WO2010006636A1

WO2010006636A1 - Inter-domain service control

Info

Publication number: WO2010006636A1
Application number: PCT/EP2008/059153
Authority: WO
Inventors: Markku JYLHÄ-OLLILA; Vesa Tiainen
Original assignee: Nokia Siemens Networks Oy
Priority date: 2008-07-14
Filing date: 2008-07-14
Publication date: 2010-01-21

Abstract

Receiving a message associated with a subscriber session in a node monitoring the session and determining, on the basis of the received message, an inter-domain hand-over in the session from a first core network domain to a second core network domain.

Description

Inter-domain service control

Field of the invention

The present invention relates to controlling services in converged mobile networks. Background of the invention

Customized Applications for Mobile network Enhanced Logic (CAMEL) is an IN (Intelligent Network) architecture within GSM (Global System for Mobile Communications) based on Core Intelligent Network Application Protocol (INAP). CAMEL provides mechanisms to support services independ- ently of the serving network. With CAMEL, it is possible to offer Operator- Specific Services (OSS)₁ that is, intelligent network services, to the subscriber while the subscriber is roaming outside the home (Public Land Mobile Network) PLMN. CAMEL is also used in the home PLMN. The current CAMEL functionality is available in stage 2 specification: 3GPP TS 23.078 V7.9.0 (2007-09); 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Customised Applications for Mobile network Enhanced Logic (CAMEL) Phase 4; Stage 2, which is incorporated herein by reference.

In CAMEL, the functioning of call control is described in the Basic Call State Model (BCSM), which is a simplified model of the different phases of call handling procedures in the MSC (Mobile Switching Center) or GMSC (Gateway Mobile Switching Center). The above-referenced TS 23.078 may be referred to for a description of CAMEL BCSMs. The components of the BCSM are called Points in Call (PIC), Detection Points (DP), transitions and tasks executed within PICs. In a PIC, the call processing logic in BCSM may initiate action, such as suspension of the call processing while a database is queried. DPs represent transitional events between PICs. A call is modeled as a sequence of these components. Handovers between cells and location or service area updates can be followed using DPs in BCSM, when the DP criteria are met. Accordingly, if the criteria for change of position DP are met, a CAMEL functional entity providing service control, GSM Service Control Function (gsmSCF), receives the handover information and may control the subscribed services accordingly.

IP Multimedia Subsystem (IMS) is an IP (Internet Protocol) based Core Network (CN) domain, which is independent of the access technologies used. Although IMS is based on IP, also radio access networks such as GSM, CDMA2000 and UTRAN carrying Circuit Switched (CS) domain traffic, may be used as Access Networks (ANs) in IMS. IP-based ANs may connect directly to IMS. These include IEEE (The Institute of Electrical and Electronics Engineers) 802.11 based Wireless Local Area Networks (WLANs), that are widely deployed in domestic and public places.

In a converged network such as IMS, mobile and fixed network functions are linked together in unified core applications. A Voice Call continuity (VCC) application in IMS provides IMS subscribers seamless continuity for voice calls between IMS and CS CN domains. With VCC, it is possible for User Equipment (UE) to perform handovers between the CS and IMS domains as VCC enables call continuity in domain transfers. For example, calls may be transferred between CS and IMS domains when IMS UE performs a handover between GSM and WLAN AN. To support intelligent network services using CAMEL in IMS, subscriber calls are monitored by an IP Multimedia Service Switching Function (IM-SSF) in IMS domain using BCSM. IM-SSF monitors the calls by following the IP-based SIP (Session Initiation Protocol) messaging related to the calls. The CS domain CAMEL gsmSCF is informed about the call processing when DPs in BCSM are met in IM-SSF. Accordingly, gsmSCF may control IMS subscribers' CAMEL services. A description of interworking between IMS and CS CN domains can be found in: 3GPP TS 23.278 V7.1.0 (2006-03) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Customised Applications for Mobile net- work Enhanced Logic (CAMEL) Phase 4; Stage 2; IM CN Interworking (Release 7), which is incorporated herein by reference.

When the IMS subscriber subscription includes a CAMEL service that needs position information for service control, a problem arises when an IMS subscriber makes a handover between an IMS domain AN and an AN that belongs to CS domain. In such a case, the service logic in gsmSCF that needs subscriber position information for controlling services does not receive change of position information regarding the change between the IMS and CS domain ANs. Thus the control of services needing subscriber position information is not possible. The problem arises with prepaid IMS subscribers in particular, where the gsmSCF controlling the tariffs of the subscribers does not receive information, for example, on the VCC call handover between CS and IMS CN domains. Accordingly, charging based on a subscriber's position is not possible.

Brief description of some examples of the invention An object of the present invention is thus to provide a solution so as to solve at least one of the above problems. The objects of the invention are achieved by a method, a system, an apparatus and a computer program for implementing the method that are characterized by what is stated in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on the idea of monitoring a subscriber session so as to notify a node controlling a service in the session about core network domain changes in the subscriber session.

In an embodiment of the invention, a node is requested to monitor an inter-domain handover event in a session. In monitoring the inter-domain handover event, messages related to the session are used to determine the inter-domain handover event. When the inter-domain handover event is detected, the node controlling the service is notified.

In an embodiment, the invention describes a method comprising, receiving a message associated with a subscriber session in a node monitoring the session, and determining, on the basis of the received message, an inter-domain handover in the session from a first core network domain to a second core network domain.

In an embodiment of the invention, the method comprises, receiving a request to report an inter-domain handover in the subscriber session between core network domains and if an inter-domain handover is detected, reporting the inter-domain handover to a node providing service control in the subscriber session.

In an embodiment of the invention, the method comprises, monitor- ing a detection point for detecting an inter-domain handover between core network domains.

In an embodiment, the invention describes a method comprising, receiving, in a node controlling a service in a subscriber session, a message comprising event information associated with the service, determining, on the basis of the event information, an inter-domain handover in the subscriber session between core network domains, and determining a service parameter for the service.

In an embodiment of the invention, the method comprises, receiving a message to invoke a service for a subscriber session, wherein the message comprises a subscriber identifier and a service key, determining, on the basis of the received subscriber identifier and the service key, that the service is to be controiled in more than one core network domain, and sending a request to report an inter-domain handover between the network domains.

In an embodiment of the invention, the service is a prepaid service, and the service parameter comprises tariff information, and the method com- prises sending a service command comprising the tariff information.

In an embodiment, the invention describes an apparatus comprising means for receiving a message associated with a subscriber session, and means for determining, on the basis of the received message, an inter-domain handover in the session from a first core network domain to a second core network domain.

In an embodiment of the invention, the apparatus comprises means for receiving a request to report an inter-domain handover in the subscriber session between core network domains, and means for reporting a detected inter-domain handover to a node providing service control in the subscriber session.

In an embodiment of the invention, the apparatus comprises means for monitoring a detection point for detecting an inter-domain handover between core network domains.

In an embodiment, the invention describes an apparatus comprising means for receiving, a message comprising event information associated with a service, means for determining, on the basis of the event information an inter-domain handover in a subscriber session between core network domains, and means for determining a service parameter for the service.

In an embodiment of the invention, the apparatus comprises means for receiving a message to invoke a service for a subscriber session, wherein the message comprises a subscriber identifier and a service key, means for determining, on the basis of the received subscriber identifier and the service key, that the service is to be controiled in more than one core network domain, and means for sending a request to report an inter-domain handover between the network domains.

In an embodiment of the invention, the service is a prepaid service, and the service parameter comprises tariff information, and the apparatus comprises means for sending a service command comprising the service parameter.

In an embodiment, the invention describes a computer program product comprising computer program code, wherein execution of the program code in an apparatus causes the apparatus to carry out a method according to the invention.

In an embodiment the invention describes a system comprising one or more apparatuses according to the invention. In an embodiment of the invention, the message comprises a message for establishing or re-establishing a leg of the session. The message may be a message associated with a subscriber session.

In an embodiment of the invention, the message comprises a Session Initiation Protocol (SIP) Invite message or a SIP Update message. In an embodiment of the invention, the message comprises an access network identifier.

In an embodiment of the invention, the access network identifier indicates at least one access network from the group comprising: WLAN, Wi- MAX, 3GPP-UTRAN, 3GPP-GERAN, 3GPP-CDMA2000. In an embodiment of the invention, the core network domains comprise an IP Multimedia Subsystem (IMS) network, and a Circuit Switched (CS) or Packet Switched (PS) Core Network (CN) domain.

In an embodiment of the invention, the first core network domain comprises an IP Multimedia Subsystem (IMS) network domain. In an embodiment of the invention the second core network domain comprises a Circuit Switched (CS) or Packet Switched (PS) Core Network (CN) domain.

In an embodiment of the invention, the session comprises a voice call. In an embodiment of the invention, the service comprises a CAMEL

(Customized Applications for Mobile network Enhanced Logic) service, such as a prepaid or a Voice Call Continuity (VCC) service.

In an embodiment of the invention, the event information indicates establishment or re-establishment of the session associated with the service. As an advantage different service control may be applied to different core network domains. This is particularly advantageous in IMS, where different types of ANs exist that may connect to IMS directly or via CS CN.

Further advantages of embodiments of the invention will become apparent from the accompanying detailed description.

Brief description of the drawings

In the following, the invention will be described in greater detail by means of preferred embodiments and with reference to the accompanying drawings, in which Figure 1 illustrates a network architecture suitable for an embodiment of the invention;

Figure 2 illustrates an embodiment of the invention, where UE changes between GSM and WLAN ANs;

Figure 3 shows a flow chart according to an embodiment of the in- vention;

Figure 4 shows a flow chart according to an embodiment of the invention;

Figure 5 illustrates signaling between functional entities according to an embodiment of the invention; Figure 6 illustrates information elements in a request message according to an embodiment of the invention;

Figure 7 illustrates information elements in a report message according to an embodiment of the invention;

Figure 8 illustrates an apparatus suitable for carrying out an em- bodiment of the invention.

Detailed description of the invention

Figure 1 illustrates a general architecture of a communication system 100 providing a plurality of network domains and ANs for UE 102 to access the communication system. Figure 1 is a simplified system architecture only showing some exemplary elements and functional entities, all being logical units whose implementation may differ from what is shown. The connections shown in Figure 1 are logical connections; the actual physical connections may be different. It is apparent to a person skilled in the art that the systems may also comprise other functions and structures. The communication system 100 in Figure 1 comprises a CN 106, an AN 104, and UE 102. The UE 102 accesses the CN via the AN. The UE may have a subscription that allows access to the communication system and defines services available to the UE. The CN comprises an IMS domain 130, a CS domain 132, and a PS domain 134. IMS 130 enables multimedia services to the UE. IMS is an IP-based network, where IP-based services are provided via Application Servers (ASs) 142 to the subscribers of the IMS network. In IMS, subscriber information is stored in a Home Subscriber Server (HSS) 144. The CS domain provides CS connections, where dedicated network resources are allocated to the connections of the UE, such as CS voice calls in CS-based ANs. The CS domain comprises a Mobile Switching Center (MSC) 146 that performs switching functions for originating and terminating connections to the UE. The CS domain also comprises a database, a Visitor Location Register (VLR) 148, that stores subscriber data on the subscribers that are within its location area. The PS domain provides packet-based connections to the UE in

CS-based ANs. A Serving GPRS Support Node (SGSN) 150 serves the UE by sending and receiving packets for the UE. The PS domain also has a Gateway GPRS Support Node (GGSN) 152 that operates as a gateway between the PS domain and packet-switched networks, such as IMS. ANs 120 to126 represent examples of ANs that may be used by the

UE to access the IMS CN. A Base Station System (BSS) 120 provides GSM radio access to the UE. The Radio Network Subsystem 122 provides UMTS radio access to the UE. WLAN 124 and WiMAX (Wireless Interoperability for Microwave Access) 126 represent IP-based access networks that may be used by the UE to access the IMS CN. The BSS and RNS ANs represent CS-based ANs that connect the UE to IMS via the PS and CS domains. IP-based ANs may be connected to IMS directly.

In the following, the term session refers to a session controlled in the packet switched domain, such as an IMS session. The session may com- prise one or more of the following: a multimedia connection, voice call and data service, that are provided to the subscribers.

In the following, a domain change is referred to as an inter-domain handover. The inter-domain handover may be performed between core network domains in a subscriber session. Voice Call Continuity as defined in 3GPP TS 23.206 V7.5.0 (2007-

12) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Voice Call Continuity (VCC) between Circuit Switched (CS) and IP Multimedia Subsystem (IMS); Stage 2 (Release 7), which is incorporated herein by reference, provides seamless handovers for voice calls between IMS and CS domains. In VCC, the call control for the LJE is anchored in VCC-AS, which is an AS in the IMS domain of the network. VCC enables the voice call continuity in domain transfers. IMS network subscription information includes an indication, if the subscription of the UE includes a VCC service. When the UE subscription includes the VCC service, the VCC-AS operates as an anchoring point for the IMS UE access leg, that is the call control connection between the UE and the VCC- AS, and for a remote leg that is the call control connection between the VCC- AS and a remote party.

Figure 2 illustrates an embodiment of the invention in an IMS 206, where the subscription of IMS UE 200 includes a VCC service. An AN 202 connects to the IMS via a CS-domain CN 204, and an AN 222 connects to IMS via a direct IP connection. In the embodiment, the AN 202 is GSM BSS and the AN 222 is IEEE 802.11-based WLAN. IMS comprises a VCC-AS 218 for enabling seamless inter-domain handovers between the CS and IMS domains. An access leg 210 is used between VCC-AS and the UE when the UE is con- nected to IMS via GSM, and an access leg 224 is used by the UE when the UE is connected to IMS via WLAN.

When the UE is connected to the GSM, the UE access leg is connected to IMS via the CS domain, and when the UE is connected to the WLAN, the UE access leg is directly in the IMS domain. The IMS further comprises a Serving Call State Control Function (S-CSCF) 219 that performs call control, service switching, and routing for the IMS UE. An IM-SSF 216 enables provisioning of CAMEL services in IMS. The S-CSCF is connected to the IM-SSF and to the VCC-AS using an IP-based connection 214. In IMS, the connection 214 is defined as an IP multimedia Subsystem Service Control Interface (ISC), where SIP messages are exchanged.

For the provisioning of CAMEL-based service data in IMS, IM-SSF has a connection 212 to an HLR 221. The protocol between IM-SSF and HLR is the Mobile Application Part (MAP). For a CAMEL-based service control connection 213, the IM-SSF is connected to the gsmSCF that stores the CAMEL service logic for the CAMEL services. The protocol used between IM-SSF and gsmSCF is the Camel Application Part (CAP) protocol. In the interworking of IMS and CAMEL, the IM-SSF monitors a subscriber's IMS session by maintaining a BCSM comprising processing logic for the session. The BCSM provides a generic representation of call processing that identifies the points where call processing may be interrupted or resumed. In the IMS session transitions between BCSM PICs may be determined on the basis of the received SIP messages. The transitions between BCSM PICs may be detected using DPs. A DP comprises criteria that define conditions for detecting the DP. Accordingly, the DP is detected when the criteria of the DP are met. For an example a DP for detecting a disconnection of a call may be de- tected when a BYE message is received.

Conventionally, the BCSM consists of two sets of call processing logic, OBCSM (Originating BCSM) and T-BCSM (Terminating BCSM). The O- BCSM models processes supporting the calling party and the T-BCSM models processes supporting the terminating party of a call. Accordingly, the DPs may be monitored for originating and terminating parties separately as there are separate BCSM models for the originating and terminating parties. Event DPs (EDPs) may be armed in IM-SSF dynamically by the gsmSCF with sending a report request message, Request Report BCSM Event (RRBE), requesting the IM-SSF to report the detection of the EDP. An example of the RRBE message may be referred to in 3GPP TS 23.278 V7.1.0 (2006-03) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Customised Applications for Mobile network Enhanced Logic (CAMEL) Phase 4; Stage 2; IM CN Interworking (Release 7), Section 4.7.2.12 pp. 141-142, or in 3GPP TS 23.078 V7.9.0 (2007-09); 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Customised Applications for Mobile network Enhanced Logic (CAMEL) Phase 4; Stage 2, Section 4.6.2.19 pp. 502-505. If an EDP is armed, the IM-SSF reports to gsmSCF when the EDP is encountered. Arming an EDP in IM-SSF, means activating a functionality to monitor the EDP in IM-SSF. The EDP is armed according to parameters received in the report request message. Once the EDP is armed it is monitored in the subscriber call or session. After encountering the EDP, the call processing may be suspended or continued in IM-SSF, depending on the type of the EDP.

An EDP may also be configured to be automatically rearmed by de- fining the rearming policy to be applied for the EDP. The indication of the rearming policy to be applied may be sent by the gsmSCF to the IM-SSF in the RRBE in an Information Element (IE). An example of such information element is the "Automatic Rearm" IE in 3GPP TS 23.078 V7.9.0 (2007-09); 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Customised Applications for Mobile network Enhanced Logic (CAMEL) Phase 4; Stage 2, Section 4.6.2.19 pp. 502-503.

Two types of EDP exist. When an EDP-I (EDP - Interrupted) is encountered in IM-SSF, the session processing is interrupted. The IM-SSF reports the detection of the EDP to gsmSCF and waits for instructions from the gsmSCF. When an EDP-N (EDP - Notification) is encountered, the detection of the EDP is reported to the gsmSCF, but the session processing in IM-SSF is not interrupted.

Figure 3 shows a flow chart describing a process performed by a node maintaining a processing logic for a subscriber session for monitoring subscriber sessions in a core network domain according to an embodiment of the invention.

In an embodiment of the invention, the process in Figure 3 may be performed by IM-SSF that is requested to monitor a DP of an IMS subscriber session in IMS domain or other CN domain. The IM-SSF may be for example the IM-SSF 216 in Figure 2. The process of Figure 3 may be performed by the apparatus described in Figure 8.

Returning to Figure 3, in 300 the IM-SSF starts a service in the originating or terminating BCSM by reporting a Trigger Detection Point (TDP) to the gsmSCF.

In 302, a request is received to report an inter-domain handover in the subscriber session between core network domains.

In an embodiment of the invention, the request may be an RRBE from the gsmSCF to request reporting a change of position EDP that meets the criteria for an inter-domain handover.

In an embodiment of the invention, the RRBE received in 302 may comprise a monitoring mode, and an indication of rearming policy to be applied for the DP.

On the basis of the request received in 302, a change of position detection point with criteria for detecting an inter-domain handover between core network domains is armed in 304. As an advantage, the core network domain changes of the subscriber may be detected. In 304, the arming of the

DP causes the subscriber session processing phases to be monitored. The monitoring may comprise receiving messages in the subscriber session.

In an embodiment of the invention, the monitoring is performed against the criteria of the armed change of position DP. The criteria may be stored in IM-SSF in association with the DP. In an embodiment of the invention in 304, the change of position DP is an EDP. The EDP may be armed (i.e. monitored) in a BCSM during the subscriber session.

In 308, the IM-SSF receives a message associated with the subscriber session. In an embodiment of the invention the message is a message used to negotiate post-handover media that may be used for establishing or re- establishing a leg in the session. In the handover, the UE of the subscriber may have performed a handover between IMS ANs such as between GSM and WLAN. After the handover one or more of the session legs are reestablished with a SIP message that meets the criteria as described above.

In 311 , it may be determined, on the basis of the received message, whether an inter-domain handover between CN domains has occurred in the subscriber session by for example, checking the received message. If the message comprises an AN identifier, it indicates an inter-domain handover, e.g. from IMS to CS or PS domain or from CS or PS to IMS domain, has happened. The received message may be, for example a message used in estab- lishing or re-establishing a leg in a session such as a SIP INVITE or a SIP UPDATE message. in an embodiment of the invention in 311 it is determined whether the received message, comprises an AN identifier. If the message comprises an AN identifier the process continues to 312. If the message does not com- prise an AN identifier the process continues to 308 to receive messages associated with the session.

In an embodiment of the invention in 311 , the AN identifier may be indicated in the received message in a SIP Private Header (P-header) extension, as defined in RFC3455 P-Access-Network_lnfo header access-type field. In RFC3455, the value of the access-type field may be "IEEE-802.11 a", ¹¹IEEE- 802.11b", "3GPP-GERAN", "3GPP-UTRAN-FDD", "3GPP-UTRAN-TDD", "3GPP-CDMA2000". The AN identifier may also be some other identifier that identifies the AN used by the UE.

In 312, the IM-SSF may report the detected inter-domain handover in an event report message to the gsmSCF that provides service control in the subscriber session. The event report message may comprise event information that indicates the detection of an inter-domain handover. The indication may be for example an IE in the report message. In this way the service such as prepaid service controlled by gsmSCF may receive a notification of the inter- domain handover performed in at least one of the legs in the subscriber ses- sion.

In 313, the IM-SSF continues the session processing according to the type of the DP.

In an embodiment of the invention where the rearming policy received in the RRBE defines that the DP should be automatically rearmed, the session processing continues to 304. Otherwise the process ends in 314.

Figure 4 shows a flow chart according to an embodiment of the invention, where a node controlling a service in a subscriber session determines that the service is to be controlled in more than one core network domain.

In an embodiment of the invention, the node controls a service in a subscriber session, and then determines that in the controlling, information about inter-domain handovers between core network domains is needed.

In an embodiment of the invention the node performing the process in Figure 4 may be the gsmSCF 220 in Figure 2 that resides in the CS domain and controls a service of the UE connected to the IMS domain. The process of Figure 4 may be performed by the apparatus described in Figure 8. In an embodiment of the invention, the controlled service may be any service for example a prepaid service or a Voice Call Continuity service.

Returning to Figure 4, the process starts in 400. In 402 the gsmSCF receives a request to invoke a service for a subscriber session. The received message comprises a service key and a subscriber identifier.

In an embodiment of the invention, the received message may comprise a Mobile Subscriber International ISDN Number (MSISDN) and/or an International Mobile Subscriber identity (IMSI) for identifying the subscriber receiving the service, and a Service Key (SK) for identifying the service logic or application to be invoked within gsmSCF for the subscriber session. An example of the Initial DP message may be referred to in 3GPP TS 23.278 V7.1.0 (2006-03) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Customised Applications for Mobile network Enhanced Logic (CAMEL) Phase 4; Stage 2; IM CN Inter- working (Release 7), Section 4.7.1.6 pp. 134-136. In an embodiment of the invention, the SK indicates for example a request for prepaid service logic to be invoked for the subscriber session.

In 404, the gsmSCF extracts the SK in 404 and the subscriber identifier in 405 from the received message.

In 406, the gsmSCF determines, whether inter-domain handovers between core network domains need to be monitored. As an advantage the inter-domain handovers are monitored only in subscriber sessions where inter- domain handovers are possible.

In an embodiment of the invention in 406, when the subscriber identifier, extracted in 405, indicates an IMS subscriber, the gsmSCF determines that CN domain changes are possible for the subscriber, for example due to handovers between IMS ANs. Therefore, in 406 the gsmSCF determines that CN domain changes need to be monitored in the subscriber session and the process continues to 408.

In an embodiment of the invention in 406, when the SK, extracted in 404, indicates a service that needs position information such as information of the CN domain used in the subscriber session, the gsmSCF determines that

CN domain changes need to be monitored in the subscriber session and the process continues to 408. In an embodiment of the invention, the SK indicates for example a prepaid service that may need CN domain information for cor- rect charging in each CN domain.

In an embodiment of the invention in 406, the process continues to 408 when both the subscriber identifier and SK indicate that CN domain changes need to be monitored, as described above.

If in 406 no need for monitoring is determined, the process contin- ues to 416 and the process ends.

In 408, a message is sent to fM-SSF, requesting to report an inter- domain handover between core network domains. In an embodiment of the invention, the message may be an RRBE message that causes a change of position DP to be armed in (M-SSF with criteria for detecting an inter-domain handover. Accordingly, the RRBE defines the DP and criteria to be used in monitoring the DP

In an embodiment of the invention in 408, the RRBE may comprise a monitoring mode to be used in the DP and an indication of the rearming policy to be applied for the DP. In 410, the gsmSCF receives a message comprising event information associated with the service for a subscriber session. The event information may indicate establishment or re-establishment of the session associated with the service. The message may be received from IM-SSF.

In 411 , the gsmSCF determines whether the event information received in 410 indicates an inter-domain handover between core network do- mains in the subscriber session. If it does, the process continues to 412, otherwise the process continues in 410 to receive further messages.

In an embodiment of the invention, the message received in 410 comprises an indication that a change of position DP meeting the criteria for an inter-domain handover has been detected. The indication may be for example an information element indicating an inter-domain handover. On the basis of the indication, in 411 the inter-domain handover in the subscriber session may be determined in the gsmSCF. As an advantage the gsmSCF that needs subscriber position information to control a service, receives change of position information regarding inter-domain handovers that are performed in the sub- scriber session.

In 412, one or more service parameters are determined on the basis of the event information received in 410 that is determined in 411 to indicate an inter-domain handover in the subscriber session.

In an embodiment of the invention, the gsmSCF applies service logic to the subscriber session as indicated by the SK and determines in 412 one or more service parameters on the basis of the applied service logic and the inter-domain handover event information. The service logic may be prepaid service logic that may determine prepaid service parameters on the basis of the inter-domain handover event information. The prepaid service parameters may comprise a tariff to be applied, session time left, etc. In this way the service logic may receive information on inter-domain handovers in the subscriber session and a service in the subscriber session may be controlled on the basis of an inter-domain handover in the subscriber session.

In 414, the service parameters determined in 412 are sent to the IM- SSF. In this way the gsmSCF controls the service in the subscriber session on the basis of the detected inter-domain handover.

In 415, if the rearming policy of the DP indicates that automatic rearming is applied to the DP, the process continues to 410 so as to receive further event information from the IM-SSF of the DP that is automatically re- armed. Otherwise the process ends in 416.

Figure 5 illustrates signaling between functional entities according to an embodiment of the invention. The signaling is illustrated with functional entities defined in the IMS: VCC-AS 500, S-CSCF 501 , IM-SSF 502, and gsmSCF 504. The functional entities may be implemented for example in the networks of Figure 1 or 2 using the apparatus described in Figure 8. The signaling be- tween the functional entities in Figure 5 may be arranged using the connections 213 and 214 as in Figure 2, where the communication between VCC-AS and IM-SSF is enabled by SIP messages routed via the ISC interface and the communication between IM-SSF and gsmSCF is enabled by the CAP protocol connection. The IM-SSF and gsmSCF in Figure 5 may be configured or ar- ranged to operate according to the processes described in Figures 3 and 4.

Returning to Figure 5, in 506 the gsmSCF determines that inter- domain handovers between core network domains need to be monitored in a subscriber session and sends a message 508 to IM-SSF that requests to report an inter-domain handover between the core network domains. In an em- bodiment of the invention, the message is an RRBE message. In 510 a change of position DP for detecting an inter-domain handover is armed in IM-SSF.

A message 511 is sent from the VCC-AS to the S-CSCF to reestablish a leg in the subscriber session after a VCC handover. The message may be a SIP INVITE or a SIP UPDATE and comprise an AN identifier. In 512 the S-CSCF routes the received message 511 in a message 513 to the IM-SSF.

In 514, the IM-SSF detects a change of position matching the inter- domain handover criteria on the basis of the received message 513. When the IM-SSF has detected the inter-domain handover, IM-SSF reports the event to the gsmSCF in a message 516.

In 518, the gsmSCF determines one or more service parameters for a service controlled in the subscriber session on the basis of the message 516. In an embodiment of the invention the gsmSCF applies prepaid service logic to the subscriber session and in 518 one or more prepaid service parameters are determined on the basis of prepaid service logic and the inter-domain handover event information received in the message 516. The determined service parameters are sent to IM-SSF in a service command message 520, to be applied to the service.

In 522 the new parameters are applied to the service in the sub- scriber session. In an embodiment of the invention in 522 new tariff is applied in the prepaid subscriber session on the basis of the detected inter-domain handover. As an advantage, the prepaid subscriber tariff may be determined on the basis of the detected inter-domain handover.

Figure 6 illustrates a data structure 600 according to an embodiment of the invention, comprising Information Element (IE) names 602 and values associated with the IEs 604. The data structure may also comprise other fields, which are not shown in Figure 6 so as to avoid obscuring the description with unnecessary details that are not essential for understanding the invention. The data structure in Figure 6, or parts of it, may be used in the above embodiments in protocol messages from a node providing service control to a node monitoring sessions in a network, for requesting monitoring a change of position EDP matching inter-domain handover criteria. In an embodiment of the invention, the data structure is an RRBE message. In the implementation of the data structure, one or more bits, bytes or characters may be used to represent the different fields and their values. In the data structure, a value 614 of an Event Type IE 606 defines the EDP to be monitored. The value in 614 may be set as 0_Change_of_Position or T_Change_of_Position, to request the IM-SSF to report the detection of a change of position event in the originating or terminating BCSM respectively. A value 620 of an IE Monitor Mode 612 may be set to "Notified" in

620 to indicate that the encountered EDP is to be reported to the gsmSCF and the session processing is to be continued in the IM-SSF without interruption after encountering the EDP. Other values for the IE 620 may be "Interrupted", where the encountered EDP is reported to the gsmSCF and the session proc- essing is interrupted in the IM-SSF until the gsmSCF sends a service command to the IM-SSF, and "Transparent", where the event is not reported to the gsmSCF and the session processing is continued in the IM-SSF after the detection of the EDP.

A DP Specific Criteria IE 622 defines the criteria for monitoring the EDP defined in an Event Type Value IE. To request monitoring the change of position EDP matching the inter-domain handover criteria, an IE 624 comprises an indication of the inter-domain handover, such as "Inter-Domain HO". With the value of the field 624 set to indicate the inter-domain handover, the IM-SSF monitors the Change of Position DP for inter-domain handovers. When the criteria for an inter-domain handover are met, the session processing in the IM-SSF continues as defined by the Monitoring Mode IE 620. In an embodiment of the invention, the DP Specific Criteria IE is a structured IE and may comprise one or more instances of IEs that may indicate location changes, such as service area or cell changes. An example of the DP Specific Criteria may be referred to in 3GPP TS 23.078 V7.9.0 (2007-09); 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Customised Applications for Mobile network Enhanced Logic (CAMEL) Phase 4; Stage 2, Section 4.6.2.19 pp. 503-505, where the Change of Location IE indicates location changes. In the embodiment of the invention, an IE that indicates that the criteria for an inter-domain handover have been met is added to the IEs indicating location changes.

Automatic Rearm IE 626 may be set to indicate whether the DP shall be automatically rearmed. The value of the IE 628 may be simply "Yes" or "No", but any other indication may also be used. If the value is "Yes" the DP is rearmed automatically after disarming the DP for example due to detecting the event that meets the criteria of the DP. If the value is "No", the DP is not automatically rearmed.

Figure 7 illustrates a data structure 700 according to an embodiment of the invention, comprising Information Element (IE) fields 702 and values 704 associated with the IEs. The data structure in Figure 7 may be used in the above embodiments in protocol messages from a node monitoring a session in a network, to report detection of a change of position DP that meets the inter- domain handover criteria. In the implementation of the data structure, one or more bits, bytes or characters may be used to represent the different fields and their values. In an embodiment of the invention, the data structure is an Event

Report BCSM that may be used in CAP messages from IM-SSF to gsmSCF to report an event related to a subscriber's session. An example of the Event Report BCSM may be referred to in 3GPP TS 23.278 V7.1 .0 (2006-03) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Customised Applications for Mobile network Enhanced Logic (CAMEL) Phase 4; Stage 2; IM CN Interworking (Release 7), Section 4.7.1.5 page 133, or in 3GPP TS 23.078 V7.9.0 (2007-09); 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Customised Applications for Mobile network Enhanced Logic (CAMEL) Phase 4; Stage 2, Section 4.6.1.6 pp. 477-481.

An Event Type IE 706 defines the EDP to be reported. The value of the Event Type IE 706 in 714 may be set as above with the exemplary data structure of the RRBE message.

In an embodiment of the invention, the Event Specific Information IE 708 is set to "Inter-Domain HO" value in 716 to indicate the detection of the in- ter-domain handover event to gsmSCF. A value 720 of the Misc Call Info IE 712 indicates the EDP type of the reported event.

Figure 8 is a block diagram of an apparatus 800 according to an embodiment of the invention. Although the apparatus has been depicted as one entity, different modules and memory may be implemented in one or more physical or logical entities. The apparatus is capable of performing the processes of Figure 3 or 4. In an embodiment of the invention, the apparatus is IM- SSF or gsmSCF in the above embodiments.

The apparatus 800 comprises an interfacing unit 802, a central processing unit (CPU) 808, and a memory 810, all being electrically intercon- nected. The interfacing unit comprises an input 804 and an output unit 806 that provide, respectively, the input and output interfaces to the apparatus. The input and output units may be configured or arranged to send and receive messages according to one or more protocols, such as CAP, SIP, IP, GSM₁ WLAN, to achieve the functionality of an embodiment of the present invention. Accord- ingly the input and output units may operate respectively as a receiver and a sender. The CPU may comprise a set of registers, an arithmetic logic unit, and a control unit. The control unit is controlled by a sequence of program instructions transferred to the CPU from the memory. The control unit may contain a number of microinstructions for basic operations. The implementation of micro- instructions may vary, depending on the CPU design. The program instructions may be coded by a programming language, which may be a high-level programming language, such as C, Java, etc., or a low-level programming language, such as a machine language, or an assembler. The electronic digital computer may also have an operating system, which may provide system ser- vices to a computer program written with the program instructions. The memory may be a volatile or a non-volatile memory, for example EEPROM, ROM, PROM, RAM, DRAM, SRAM, firmware, programmable logic, etc.

An embodiment provides a computer program embodied on a distribution medium, comprising program instructions which, when loaded into an electronic apparatus, cause the CPU to perform according to an embodiment of the present invention. The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, elec- trical carrier signal, telecommunications signal, and software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers.

The apparatus 800 may also be implemented as one or more inte- grated circuits, such as application-specific integrated circuits ASIC. Other hardware embodiments are also feasible, such as a circuit built of separate logic components. A hybrid of these different implementations is also feasible.

When selecting the method of implementation, a person skilled in the art will consider the requirements set for the size and power consumption of the appa- ratus 800, necessary processing capacity, production costs, and production volumes, for example.

The steps/points, signaling messages and related functions described above in Figures 3, 4 and 5 are in no absolute chronological order, and some of the steps/points may be performed simultaneously or in an order dif- fering from the given one. Other functions can also be executed between the steps/points or within the steps/points and other signaling messages sent between the illustrated messages. Some of the steps/points or part of the steps/points can also be left out or replaced by a corresponding step/point or part of the step/point. The IM-SSF and gsmSCF operations illustrate a proce- dure that may be implemented in one or more physical or logical entities. The signaling messages are only exemplary and may even comprise several separate messages for transmitting the same information. In addition, the messages may also contain other information.

The present invention is applicable to any user terminal, server, cor- responding component, and/or to any communication system or any combination of different communication systems that support inter-domain handovers. The communication system may be a fixed communication system or a wireless communication system or a communication system utilizing both fixed networks and wireless networks. The protocols used, the specifications of communication systems, servers and user terminals, especially in wireless communication, develop rapidly. Such development may require extra changes to an embodiment. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment.

Apparatuses, such as servers, or corresponding server components, user terminals and/or other corresponding devices or apparatuses implementing the functionality of a corresponding apparatus described with an embodiment comprise not only prior art means, but also means for receiving a message associated with a subscriber session in a node maintaining processing logic for the session, means for receiving a message associated with the session, means for determining, on the basis of the received message, an inter-domain handover in the session from a first core network domain to a second core network domain. In addition, they may comprise means for receiving a message comprising event information associated with a service in a subscriber session, means for determining whether the event information indicates an inter-domain handover in the subscriber session between core network domains, and means for determining a service parameter for the service. More precisely, they comprise means for implementing a functionality of a corre- sponding apparatus described by an embodiment, and they may comprise separate means for each separate function, or means may be configured or arranged to perform two or more functions. Present apparatuses comprise processors and memory that can be utilized in an embodiment. For example, the IM-SSF or gsmSCF may be a software application, or a module, or a unit con- figured as arithmetic operation, or as a program (including an added or updated software routine), executed by an operation processor. Programs, also called program products, including software routines, applets and macros, can be stored in any apparatus-readable data storage medium and they include program instructions to perform particular tasks. All modifications and configu- rations required for implementing a functionality of an embodiment may be performed as routines, which may be implemented as added or updated software routines, application circuits (ASIC) and/or programmable circuits. Further, software routines may be downloaded into an apparatus. The apparatus, such as a server, or a corresponding server component, or a user terminal, may be configured as a computer or a microprocessor, such as a single-chip computer element, including at least a memory for providing storage area used for arith- metic operation and an operation processor for executing the arithmetic operation. An example of the operation processor includes a central processing unit. The memory may be removable memory detachably connected to the apparatus.

It will be obvious to a person skilled in the art that as technology ad- vances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A method comprising: receiving a message associated with a subscriber session in a node monitoring the session; and determining, on the basis of the received message, an inter-domain handover in the session from a first core network domain to a second core network domain.

2. A method according to claim 1 , comprising: receiving a request to report an inter-domain handover in the subscriber session between core network domains; and if an inter-domain handover is detected, reporting the inter-domain handover to a node providing service control in the subscriber session.

3. A method according to claim 1 or 2, comprising: monitoring a detection point for detecting an inter-domain handover between core network domains.

4. A method according to claim I ₁ 2 or 3, wherein the message comprises a message for establishing or re-establishing a leg of the session.

5. A method according to claim 1 , 2, 3 or 4, wherein the message comprises an access network identifier.

6. A method according to claim 1 , 2, 3, 4 or 5, wherein the message comprises a Session Initiation Protocol (SIP) Invite message or a SIP Update message.

7. A method according to claim 1 , 2, 3, 4, 5 or 6, wherein the session comprises a voice call.

8. A method according to claim 1 , 2, 3, 4, 5, 6 or 7, wherein the access network identifier indicates at least one access network from the group comprising: WLAN, WiMAX, 3GPP-UTRAN, 3GPP-GERAN, 3GPP-CDMA2000.

9. A method according to any of the preceding claims, wherein the first core network domain comprises an IP Multimedia

Subsystem (IMS) network domain.

10. A method according to any of the preceding claims, wherein the second core network domain comprises a Circuit Switched (CS) or Packet Switched (PS) Core Network (CN) domain.

11. A method comprising: receiving, in a node controlling a service in a subscriber session, a message comprising event information associated with the service; determining, on the basis of the event information, an inter-domain handover in the subscriber session between core network domains; determining a service parameter for the service.

12. A method according to claim 1 1 , comprising: receiving a message to invoke a service for a subscriber session, wherein the message comprises a subscriber identifier and a service key; determining, on the basis of the received subscriber identifier and the service key, that the service is to be controlled in more than one core network domain, and sending a request to report an inter-domain handover between the network domains.

13. A method according to claim 1 1 or 12, wherein the event information indicates establishment or re-establishment of the session associated with the service.

14. A method according to claim 11 , 12 or 13, wherein the service is a prepaid service, and the service parameter com- prises tariff information, and the method comprises sending a service command comprising the tariff information.

15. A method according to any of claim 11 to 14, wherein the core network domains comprise an IP Multimedia Subsystem

(IMS) network, and a Circuit Switched (CS) or Packet Switched (PS) Core Network (CN) domain.

16. A method according to any of claim 11 to 15, wherein the session comprises a voice call.

17. A method according to any of claim 11 to 16, wherein the service comprises a CAMEL (Customized Applications for Mobile network Enhanced Logic) service, such as a prepaid or a Voice Call Continuity (VCC) service.

18. An apparatus comprising: means for receiving a message associated with a subscriber session; and means for determining, on the basis of the received message, an inter-domain handover in the session from a first core network domain to a second core network domain.

19. An apparatus according to claim 18, comprising: means for receiving a request to report an inter-domain handover in the subscriber session between core network domains; and means for reporting a detected inter-domain handover to a node providing service control in the subscriber session.

20. An apparatus according to claim 18 or 19, comprising: means for monitoring a detection point for detecting an inter-domain handover between core network domains.

21. An apparatus according to claim 18, 19 or 20, wherein the message associated with the session comprises a message for establishing or re-establishing a leg of the session.

22. An apparatus according to claim 18, 19, 20 or 21 , wherein the message comprises an access network identifier.

23. An apparatus according to claim 18, 19, 20, 21 or 22, wherein the message comprises a Session Initiation Protocol (SIP) Invite message or a SIP Update message.

24. An apparatus according to claim 18, 19, 20, 21 , 22 or 23, wherein the session comprises a voice call.

25. An apparatus according to claim 18, 19, 20, 21 , 22, 23 or 24, wherein the access network identifier indicates at least one access network from the group comprising: WLAN, WiMAX, 3GPP-UTRAN, 3GPP-GEFiAN, 3GPP-CDMA2000.

26. An apparatus according to any of claim 18 to 25, wherein the first core network domain comprises an IP Multimedia

Subsystem (IMS) network domain.

27. An apparatus according to any of claim 18 to 26, wherein the second core network domain comprises a Circuit Switched (CS) or Packet Switched (PS) Core Network (CN) domain.

28. An apparatus comprising: means for receiving, a message comprising event information associated with a service; means for determining, on the basis of the event information an inter-domain handover in a subscriber session between core network domains; and means for determining a service parameter for the service.

29. An apparatus according to claim 28, comprising: means for receiving a message to invoke a service for a subscriber session, wherein the message comprises a subscriber identifier and a service key; means for determining, on the basis of the received sub- scriber identifier and the service key, that the service is to be controlled in more than one core network domain, and means for sending a request to report an inter-domain handover between the network domains.

30. An apparatus according to claim 28 or 29, wherein the event information indicates establishment or re-establishment of the session associated with the service.

31. An apparatus according to claim 28, 29 or 30, wherein the service is a prepaid service, and the service parameter comprises tariff information, and the apparatus comprises means for sending a service command comprising the service parameter.

32. An apparatus according to any of claim 28 to 31 , wherein the core network domains comprise an IP Multimedia Subsystem (IMS) network, and a Circuit Switched (CS) or Packet Switched (PS) Core Network (CN) domain.

33. An apparatus according to any of claim 28 to 32, wherein the session comprises a voice call.

34. An apparatus according to any of claim 28 to 33, wherein the service comprises a CAMEL (Customized Applications for Mobile network Enhanced Logic) service, such as a prepaid or a Voice Call Continuity (VCC) service.

35. A computer program product comprising computer program code, wherein execution of the program code in an apparatus causes the apparatus to carry out a method according to any of claims 1 to 10.

36. A computer program product comprising computer program code, wherein execution of the program code in an apparatus causes the apparatus to carry out a method according to any of claims 11 to 17.

37. A system comprising one or more apparatuses as claimed in any one of the claims 18 to 34.