GB2482806A - Selection of method for performing a packet-switched to circuit-switched session transfer - Google Patents

Abstract

A network element for a mobile communication network comprising a signal processing module is arranged to: receive a packet-switched (PS) to circuit-switched (CS) transfer request for a first session corresponding to a wireless communication unit, the PS to CS transfer request comprising an indication of Dual Transfer Mode (DTM) capabilities of a target access system; receive, from a centralized service continuity network entity, an indication of the additional session transfer capabilities of the wireless communication unit; and determine whether or not to perform assisted additional session transfer handling for the wireless communication unit based at least partly on the received indication of the additional session transfer capabilities thereof. The network element is also arranged to: initiate a session transfer for the wireless communication unit, and if additional sessions are to be transferred then a timer is initialised; upon expiration of the timer a session transfer is initiated for an additional session corresponding to the wireless communication unit.

Description

Title: SELECTION OF METHOD FOR PERFORMING A PACKET-SWITCHED TO CIRCUIT-SWITCHED SESSION TRANSFER AND A NEThVORK ELEMENT THEREFOR

Description

Field of the invention

The field of this invention relates to a method for performing a packet-switched to circuit -switched session transfer and a network element adapted for implementing such a method. The invention is applicable to, but not limited to, the packet-switched to circuit-switched transfer of a session corresponding to a wireless communication unit within a mobile communication network.

Background of the Invention

In the field of mobile communications, conventional mobile communication networks typically comprise circuit-switched (CS) systems for establishing voice calls between wireless communication units (referred to as user equipment (UE5) in 3rd generation cellular communication parlance). For example, current legacy wireless communication systems that employ CS data transfer include Global System for Mobile communications (GSM) networks, often referred to as T 20 the second generation (2G) of mobile communications, or third generation (3G) networks such as a Universal Mobile Telecommunications System (UMTS) network.

More recently, packet-switched (PS) technologies for establishing calls between UEs have C\J been developed, for example based on Voice over internet protocol (IP) (V0IP), whereby voice calls may be transmitted over IP (Internet Protocol) based networks. One such PS based technology currently under development is the Evolved Packet System (EPS) that forms the basis of the architecture for the Long Term Evolution (LTE) of radio technologies currently being developed by the 3rd Generation Partnership Project (3GPP).

EPS, as has been currently specified in 3GPP TS 23.401, is a PS only system. As a result there is no CS domain and voice calls that are supported in EPS are provided through the PS domain when the underlying access technology is capable of supporting good quality voice calls.

Typically, these voice calls will be VoIP calls and the underlying call control protocol will be SIP (Session Initiation Protocol) supported through an IP Multimedia Subsystem (IMS), for example as defined in 3GPP TS 23.228.

Whilst legacy CS systems such as 2G and 3G networks provide a generally ubiquitous geographical coverage, access technologies that provide suitable characteristics required for supporting PS voice systems, such as VoIP, are initially likely to only provide discrete pockets of coverage. Furthermore, a more substantial coverage for PS voice systems, approaching that of the more ubiquitous geographical coverage provided by the CS legacy systems, is unlikely to be achieved for a long time.

As will be appreciated, when a UE establishes a voice call within a PS domain, and subsequently moves out of the coverage area for PS voice systems whilst the voice call is still active, it would be unacceptable for the voice call to have to be dropped due to a lack of PS coverage. Accordingly, there is a need for such PS voice calls to be able to be handed over to, say, a legacy CS system comprising a more ubiquitous geographical coverage when a UE moves out of the PS coverage area.

In Release 7 of the 3GPP specifications, a mechanism for handing over a voice call from a PS domain to a CS domain for dual radio technologies, called Dual Radio-Voice Call Continuity (DR-VCC), was originally defined within 3GPP TS 23.206 for Release 7 of the 3GPP specifications.

The DR-VCC mechanism, works on the basis that the PS access is provided via a non-3GPP access technology, such as a Wireless Local Area Network (WLAN). Strictly speaking, the DR-VCC mechanism does not employ a handover' of the data session, but employs a domain transfer involving two separate calls, one for each domain. However, this standard was superseded in Release 8+ of the 3GPP specifications by 3GPP TS 23.237.

In Release 8 of the 3GPP specifications, a mechanism for handing over a voice call from a PS domain to a CS domain for single radio technologies, called Single Radio-Voice Call Continuity (SR-VCC), is defined in 3GPP TS 23.216 (and 3GPP TS 23.237 for the IMS components). The SR-VCC mechanism works on the basis that the PS access is provided via a 3GPP access technology, such as an Evolved-Universal Terrestrial Radio Access Network (E-UTRAN) system.

T 20 In Release 8 of the 3GPP specifications (TS 23.237 and TS 23.2 16), three cases for PS-to-CS mobility are covered (for both SR-VCC and DR-VCC): (i) Where a UE is enhanced to support IMS Centralized Services (ICS) in order to (\J trigger the transfer of additional voice calls to the target access (sometimes referred to as ICS UE); (ii) A non-ICS UE with ICS enhanced Mobile Switching Centre Server (MSC-S), where the MSC-S is ICS enhanced and is capable of supporting unmodified UEs; (iii) A non-ICS UE with MSC-S not enhanced for ICS.

In each of the above cases for SR-VCC, the MSC-S is enhanced for SR-VCC.

An important requirement when transferring voice sessions from a PS domain to a CS domain is that, where the UE has more than one existing voice call session active, the additional voice call session(s) in the PS domain and their status (e.g. active or on hold/inactive) must also be transferred to the CS domain during the handover/transfer procedure. This is required irrespective of the UE or network capability to signal using the SIP/IMS mechanism when it moves to the target access system that provides the CS domain functionality. For example, simultaneous PS and CS connectivity may not be possible due to the characteristics of the access network (e.g. in case of handing over to a 2G system that does not support Dual Transfer Mode (DTM)).

In Release 7 of the 3GPP specifications, mid-call services support could not be provided as the solution was limited to domain transfer of only one active call between the PS domain and CS domain, because both the UE and MSC-S were not enhanced in Release 7.

In Release 8 of the 3GPP specifications, mid-call services (for example those transferring additional/on hold voice calls) can only be supported for the first of the above PS-to-CS mobility cases (ICS UE) when the UE moves to a CS system, such as a Universal Terrestrial Radio Access Network (UTRAN) or GSM/EDGE Radio Access Network (GERAN) system, that supports DIM (in the case of SR-VCC, transfer of additional voice calls to the target access only occurs after the access handover is complete). This PS-to-CS handover/transfer mechanism (hereinafter referred to as the Gm' mechanism) relies on the UE establishing a PS signalling channel towards the network using a Gm reference point (defined in 3GPP T5 23.228) between the UE and a Proxy-Call Session Control Function (P-CSCF). Accordingly, simultaneous transmissions of PS and CS signalling are required, which is inherent for UTRAN access but requires access networks that do not support simultaneous transmission of PS and CS signalling to support DIM. If the UE does not have the capability to transfer the inactive call, then, prior to transfer of the active call, the UE has to release the inactive call in the case of DR-VCC, and the SCC AS has to release the inactive call in the case of SR-VCC i.e. the inactive call is lost.

During the timeframe of Release 8 of the 3GPP specifications, a new PS-to-CS handover/transfer mechanism (hereinafter referred to as the Ii' mechanism) was discussed. The Ii mechanism provides a UE with a signalling control channel over CS access when the access network is unable to support simultaneous transmission of PS and CS signalling (e.g. where the access network does not support DIM). However, due to lack of time and little network operator T 20 support, the II' solution was abandoned in Release 8. Accordingly, even with an ICS UE, a complete solution could not be provided for mid-call services. In addition, some Network Operators were not interested in upgrading UEs on their network, and wanted solutions for mid-call services (\J that did not require an enhanced UE.

In Release 9 of the 3GPP specifications, an attempt to address the above limitations was made by introducing a new solution, where the MSC-S is enhanced to support mid-call capability (termed MSC-assisted mid-call feature) in order to cover the case that the UE is not capable of using, or unable to use, ICS UE procedures in order to perform the handover/transfer. Here, the MSC-S receives the active/inactive sessions' status from a Service Centralization and Continuity Application Server (SCC AS) during the execution of the session handover/transfer for the current active session, and decides to execute subsequent session transfers for remaining active/inactive sessions of the UE.

A problem with this solution proposed in Release 9 of the 3GPP specifications is that the UE-based mechanisms (Gm' and Ii') could also be used in Release 9 as an alternative to supporting the MSC-assisted mid-call feature for enhanced UEs when an MSC enhanced for mid-call was deployed in the network. As such, an MSC-S could only use its MSC-assisted mid-call feature when a UE was unable to use its ICS capabilities. This conditional co-existence of the MSC-assisted mid-call feature of the MSC-S and ICS capabilities of UEs introduces the need for the MSC-S to decide whether or not to initiate the MSC-assisted mid-call handling during a PS-to-CS handover/transfer.

Thus, a need exists for an improved method for performing packet-switched (PS) to circuit-switched (CS) transfer of a session corresponding to a wireless communication unit, such as a user equipment (UE) and a network element and integrated circuit therefor.

Summary of the invention

Accordingly, the invention seeks to mitigate, alleviate or eliminate one or more of the above mentioned disadvantages, singularly or in any combination. Aspects of the invention provide a network element, an integrated circuit, a method for performing packet-switched (PS) to circuit-switched (CS) transfer for a wireless communication unit, such as a user equipment (UE) and an associated computer program product, as described in the appended claims.

According to a first aspect of the invention, there is provided a network element for performing a packet-switched (PS) to circuit-switched (CS) session transfer in a mobile communication network, the network element comprises a signal processing module arranged to: receive a PS to CS session transfer request corresponding to a wireless communication unit; initiate a session transfer for the wireless communication unit, and if additional sessions are to be transferred, then; initialise a timer; and upon expiration of the timer initiate a session transfer for at least one additional session corresponding to the wireless communication unit.

According to an optional feature of the invention, the signal processing module may be T 20 further arranged to initiate the at least one additional session transfer by transmitting a session transfer initiation message to a centralized service continuity network entity.

According to an optional feature of the invention, the signal processing module may be C\J further arranged, following receipt of a response to the session transfer initiation message from the centralized service continuity network entity, to perform assisted additional session transfer handling for the at least one additional session corresponding to the wireless communication unit.

According to an optional feature of the invention, the signal processing module may be arranged to receive a session state information message in response to transmitting the session transfer initiation message and determine therefrom whether or not additional sessions corresponding to the wireless communication unit are to be transferred.

According to an optional feature of the invention, the signal processing module may be arranged to initialise a timer to comprise a duration of at least an estimated time for a wireless communication unit to initiate a transfer of additional sessions According to a second aspect of the invention, there is provided an integrated circuit for a network element for performing a packet-switched (PS) to circuit-switched (CS) session transfer in a mobile communication network. The integrated circuit comprises a signal processing module arranged to: receive a PS to CS session transfer request corresponding to a wireless communication unit; initiate a session transfer for the wireless communication unit, and if additional sessions are to be transferred, then; initialise a timer; and upon expiration of the timer initiate a session transfer for at least one additional session corresponding to the wireless communication unit.

According to a third aspect of the invention, there is provided a method for performing packet-switched (PS) to circuit-switched (CS) transfer of a session corresponding to a wireless communication unit. The method comprises: receiving a PS to CS session transfer request corresponding to the wireless communication unit; initiating a session transfer for said first session, and if additional sessions are to be transferred, then; initialising a timer; and upon expiration of the timer initiating a session transfer for at least one additional session corresponding to the wireless communication unit.

According to a fourth aspect of the invention, there is provided a computer program product having computer-readable code stored thereon for programming signal processing module for performing packet-switched (PS) to circuit-switched (CS) session transfer in a mobile communication networks. The code is operable for: receiving a PS to CS session transfer request corresponding to a wireless communication unit; initiating a session transfer for the wireless communication unit, and if additional sessions are to be transferred, then; initialising a timer; and upon expiration of the timer initiating a session transfer for at least one additional session corresponding to the wireless communication unit.

These and other aspects of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter.

Brief Description of the Drawings T 20

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity (\J and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

FIG. 1 illustrates an example of a part of a mobile communication network.

FIG. 2 illustrates an example of a simplified flowchart of a method for performing packet-switched (PS) to circuit-switched (CS) transfer of a session corresponding to a UE.

FIG. 3 illustrates an example of a signalling flow where the PS domain and the CS domain are both provided by common access technologies.

FIG. 4 illustrates an example of a signalling flow where the PS domain and the CS domain are provided by different access technologies.

FIG. 5 illustrates an example of a simplified flowchart of an alternative method for performing packet-switched (PS) to circuit-switched (CS) transfer of a session corresponding to a UE.

FIG. 6 illustrates an example of an alternative signalling flow where the PS domain and the CS domain are both provided by common access technologies.

FIG. 7 illustrates an example of an alternative signalling flow where the PS domain and the CS domain are provided by different access technologies.

FIG. 8 illustrates a typical computing system that may be employed to implement signal processing functionality in embodiments of the invention.

Detailed Description

Examples of the invention will be described in terms of a mobile communication system adapted in accordance with 3rd Generation Partnership Project (3GPP) specifications. However, it will be appreciated by a skilled artisan that the inventive concept herein described may be embodied in any type of mobile communication system in which a voice call session or the like is required to be handed over or transferred from a packet-switched (PS) domain to a circuit-switched (CS) domain. In a number of applications, the adaptation of a network element in accordance with the examples of the invention effectively enables the network element to determine whether or not to perform additional session transfer handling upon receipt of a packet-switched (PS) to circuit-switched (CS) transfer request for a session corresponding to a user equipment (UE), based on the additional session transfer capabilities of the UE. In this manner, in the case where the network element forms a part of a 3GPP network, the network element is able to decide whether or not to initiate assisted mid-call handling during a PS-to-CS handover/transfer or not in accordance with

the requirements of the 3GPP specifications.

In the context of the present invention, the term transfer', hereinafter used, is meant to encompass at least the following definitions: (i) handing over of a voice call from a PS domain to a CS domain for single radio T 20 technologies; and (ii) handing over/transferring of a voice call from a PS domain to a CS domain for dual radio technologies. (\J

Referring now to FIG. 1, there is illustrated an example of a part of a mobile communication network 100 adapted according to some embodiments of the present invention.

The mobile communication network 100 comprises a CS domain comprising a CS access system 110, which for the illustrated example comprises a 3rd Generation Partnership Project (3GPP) CS access technology such as a Universal Terrestrial Radio Access Network (UTRAN) or a GSM/EDGE Radio Access Network (GERAN). The mobile communication network 100 further comprises various core network elements to which the CS access system 110 is connected (either directly or indirectly), which for the illustrated example include, by way of example only, a Mobile Switching Centre Server (MSC-S) 120, a Serving GPRS (General Packet Radio Service) Support Node (SGSN) 130, a Mobility Management Entity (MME) 140 and a Home Subscriber Server (HSS) 150. In this manner, a mobile/wireless communication unit such as user equipment (UE) 160 is able to connect to the mobile communication network 100 via the CS access system 110, and establish voice calls and the like within the CS domain.

The mobile communication network 100 further comprises a PS domain comprising a PS access system 170, which for the illustrated example comprises a 3GPP PS access technology such as Evolved-UTRAN (E-UTRAN) 170. The PS access system 170 is also connected to the core network elements of the mobile communication network 100, as well as a serving/Public Data Network (PDN) gateway 180, thereby enabling a UE 160 to connect to the communication network via the PS access system 170, and to establish voice calls and the like within the PS domain.

For the illustrated example, the mobile communication network 100 further comprises an IP (Internet Protocol) Multimedia Subsystem (IMS), illustrated generally at 190. The IMS 190 provides an architectural framework for enabling IP multimedia services to be provided over mobile communication networks. The IMS 190 comprises a centralized service continuity network entity, which for the illustrated example is in a form of a Service Centralization and Continuity Application Server (SCC AS) 195, as defined in TS 23.292 and TS 23.237.

Although the illustrated example comprises a mobile communication network adapted in accordance with 3GPP technologies, it will be appreciated that the present invention is not limited to implementation within such a network, but may be equally applied within any mobile communication network implementing alternative technologies in which mobile communication devices may require voice calls or the like to be handed over or transferred from a packet-switched domain to a circuit-switched domain.

In accordance with some examples, a network element of the mobile communication network 100 comprises a signal processing module arranged to receive a packet-switched (PS) to circuit-switched (CS) transfer request for a session corresponding to a wireless communication unit, such as user equipment (UE), the PS to CS transfer request comprising an indication of one or more Dual Transfer Mode (DTM) capabilities of a target access system (as specified in TS T 20 43.055). The signal processing module of the network element is further arranged to receive, from a centralized service continuity network entity, an indication of additional session transfer capabilities of the UE, and to determine whether or not to perform assisted additional session (\J transfer handling for the UE based at least partly on the received indication of the additional session transfer capabilities thereof.

In this manner, the network element is able to determine whether or not to perform additional session transfer handling, for example in a form of mid-call handling procedures within a 3GPP communication network, upon receipt of a packet-switched (PS) to circuit-switched (CS) transfer request for a session corresponding to a user equipment (UE), based on the additional session transfer capabilities of the UE. Accordingly, in the case where the network element forms a part of a 3GPP network, the network element is able to decide whether or not to initiate assisted mid-call handling during a PS-to-CS handover/transfer, in accordance with the requirements of the

3GPP specifications.

For the example illustrated in FIG.1, the network element may comprise the MSC-S 120, which comprises a signal processing module 122. Since the PS domain and the CS domain within the mobile communication network 100 of FIG. 1 are both provided by common access technologies, namely 3GPP access technologies, a PS to CS transfer mechanism may be implemented similar to the mechanism for handing over a voice call from a PS domain to a CS domain for single radio technologies, called Single Radio-Voice Call Continuity (SR-VCC), defined in 3GPP TS 23.216 (and 3GPP TS 23.237 for the IMS components).

Accordingly, when a voice call session corresponding to the UE 160 requires transferring from the PS domain to the CS domain of the mobile communication network 100, a PS to CS transfer request may be received by the MSC-S 120 from either the SGSN 130 or the MME 140, by way of a transfer request message received via an Sv interface 145. The indication of the DTM capabilities of the target access system 110 may therefore be contained within an information element (IE) of the transfer request message.

Whilst for the example illustrated in FIG.1, the PS domain and the CS domain within the mobile communication network 100 are both provided by common access technologies, namely 3GPP access technologies, it is contemplated that PS access to, say, IP services, may be provided via a non-3GPP access technology (not shown), such as a Wireless Local Area Network (WLAN).

Accordingly, when a session corresponding to the UE 160 is required to be transferred from, in the case of the illustrated example, such a non-3GPP PS domain to the CS domain of the 3GPP mobile communication network 100, a different PS to CS mechanism is required to be implemented, such as one similar to the mechanism for handing over a voice call from a PS domain to a CS domain for dual radio technologies, called Dual Radio-Voice Call Continuity (DR- VCC). The DR-VCC mechanism works on the basis that the PS access is provided via a non- 3GPP access technology, such as a Wireless Local Area Network (WLAN). Strictly speaking, the DR-VCC mechanism is not a handover but a domain transfer involving two separate calls, one for each domain.

T 20 In the case of a DR-VCC type mechanism, the PS to CS transfer request may be received by the MSC-S 120 from the UE 160, as opposed to being received from the SGSN 130 or the MME 140. The indication of the DTM capabilities of the target access system may be provided within a (\J dedicated DTM capability information element within a DTAP (Direct Transfer Application Part) setup message therefor. Alternatively, the indication of the DTM capabilities of the target access system may be provided within, by way of a pre-defined value for, a non dedicated information element with a DTAP setup message, such as an STN (Session Transfer Number) information element.

For the illustrated example, the centralized service continuity network entity, from which an indication of the additional session transfer capabilities of the UE 160 are received, may comprise the SCC AS 195 located within the IMS 190. The SCC AS 195 may provide the indication of the additional session transfer capabilities of the UE to the network element within a Session Initiation Protocol (SIP) message, such as may be defined within Internet Engineering Task Force (IETF) Request For Comments (RFC) 3840. For example, the indication of the additional session transfer capabilities of the UE 160 may be provided within one or more media feature tags contained within final response of a session transfer request procedure. Alternatively, the indication of the additional session transfer capabilities of the UE 160 may be provided within one or more information elements within, say, a SIP NOTIFY message.

The additional transfer capabilities of the UE 160 received by the signal processing module 122 may comprise an indication of whether or not the UE 160 is capable of supporting the transfer of additional sessions using signalling within the CS domain. For example, the UE 160 may support a PS-to-CS handover/transfer mechanism (hereinafter referred to as the Ii' mechanism) that provides a UE with a signalling control channel over CS access, for example when the access network is unable to support simultaneous transmission of PS and CS signalling The additional transfer capabilities of the UE 160 received by the signal processing module 122 may further comprise an indication of whether or not the UE 160 is capable of supporting the transfer of additional sessions using signalling within the PS domain. For example, the UE 160 may support a PS-to-CS handover/transfer mechanism (hereinafter referred to as the Gm' mechanism) that relies on the UE 160 establishing a PS signalling channel towards the network using a Gm reference point (defined in 3GPP TS 23.228) between the UE 160 and a Proxy-Call Session Control Function (P-CSCF). Accordingly, simultaneous transmissions of PS and CS signalling are required, thus requiring the access network to support DTM.

In particular, the additional session transfer capabilities of the UE 160, as received by the signal processing module 122, may comprise an indication that the UE supports at least one from a group of: additional session transfers using signalling within the PS domain (e.g. Gm mechanism); additional session transfers using signalling within the CS domain (e.g. Ii mechanism); and additional session transfers using signalling within the PS domain and using signalling within the CS domain (e.g. Gm and Ii mechanisms).

Upon receipt of the PS to CS transfer request, the signal processing module 122 of the MSC-S 120 may be arranged to transmit a session transfer initiation message to the centralized T 20 service continuity network entity, which for the illustrated example may comprise the SCC AS 195, and to receive in response thereto an indication of the additional session transfer capabilities of the UE 160 therefrom.

C\J The additional session transfer capabilities of a UE may be communicated to the SCC AS by the UE during, for example, 3rd party registration of the UE through the usage of, say, a SIP media feature tag as defined in Annex B of 3GPP TS 24.292 and RFC3840, whereby the UE indicates with separate feature tags its additional session transfer capabilities. For example, the UE may indicate within a SIP REGISTER request message that it supports: both Gm and Ii mechanisms by including, say, a tag g.3gpp.ics'; or only the Ii mechanism by including, say, a tag g.3gpp.ics-il'; or only the Gm mechanism by including, say, a tag g.3gpp.ics'.

The SCC AS 195 may then pass this information on to the MSC-S 120 through the use of the same media feature tag in, for example, a 200 OK response (as defined in TS 24.229) to the session transfer request, or as a special XML (eXtensible Markup Language) element within a SIP NOTIFY request as an extension to the XML schema defined in RFC4235, in a case where the dialog event package is used to provide the session state information from the SCC AS 195 to the MSC-S 120.

Referring now to FIG. 2, there is illustrated an example of a simplified flowchart 200 of a method for performing packet-switched (PS) to circuit-switched (CS) transfer of a session corresponding to a UE in accordance with some embodiments of the present invention. For the illustrated example, the method is performed by signal processing module 122 of the MSC-S 120, -10-such as by way of executing computer-readable program code stored within a memory element 124 thereof.

The method starts at step 205 with a receipt of a PS to CS transfer request for an initial session corresponding to the UE 160, the PS to CS transfer request comprising an indication of DTM capabilities of the target access system. The PS to CS transfer request may be received on the Sv interface 145, for example from the SGSN 130 or the MME 140, when the PS domain and the CS domain are both provided by common access technologies such as 3GPP access technologies (for example a SR-VCC type transfer mechanism). Alternatively, the PS to CS transfer request may be received from the UE 160 when the PS domain and the CS domain are provided by different access technologies (for example a DR-VCC type mechanism).

The method then moves on to step 210, with a receipt of an indication of additional session transfer capabilities of the UE 160 from a centralized service continuity network entity, which for the illustrated example comprises the SCC AS 195, and for the illustrated example performing the PS to CS transfer for the initial session. Additional session transfer capabilities for an indication is received may comprise an indication of whether the UE 160 is capable of Gm and/or Ii support.

In this manner, it may be determined whether or not additional sessions corresponding to the UE require transferring, as shown in step 215. If it is determined that at least one additional session corresponding to the UE 160 requires transferring, to determine whether or not to perform assisted additional session transfer handling for the UE 160.

T 20 If it is determined that no additional session corresponding to the UE requires transferring, the method moves on to step 220, where no further session transfer procedures are performed.

However, if it is determined in step 215 that at least one additional session corresponding to the UE (\J 160 requires transferring, the method moves on to step 225, and the additional session transfer capabilities of the UE 160 are determined.

If it is determined that the UE 160 is capable of supporting additional session transfers within both the PS domain (for example using a Gm mechanism), the method moves on to step 230. Such a transfer of additional sessions relies on the UE 160 establishing a PS signalling channel towards the network. Accordingly, simultaneous transmissions of PS and CS signalling are required, thus requiring the target access system to support DTM. Accordingly, in step 230, it is determined whether or not the target access system is capable of DTM, based on the indication provided within the received PS to CS transfer request. If it is determined that the target access system is capable of DTM, in step 230, the UE 160 is capable of supporting additional session transfers, and accordingly the method moves on to step 235 and assisted additional session transfer handling is not required to be performed. Conversely, if it is determined that the target access system is not capable of DIM, the UE 160 is unable to support additional session transfers, and accordingly the method moves on to step 240, where it is determined whether the UE 160 and the MSC-S 120 are capable of supporting additional session transfers within the CS domain (for example using an Ii mechanism).

Referring back to step 225, if it is determined that the UE 160 is not capable of supporting additional session transfers within the PS domain (for example using a Gm mechanism), the method moves on to step 240 where it is determined whether the UE 160 and the MSC-S 120 are capable of supporting additional session transfers within the CS domain (for example using an Ii mechanism).

If it is determined that the UE 160 and the MSC-S 120 are capable of supporting additional session transfers within the CS domain (for example using the Ii mechanism), in step 240, the UE is capable of supporting additional session transfers, and accordingly the method moves on to step 245 and assisted additional session transfer handling is not required to be performed.

Conversely, if it is determined that the UE 160 and/or the MSC-S 120 is/are not capable of supporting additional session transfers within the CS domain (for example using the Ii mechanism), in step 240, the UE 160 is not able to support additional session transfers, and accordingly the method moves on to step 250 and the MSC-S 120 performs assisted additional session transfer handling for the UE 160.

Referring now to FIG. 3, there is illustrated an example of a signalling flow 300 where the PS domain and the CS domain are both provided by common access technologies, such as 3GPP access technologies. The signalling flow 300 for the illustrated example is based on the signalling flow for the SR-VCC session transfer mechanism as defined in 3GPP TS 23.216. Accordingly, only those aspects of the signalling flow relevant to implementing the inventive concept will be described herein.

T 20 A Voice over IP (VoIP) session, illustrated at 305, is active between UE 160 and a remote UE 310 via the PS access system 170 (illustrated by way of an eNodeB in FIG. 3) of a mobile/wireless communication network. The PS access system 170 decides, at 315, that a hand (\J over from the PS access system 170 is required based on measurement reports 320 received from the UE 160. In response thereto, the PS access system 170 sends a relocation request message 325 to the MME 140, which in turn sends a PS to CS transfer request 330 for the active session 305 to the MSC-S 120 comprising an indication of the DTM capabilities of a target access system, which for the illustrated example comprises CS access system 110 (illustrated as target BSS in FIG. 3). Upon receipt of the PS to CS transfer request (and following a handover request/acknowledgement procedure), the MSC-S 120 transmits a session transfer initiation message 335 to the SCC AS 195, which initiates the transfer at 340 of the active session 305. The SCC AS 195 subsequently transmits a session state information message 345 back to the MSC-S comprising an indication of the additional session transfer capabilities of the UE 160. The MSC-S 120 then determines, at 350, whether or not to perform assisted additional session transfer handling for the UE 160, based at least partly on the received indication of the additional session transfer capabilities of the UE 160, for example as illustrated in FIG. 2. If it is determined that the MSC-S 120 should perform assisted additional session transfer handling for the UE 160, the MSC- 120 then transfers additional sessions corresponding to the UE 160 at 355, for example using MSC-S assisted mid-call procedures defined in 3GPP TS 23.216 (and 3GPP TS 23.237 for the IMS components). -12-

Referring now to FIG. 4, there is illustrated an example of a signalling flow 400 where the PS domain and the CS domain are provided by different access technologies. The signalling flow 400 for the illustrated example is based on the signalling flow for the DR-VCC session transfer mechanism, as defined in 3GPP TS 23.237. Accordingly, only those aspects of the signalling flow relevant to implementing the inventive concept will be described herein. A Voice over IP (V0IP) session, illustrated at 405, is active between UE 160 and a remote UE 410 via a PS access system (not shown) located outside of the wireless communication network 100. The UE establishes a connection 420 with the CS access system, for example CS access system 110 of the wireless communication network 100 of FIG. 1, and sends a PS to CS transfer request 430 for the active session 405 to the MSC-S 120, where the transfer request 430 comprises an indication of the DTM capabilities of a target access system, for example CS access system 110. Upon receipt of the PS to CS transfer request, the MSC-S 120 transmits a session transfer initiation message 435 to the SCC AS 195, which initiates the transfer 440 of the active VOIP session 405. The SCC AS 195 subsequently transmits a session state information message 445 back to the MSC-S 120 comprising an indication of the additional session transfer capabilities of the UE 160. The MSC-S then determines, at 450, whether or not to perform assisted additional session transfer handling for the UE 160 based at least partly on the received indication of the additional session transfer capabilities of the UE 160, for example as illustrated in FIG. 2. If it is determined that the MSC-S 120 should perform assisted additional session transfer handling for the UE 160, the MSC-T 20 S 120 then transfers additional sessions corresponding to the UE 160 at 455, for example using MSC-S assisted mid-call procedures defined in 3GPP TS 23.237.

C\J Referring back to FIG. 1, and in accordance with alternative examples, the network element of the mobile communication network 100 comprises a signal processing module that is arranged to receive a PS to CS transfer request for a first session corresponding to UE 160, initiate a session transfer for said first session, initialise a timer, and, upon expiration of the timer, initiate a session transfer for at least one additional session corresponding to the UE 160. In this manner, by waiting for the expiration of the timer, the network element is allowing the UE 160 to initiate the transfer of additional sessions itself before the network element attempts to initiate the transfer of additional sessions. Accordingly, if the UE 160 is capable of supporting the transfer of additional sessions, when the network element attempts to initiate the transfer of additional sessions, such an initiation will be rejected. As a result, the network element is able to determine that it is not required to perform assisted additional session transfer handling for the UE 160. Conversely, if the UE 160 is not capable of supporting the transfer of additional sessions, when the network element attempts to initiate the transfer of additional sessions, such an initiation will not be rejected. As a result, the network element is able to determine that it is required to perform assisted additional session transfer handling for the UE 160.

For the illustrated example, the network element may comprise the MSC-S 120, and the signal processing module 122 of the MSC-S 120 may be arranged to initiate a session transfer by -13-transmitting a session transfer initiation message to a centralized service continuity network entity, for example the 5CC AS 195 within the IMS 190.

Upon receipt of a session transfer initiation message corresponding to one or more additional sessions from the MSC-S 120, the SCC AS 195 may be arranged to determine whether or not a session transfer has already been initiated for the, or each, additional session. If a session transfer has not already been initiated for the, or each, additional session, the SCC AS 195 may then respond to the session transfer initiation message received from the MSC-S 120 by transferring the one or more additional sessions to the MSC-S 120. Accordingly, upon the one or more additional sessions being transferred to the MSC-S 120, the signal processing module 122 may then perform assisted additional transfer handling for the one or more additional sessions on behalf of the UE 160. Conversely, the SCC AS 195 may determine that a session transfer has already been initiated, for example by the UE 160 itself, and in this scenario the SCC AS 195 sends a session transfer initiation reject message back to the MSC-S 120. Accordingly, upon receipt of the session transfer initiation reject message, the signal processing module 122 does not perform assisted additional transfer handling on behalf of the UE 160.

It is contemplated that the signal processing module 122 is arranged to initialise the timer to comprise a duration of at least an estimated period of time that would allow the UE to initiate a transfer of additional sessions. Such a duration may be configurable by a Network Operator.

The signal processing module 122 of the MSC-S 120 may be arranged to receive a T 20 session state information message for the UE from the SCC AS 195, in response to a session transfer initiation message for the first session, and to determine whether one or more additional sessions corresponding to the UE require transferring. If it is determined that at least one (\J additional session corresponding to the UE requires transferring, the signal processing module 122 may then initialise the timer and, upon expiration of the timer, initiate a session transfer for the at least one additional session corresponding to the UE.

Since the PS domain and the CS domain within the mobile communication network 100 of FIG. 1 are both provided by common access technologies, namely 3GPP access technologies, a PS to CS transfer mechanism may be implemented similar to the SR-VCC mechanism for handing over a voice call from a PS domain to a CS domain for single radio technologies, defined in 3GPP TS 23.216 (and 3GPP TS 23.237 for the IMS components).

Accordingly, when a voice call session corresponding to the UE 160 requires transferring from the PS domain to the CS domain of the mobile communication network 100, a PS to CS transfer request may be received by the MSC-S 120 from either the SGSN 130 or the MME 140, for example by way of a transfer request message received via an Sv interface 145.

Whilst for the example illustrated in FIG.1, the PS domain and the CS domain within the mobile communication network 100 are both provided by common access technologies, namely 3GPP access technologies, in other examples the PS access to, say, IP services, may be provided via a non-3GPP access technology (not shown), such as a Wireless Local Area Network (WLAN).

Accordingly, when a session corresponding to the UE 160 is required to be transferred from, in the case of the illustrated example, such a non-3GPP PS domain to the CS domain of the 3GPP -14-mobile communication network 100, a different PS to CS mechanism is required to be implemented, such as one similar to the mechanism for handing over a voice call from a PS domain to a CS domain for dual radio technologies, called Dual Radio-Voice Call Continuity (DR-VCC). In the case of a DR-VCC type mechanism, the PS to CS transfer request may be received by the MSC-S 120 from the UE 160, as opposed to being received from the SGSN 130 or the MME 140.

Referring now to FIG. 5, there is illustrated an example of a simplified flowchart 500 of a method for performing packet-switched (PS) to circuit-switched (CS) transfer of a session corresponding to a UE in accordance with some embodiments of the invention. For the illustrated example, the method may be performed by signal processing module 122 of the MSC-S 120 of FIG. 1, such as by way of executing computer-readable program code stored within a memory element 124 thereof.

The method starts at step 510 with a receipt of a PS to CS transfer request for an initial session corresponding to the UE 160. The PS to CS transfer request may be received on the Sv interface 145 of FIG. 1, for example from the SGSN 130 or the MME 140, when the PS domain and the CS domain are both provided by common access technologies such as 3GPP access technologies (for example a SR-VCC type transfer mechanism). Alternatively, the PS to CS transfer request may be received from the UE 160 when the PS domain and the CS domain are T 20 provided by different access technologies (for example a DR-VCC type mechanism).

The method then moves on to step 520, with the initiation of an initial session transfer, and the receipt of a session status information message comprising an indication of a status of the (\J initial session for the UE 160, as well as the status of any additional sessions corresponding to the UE. In this manner, it may be determined, in step 530, whether or not additional sessions corresponding to the UE 160 require transferring, and if it is determined that at least one additional session corresponding to the UE 160 requires transferring, to determine whether or not to perform assisted additional session transfer handling for the UE 160.

If it is determined that no additional session corresponding to the UE require transferring, in step 530, the method moves on to step 540, where no further session transfer procedures are performed. However, if it is determined in step 530 that at least one additional session corresponding to the UE requires transferring, the method moves on to step 550, where the MSC-S initialises a timer 550. Upon expiration of the timer, a session transfer is initiated for the at least one additional session, at step 560. Next, at step 570, it is determined whether or not the session transfer initiation for the at least one additional session was successful, for example based on whether or not the session transfer initiation for the at least one additional session was rejected, or the at least one additional session was transferred to the MSC-S. If the session transfer initiation for the at least one additional session was not successful, the method moves to step 580, and the MSC-S does not perform assisted additional session transfer handling. In this case, the UE uses ICS capabilities. Conversely, if the session transfer initiation for the at least one additional session was successful, the method moves to step 590, and the MSC-S does perform assisted additional session transfer handling.

Referring now to FIG. 6, there is illustrated an example of a signalling flow 600 where the PS domain and the CS domain are both provided by common access technologies, such as 3GPP access technologies. The signalling flow 600 for the illustrated example is based on the signalling flow for the SR-VCC session transfer mechanism as defined in 3GPP TS 23.216. Accordingly, only those aspects of the signalling flow relevant to implementing the inventive concept will be described herein.

A Voice over IF (V0IP) session, illustrated at 605, is active between UE 160 and a remote UE 610 via the PS access system 170 (illustrated by way of an eNodeB in FIG. 6) of a mobile/wireless communication network 100. The PS access system 170 decides, at 615, that a hand over from the PS access system 170 is required based on measurement reports 620 received from the UE 160. In response thereto, the PS access system 170 sends a relocation request message 625 to the MME 140, which in turn sends a PS to CS transfer request 630 for the active session 605 to the MSC-S 120. Upon receipt of the PS to CS transfer request (and following a handover request/acknowledgement procedure), the MSC-S 120 transmits a session transfer initiation message 635 to the SCC AS 195, which initiates the transfer, at 640, of the active session 605. The SCC AS 195 subsequently transmits a session state information message 645 back to T 20 the MSC-S 120 comprising an indication of the additional session transfer capabilities of the UE 160. The MSC-S 120 then determines, at 650, whether or not to additional sessions require transferring based on the content of session state information message 645. If it is determined that (\J additional sessions do require transferring, the MSC-S 120 initiates a timer 655, and at the expiration of the timer 655, the MSC-S 120 sends a request to the SCC AS 195 for transferring the additional sessions at 660. At 665, upon receipt of the request 660 by the SCC AS 195, if additional sessions corresponding to the UE 160 exist that have not already been transferred (for example to the UE 160 as initiated by itself), the SCC AS 195 transfers the additional sessions to the MSC-S 120, which is then able to perform assisted additional session transfer handling for the UE 160, for example using MSC-S assisted mid-call procedures defined in 3GPP TS 23.216 (and 3GPP TS 23.237 for the IMS components). Alternatively, if no additional sessions corresponding to the UE 160 exist that have not already been transferred, the SCC AS 195 rejects the request 660.

Referring now to FIG. 7, there is illustrated an example of a signalling flow 700 where the PS domain and the CS domain are provided by different access technologies. The signalling flow 700 for the illustrated example is based on the signalling flow for the DR-VCC session transfer mechanism, as defined in 3GPP TS 23.237. Accordingly, only those aspects of the signalling flow relevant to implementing the inventive concept will be described herein. A Voice over IF (V0IP) session, illustrated at 705, is active between UE 160 and a remote UE 710 via a PS access system (not shown) located outside of the wireless communication network 100. The UE establishes a connection 720 with the CS access system, for example CS access system 110 of the wireless communication network 100 of FIG. 1, and sends a PS to CS transfer request 730 for the active session 705 to the MSC-S 120. Upon receipt of the PS to CS transfer request, the MSC-S 120 transmits a session transfer initiation message 735 to the SCC AS 195, which initiates the transfer 740 of the active session 705. The SCC AS 195 subsequently transmits a session state information message 745 back to the MSC-S 120. The MSC-S 120 then determines, at 750, whether or not to additional sessions require transferring, based on the content of session state information message 745. If it is determined that additional sessions do require transferring, the MSC-S 120 initiates a timer 755, and at the expiration of the timer 755, the MSC-S 120 sends a request to the SCC AS 195 for transferring the additional sessions, at step 760. At step 765, upon receipt of the request 760 by the SCC AS 195, if it is determined that additional sessions corresponding to the UE 160 exist and have not already been transferred (for example to the UE by initiating the transfer itself), the SCC AS 195 transfers the additional sessions to the MSC-S 120. The MSC-S 120 is then able to perform assisted additional session transfer handling for the UE 160, for example using MSC-S assisted mid-call procedures defined in 3GPP TS 23.237.

Alternatively, if no additional sessions corresponding to the UE 160 exist that have not already been transferred, the SCC AS 195 rejects the request, in step 760.

Whilst examples of the aforementioned two solutions have been hereinbefore described T 20 separately, the two solutions are not considered to be mutually exclusive. For example, it is contemplated that a network element may be arranged to implement the first solution, illustrated in FIG's 2 to 4 and described with reference thereto, for performing PS to CS transfers when the PS (\J domain and the CS domain are both provided by common access technologies such as 3GPP access technologies (SR-VCC type transfer mechanism), since this solution does not impose any additional impact to the UE in executing the SR-VCC transfer procedures. Conversely, the network element may be arranged to implement the second solution, illustrated in FIG's 5 to 7 and described with reference thereto, for performing PS to CS transfers when the PS domain and the CS domain are provided by different access technologies (DR-VCC type mechanism), since this solution does not impact the UE generally in this scenario.

Advantageously, embodiments of the present invention provide a mechanism for resolving the problem of the conditional co-existence of the MSC-assisted mid-call feature of the MSC-S and ICS capabilities of UEs introducing the need for the MSC-S to decide whether or not to initiate the MSC-assisted mid-call handling during a PS-to-CS handover/transfer.

Although some aspects of the invention have been described with reference to their applicability to a 3GPP cellular communication system and in particular to a Universal Terrestrial Radio Access Network (UTRAN) of a 3rd generation partnership project (3GPP) system, it will be appreciated that the examples are not limited to this particular cellular communication system. It is envisaged that the example described above may be applied to any other cellular communication system in which a voice call session, or the like, is required to be handed over or transferred from a packet-switched (PS) domain to a circuit-switched (CS) domain. -17-

Referring now to FIG. 8, there is illustrated a typical computing system 800 that may be employed to implement signal processing functionality in embodiments of the invention.

Computing systems of this type may be used in network elements and wireless communication units. Those skilled in the relevant art will also recognize how to implement the invention using other computer systems or architectures. Computing system 800 may represent, for example, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment. Computing system 800 can include one or more processors, such as a processor 804. Processor 804 can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module. In this example, processor 804 is connected to a bus 802 or other communications medium.

Computing system 800 can also include a main memory 808, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by processor 804. Main memory 808 also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor 804.

Computing system 800 may likewise include a read only memory (ROM) or other static storage device coupled to bus 802 for storing static information and instructions for processor 804.

T 20 The computing system 800 may also include information storage system 810, which may include, for example, a media drive 812 and a removable storage interface 820. The media drive 812 may include a drive or other mechanism to support fixed or removable storage media, (\J such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media 818 may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive 812. As these examples illustrate, the storage media 818 may include a computer-readable storage medium having particular computer software or data stored therein.

In alternative embodiments, information storage system 810 may include other similar components for allowing computer programs or other instructions or data to be loaded into computing system 800. Such components may include, for example, a removable storage unit 822 and an interface 820, such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units 822 and interfaces 820 that allow software and data to be transferred from the removable storage unit 818 to computing system 800.

Computing system 800 can also include a communications interface 824.

Communications interface 824 can be used to allow software and data to be transferred between computing system 800 and external devices. Examples of communications interface 824 can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via communications interface 824 are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by communications interface 824. These signals are provided to communications interface 824 via a channel 828. This channel 828 may carry signals and may be implemented using a wireless medium, wire or cable, fiber optics, or other communications medium. Some examples of a channel include a phone line, a cellular phone link, an RF link, a network interface, a local or wide area network, and other communications channels.

In this document, the terms computer program product' computer-readable medium' and the like may be used generally to refer to media such as, for example, memory 808, storage device 818, or storage unit 822. These and other forms of computer-readable media may store one or more instructions for use by processor 804, to cause the processor to perform specified operations. Such instructions, generally referred to as computer program code' (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system 800 to perform functions of embodiments of the present invention. Note that the code may directly cause the processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system 800 using, for T 20 example, removable storage drive 822, drive 812 or communications interface 824. The control module (in this example, software instructions or computer program code), when executed by the processor 804, causes the processor 804 to perform the functions of the invention as described (\J herein.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices. Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term comprising' does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual -19-features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to a', an', first', second', etc. do not preclude a plurality.

Thus, an improved method for performing packet-switched (PS) to circuit-switched (CS) transfer of a session corresponding to a wireless communication unit, such as a UE, and a network element adapted for implementing such a method, have been described, wherein the aforementioned disadvantages with prior art arrangements have been substantially alleviated. (\J

Claims (11)

1. -20 -Claims 1. A network element for performing a packet-switched (PS) to circuit-switched (CS) session transfer in a mobile communication network, wherein the network element comprises a signal processing module arranged to: receive a PS to CS session transfer request corresponding to a wireless communication unit; initiate a session transfer for the wireless communication unit, and if additional sessions are to be transferred then; initialise a timer; and upon expiration of the timer initiate a session transfer for at least one additional session corresponding to the wireless communication unit.
2. 2. The network element of Claim 1 wherein the signal processing module is further arranged to initiate the at least one additional session transfer by transmitting a session transfer initiation message to a centralized service continuity network entity.
3. 3. The network element of Claim 2 wherein the signal processing module is further arranged, following receipt of a response to the session transfer initiation message from the centralized y-20 service continuity network entity, to perform assisted additional session transfer handling for the at least one additional session corresponding to the wireless communication unit.
4. 4. The network element of Claim 2 or Claim 3 wherein the signal processing module is arranged to receive a session state information message in response to transmitting the session transfer initiation message and determine therefrom whether or not additional sessions corresponding to the wireless communication unit are to be transferred.
5. 5. The network element of any preceding Claim wherein the signal processing module is arranged to initialise a timer to comprise a duration of at least an estimated time for a wireless communication unit to initiate a transfer of additional sessions.
6. 6. The network element of any preceding Claim wherein the network element comprises a mobile switching centre server (MSC-S).
7. 7. The network element of any preceding Claim wherein the PS to CS transfer request is received from one of: a mobility management entity (MME); a serving GPRS (General Packet Radio Service) support node (SGSN); the wireless communication unit to which the session to be transferred relates.

   -21 -
8. 8. An integrated circuit for a network element for performing a packet-switched (PS) to circuit-switched (CS) session transfer in a mobile communication network, wherein the integrated circuit comprises a signal processing module arranged to: receive a PS to CS session transfer request corresponding to a wireless communication unit; initiate a session transfer for the wireless communication unit; and if additional sessions are to be transferred then; initialise a timer; and upon expiration of the timer initiate a session transfer for at least one additional session corresponding to the wireless communication unit.
9. 9. A method for performing packet-switched (PS) to circuit-switched (CS) session transfer in a mobile communication, the method comprising, at a network element: receiving a PS to CS session transfer request corresponding to a wireless communication unit; initiating a session transfer for the wireless communication unit; and if additional sessions are to be transferred then; initialising a timer; and upon expiration of the timer initiating a session transfer for at least one additional session T 20 corresponding to the wireless communication unit.
10. 10. A computer program product having computer-readable code stored thereon for programming signal processing module for performing packet-switched (PS) to circuit-switched (CS) session transfer in a mobile communication networks, the code operable for: receiving a PS to CS session transfer request corresponding to a wireless communication unit; initiating a session transfer for the wireless communication unit; and if additional sessions are to be transferred then; initialising a timer; and upon expiration of the timer initiating a session transfer for at least one additional session corresponding to the wireless communication unit.
11. 11. The computer-readable storage element of Claim 10, wherein the computer readable storage medium comprises at least one of a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), a EPROM (Erasable Programmable Read Only Memory), a EEPROM (Electrically Erasable Programmable Read Only Memory) and a Flash memory.