new parameter in the PCO information element, or the combination thereof, such as a new cause code in combination with a new information element. For example, the new cause code may indicate a failure of a core network element like P-CSCF, while the new information element indicates the IP address of the failed P-CSCF. The cause code and information element can be defined in the network signaling of the IMS as desired. For example, they may be defined in the non-access-stratum (NAS) signaling, general packet radio service tunneling protocol (GTP) signaling or proxy mobile IPv6 protocol (ΡΜΙΡνό) signaling.

The sending unit 511 of the UE 510 may send the capability indication during Initial

Attach procedure, a PDP Context activation procedure or a UE request PDN connectivity procedure, i.e. when setting up a PDN, e.g. a IMS PDN connection. In an embodiment, the capability indication may be sent in a NAS message such as Attach Request, Activate PDP Context Request or PDN Connectivity Request. Alternatively, the capability indication may also be sent in the PCO.

The first receiving unit 521 of the CN-GW 520 receives the capability indication from the sending unit 511of the UE 510. After receiving the capability indication, The first receiving unit 521 may obtain the failure indicator from the capability indication. The failure indicator from the UE 510 may indicate to the CN-GW 520 how the UE can be informed when for example attached P-CSCF has a failure. In an embodiment, the failure indicator may comprise a new information element defined in NAS signaling. The inclusion of this new information element may indicate that the UE can be informed about P-CSCF failure via NAS signaling using the new information element. In another embodiment, the failure indicator may comprise a new parameter in the PCO. The inclusion of this new parameter in the PCO may indicate that the UE can be informed about P-CSCF failure via PCO using the new parameter.

The acquiring unit 522 of the CN-GW 520 acquires a failure of a core network element. In the operation, the acquiring unit 522 may monitor the health of the core network elements. For example, the acquiring unit 522 may imitatively poll the core network elements in the IMS for failure. Alternatively, the acquiring unit 522 may also passively accept the report of the core network element failure.

upon the acquiring unit 522 acquires a failure of a core network element, the notifying unit 523 of the CN-GW 520 notifies the UE 510 of the failure of the core network element by means of the failure indicator using network signaling. The failure indicator includes an identification of the failed core network element, such as the IP address or identity of the failed core network element. The notification can be performed during PDN-GW Initiated bearer context modification procedure or GGSN initiated PDP context modification procedure.

For example, the failure indicator uses a new cause code and a new information element in the NAS signaling, the new cause code indicates the occurrence of a core network element failure, and the new information element stores the IP address of the failed core network element. In this case, the notifying unit 523 may send the new cause code and the new information element to UE 510 in a NAS message.

For another example, the failure indicator uses one or more new parameters in a PCO. It is the new parameters that store the failure indication and the IP address of the failed core network element. In this case, the notifying unit 523 may send the new parameters to the UE 510 using PCO via the GTPv2 message Update Bearer Request, or GTPvl message Update PDP Context Request or ΡΜΙΡνό Update Notification message, and then via NAS messages Modify EPS bearer context request or Modify PDP Context Request message.

The second receiving unit 512 of the UE 510 receives from the notifying unit 523 of the CN-GW 520 the notification of the core network element failure and acknowledges the notification. For example, the second receiving unit 512 may send the acknowledgement to the CN-GW 520 via NAS message, and then via GTPvl /GTPv2/PMIPv6 message, which will be described in detail later.

After the second receiving unit 512 receives the notification of the core network element failure, the determining unit 513 of the UE 510 determines if a core network element associated with the UE has failed based on the notification. Specifically, the determining unit 513 may obtain the failure indicator from the notification; obtain the identification of the failed core network element from the failure indicator, and then compare the identification of the failed core network element with the identification of the core network element failure associated with the UE 510, so as to determine if the core network element associated with the UE 510 has failed. For example, the determining unit 513 may obtain the IP address of the failed core network element from the notification, and then compare the IP address of the failed core network element with that of the core network element attached by the UE 510 . If the IP addresses are the same address, then determining unit 513 can determine that the core network element associated with the UE 510 has failed.

Optionally, as the steps 14 and 15 illustrated in Fig.l, when determining that the core network element associated with the UE has failed, the UE 510 may request to associate with another core network element via a new DHCP request and initiating a new IMS registration. For example, the UE 510 may request P-CSCF addresses via new DHCP request; select a new P-CSCF and then reinitiate an initial IMS registration. Since the IMS registration process is known in the art, thus it will not be described in more detail here,

//apparatus claims description end

While the embodiments have been illustrated and described herein, it will be understood by those skilled in the art that various changes and modifications may be made, any equivalents may be substituted for elements thereof without departing from the true scope of the present technology. In addition, many modifications may be made to adapt to a particular situation and the teaching herein without departing from its central scope. Therefore it is intended that the present embodiments not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the present technology, but that the present embodiments include all embodiments falling within the scope of the appended claims.

Claims

What is claimed is:

1. A method in a core network gateway, CN-GW, (520) for notifying a user equipment, UE, (510) of a core network element failure in an internet protocol multimedia subsystem, IMS, the UE initially associates with a core network element based on dynamic host configuration protocol (DHCP), comprising:

receiving (220) a capability indication from the UE to obtain a failure indicator to be used by the CN-GW to notify the UE of the core network element failure;

acquiring (230) a failure of a core network element; and

notifying (240) the UE of the failure of the core network element by means of the failure indicator using network signalling, wherein the indicator includes an identification of the failed core network element.

2. The method of claim 1, wherein the failure indicator comprising:

a new cause code in non-access-stratum, NAS, signalling, and general packet radio service tunnelling protocol, GTP, signalling or proxy mobile IPv6 protocol, ΡΜΙΡνό, signalling; or a new information element in NAS signalling, and GTP signalling or ΡΜΙΡνό signalling; or a new parameter in an protocol configuration option, PCO, information element.

3. The method of claim 1, wherein the CN-GW is a gateway general packet radio service support node, GGSN, or a packet data network gateway, PDN-GW.

4. The method of claim 1, wherein the core network element is a proxy call session control function, P-CSCF, a domain name server, DNS, or a dual stack mobile IPv6 home agent, DSMIPv6 HA.

5. The method of claim 1 , wherein the identification of the failed core network element is the internet protocol, IP, address of the failed core network element.

6. The method of claim 1, the IMS is built upon a 3rd generation partnership project, 3GPP, radio access network.

7. A method in a user equipment, UE, (510) for assisting a core network gateway, CN-GW, (520) to notify the UE of a core network element failure in an internet protocol multimedia subsystem, IMS, the UE initially associates with a core network element based on dynamic host configuration protocol (DHCP), comprising:

sending (210) a capability indication to the CN-GW, the capability indication designates a failure indicator to be used by the CN-GW to notify the UE of the core network element failure;

receiving (250) from the CN-GW a notification of the core network element failure and acknowledging the notification; and

determining (260) if a core network element associated with the UE has failed based on the notification.

8. The method of claim 7, wherein the determining (260) if a core network element failure associated with the UE has failed comprises obtaining a corresponding failure indicator from the notification, obtaining an identification of the failed core network element from the corresponding failure indicator, and comparing the identification of the failed core network element with an identification of the core network element failure associated with the UE.

9. The method of claim 7, wherein if it is determined that the core network element associated with the UE has failed, requesting to associate with another core network element via a new DHCP request and initiating a new IMS registration.

10. A core network gateway, CN-GW, (520) configured to notify a user equipment, UE, (510) of a core network element failure in an internet protocol multimedia subsystem, IMS, the UE initially associates with a core network element based on dynamic host configuration protocol (DHCP), comprising:

a first receiving unit (521) adapted to receive a capability indication from the UE to obtain a failure indicator to be used by the CN-GW to notify the UE of the core network element failure;

an acquiring unit (522) adapted to acquire a failure of a core network element; and a notifying unit (523) adapted to notify the UE of the failure of the core network element by means of the failure indicator using network signalling, wherein the indicator includes an identification of the failed core network element.

11. The CN-GW of claim 10, wherein the failure indicator comprising:

a new cause code in non-access-stratum, NAS, signalling, and general packet radio service tunnelling protocol, GTP, signalling or proxy mobile IPv6 protocol, PMIPv6, signalling; or a new information element in NAS signalling, and GTP signalling or PMIPv6 signalling; or a new parameter in an protocol configuration option, PCO, information element.

12. The CN-GW of claim 10, wherein the CN-GW is a gateway general packet radio service support node, GGSN, or a packet data network gateway, PDN-GW.

13. The CN-GW of claim 10, wherein the core network element is a proxy call session control function, P-CSCF, a domain name server, DNS, or a dual stack mobile IPv6 home agent, DSMIPv6 HA.

14. The CN-GW of claim 10, wherein the identification of the failed core network element is the internet protocol, IP, address of the failed core network element.

15. The CN-GW of claim 10, the IMS is built upon a 3rd generation partnership project, 3 GPP, radio access network.

16. A user equipment, UE, (510) configured to assist a core network gateway, CN-GW, (520) to notify the UE of a core network element failure in an internet protocol multimedia subsystem, IMS, the UE initially associates with a core network element based on dynamic host configuration protocol (DHCP), comprising:

a sending unit (511) adapted to send a capability indication to the CN-GW, the capability indication designates a failure indicator to be used by the CN-GW to notify the UE of the core network element failure;

a second receiving unit (512) adapted to receive from the CN-GW a notification of the core network element failure and acknowledge the notification; and

a determining unit (513) adapted to determine if a core network element failure associated with the UE has failed based on the notification.

17. The UE of claim 16, wherein the determining unit (513) adapted to obtain a corresponding failure indicator from the notification, obtain an identification of the failed core network element from the corresponding failure indicator, and compare the identification of the failed core network element with an identification of the core network element failure associated with the UE.

18. The UE of claim 16, wherein when determining that the core network element associated with the UE has failed, the UE is adapted to requests to associate with another core network element via a new DHCP request and initiate a new IMS registration.

19. A system configured to notify a core network element failure in an internet protocol multimedia subsystem, comprising a core network gateway, CN-GW, according to any one of the claims 10-15 and a user equipment, UE, according to any one of the claims 16-18.

20. A computer readable storage medium which stores instructions which, when run on a core network gateway, CN-GW, cause the CN-GW to perform the steps of the method according to any one of the claims 1-6.

21. A computer readable storage medium which stores instructions which, when run on a user equipment, UE, cause the UE to perform the steps of the method according to any one of the claims 7-9.