WO2016091287A1

WO2016091287A1 - Handover between circuit switched gateways

Info

Publication number: WO2016091287A1
Application number: PCT/EP2014/077035
Authority: WO
Inventors: Ulrich Wiehe; Peter Leis; Martin Oettl; Lauri Kalevi LAHTINEN
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2014-12-09
Filing date: 2014-12-09
Publication date: 2016-06-16

Abstract

A first apparatus of a communication network system opens (S31) at least one session according to at least one internet protocol between the first apparatus and a second apparatus of the communication network system, the first and second apparatuses providing access to an IP multimedia system for user equipments accessing first and second access entities using circuit switched radio access. Thereupon, a handover of a call of a user equipment processed by the first apparatus is caused (S32) from the first access entity to the second access entity. Upon completion of the handover, the call is transferred (S33) from the first apparatus to the second apparatus for processing the call and for providing access for the user equipment to the IP multimedia subsystem. Upon an end of the call, the at least one session between the first and second apparatuses is closed (S34).

Description

DESCRIPTION TITLE

HANDOVER BETWEEN CIRCUIT SWITCHED GATEWAYS

BACKGROUND OF THE INVENTION Field of the invention

The present invention relates to handover between circuit switched gateways in a communication network system, which provide access to IP multimedia services. In particular, the present invention relates to an inter CS-GW handover for Service Domain Centralization as an alternative to ICS using MSC Servers enhanced for ICS.

Related background Art

An IP multimedia core network (IM CN) subsystem enables PLMN operators to offer their subscribers multimedia services based on and built upon Internet applications, services and protocols. The IM CN subsystem (IMS) should enable the convergence of, and access to, voice, video, messaging, data and web-based technologies for a wireless user, and combine the growth of the Internet with the growth in telecommunications. The complete solution for the support of IP multimedia applications comprises terminals, IP- Connectivity Access Networks, and specific functional elements of the IM CN subsystem. ICS (IMS Centralized Services) enable IMS services when using CS access for media transport. ICS therefore enables IMS services to be provided using the CS domain access to transport the media. Users are provided with a consistent experience of services. When using PS access networks which support a full duplex speech media component of an IMS service, procedures defined in a specification of the standard are used to provide IMS services. For other access networks, media established via the CS domain is used in conjunction with IMS service control. When using a UE which has not been enhanced for ICS, IMS service control can be enabled by an MSC Server enhanced for ICS.

Fig. 1 shows a reference architecture for IMS sessions established using CS bearers. As can be seen from Fig. 1 , the MSC server enables IMS service control for the UE using CS. The MSC service has interfaces Mc, I2 and I3 with CS-MGW, CSCF and TAS. The CSCF has ISC interface with SCC AS. With the current ICS solution, there are drawbacks with respect to the need for having legacy GSM entities (enhanced MSC, HLR), #7 interfaces (internal, NNI) and having two service domains (CS, IMS) which raises service synchronization issues. ICS offers a unique IMS based service (one Service Domain, one Service Logic) for a given user independent from access network (2/3/4G), but does not allow replacing service execution within the GSM domain (MSC, HLR) for all users. Further the interconnection of inbound roaming ICS subscribers towards the HPLMN is based on IMS interconnection, what means the HPLMN must support IMS. ICS assumes that emergency calls originated in 2/3G CS RAN will be established via legacy means (MSC Call Control only, ISUP/TDM rsp. BICC/RTP links towards PSAP) without usage of IMS Service Domain.

The following meanings for the abbreviations used in this specification apply:

3GPP 3^rd Partnership Project ATCF Access Transfer Control Function

BICC Bearer Independent Call Control

BSS Base Station System

CS Circuit Switched

CS-GW Circuit Switched Gateway CSCF Call Session Control Function

DTAP Direct Transfer Application sub-Part

GERAN GSM EDGE Radio Access Network

HLR Home Location Register

HPLMN Home Public Land Mobile Network IMS IP Multimedia Subsystem

ICS IMS Centralized Services

ISC IMS Service Control ISUP ISDN User Part

MAP Mobile Application Part

MGW Media Gateway

MME Mobility Management Entity

MS Mobile Station

MSC Mobile Switching Centre

NNI Network to Network Interface

PLMN Public Land Mobile Network

PS Packet Switched

PSAP Public Safety Answering Point

RTP Real-Time Transport Protocol

RAT Radio Access Technology

SCC AS Service Centralization and Continuity Application Server

SIP Session Initiation Protocol

SGSN Serving GPRS Support Node

SS7 Signaling System 7

TDM Time Division Multiplexing

TAS Telephony Application Server

UMTS Universal Mobile Telecommunications System

URI Uniform Resource Identifier SUMMARY OF THE INVENTION

The present invention aims at overcoming at least some of the above drawbacks.

For example, at least one embodiment of the invention aims at providing a handover between gateways which provide access to centralized Internet services and process calls of user equipments using circuit switched access to a communication network system.

The above objects are achieved, at least in part, by a method, a first apparatus, a second apparatus and a computer program product as defined in the appended claims.

With at least one embodiment of the present invention, synchronization of handover for user equipments of the CS access domain is enabled.

In the following the invention will be described by way of embodiments and

implementation examples thereof with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a block diagram illustrating an IMS service centralization and continuity reference architecture.

Fig. 2 shows a block diagram illustrating an enhanced ICS functional architecture.

Fig. 3 shows a flowchart illustrating a process of an inter CS-GW handover for enhanced ICS according to an embodiment of the invention. Fig. 4 shows a schematic block diagram illustrating a configuration of a control unit in which examples of embodiments of the invention are implementable.

Fig. 5 shows a signaling diagram illustrating between two CS-GWs for providing the inter CS-GW handover according to the embodiment of the invention.

Fig. 6 shows a signaling diagram illustrating an inter CS-GW handover with Diameter and SIP between the CS-GWs according to a first implementation example of the invention. Fig. 7 shows a signaling diagram illustrating an inter CS-GW handover only using SIP between the CS-GWs according to a second implementation example of the invention.

DESCRIPTION OF THE EMBODIMENTS Before the description of embodiments and implementation examples of the invention, reference is made to Fig. 2 illustrating an enhanced ICS functional architecture.

A gateway function (CS-GW in Fig. 2) performs the following functionality on the control plane.

Towards a UE, the CS-GW terminates A (GERAN) and lu-cs interfaces (UTRAN) when the UE accesses via a CS RAT, and terminates a Gs interface towards "legacy" SGSNs as well as SGs and Sv interfaces towards an MME when the UE accesses via a PS domain of GERAN or UTRAN.

Towards an IP Multimedia Subsystem, the CS-GW terminates an 12 interface to an ATCF, terminates an Mw interface to a P/I/S-CSCF, and terminates an Ut like (13) interface to a Telephony Application Server (Telephony AS).

Towards legacy networks, the CS-GW terminates a G and E interface towards MSC Servers, and terminates ISUP signaling towards PSTN.

On the media plane the CS-GW controls a CS-MGW via an Mc interface.

Inter MSC handover between MSC or MSC enhanced for ICS is based on MAP and ISUP. There is currently no procedures that describes this type of handover based on any other protocols.

Now reference is made to Figs. 3 and 4 illustrating an embodiment of the present invention.

Fig. 3 shows a flowchart illustrating a handover process 30 between first and second apparatuses (e.g. gateways) of a communication network system, which process calls of user equipments accessing the communication network system via first and second access entities (e.g. BSSs, RANs, etc.) using circuit switched radio access, and provide access to an IP multimedia subsystem of the communication network system for the user equipments. In step S31 , e.g. in response to deciding the second apparatus for a transfer of a call of a user equipment upon receipt of a handover requirement to hand over the user equipment from a first area served by a first access entity to a second area served by a second access entity, at least one session according to at least one internet protocol is opened between the first apparatus and the second apparatus. According to an implementation example to be described later on, a first session is opened using a diameter protocol, and a second session is opened using SIP. According to another implementation example to be described later on, a session is opened using only SIP.

For example, referring to Fig. 4, in step S1 an anchor CS-GW 10 (i.e. first apparatus) decides a target CS-GW 20 (i.e. second apparatus) for the transfer of the call of the user equipment and, in step S2, opens a session for requesting handover and call transfer by transmitting a request message to the target CS-GW 20 according to an application layer internet protocol such as diameter and SIP.

For example, the anchor CS-GW 10 and the target CS-GW 20 are implemented in the architecture shown in Fig. 2 as first and second CS-GWs.

According to Fig. 3, in step S32, in response to opening the at least one session, a handover of the call of the user equipment from the first access entity to the second access entity is caused.

For example, referring to Fig. 4, in response to receiving the request message, the target CS-GW 20 processes the request in step S3. Processing the request may comprise transmitting a handover request to and receiving a handover request acknowledgment from an access entity (i.e. second access entity) such as a BSS or RAN, for which the target CS-GW 20 processes calls of user equipments which access the communication network system via this access entity. Then, in step S4, the target CS-GW 20 sends an indication message to the anchor CS-GW 10 indicating progress of the session and progress of the handover process.

In step S5, the anchor CS-GW 10 commands handover e.g. by transmitting a command message to an access entity (i.e. first access entity) such as a BSS or RAN, for which the anchor CS-GW 10 processes calls of user equipments which access the communication network system via this access entity. To be more precise, the anchor CS-GW 10 transmits the command message to the access entity from which it has received a message that handover is required for the user equipment accessing the communication network system via this access entity using circuit switched access. According to Fig. 3, in step S33, in response to completion of the handover, the call is transferred from the first apparatus to the second apparatus for processing the call and for providing access for the user equipment to the IP multimedia subsystem.

For example, referring to Fig. 4, in step S6 the target CS-GW 20 detects completion of the handover of the user equipment from the first access entity to the second access entity and indicates the detected handover completion in an indication message in step S7 to the anchor CS-GW 10, thereby transferring the call from the anchor CS-GW 10 to the target CS-GW 20.

In step S8, the anchor CS-GW 10 releases the connection with the user equipment via the first access entity.

According to Fig. 3, in step S34 in response to an end of the call, the at least one session between the first and second apparatuses is closed.

For example, referring to Fig. 4, in response to an end of the call, in step S9 messages are transmitted between the anchor CS-GW 10 and the target CS-GW 20 in order to close the session opened in step S2.

Now reference is made to Fig. 5 for illustrating a simplified block diagram of an electronic device that is suitable for use in practicing the exemplary embodiments of this invention.

Fig. 5 shows a control unit 40 comprising processing resources (e.g. processing circuitry) 41 , memory resources (e.g. memory circuitry) 42 that may store a program, and interfaces (e.g. interface circuitry) 43, which are connected via a link 44. The control unit 40 may be part of and/or used by a CS-GW such as the anchor CS-GW 10 and the target CS-GW 20. The control unit 40 may execute the process illustrated in Fig. 3.

The terms "connected," "coupled," or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements, and may encompass the presence of one or more intermediate elements between two elements that are

"connected" or "coupled" together. The coupling or connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements may be considered to be "connected" or "coupled" together by the use of one or more wires, cables and printed electrical connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and the optical (both visible and invisible) region, as non-limiting examples. The program stored in the memory resources 42 is assumed to include program instructions that, when executed by the processing resources 41 , enable the control unit 40 to operate in accordance with the exemplary embodiments of this invention.

In general, the exemplary embodiments of this invention may be implemented by computer software stored in the memory resources 42 and executable by the processing resources 41 of the control unit 40, or by hardware, or by a combination of software and/or firmware and hardware.

The memory resources 42 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as

semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The processing resources 41 may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples.

Now implementation examples of the present invention will be described by referring to Figs. 6 and 7.

According to a first implementation example illustrated in Fig. 6, inter CS-GW handover signaling between an anchor CS-GW_A and a target CS-GW_B is based on DIAMETER and SIP.

According to a second implementation example illustrated in Fig. 7, inter CS-GW handover signaling between an anchor CS-GW A and a target CS-GW B is based on SIP only.

For the first implementation example, a new Diameter application for use on an interface between CS-GWs is defined, comprising commands that allow to transport handover signaling between CS-GWs. The commands used may include:

- Prepare-Handover Request (PHR)

- Prepare-Handover Answer (PHA)

- Process-Access-Signaling Request (PAR)

- Forward-Access-Signaling Request (FAR) - Send-End-Signal Request (SER)

- Send-End-Signal Answer (SEA)

- Prepare-Subsequent-Handover Request (PSR)

- Prepare-Subsequent-Handover Answer (PSA) Further, for the first implementation example, the target CS-GW B allocates a temporary e.164 number or URI based identifier that is used for session transfer.

For the first and second implementation example, SIP session setup to transfer a call between anchor and target CS-GW contains information about direction and state of the call to be transferred. An inter CS-GW handover call flow according to the first implementation example is shown in Fig. 6.

It is to be noted that Fig. 6 shows A-interface signaling between MS/BSS-A and CS- GW_A and between CS-GW_B and BSS-B/MS for the case where the radio access type on both sides is GERAN. When the radio access type is UMTS, however, corresponding lu-Cs interface signaling is used between UE/RNS-A and CS-GW A an between CS- GW_B and RNS-B/UE.

Transfer of DTAP-messages (MM/CC-level) and e.g. subsequent-inter-MSC-handover related information can be carried with e.g. Diameter Process-Access-Signaling Request (PAR), Forward-Access-Signaling Request (FAR), Prepare-Subsequent-Handover Request (PSR) and Prepare-Subsequent-Handover Answer (PSA) messages, which is not shown in Fig. 6.

The following steps refer to the signaling diagram shown in Fig. 6.

In step 1 , BSS-A (i.e. first access entity) detects that an MS accessing the communication network system via the BSS-A requires to be handed over and sends A-HO-REQUIRED to CS-GW_A (i.e. first apparatus). CS-GW_A detects that a target cell is within CS- GW B's serving area.

In step 2, CS-GW A sends a Diameter-Prepare-Handover Request message (PHR) to CS-GW B (i.e. second apparatus). This message opens a Diameter session which will be closed in step A3. The PHR message contains enough information for CS-GW B to send an A-HO-REQUEST message to a BSS-B (i.e. second access entity) which serves the target cell.

In step 3, CS-GW B receives the Diameter PHR message and sends an A-HO- REQUEST to BSS-B. CS-GW-B also allocates a temporary handover-number (or handover-URI) used for session transfer.

In step 4, BSS-B acknowledges the receipt of A-HO-REQUEST.

In step 5, CS-GW B sends a Diameter-Prepare-Handover-Answer message (PHA) to CS- GW A. This message contains the allocated handover-number (or handover-URI).

In step 6, the anchor CS-GW_A sends SIP INVITE to the target CS-GW_B. An R-URI of the SIP INIVTE contains the session transfer number (temporary handover number) or session transfer URI (handover-URI) as received in step 5. The SIP INVITE contains an indication of the direction of the call to be transferred (i.e. originating call or terminating call) and an indication of the state of the call that is transferred (prior alerting, alerting, stable). Further, the SIP INVITE contains information regarding needed resources between the CS-GW-A and CS-GW-B. This allows the target CS-GW_B to setup appropriate bearer resources for the call. During the inter CS-GW handover (equivalent to inter-MSS handover) the CS-GW B acts as relay node for the DTAP signaling (MM and CM sublayers of UE signaling), while the actual MM and CM-sublayers of UE protocol remain in the anchor CS-GW-A. Other options are not ruled out. With the receipt of SIP INVITE the temporary session transfer number (or URI) is released.

In step 7, CS-GW-B (target CS-GW) sends an appropriate SIP response to confirm the reception of the SIP INVITE, e.g. a 183 (session progress).

In step 8, CS-GW_A sends A-HO-COMMAND to BSS-A/MS so that the MS tunes to the target cell.

In step 9, BSS-B detects that the MS has switched to the target cell and sends A-HO- DETECT to CS-GW_B.

In step 1 0, CS-GW B forwards the information to CS-GW A within a Diameter-Process- Access-Signaling Request message (PAR). In step 1 1 , CS-GW_B receives A-HO-COMPLETE from BSS-B.

In step 12, CS-GW_B sends Diameter-Send-End-Signal Request (SER) to CS-GW_A indicating that the connection to BSS_A can be released.

In step 13, the connection to BSS-A is released. In step 14, the target CS-GW-B indicates via SIP 200 (OK) that the Handover is completed.

In step 15, the CS-GW-A acknowledges the reception of the SIP 200 (OK) with SIP ACK.

In steps A1 and A2, once end of call happens, the SIP session between CS-GW-A and CS-GW-B is released with SIP BYE and SIP 200 (OK). In step A3, the Diameter session opened at step 2 is closed by sending Diameter Send- End-Signal Answer (SEA).

It is to be noted that between steps 12 and A3 several Diameter messages may be sent from CS-GW_A to CS-GW_B (Diameter Forward-Access-Signaling Request (FAR)) or from CS-GW_B to CS-GW-A (Diameter Process-Access-Signaling Request (PAR)) to relay any access signaling exchanged between CS-GW A and BSS-B/MS.

When comparing Figs. 4 and 6, step S1 in Fig. 4 may comprise steps 2 and 6 of Fig. 6. Step S4 in Fig. 4 may comprise steps 5 and 7 of Fig. 6. Step S7 in Fig. 4 may comprise steps 10, 12 and 14 of Fig. 6. Step S9 may comprise steps A1 , A2 and A3 of Fig. 6.

An inter CS-GW handover call flow according to the second implementation example is shown in Fig. 7.

In Fig. 7, the radio access type is UMTS.

The following steps refer to the signaling diagram shown in Fig. 7.

In step 1 , RAN A (i.e. first access entity) detects that a UE accessing the communication network system via the RAN A requires to be handed over and sends A-HO-REQU IRED to CS-GW_A (i.e. first apparatus). CS-GW_A detects that a target cell is within CS- GW B's serving area.

In step 2, CS-GW_A sends a SIP INVITE + HO-REQ-INFO (handover specific content) to CS-GW B. In step 3, CS-GW_B receives the SIP INVITE + HO-REQ-INFO message and sends an A- HO-REQUEST to RAN B (i.e. second access entity).

In step 4, RAN B acknowledges the receipt of A-HO-REQUEST.

In step 5, CS-GW_B responds with a SIP 183 (Session Progress) + HO-Resp-lnfo (handover specific content).

In step 6, CS-GW_A sends A-HO-COMMAND to RAN A/UE so that the UE tunes to the target cell.

In step 7, RAN B detects that the UE has switched to the target cell and sends A-HO- DETECT to CS-GW_B. In step 8, the target CS-GW-B indicates via SIP 200 (OK) that the Handover is completed. In step 9, CS-GW_B receives A-HO-COMPLETE from RAN B.

In step 10, the CS-GW-A acknowledges the reception of the SIP 200 (OK) with SIP ACK. In step 1 1 , the connection to RAN A is released.

In steps A1 and A2, once end of call happens, the session between CS-GW-A and CS- GW-B is released with SIP BYE and SIP 200 (OK).

The handover specific content that is defined as +HO-REQ-INFO and + HO-RSP-INFO needs to be carried in SIP requests and SIP responses, and can be encoded e.g. as mime coded content.

The transfer of DTAP-messages (MM/CC-level) and e.g. subsequent-inter-MSC-handover related information can be carried with e.g. SIP INFO messages.

When comparing Figs. 4 and 7, step S1 in Fig. 4 may comprise step 2 of Fig. 7. Step S4 in Fig. 4 may comprise step 5 of Fig. 7. Step S7 in Fig. 4 may comprise step 8 of Fig. 7. Step S9 may comprise steps A1 and A2 of Fig. 7.

When using the SIP only option according to the second implementation example, there is no handover-number on a per call basis required and the routing of the SIP messages can be based on routing information linked to the target cell's location area. Routing info may be SIP-URI of TEL-URI. According to an aspect of the invention, an apparatus of a communication network system is provided. According to an exemplary embodiment of the invention, the apparatus may comprise the anchor CS-GW 10 shown in Fig. 4 and/or the CS-GW A shown in Figs. 6 or 7. Alternatively or in addition, the apparatus may comprise a control unit 40 shown in Fig. 5 and/or may be configured to perform the process of Fig. 3.

The apparatus comprises means for processing a call of a user equipment which accesses the communication network system via a first access entity using circuit switched radio access, wherein the apparatus comprises means for providing access to an IP multimedia subsystem of the communication network system for user equipments accessing the communication network system via the first access entity. The apparatus further comprises means for opening at least one session according to at least one internet protocol towards a target apparatus of the communication network system, and means for, in response to the means for opening having opened the at least one session, causing a handover of the call of the user equipment from the first access entity to a second access entity for accessing the communication network system, the target apparatus providing access to the IP multimedia system for user equipments accessing the second access entity. The apparatus further comprises means for, in response to completion of the handover, transferring the call to the target apparatus for processing the call and for providing access for the user equipment to the IP multimedia subsystem, and means for, in response to an end of the call, closing the at least one session.

According to an embodiment of the invention, the apparatus comprises means for deciding the target apparatus for a transfer of the call upon receiving means of the apparatus having received a handover requirement to hand over the user equipment from a first area served by the first access entity to a second area served by the second access entity, and the means for opening opens the at least one session in response to the means for deciding having decided the second apparatus for the transfer.

According to an embodiment of the invention, the apparatus comprises means for, in response to the means for opening having opened the at least one session, indicating at least one of direction of the call and state of the call. According to an embodiment of the invention, the at least one session comprises a first and a second session respectively corresponding to a first and a second application layer internet protocol, wherein the means for opening opens the first session using the first application layer internet protocol in response to the means for deciding having decided the target apparatus for transfer of the call, for transporting handover signaling, and opens the second session using the second application layer internet protocol, utilizing a session transfer number allocated by the target apparatus in the first session, for transferring the call, and the means for indicating indicates at least one of direction of the call and state of the call via the second session. According to an embodiment of the invention, the apparatus comprises means for relaying access signaling between the apparatus and the first access entity to the target apparatus via the first session. Alternatively or in addition, the apparatus comprises means for relaying handover related information on a mobility management or call control level via the second protocol. According to an embodiment of the invention, the at least one session comprises one session corresponding to a second application layer internet protocol, and the means for opening opens the session using the second application layer internet protocol in response to the means for deciding having decided the second apparatus for transfer of the call, for transporting handover signaling and for transferring the call. According to a further aspect of the invention, an apparatus of a communication network system is provided. According to an exemplary embodiment of the invention, the apparatus may comprise the target CS-GW 20 shown in Fig. 4 and/or the CS-GW B shown in Figs. 6 or 7. Alternatively or in addition, the apparatus may comprise a control unit 40 shown in Fig. 5 and/or may be configured to perform at least part of the process of Fig. 3.

The apparatus comprises means for providing access to an IP multimedia subsystem of the communication network system for user equipments accessing the communication network system via a second access entity using circuit switched radio access, and means for receiving at least one request for opening at least one session according to at least one internet protocol from an anchor apparatus of the communication network system, wherein the anchor apparatus processes a call of a user equipment which accesses the communication network system via a first access entity using circuit switched radio access, and provides access to the IP multimedia subsystem for user equipments accessing the communication network system via the first access entity. The apparatus further comprises means for, in response to the receiving means having received the at least one request, requesting a handover of the call of the user equipment to the second access entity, means for detecting completion of the handover, and means for, in response to the means for detecting having detected completion of the handover, processing the call. According to an embodiment of the invention, the request comprises a first request for opening a first session and a second request for opening a second session, which respectively correspond to a first and a second application layer internet protocol, wherein the means for requesting requests the handover of the call in response to the means for receiving having received the first request, and the apparatus comprises means for allocating a session transfer number and means for reporting the session transfer number to the anchor apparatus, wherein the means for receiving receives the second request for transferring the call, indicating at least one of direction of the call and state of the call via the second session, and the means for allocating allocates resources for the call in response to the means for receiving having received the second request and the means for reporting reports session progress to the anchor apparatus in the second session, and reports the completion of the handover to the anchor apparatus in the first session.

According to an embodiment of the invention, the at least one request comprises one request for opening a session, and the at least one session comprises the session which corresponds to a second application layer internet protocol, and the means for requesting requests the handover of the call in response to the means for receiving having received the request, the request indicating at least one of direction of the call and state of the call, the means for reporting reports session progress to the anchor apparatus, and reports the completion of the handover to the anchor apparatus. According to an embodiment of the invention, the first application layer internet protocol is the diameter protocol, and the second application layer internet protocol is the session initiation protocol. The diameter protocol may comprise at least one of the following commands for transporting handover signaling between the anchor apparatus and the target apparatus: prepare-handover request, prepare-handover answer, process-access- signalling request, forward-access-signalling request, send-end-signal request, send-end- signal answer, prepare-subsequent-handover request, and prepare-subsequent-handover answer.

The means of the above-described apparatuses may be implemented by processing means 41 and/or memory means 42 and/or interfaces 43 of control units of which one is shown in Fig. 5.

It is to be understood that the above description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.

Claims

CLAIMS:

1 . A method for use by an apparatus of a communication network system, comprising: opening at least one session according to at least one internet protocol between a first apparatus of the communication network system and a second apparatus of the communication network system, wherein the first apparatus processes a call of a user equipment which accesses the communication network system via a first access entity using circuit switched radio access, and provides access to an IP multimedia subsystem of the communication network system for user equipments accessing the communication network system via the first access entity, and in response to opening the at least one session, causing a handover of the call of the user equipment from the first access entity to a second access entity for accessing the communication network system, the second apparatus providing access to the IP multimedia system for user equipments accessing the second access entity; in response to completion of the handover, transferring the call from the first apparatus to the second apparatus for processing the call and for providing access for the user equipment to the IP multimedia subsystem; and in response to an end of the call, closing the at least one session between the first and second apparatuses.

2. The method of claim 1 , comprising: deciding the second apparatus for a transfer of the call upon receipt of a handover requirement to hand over the user equipment from a first area served by the first access entity to a second area served by the second access entity, wherein the at least one session is opened in response to deciding the second apparatus for the transfer.

3. The method of claim 1 or 2, comprising: in response to opening the at least one session, indicating at least one of direction of the call and state of the call.

4. The method of any one of claims 1 to 3, wherein the at least one session comprises a first and a second session respectively corresponding to a first and a second application layer internet protocol, and opening the at least one session comprises: opening the first session using the first application layer internet protocol in response to deciding the second apparatus for transfer of the call, for transporting handover signaling between the first apparatus and the second apparatus; allocating a session transfer number in the first session; and opening the second session using the second application layer internet protocol, utilizing the session transfer number, for transferring the call between the first apparatus and the second apparatus, and indicating at least one of direction of the call and state of the call via the second session.

5. The method of claim 4, wherein transporting handover signaling comprises relaying access signaling between the first apparatus and the first access entity to the second apparatus via the first session.

6. The method of claim 4 or 5, wherein transferring the call comprises relaying handover related information on a mobility management or call control level between the first apparatus and the second apparatus via the second protocol.

7. The method of any one of claims 1 to 3, wherein the at least one session comprises one session corresponding to a second application layer internet protocol, and opening the at least one session comprises: opening the session using the second application layer internet protocol in response to deciding the second apparatus for transfer of the call, for transporting handover signaling between the first apparatus and the second apparatus and for transferring the call between the first apparatus and the second apparatus.

8. The method of any one of claims 4 to 7, wherein the first application layer internet protocol is the diameter protocol, and/or the second application layer internet protocol is the session initiation protocol.

9. The method of claim 8, wherein the diameter protocol comprises at least one of the following commands for transporting handover signaling between the first apparatus and the second apparatus: prepare-handover request, prepare-handover answer, process- access-signalling request, forward-access-signalling request, send-end-signal request, send-end-signal answer, prepare-subsequent-handover request, and prepare- subsequent-handover answer.

10. A computer program product including a program for a processing device, comprising software code portions for performing the steps of any one of claims 1 to 9 when the program is run on the processing device.

1 1 . The computer program product according to claim 10, wherein the computer program product comprises a computer-readable medium on which the software code portions are stored.

12. The computer program product according to claim 10, wherein the program is directly loadable into an internal memory of the processing device.

13. An apparatus of a communication network system, comprising: a processor configured to process a call of a user equipment which accesses the communication network system via a first access entity using circuit switched radio access, wherein the apparatus is configured to provide access to an IP multimedia subsystem of the communication network system for user equipments accessing the communication network system via the first access entity; and a controller configured to open at least one session according to at least one internet protocol towards a target apparatus of the communication network system, and in response to opening the at least one session, cause a handover of the call of the user equipment from the first access entity to a second access entity for accessing the communication network system, the target apparatus providing access to the IP multimedia system for user equipments accessing the second access entity, wherein in response to completion of the handover, the processor is configured to transfer the call to the target apparatus for processing the call and for providing access for the user equipment to the IP multimedia subsystem, and the controller, in response to an end of the call, is configured to close the at least one session.

14. The apparatus of claim 13, wherein the controller is configured to decide the target apparatus for a transfer of the call upon receipt of a handover requirement to hand over the user equipment from a first area served by the first access entity to a second area served by the second access entity, and open the at least one session in response to deciding the second apparatus for the transfer.

15. The apparatus of claim 13 or 14, wherein in response to opening the at least one session, the controller is configured to indicate at least one of direction of the call and state of the call.

16. The apparatus of any one of claims 13 to 15, wherein the at least one session comprises a first and a second session respectively corresponding to a first and a second application layer internet protocol, wherein the controller is configured to open the first session using the first application layer internet protocol in response to deciding the target apparatus for transfer of the call, for transporting handover signaling, and open the second session using the second application layer internet protocol, utilizing a session transfer number allocated by the target apparatus in the first session, for transferring the call, and indicate at least one of direction of the call and state of the call via the second session.

17. The apparatus of claim 16, wherein the controller is configured to relay access signaling between the apparatus and the first access entity to the target apparatus via the first session, and/or relay handover related information on a mobility management or call control level via the second protocol.

18. The apparatus of any one of claims 13 to 1 5, wherein the at least one session comprises one session corresponding to a second application layer internet protocol, and the controller is configured to: open the session using the second application layer internet protocol in response to deciding the second apparatus for transfer of the call, for transporting handover signaling and for transferring the call.

19. An apparatus of a communication network system, which is configured to provide access to an IP multimedia subsystem of the communication network system for user equipments accessing the communication network system via a second access entity using circuit switched radio access, the apparatus comprising: a controller configured to receive at least one request for opening at least one session according to at least one internet protocol from an anchor apparatus of the communication network system, wherein the anchor apparatus processes a call of a user equipment which accesses the communication network system via a first access entity using circuit switched radio access, and provides access to the IP multimedia subsystem for user equipments accessing the communication network system via the first access entity, and the controller, in response to receiving the at least one request, is configured to request a handover of the call of the user equipment to the second access entity; and a processor configured to, in response to the controller detecting completion of the handover, process the call.

20. The apparatus of claim 19, wherein the request comprises a first request for opening a first session and a second request for opening a second session, which respectively correspond to a first and a second application layer internet protocol, wherein the controller is configured to request the handover of the call in response to receiving the first request, allocate a session transfer number and report the session transfer number to the anchor apparatus, and receive the second request for transferring the call, indicating at least one of direction of the call and state of the call via the second session, allocate resources for the call in response to receiving the second request and report session progress to the anchor apparatus in the second session, and report the completion of the handover to the anchor apparatus in the first session.

21 . The apparatus of claim 19, wherein the at least one request comprises one request for opening a session, and the at least one session comprises the session which corresponds to a second application layer internet protocol, and the controller is configured to: request the handover of the call in response to receiving the request, the request indicating at least one of direction of the call and state of the call, report session progress to the anchor apparatus, and report the completion of the handover to the anchor apparatus.