WO2010051873A1

WO2010051873A1 - Technique for controlling a mobile communication network supporting circuit-switched fallback functionality

Info

Publication number: WO2010051873A1
Application number: PCT/EP2009/006297
Authority: WO
Inventors: Peter Hedman; Magnus HALLENSTÅL; Magnus Olsson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2008-11-10
Filing date: 2009-08-31
Publication date: 2010-05-14

Abstract

A technique for controlling a mobile communication network supporting Circuit- Switched Fallback (CSFB) is provided. The technique makes the SGSN in the network aware of whether a user terminal (UE) of the network supports CSFB. It is thus possible for the SGSN to activate ISR or to keep ISR activated for the UE even if the UE does not support CSFB. A specific implementation extends the Mobile Station / UE Network Capability information element by including therein an indication indicating whether the UE supports CSFB. Another implementation extends the Mobility Man- agement and Evolved Packet System Bearer Context in the same manner. In a third implementation, an MME determines whether to indicate to an SGSN whether ISR is to be kept activated for a UE. The technique disclosed enables Idle mode Signalling Reduction to be activated even for UEs not supporting CSFB, thus effectively limiting the signalling caused by them.

Description

Technique for controlling a mobile communication network supporting Circuit-Switched Fallback functionality

Technical Field

The present invention relates to mobile communication and in particular to methods and devices for controlling a mobile communication network which supports Circuit- Switched Fallback (CSFB) functionality.

Background

The Idle state Signalling Reduction (ISR) function, or Idle mode Signalling Reduction function, has been proposed by the 3rd Generation Partnership Project (3GPP) standardization body as a mobile communication mechanism for limiting signalling during inter-radio access technology (RAT) procedures. Particularly, it serves to limit the signalling caused by user terminals during inter-RAT cell-reselection in their idle mode. ISR is briefly described in 3GPP ^'s Technical Specification TS 23.401 entitled "General Packet Radio Service (GPRS) enhancement for an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access" release 8.

According to a Change Request (3GPP CR0640revl, located in tdoc S2-087157) entitled "Update of ISR annex" made the above technical specification, ISR aims at reducing the frequency of Tracking Area Update (TAU) and Routing Area Update (RAU) procedures caused by user terminals reselecting between E-UTRAN and GSM GPRS/EDGE Radio Access (GERAN) / UMTS Terrestrial Radio Access (UTRAN) networks. Particularly, the update signalling between user terminals and the networks is reduced, although network internal signalling is reduced as well.

ISR requires special functionality in both the user terminal and the network to acti- vate ISR for a user terminal. The network can decide for ISR activation individually for each user terminal. Network entities which can be configured to incorporate this decision-making capability include Serving GPRS Support Node (SGSN), Mobility Management Entity (MME), Signalling Gateway (SGW), Home Subscriber Server (HSS), etc. More information on ISR can be found in 3GPP TS 23.401 Version 8.3.0, released in September 2008 and 3GPP CR0640revl made in October 2008.

The CSFB functionality in Evolved Packet Systems (EPS) enables the provisioning of 5 voice and other circuit-switched (CS) domain services (e.g. CS UDI video/ SMS/ LCS/ USSD) by reuse of CS infrastructure when the user terminal is served by an E-UTRAN network. A CSFB enabled user terminal connected to E-UTRAN may use GERAN or UTRAN to establish one or more CS-domain services. This function is only available in case E-UTRAN coverage is overlapped by either GERAN coverage or UTRAN cover-o age. The architecture and specification for the CSFB for EPS are defined in 3GPP TS 23.272 entitled "Circuit-Switched Fallback in Evolved Packet System" Stage 2, Version 8.1.0, released in September 2008.

The practice of applying ISR for a CSFB enabled system is described in "Clarifications of ISR usage for CSFB", a 3GPP Change Request CR0049rev 4 (located in tdoc S2- 087348) made to 3GPP TS 23.272. This practice however removes for all user terminals the possibility to keep ISR activated, i.e. even for user terminals not supporting CSFB. o Summary

It is desired to provide a feasible solution so that in a CSFB enabled mobile communication system ISR can be activated or maintained activated for user terminals not supporting CSFB. 5

The basic solution is to make the SGSN in a CSFB enabled network aware whether the user terminal concerned is supporting CSFB. This knowledge makes it possible for the SGSN to keep ISR activated for user terminals not supporting CSFB (while deactivating ISR for CSFB capable user terminals). 0

To realize the solution, a first method for controlling a mobile communication network supporting CSFB is provided. The method is performed by the mobile communi^¬ cation network and comprises the steps of receiving a message comprising an information element indicating whether a user terminal of the network supports CSFB5 functionality, and determining, by a SGSN of the network and based on the received message, whether or not the user terminal supports CSFB. In the context of the present disclosure, the expression "a user terminal of the network" means that the user terminal has a valid registration with the network or is served by the network. Depending on the result of the determination, the SGSN may decide about a change of the activation state of ISR for the user terminal. Particularly, if it is determined that the user terminal does not support CSFB, the SGSN decides to activate the ISR for the user terminal or, in case that the ISR has already been activated, keep the activation status for the user terminal. To do so, the SGSN in one implementation transmits a message to the user terminal to control the latter to either activate ISR or to keep the activation status of ISR. In other words, with this message, the SGSN "informs" the user terminal to use or to continue using the ISR. In view of its function, this message may be termed as an activation message. From another perspective, since the message is sent from the core network to the user terminal as a response to the user terminal's request (e.g. Attach request, RAU request, combined RAU/LAU request etc.), the message can be considered as a respective response/accept message (e.g. Attach accept, RAU accept, combined RAU/LAU accept, etc.)

Further, if it is determined that the user terminal supports CSFB, the SGSN may de- cide to deactivate ISR for the user terminal.

To realize the solution, a second method for controlling a mobile communication network supporting CSFB is provided. The method comprises the step of transmitting a message to the network wherein the message comprises an information element indicating whether a user terminal of the network supports CSFB. The message is transmitted by a network component. In principle, the network component may be any kind of technical means involved in realizing the mobile communication provided by the network, as long as the network component is able to output a message comprising the information element mentioned above. The network component may reside in any subsystem of the mobile communication network, such as in the core network subsystem; an example of such a network component is an MME. Alternatively, the network component may also reside outside of the core network. For in^¬ stance, the network component can be a user terminal of the network.

Regardless of the specifics of the network component providing the message, the information element comprised in the message is destined at an SGSN of the net- work. In such a case, the information element is to be at least partially processed by the SGSN.

For both the first and second methods outlined above, the information element may be a Mobile Station (MS) Network Capability information element or a User Terminal (UE) Network Capability information element used in GPRS as defined in 3GPP TS24.008 Version 8.3.0. The message that comprises such information element can be any of the following: an Attach request, a RAU request, or the like; a user terminal is usually capable of generating such requests. Alternatively, the information element may be comprised in a Mobility Management and Evolved Packet System Barrier Context; an MME is capable of generating messages comprising this context. The MME transfers the message comprising the above Context to the SGSN. The transferring can be carried out over the S3 reference point during Serving Radio Network Subsystem (SRNS) relocation procedures.

According to a hardware aspect, a network component such as an SGSN configured for use in a mobile communication network that supports CSFB is provided. The SGSN is adapted to determine whether or not a user terminal of a network supports CSFB. The SGSN performs this determination based on a message received by the network, wherein the message comprises an information element indicating whether the CSFB functionality is supported by the user terminal.

The SGSN may be further adapted to decide about the change of the activation state of ISR for the user terminal. Particularly, if it is determined that the user terminal does not support CSFB, the SGSN activates or keeps activated the ISR for the user terminal. To do so, the SGSN transmits an activation message to the user terminal to control the latter to either activate ISR or to keep the activation status of ISR. Conversely, if it is determined that the user terminal supports CSFB, the SGSN works to deactivate the ISR for the user terminal.

According to another hardware aspect, a network component configured to control a mobile communication network supporting CSFB is provided. The network component comprises a transmission unit for transmitting a message to the network wherein the message comprises an information element indicating whether the CSFB functionality is supported by a user terminal of the network. By "transmitting a message to the network", it is meant that the message is intended for a certain technical means residing within the network, such as but not limited to within the core net- work subsystem of the network. The transmitting network component, however, can be an entity residing either outside of or within the core network. .Examples of the network component are the user terminal (itself) or an MME of the network.

The solution can also be realized by the methods and devices defined below:

A third method is provided for controlling a mobile communication network which supports CSFB functionality. The mobile communication network comprises an MME and an SGSN. The method is mainly performed by the MME and comprises a deter- mination step and a transmission step: The MME determines whether or not to include an information element in a message to be transmitted to the SGSN, the information element indicating whether ISR is to be kept activated for a user terminal; the user terminal may be registered in the MME. Thereafter, the MME transmits the message to the SGSN.

A fourth method is provided for controlling a mobile communication network which supports CSFB. The mobile communication network comprises an MME and an SGSN. The method is mainly performed by the SGSN and comprises a reception step and a determination step: The SGSN receives a message which comprises an information element which indicates whether ISR is to be kept activated for a user terminal; the user terminal may be registered in the MME. Based on this information element, the SGSN determines whether or not to activate or keep activated the ISR for the user terminal.

The fourth method may comprise a further step: Based on the result of the determination, the SGSN transmits an activation message to the user terminal to control the latter to activate or keep activated the ISR function. The activation message may be any of an Attach accept, an RAU accept, a combined RAU/LAU accept, etc.

An MME configured for use in a mobile communication network supporting CSFB is provided also. The MME primarily comprises a logic unit for determining whether or not to include an information element in a message wherein the message is to be transmitted to an SGSN. The information element indicates whether ISR is to be kept activated for a user terminal; the user terminal may be registered in the MME. The MME further comprises a transmission unit for transmitting the message to the SGSN. An SGSN for use in a mobile communication network supporting CSFB is also provided. The mobile communication network comprises the SGSN and an MME. The SGSN comprises a receiving unit for receiving a message which comprises an information element indicating whether ISR is to be kept activated for a user terminal; the user terminal may be registered in the MME. The SGSN further comprises a logic unit for determining, based on the information element, whether or not to activate or keep activated the ISR for the user terminal.

Based on the result of the determination, the SGSN may further transmit an activa- tion message to the user terminal so as to control the latter to activate or keep activated the ISR function. The activation message may be any of an Attach accept, an RAU accept, a combined RAU/LAU accept, etc. The SGSN may support the S3 reference point including other capabilities required for ISR to be activated. Such capabilities include paging forward.

Still further, the solution is achieved by a computer program product comprising program code portions for performing the steps of the above-mentioned methods when the computer program product is run on a computing device. The computing device may be a user terminal, an SGSN, or an MME, but it is not limited to these three entities. The computer program product may be stored on a computer readable recording medium.

Brief Description of the Drawings

In the following, the invention is further described with reference to the exemplary embodiments illustrated in the figures, in which:

Fig. 1 is a block diagram illustrating an overview of a mobile communication network supporting CSFB;

Fig. 2 is a block diagram illustrating a system embodiment for controlling the mobile communication network of Fig. 1;

Fig. 3 is a block diagram illustrating another system embodiment for control- ling the mobile communication network of Fig. 1;

Fig. 4 is a flow chart illustrating a method embodiment; Rg. 5 is a flow chart illustrating another method embodiment;

Rg. 6 shows an embodiment of an information element;

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Rg. 7 is a block diagram illustrating a further system embodiment for controlling the mobile communication network of Rg. 1;

Rg. 8 is a block diagram illustrating an exemplary transfer of another informa-o tion element within the system embodiment of Rg. 7;

Rg. 9 is a flow chart illustrating yet another method embodiment; and

Rg. 10 is a flow chart illustrating a further method embodiment. 5

Detailed Description

In the following, for purposes of explanation and not limitation, specific details are set forth in order to provide a thorough understanding of the present invention. Ito will be apparent to those skilled in the art that the invention may be practiced in embodiments that depart from these specific details. For instance, although the exemplary embodiments are described in connection with the specific network layout of Rg. 1, it can be easily appreciated by those skilled in the art that the invention is also applicable to network layouts of other types. 5

Those skilled in the art will further appreciate that the functions explained herein below may be implemented using hardware circuitry, software means, or a combination thereof. The software means may be in conjunction with a programmed microprocessor or a general purpose computer, using an Application Specific Integratedo Circuit (ASIC) and/or Digital Signal Processors (DSPs). It will also be appreciated that when the present invention is described as a method, it may also be embodied in a computer processor and a memory coupled to the processor, wherein the memory is encoded with one or more programs that perform the method when executed by the processor. 5

As a system overview, Fig. 1 depicts a mobile communication network supporting CSFB. The network components relevant to the embodiments include a user terminal (UE), an SGSN, and an MME. The SGSN and the MME form parts of the core network subsystem and they can communicate with each other over the S3 reference point. Of course, the core network subsystem may comprise further network components, such as the MSC server shown in Fig. 1. The SGSN and the MME communicate with the MSC server over the Gs and SGs interfaces, respectively. Also shown in Fig. 1 is an exemplary radio access network subsystem through which the UE communicates with the core network subsystem. The radio access network subsystem comprises a number of different RATs: UTRAN, GERAN, and E-UTRAN. Of course, other types of RATs can be used as well. The UE communicates with the RATs over respective in- terfaces. As indicated in Fig. 1, the interfaces between the UE and UTRAN, GERAN, and E-UTRAN are the Uu, Um, and LTE-Uu interfaces, respectively.

At times the UE performs inter-RAT or intra-RAT cell-reselection, during which the UE sends certain request messages (e.g. Attach request, RAU request, combined RAU/LAU request) to the concerned RAT or RATs. The messages, or partial content thereof, are intended for the core network to be processed there, e.g. by the SGSN and/or MME. The partial content means certain information element(s) comprised in the messages. After processing the messages or the information elements, the core network may control the concerned RAT or RATs to transmit, in response to the request messages, appropriate accept/grant messages (e.g. Attach accept, RAU accept, combined RAU/LAU accept, respectively) to the UE so as to complete the cell reselection.

In the following embodiments, the SGSN in the CSFB enabled mobile communication network of Fig. 1 is made aware whether the UE supports the CSFB functionality. This knowledge makes it possible for the SGSN to keep ISR activated for user terminals not supporting CSFB (while deactivating ISR for CSFB capable user terminals). Support of CSFB and whether ISR is to be activated or to be kept activated can be made known to the SGSN by numerous mechanisms as will now be described in more detail.

Depicted in Fig. 2 is an embodiment of a network component 2. A specific implementation of the network component 2 is the user terminal (UE) itself, as indicated in Fig. 2. The network component 2 is adapted to control a mobile communication network like the one of Fig. 1 which supports CSFB. The network component 2 comprises, among other things, a transmitting unit 4 for transmitting a message 6 to the network. The message 6 comprises, inter alia, an information element 8 for indicating whether a specific user terminal (i.e., the UE itself) of the network supports CSFB. The network comprises a core network 10 with an SGSN 12. As illustrated by the arrow in the dashed line, the information element 8 is intended for at least the SGSN 12 and will be processed there upon its arrival at SGSN 12.

Depicted in Hg. 3 is another embodiment of a network component 22. A specific implementation of the network component 22 resides in the core network 30, as shown in Fig. 3. For example, the network component 22 is an MME and in this case the message 26 is transmitted from the MME 22 to the SGSN 32. Like the network component 2 shown in Fig. 2, the network component 22 is also adapted to control a mobile communication network which supports CSFB (like the one of Fig. 1) and also comprises, among other things, a transmitting unit 24 for transmitting a message 26 to the network. Further, the message 26 also comprises, inter alia, an information element 28 for indicating whether a specific user terminal (UE), shown as 2 ^', of the network supports CSFB. The network comprises a core network 30 which comprises an SGSN 32. The information element 28 is intended for the SGSN 32 and will be processed there upon its arrival at the SGSN 32.

Despite the difference in their specific implementation, the network components 2 and 22 both can perform a method embodiment illustrated in Fig. 4. As shown in Fig. 4, a method 400 is provided for controlling a mobile communication network supporting CSFB. The method 400 comprises a step 402 which is to transmit, by the network component 2, 22, a message 6, 26 to the network. The message 6, 26 comprises an information element 8, 28 indicating whether a user terminal of the network supports CSFB.

Another method embodiment associated with the network components 2 and 22 is illustrated in Fig. 5, in which a method 500 is defined for controlling a mobile communication network supporting CSFB. The method 500 comprises steps 502 and 504. At step 502, the network receives a message, i.e. the message 6, 26 shown in Figs. 2 and 3 respectively. The message comprises an information element 8, 28 indicating whether a user terminal 2, 2 ^' of the network supports CSFB. Then, at step 504, an SGSN 12, 32 of the network determines whether or not the user terminal 2, 2 ^' supports CSFB based on the received message 6, 26.

Further, based on the result of the determination, the SGSN 12, 32 can decide about a change of an activation state of ISR for the user terminal 2, 2 ^' . This is to say, if the result of the determination is negative, i.e. the user terminal 2, 2 ^'does not support CSFB, the SGSN 12, 32 controls the user terminal 2, 2 ^'to activate ISR or keep the ISR activation state; conversely, if the result of the determination indicates that the user terminal 2, 2 ^'supports CSFB, the SGSN 12, 32 may deactivate ISR for the user terminal 2, 2 ^'. As indicated in Figs. 2 and 3, the SGSN 12, 32 transmits a message 14, 34 to the user terminal 2, 2 ^'to accomplish this controlling.

The information element 8, 28 comprised in the message 6, 26 can be of any format which can be read and processed by the SGSN 12, 32.

An embodiment of the information element 8 is shown in Fig. 6, which is a "Mobile Station (MS) Network Capability" or "User Terminal (UE) Network Capability" information element used in GPRS. The purpose of the MS/UE Network Capability information element used in GPRS is to provide the network with information concerning aspects of the user terminal related to GPRS. The contents may affect the manner in which the network handles the operation of the user terminal.

As can be seen in Fig. 5, the MS/UE Network Capability as defined in GPRS is a type- 4 information element with a length of 10 octets in maximum. The value part of a MS/UE Network Capability information element may be coded as shown in Figure 10.5.128 and Table 10.5.145 of 3GPP TS24.008 Version 8.3.0.

The "MS/UE Network Capability" information element can be extended by including an indication indicating whether CSFB is supported by the MS/UE or not. For in- stance, a new entry can be created in the value part and a simple binary bit of 1 or 0 can be used to indicate that the user terminal supports or does not support CSFB, respectively.

Preferably, this embodiment of the information element 8 is used in association with the implementation that the network component 2 is the user terminal itself as shown in Fig. 2. The "MS/UE Network Capability" information element 8 can be sent from the user terminal 2 to the network in a request message such as Attach request, RAU request, combined RAU/LAU request, etc.

Another embodiment of the information element 28 is the Mobility Management (MM) and Evolved Packet System (EPS) Bearer Context. The MM and EPS Bearer Context is a set of information elements grouped together as a "context" and is transferred between network components for purposed including mobility management. Usually, a message sent from an MME to an SGSN would includes this context. Of course, other information elements may be included in the message.

Similar to the embodiment referred to in Fig. 2, the MME 22 shown in Fig. 2 can add a new parameter into the MM and EPS Bearer Context to indicate whether CSFB is supported by a user terminal. That is, the MM and EPS Bearer Context 28 includes an information element (the new parameter) to indicate whether CSFB is supported by a user terminal. With the message 26, the MM and EPS Bearer Context 28 is trans- ferred to the SGSN 32. The transfer may take place over the S3 reference point during SRNS relocation procedures, as shown in Fig. 1. More information on SRNS relocation between MME to SGSN can be found in 3GPP Change Request CR0049rev 4 of 3GPP TS 23.272 and 3GPP TS 23.401.

For both the embodiments illustrated in Figs. 2 and 3, the respective SGSN 12, 32 understands the "UE support of CSFB" indication and can use the presence or lack of this information to optimize the overall signaling in the network. Specifically an SGSN that supports CSFB, ISR and understands the "UE support of CSFB" indication can respond to user terminals, such as in RAU accept and RAU/LAU accept messages, to continue to use ISR for the case where they do not support CSFB (i.e. the indication is not available).

As mentioned above, the SGSN 12, 32 can decide about a change of the activation state of ISR for the user terminal 2, 2 ^'and control the user terminal 2, 2 ^'. To this end, the SGSN 12, 32 may transmit a message 14, 34 to the user terminal 2, 2 ^'to, among other things, inform or control the user terminal 2, 2 ^' to activate ISR or to keep the activation state of ISR for the user terminal 2, 2 ^'. Hence, the message 14, 34 can be viewed as an activation message. The message 14, 34 may be an accept message in response to the user terminal's request; i.e., the message 14, 34 may be an Attach accept, a TAU accept, a RAU accept, a LAU accept, etc. respectively.

For the case that the user terminal supports CSFB or the SGSN does not understand the "UE support of CSFB" (e.g. pre rel-8 SGSN) the SGSN, will not include ISR indication in the RAU accept or combined RAU/LAU accept messages. For such situations there will be no ISR optimization in the network Since the UE updates the network at every RAT change (RAU, combined RAU/LAU or TAU) the network always knows in which RAT to page the UE. When ISR is not active the UE always updates the net- work when moving between RAT's and the network hence always knows where to send a page to the UE.

Fig. 7 illustrates another embodiment for controlling a mobile communication network supporting CSFB functionality. While the embodiments of Figs. 2 and 3 are to extend conventional information elements (e.g. MS/UE Network Capability Value, MM and EPS Bearer Context) by including a new parameter indicating ^WUE support of CSFB", the embodiment according to Fig. 7 is to reuse an existing parameter "ISR supported" in a conventional information element (e.g. MM and EPS Bearer Context) but to change the logic on how the MME shall set this information element.

Depicted in Fig. 7 is a core network 70 of a mobile communication network which supports CSFB (such as the network illustrated in Fig. 1). An MME 71 and an SGSN 72 are implemented in the core network 70. The MME 71 comprises, among other components, a logic unit 73 and a transmission unit 74. The logic unit 73 determines whether or not to include in a message 76 to be transmitted from the MME 71 to the SGSN 72 an information element 78 indicating whether ISR is to be kept activated for a user terminal (UE), denoted as 7 ^' in Fig. 7. The transmission unit 74 transmits the message 76 to the SGSN 72.

With respect to the SGSN 72, it comprises, inter alia, a receiving unit 79 and a (different) logic unit 80. The receiving unit receives the message 76 from the MME 71. Of course, the message 76 may or may not comprise the information element 78 indicating whether ISR is to be kept activated for the user terminal 7 ^'. Based on the presence of or lack of this information element 78, the logic unit 80 of the SGSN 72 determines whether or not to activate or keep activated the ISR for the user terminal 7 ^' concerned.

The embodiment referred to in Fig. 7 can be implemented as various methods. Figs. 9 and 10 present two method embodiments, corresponding to the aspects of trans- mission and reception, respectively.

In Fig. 9, a method 900 is defined to comprise steps 902 and 904. At step 902, the MME 71 determines whether or not to include in a message 76 to be transmitted to the SGSN 72 an information element 78 indicating whether ISR is to be kept acti- vated for a user terminal 7 ^'. Thereafter, at step 904, the MME 71 transmits the mes^¬ sage 76 to the SGSN 72. As shown in Fig. 10, a method 1000 comprises two steps 1002 and 1004, both performed by the SGSN 72. At step 1002, the SGSN 72 receives a message 76 comprising an information element 78 indicating whether ISR is to be kept activated for a user terminal 7 ^'. Then at step 1004, based on the information element 78, the SGSN determines whether or not to activate or keep activated the ISR for the user terminal 7 ^'.

The information element 78 can be of any format which can be read and processed by the SGSN 72. An example of the information element 78 is the MM and EPS Bearer Context as explained above. The MME logic unit 73 decides whether an indication of "ISR supported" is to be sent to the SGSN 72 as part of the MM and EPS Bearer Context. The MME 71 sends the "ISR supported" indication when the user terminal concerned supports ISR and SGs is not active (unless SGs is active and can remain active after the user terminal handovers to GPRS). That is to say, the MME 71 uses the information whether SGs is activated for a user terminal to decide whether to indicate to the SGSN 72 whether ISR can be kept activated or not.

Returning to Fig. 7, once the SGSN 72 determines that ISR is to be activated or kept activated for the user terminal 7 ^', it transmits a message 82 to the user terminal 7 ^', wherein the message comprises the information "ISR active". The message 82 can be a context response. It can be sent, as shown in Fig. 8, as part of an RAU accept if the UE Context received from the MME indicates "ISR supported" and the SGSN supports the S4 reference point including other capabilities required for ISR to be activated e.g. paging forwarding.

All the above embodiments enable ISR to be activated for non-CSFB capable user terminals in CSFB enabled networks. Hence, the signalling caused by such user terminals during inter-RAT or intra-RAT procedures in their idle mode can be effectively limited. A further advantage provided is the implementation simplicity.

While the present invention has been described with reference to the above embodiments, it is to be understood that the description is for illustration purposes only. Accordingly, it is intended that the invention be limited only by the scope of the claims appended hereto.

Claims

1. A method for controlling a mobile communication network supporting Circuit- Switched Fallback, or CSFB, functionality, the method comprising: receiving, by the network, a message comprising an information element (8, 28) indicating whether the CSFB functionality is supported by a user terminal (2, T)₁ or UE, of the network; and determining, by a Serving GPRS Support Node (12, 32), or SGSN, of the net- work, whether or not the UE (2, 20 supports the CSFB functionality based on the received message (6, 26).

2. The method of claim 1, further comprising: deciding, by the SGSN (12, 32), about a change of an activation state of Idle state Signalling Reduction, or ISR, for the UE (2, T)₁ depending on a result of the determination.

3. The method of claim 2, wherein if it is determined that the UE (2, T) does not support the CSFB functionality, the method further comprises: activating or keeping activated, by the SGSN (12, 32), the ISR for the UE (2,

T); and transmitting, by the SGSN (12, 32), an activation message (14, 34) to the UE (2, T) to control the UE (2, T) to activate or to keep activated the ISR.

4. The method of claim 2 or 3, further comprising: deactivating, by the SGSN (12, 32), the ISR for the UE (2, T) if it is determined that the UE (2, T) supports the CSFB functionality.

5. A method for controlling a mobile communication network supporting Circuit- Switched Fallback, or CSFB, functionality, the method comprising: transmitting, by a network component (2, 22), a message (6, 26) to the network, wherein the message (6, 26) comprises an information element (8, 28) indicating whether the CSFB functionality is supported by a user terminal (2, T)₁ or UE, of the network.

6. The method of claim 5, wherein the information element (8, 28) is destined at a Serving GPRS Support Node (12, 32), or SGSN, of the network.

7. The method of any of the preceding claims, wherein the information element (8) is a Mobile Station Network Capability information element or a UE Network Capability information element.

8. The method of any of the preceding claims, wherein the message (6) is one of an Attach request, a Routing Area Update request, and a combined Routing Area Update/Location Area update request.

9. The method of claim 5 or 6, wherein the network component (2) is the UE (2) itself.

10. The method of any of claims 5 to 8, wherein the network component (22) is a Mobility Management Entity (22), or MME, of the network.

11. The method of any of the preceding claims, wherein the information element (28) is comprised in a Mobility Management and Evolved Packet System Bearer Context.

12. A Serving GPRS Support Node (12, 32), or SGSN, for a mobile communication network supporting Circuit-Switched Fallback, or CSFB, functionality, the SGSN (12, 32) adapted to determine whether or not a user terminal (2, T), or UE, of the network supports the CSFB functionality based on a message (6, 26) received by the network, wherein the message (6, 26) comprises an information element (8, 280 indicating whether the CSFB functionality is supported by the UE (2, 20-

13. The SGSN (12, 32) of claim 12, further adapted to activate or keep activated ISR for the UE (2, 20 if it is determined that the UE (2, 20 does not support the CSFB functionality.

14. The SGSN (12, 32) of claim 12 or 13, further adapted to deactivate the ISR for the UE (2, 20 if it is determined that the UE (2, 20 supports the CSFB functionality.

15. A network component (2, 22) adapted to control a mobile communication network supporting Circuit-Switched Fallback, or CSFB, functionality, the network component (2, 22) comprising: a transmission unit (4, 24) for transmitting a message (6, 26) to the network, wherein the message (6, 26) comprises an information element (8, 28) indicating whether the CSFB functionality is supported by a user terminal (2, T), or UE, of the network.

5

16. The network component (2, 22) of claim 15, wherein the network component (2, 22) is the UE itself (2) or a Mobility Management Entity (22), or MME, of the network. o

17. A method for controlling a mobile communication network comprising a Mobility Management Entity (71), or MME, and a Serving GPRS Support Node (73), or SGSN, wherein the network supports Circuit-Switched Fallback, or CSFB, functionality, the method comprising: determining, by the MME (71), whether or not to include in a message (76) tos be transmitted to the SGSN (72) an information element (78) indicating whether Idle state Signalling Reduction, or ISR, is to be kept activated for a user terminal (71), or UE; and transmitting, by the MME (71), the message (76) to the SGSN (72). o

18. A method for controlling a mobile communication network comprising a Mobility Management Entity (71), or MME, and a Serving GPRS Support Node (72), or SGSN, wherein the network supports Circuit-Switched Fallback, or CSFB functionality, the method comprising: receiving, by the SGSN (72), a message (76) comprising an information ele-5 ment (78) indicating whether Idle state Signalling Reduction, or ISR, is to be kept activated for a user terminal (71), or UE; and determining, by the SGSN (72), whether or not to activate or keep activated the ISR for the UE (71) based on the indication. o

19. A Mobility Management Entity (71), or MME, for a mobile communication network supporting Circuit-Switched Fallback, or CSFB, functionality, the MME (71) comprising: a logic unit (73) for determining whether or not to include in a message (76) to be transmitted to a Serving GPRS Support Node (72), or SGSN, an information5 element (78) indicating whether Idle state Signalling Reduction, or ISR, is to be kept activated for a user terminal (70, or UE; and a transmission unit (74) for transmitting the message to the SGSN (72).

20. A Serving GPRS Support Node (72), or SGSN for a mobile communication network comprising a Mobility Management Entity (71), or MME, and the SGSN (72), wherein the network supports Circuit-Switched Fallback, or CSFB, functionality, the SGSN (72) comprising: a receiving unit (79) for receiving a message (76) comprising an information element (78) indicating whether Idle state Signalling Reduction, or ISR, is to be kept activated for a user terminal (70, or UE; and a logic unit (80) for determining whether or not to activate or keep activated the ISR for the UE (7¹) based on the information element (78).

21. A computer program product comprising program code portions for performing the steps of the method of any one of the claims 1 to 11 and 17 to 18 when the computer program product is run on a computing device.

22. The computer program product of claim 21, stored on a computer readable recording medium.