WO2012143397A1

WO2012143397A1 - Restoration of mobile terminating cs services in case of failure of a ps core network entity in a mobile communication system

Info

Publication number: WO2012143397A1
Application number: PCT/EP2012/057084
Authority: WO
Inventors: Bruno Landais
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2011-04-19
Filing date: 2012-04-18
Publication date: 2012-10-26
Anticipated expiration: 2013-10-19
Also published as: ES2925684T3; KR20140009498A; EP2736286A1; TW201306611A; EP2515573A1; CN103621135A; JP2017022786A; JP6367711B2; US20140106742A1; EP2736286B1; JP2014516495A; US10477419B2; KR20160113742A; ES2498919T3; EP2515573B1; CN103621135B; KR101896234B1; TWI475901B

Abstract

In an embodiment, a method for restoration of MT (Mobile Terminating) CS services in case of failure of a PS Core Network CN entity, referred to as original CN entity, originally identified as to be contacted for a paging request towards a User Equipment UE for said MT CS services, in a mobile communication system, comprises a step of: - providing that an alternative CN entity is contacted instead of said original CN entity, and that said alternative CN entity is forced to accept said paging request even if said UE is unknown to said alternative CN entity.

Description

RESTORATION OF MOBILE TERMINATING CS SERVICES IN CASE OF FAILURE OF A PS CORE NETWORK ENTITY IN A MOBILE COMMUNICATION

SYSTEM The present invention generally relates to mobile communication networks and systems.

Detailed descriptions of mobile communication networks and systems can be found in the literature, such as in particular in Technical Specifications published by standardization bodies such as for example 3GPP (3^rd Generation Partnership

Project).

In such systems, a mobile terminal (or User Equipment UE) has access via a Radio Access Network (RAN) to a Core Network (CN) providing mobile

communication services.

Examples of systems, such as for example 3GPP systems, include: 2G-GSM, 3 G- UMTS, 3GLTE-EPS (Evolved Packet System).

For example, an architecture for EPS is recalled in figure 1 taken from 3GPP TS 23.401 . EPS Core Network comprises a PS (Packet-Switched) domain called EPC (Evolved Packet Core). EPC comprises entities such as in particular MME (Mobility Management Entity) in charge of control plane functions such as in particular mobility management and paging procedure for MT (Mobile Terminating) services towards UEs in idle mode. In EPS, CS (Circuit-Switched) services (such as for example voice services or other services such as SMS (Short Message Service)) can be delivered as IP-based services, via PS domain EPC providing IP connectivity to an operator's IP network (for example IMS network).

On the contrary, in systems such as GSM or UMTS (not specifically illustrated), CS services (such as for example voice services or other services such as SMS (Short Message Service)) are delivered via CS (Circuit-Switched) domain. CS domain comprises entities such as in particular MSC VLR or MSG Server VLR) in charge of control plane functions such as in particular mobility management and paging procedure for MT (Mobile Terminating) services towards UEs in idle mode.

New functionalities may be introduced to allow reuse of already deployed CS infrastructures co-existing with newly deployed EPS infrastructures.

Embodiments of the present invention in particular enable to solve such problem or avoid such drawbacks.

Embodiments of the present invention provide that the network continues to deliver CS services to UEs via an alternative MME in the MME pool where the UE is located. It is recalled that an MME pool comprises several MMEs serving a same area called pool area, In an embodiment, following steps may be provided:

1 , During normal operations, the (original) MME may signal to the

MSC/VLR(s) the identities of alternative MME(s) within the MME pool. Alternatively, the MSC VLR may be pre-configured with the set of MME identities pertaining to the same MME pool.

2. Upon receipt of mobile terminated services (e.g. CS call), the

MSC VLR may select one of these alternative MMEs if it detects that the (original) MME serving the UE is no longer in service (e.g. by detecting that there is no more SCTP associations in service with that (original) MME), and may send a SGs paging request to this (single) alternative MME with a new 'restoration indicator¹ parameter in the message to force the receiving (alternative) MME to accept the SGs paging request and to proceed with the CSFB or SMS procedure even if the UE (i.e. IMSI) is unknown to this MME and even if the MME has not restarted recentl (i.e. even in the 'MME- reset = false' state).

3. Upon receipt of such a request including the new 'restoration indicator¹ flag, the (alternative) MME may proceed with the existing restoration procedure specified in 3GPP TS 29.1 18 clause 5.1.3 for the case where the MME has restarted recently (i.e. for the case where MME -reset = true).

Note: without the above-mentioned ne 'restoration indicator¹ flag, MMEs would reject SGs paging request (as per existing specification) for unknown UEs to avoid that multiple MMEs page the UE if the VLR broadcasts the SGs paging request to multiple MMEs after an MSC/VLR restart.

In other embodiments, following steps may be provided, for example as illustrated in figure 3.

During normal operations, the (original) MME, noted MME 1 , signals to the MSC/VLR with which it has SGs association (s) the identities of alternative MME(s) within the MME pool (such as MME2, MMEx as illustrated). The (original) MME may e.g. send those MMEs identities under the form of additional MME names sent in existing SGs signaling message, e.g. in the SGsAP Location Update Request (as illustrated at step 1 ) or SGsAP Reset Indication message. Alternatively, the MSC/VLR may be pre-configured with the set of MME identities pertaining to the same MME pool.

As specified in TS 29.1 18 clause 6, SCTP (see IETF RFC 4960) is defined as the transport layer of SGsAP messages. Semi-permanent SCTP associations shall be established between the MME and VLR, i.e. the SCTP associations shall remain up under normal circumstances. The MME shall establish the SCTP association.

Transport network redundancy may be achieved by SCTP multi-homing between two end-points, of which one or both is assigned with multiple IP addresses. MME and VLR shall support a configuration with a single SCTP association per MME VLR pair. Configurations with multiple SCTP end points per MME VLR pair may be supported.

If the original MME fails (as illustrated at step 2), the MSC VLR may detect such failure, e.g. by detecting that there is no more SCTP associations in service with the (original) MME, as illustrated at step 2'.

Upon receipt of mobile terminated services (e.g. CS call) as illustrated at step 3, if the MSC/VLR detects a failure of the (original) MME (i.e. MME via which the UE was registered to non EPS or SMS services), the MSC VLR may, as illustrated at step 4, select one alternative MME (noted MME 2) among the list of MMEs previously received from the failed MME, and may, as illustrated at step 5, send an SGs paging request to this (single) alternative MME (via one of the SCTP associations in service with that MME), including a new 'restoration indicator¹ parameter in the message.

The receiving MME (alternative) may, as illustrated at step 6, process an SGsAP Paging Request with the new 'restoration indicator¹ flag set, like specified today in TS 29.1 1 8 clause 5.1 .3 for the case where it has restarted recently, but regardless of its own 'MME reset' value, i.e. as follows:

If the Service indicator information element in the SGsAP-PAGING- REQUEST message indicates "CS call indicator", the MME shall handle the paging request as follows:

c) If the UE is not known and regardless of the "MME- Reset" restoration

indicator at the MME, the MME shall handle the paging request as follows:

- if the MME only supports "SMS only", the MME shall return an SGsAP- PAGING-REJECT message to the VLR indicating in the SGs cause information element "Mobile terminating CS fallback call rejected by the user";

- if the SGsAP-PAGING-REQUEST message includes the Location area identifier information element, the MME shall page the UE in all the tracking areas served by the MME that can be mapped to the location area indicated in the Location area identifier information element; or

- if the S Gs AP- PAGI N G- EQ U EST message does not include the Location area identifier information element, the MME may page in all the tracking areas served by the MME, or the tracking areas served by the MME and by the VLR.

If the Service indicator information element in the SGsAP- PAGI NG- REQUEST message indicates "SMS indicator", the MME shall handle the paging request as follows:

c) If the UE is not known and regardless of the "MME- eset" restoration

indicator at the MME, the MME shall handle the paging request as follows:

signaling for SMS transfer over LTE), e.g. if such parameters are stored in non-volatile memory; or

- page the UE with IMSI (and CN domain indicator set to "PS") to force UEs

(in idle mode) to re-attach to EPC. This would lead the UE to re-attach to any MME in the pool (not necessarily the same MME), which would lead to restore an SGs association between likely (but not necessarily either) the same MSC and the new MME. From that point in time, subsequent SMS will succeed. The on-going SMS transfer will fail (paging timer will ex ire in the original MSC), but the existing SMS procedures (SMS alert) allows to resume the SMS transfer after the new combined attach procedure.

In one aspect, there is provided a method for restoration of MT (Mobile Terminating) CS services in case of failure of a PS Core Network CN entity, referred to as original CN entity, originally identified as to be contacted for a paging request towards a User Equipment UE for said MT CS services, in a mobile communication system.

Various embodiments are provided, which can be used alone or in combination (according to various combinations).

In an embodiment, said method comprises a step of:

- during normal operation, the original MME signalling to the MSC VLR, in an SGSAP- Reset- 1 nd ication message, identity information of at least one alternative MME.

In an embodiment, said method comprises a step of:

- pre-configuring the MSC/VLR with identity information of at least one alternative MME.

In an embodiment, said method comprises a step of:

- the MSC VLR detecting a failure of the original MME by detecting that there is no more SCTP association in service with that MME.

In an embodiment, said method comprises a step of:

- upon reception of a request for MT CS services delivery to said UE, in case of failure of the original MME, the MSC VLR selecting an alternative MME and sending an SGSAP Paging Request to the selected alternative MME.

In an embodiment, said method comprises a step of:

- upon reception of a request for MT CS services delivery to said UE, in case of failure of the original MME, the MSC/VLR selecting an alternative MME and sending an SGSAP-Paging-Request to the selected alternative MME, said SGSAP- Paging-Request containing a restoration indicator flag forcing the alternative MME to accept said Paging Request.

In an embodiment, said method comprises a step of:

- upon reception of an SGSAP-Paging-Request containing a restoration indicator flag forcing the alternative MME to accept said Paging Request, the alternative MME handling said Paging Request as if the MME- Reset parameter at the alternative MME were set to true, even if the MME-Reset parameter at the alternative MME is set to false.

In an embodiment, said method comprises a step of:

- upon reception of an SGSAP-Paging-Request containing a restoration indicator flag forcing the alternative MME to accept said Paging Request, the alternative MME handling the paging request such that, regardless of the state of the MME-Reset parameter at the alternative MME :

• if the SGsAP-Paging-Request message includes a Location Area Identifier information element, the MME pages the UE in all the Tracking Areas served by the MME that can be mapped to the Location Area indicated in the Location Area Identifier information element; or

• if the SGsAP- Paging- Request message does not include the

Location Area Identifier information element, the MME may page in all the Tracking Areas served by the MME, or the Tracking Areas served by the MME and by the VLR.

Other aspects relate to CN entities comprising means for performing such method(s), such as in particular MME and MSC/VLR (or MSG Server VLR) supporting the CSFB and/or SMS over SGs in EPS functionality.

In an embodiment, there is provided a Core Network entity for a mobile communication system, comprising means for performing such method(s).

In an embodiment, there is provided a Mobility Management Entity MME supporting CS Fallback and/or SMS over SGs in EPS, comprising means for acting as an original MME, and means for acting as an alternative MME, according to such method (s).

In an embodiment, there is provided a MSC/VLR or MSC Server/VLR supporting CS Fallback and/or SMS over SGs in EPS, comprising means for performing such method(s).

The detailed implementation of the above-mentioned means does not raise any special problem for a person skilled in the art, and therefore such means do not need to be more fully disclosed than has been made above, by their function, for a person skilled in the art.

A person of skill in the art would readily recognize that steps of various above-described methods can be performed by programmed computers. Herein, some embodiments are also intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machine- executable or computer-executable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods. The program storage devices may be, e.g., digital memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. The embodiments are also intended to cover computers

programmed to perform said steps of the above-described methods.

Claims

1 . A method for restoration of MT (Mobile Terminating) CS services in case of failure of a PS Core Network CN entity, referred to as original CN entity, originally identified as to be contacted for a paging request towards a User Equipment UE for said MT CS services, in a mobile communication system, said method comprising a step of:

- providing that an alternative CN entity is contacted instead of said original CN entity, and that said alternative CN entity is forced to accept said paging request even if said UE is unknown to said alternative CN entity.

2. A method according to claim 1 , comprising a step of:

- providing that said alternative CN entity is forced to perform a restoration procedure as if the alternative CN entity were restarting after a failure, even if the alternative CN entity is not restarting after a failure.

3. A method according to claim 1 or 2, wherein said original and

alternative CN entity belong to a pool of CN entities serving a same area.

4. A method according to any of claims 1 to 3, for restoration in case of failure of a Mobility Management Entity MME in Evolved Packet System EPS, referred to as original MME, originally identified by a MSC VLR in CS domain having an SGs association with said original MME for said UE, as to be contacted for a paging request for MT CS services delivery to said UE, in a system supporting CS Fallback and/or SMS over SGs in EPS, said method comprising a step of:

- providing that an alternative MME is contacted instead of said original MME, and that said alternative MME if forced to accept said paging request even if said UE is unknown to said alternative MME.

5. A method according to claim 4, comprising a step of:

- providing that said alternative MME is forced to handle said paging request as if the MME-Reset parameter at the alternative MME were set to true, even if the MME-Reset parameter at the alternative MME is set to false. Π

6. A method according to claim 4 or 5, comprising a step of:

- during normal operation, the original MME signalling to the MSC VLR identity information of at least one alternative MME,

7. A method according to any of claims 4 to 6, comprising a step of:

- during normal operation, the original MME signalling to the MSC/VLR, in an SGSAP-Location-Update-Request, identity information of at least one alternative

MME.

8. A method according to any of claims 4 to 7, comprising a step of:

- during normal operation, the original MME signalling to the MSC VLR, in an SGSAP-Reset-lndication message, identity information of at least one alternative MME.

9. A method according to any of claims 4 to 8, comprising a step of:

- pre-configuring the MSC/VLR with identity information of at least one alternative MME,

Ί 0. A method according to any of claims 4 to 9, comprising a step of:

- the MSC/VLR detecting a failure of the original MME by detecting that there is no more SCTP association in service with that MME.

1 1 . A method according to any of claims 4 to 10, comprising a step of:

- upon reception of a request for MT CS services delivery to said UE, in case of failure of the original MME, the MSC/VLR selecting an alternative MME and sending an SGSAP Paging Request to the selected alternative MME.

1 2. A method according to any of claims 4 to 1 1 , comprising a step of:

13. A method according to any of claims 4 to 12, comprising a step of: - upon reception of an SGSAP- Pag i ng- Req uest containing a restoration indicator flag forcing the alternative MME to accept said Paging Request, the alternative MME handling said Paging Request as if the MME- eset parameter at the alternative MME were set to true, even if the MME -Reset parameter at the alternative MME is set to false.

14. A method according to any of claims 4 to 13, comprising a step of: - upon reception of an SGSAP-Paging-Request containing a restoration indicator flag forcing the alternative MME to accept said Paging Request, the alternative MME handling the paging request such that, regardless of the state of the MME-Reset parameter at the alternative MME :

• if the SGsAP- Pag ί ng - Request message includes a Location Area Identifier information element, the MME pages the UE in all the Tracking Areas served by the MME that can be mapped to the Location Area indicated in the Location Area Identifier information element; or

• if the SGsAP-Paging-Request message does not include the

15. A Core Network entity for a mobile communication system, comprising means for performing a method according to any of claims 1 to 3.

1 6. A Mobility Management Entity MME supporting CS Fallback and/or SMS over SGs in EPS, comprising means for acting as an original MME, and means for acting as an alternative MME, according to any of claims A to 1 . , A MSCA'LR or MSC Server VLR supporting CS Fallback and/or SMS over comprising means for performing a method according to any of claims