GB2499673A

GB2499673A - Indicating circuit switched fallback (CSFB) support for voice calls

Info

Publication number: GB2499673A
Application number: GB1203367.6A
Authority: GB
Inventors: Samuli Heikkinen; Matti Moisanen
Original assignee: Renesas Mobile Corp
Current assignee: Renesas Electronics Corp
Priority date: 2012-02-27
Filing date: 2012-02-27
Publication date: 2013-08-28
Also published as: GB201203367D0

Abstract

A terminal device configured to operate solely in a packet switched mode S1 may be unable to make voice calls. To address this problem the terminal device registers S2 into a cellular communication network by indicating that it supports only a packet switched connection type but also indicates that it supports circuit-switched fallback (CSFB) in case a voice call is triggered. When a voice call is triggered S5 the terminal device transmits a CSFB service request for the call S6. Support for CSFB may be indicated by transmission of a code word indicating support for fallback for all voice calls or just emergency calls. The code word may be a one-bit indicator and may be included in an attach request and/or tracking area update request message. The device may transmit capability information related to the fallback. The device may be configured for use in a Long-Term Evolution (LTE) (RTM) or Long-Term Evolution Advanced (LTE-A) network.

Description

INTELLECTUAL

PROPERTY OFFICE

Application No. GB1203367.6 RTM ^at6

The following terms are registered trademarks and should be read as such wherever they occur in this document:

3GPP

LTE

UMTS

Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk

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Cellular Communication Systems

Technical Field

The invention relates to the field of radio communications and, particularly, although not exclusively, it relates to handling calls in a cellular 5 communication system.

Background

A packet-based radio communication network, such as the Long Term Evolution (LTE) or the LTE-Advanced (LTE-A) of the 3rd Generation Partnership Project (3GPP), may offer a large variety of services. However, there may be a need to 10 request a circuit switched fallback (CSFB) service for example when voice data is to be transferred. However, some terminal devices may be configured to operate in a communication mode which supports only a packet switched connection type and excludes any circuit switched connection types. The CSFB may become problematic for such a terminal device, and such problems may cause a malfunction when the user 15 of the terminal device attempts a voice call, for example.

Brief description

According to a first aspect, the present invention provides a method of configuring support for emergency calls in a terminal device, the method comprising: initiating in the terminal device a packet communication mode in which the 20 terminal device is configured to operate solely in a packet switched connection mode;

causing the terminal device in the packet communication mode to register into a cellular communication network, wherein the registration comprises indicating to the cellular communication network that the terminal device supports only a packet switched connection type and indicating to the cellular communication network that 25 the terminal device supports fallback to a circuit-switched connection in case a voice call is triggered;

triggering a voice call in the terminal device; and upon triggering the voice call, causing the terminal device to transmit a service request related to the fallback to the circuit switched connection for the voice 30 call.

According to a second aspect, the present invention provides a method of determining support for voice calls in a network apparatus of a cellular communication network, the method comprising:

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acquiring from a terminal device a registration message to register the terminal device into a cellular communication network, wherein the registration comprises an indication from the terminal device that the terminal device supports only a packet switched connection type and an indication from the terminal device that the 5 terminal device supports fallback to a circuit-switched connection in case a voice call is triggered;

acquiring a service request related to a voice call from the terminal device;

and in response to the service request, preparing the fallback of the terminal 10 device from the packet switched connection type to the circuit switched connection for the voice call.

According to a further aspect, the present invention provides an apparatus for configuring support for emergency calls, the apparatus comprising:

a processing system arranged to:

15 cause a terminal device to initiate a packet communication mode in which the terminal device is arranged to operate solely in a packet switched connection mode;

cause the terminal device in the packet communication mode to register into a cellular communication network, wherein the registration comprises indicating to the cellular communication network that the terminal device supports only a packet 20 switched connection type and indicating to the cellular communication network that the terminal device supports fallback to a circuit-switched connection in case a voice call is triggered;

trigger a voice call in the terminal device; and upon triggering the voice call, cause the terminal device to transmit a 25 service request related to the fallback to the circuit switched connection for the voice call.

According to a further aspect, the present invention provides an apparatus for determining support for voice calls in a network apparatus of a cellular communication network, the apparatus comprising:

30 a processing system arranged to:

acquire from a terminal device a registration message to register the terminal device into a cellular communication network, wherein the registration comprises an indication from the terminal device that the terminal device supports only a packet switched connection type and an indication from the terminal device that the 35 terminal device supports fallback to a circuit-switched connection in case a voice call is triggered;

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acquire a service request related to a voice call from the terminal device;

and in response to the service request, prepare the fallback of the terminal device from the packet switched connection type to the circuit switched connection for 5 the voice call.

Yet further aspects and embodiments of the present invention will become apparent from the following description, claims and drawings.

Brief Description of the Drawings

Exemplary embodiments of the present invention are described below, by 10 way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram that illustrates communication between a terminal device and a cellular communication network;

Figure 2 is a process flow diagram that illustrates a generic procedure for configuring circuit-switched fallback capability in a cellular communication network 15 and in a terminal device;

Figures 3 to 5 are process flow diagrams that illustrate embodiments for the carrying out the procedure of Figure 2;

Figure 6 is a process flow diagram that illustrates yet another embodiment for configuring a circuit-switched fallback capability in a cellular communication 20 network and in a terminal device; and

Figures 7 and 8 are block diagrams illustrating apparatuses according to some embodiments of the invention.

Detailed Description

The following embodiments are exemplary. Although the specification 25 may refer to "an", "one", or "some" embodiment(s) in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, words "comprising" and "including" should be understood as not limiting the described 30 embodiments to consist of only those features that have been mentioned and such embodiments may contain also features/structures that have not been specifically mentioned.

With reference to Figure 1, cellular communication networks, such as the LTE or the LTE-A of the 3GPP, are typically composed of at least one base station 100 35 (also called a base transceiver station, a radio network controller, a Node B, or an

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evolved Node B, for example), at least one mobile station (MS) 102 (also called a user terminal, terminal device or user equipment, for example) and optional network elements that provide the interconnection towards a core network. The base station 100 connects the MS 102 via a radio interface to the other network elements of the cellular 5 communication network, e.g. a mobility management entity (MME) 104 handling at least some of non-access stratum (NAS) signaling of the MS together with the base station 102. The base station 100 may provide radio coverage within at least one cell, control radio resource allocation, perform data and control signaling, etc. The cell may be a macrocell, a microcell, a picocell, a femtocell, or any other type of cell where 10 radio coverage is present.

In general, the base station 100 may be configured to provide communication services according to at least one of the following radio access technologies (RATs): Worldwide Interoperability for Microwave Access (WiMAX), Global System for Mobile communications (GSM), GSM EDGE radio access Network 15 (GERAN), General Packet Radio Service (GPRS), Universal Mobile Telecommunication System (UMTS) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), LTE, and/or LTE-A. The present embodiments are not, however, limited to these protocols. The base station 100 may be a node B (NB), an evolved node B (eNB) as in the LTE and LTE-A, a base 20 station (BS) of the GSM/GERAN, or any other apparatus capable of controlling radio communication and managing radio resources within the cell. Depending on the system specification, the base station 100 may need to communicate with another entity of the cellular communication network when controlling the radio communication with the MS 120, e.g. with a radio network controller or a base station 25 controller.

As an example, the 2G and the 3G RATs may be able to perform circuit switching. Circuit switching, or a circuit switched (CS) connection is a technology where two network nodes establish a dedicated communication channel (i.e. a circuit) through the network before the nodes may communicate, and the cellular 30 communication system may ensure that at any time there is a certain amount of radio resource reserved for the CS connection. This may be advantageous because the circuit may guarantee wide bandwidth of the channel and ensure that the nodes remain connected for the duration of the communication session. Such circuit switching may be applied for voice data transfers, for example, in order to reach high quality of 35 service (QoS) without interruptions. As such, CS domain services may comprise at least those services that may be offered in the CS capable RATs, such as in the 2G and

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the 3G networks. Examples of such services may include: voice and its supplementary services (e.g. call waiting, call forwarding) and video streaming, etc. However, for example, 4G may apply packet switching in contrast to the circuit switching. Packet switching shares available network bandwidth between multiple communication 5 sessions, and packet switching technology provides better capacity and higher throughput. It should be noted that in this application the 2G and the 3G comprise all RATs that may provide CS domain capability whereas the 4G may be used to commonly denote all RATs without such CS domain capability.

Although, for example, voice services may be provided by 4G as a packet 10 service, such as voice over IP (VOIP), there may be a need to provide 4G (or any packet network) services to allow a circuit switched fallback (CSFB) in order to provide better QoS, for example. There may be a need for a user applying 4G, for example, to request CSFB in order to use services requiring or preferably provided by circuit switching, e.g. conventional voice calls and emergency calls. The MS 102 may 15 decide to request CSFB from the 4G RAT by transmitting a CSFB request to the serving base station 100. In the CSFB request, or in an extended service request, as the CSFB request may also be called, the MS 102 requesting the CSFB may first register to the CS domain via an evolved packet system (EPS), in case the MS 102 is currently served by the LTE cellular communication network, for example. The MS 102 may 20 then perform a CSFB request procedure with the EPS. This may comprise switching the MS 104 to another RAT capable of providing such circuit switching services. Such RAT may be, for example, the 2G (GSM) or the 3G (UMTS). The RAT change may be controlled by the current packet network, such as LTE. The LTE may control the RAT change by means of a handover, a redirection, or a cell change order, for 25 example. The cellular communication network may then indicate back to the MS 102 whether the CSFB request is supported and successful or not. When the request is successful, the MS 102 may begin using the CS related service. For example, the MS 102 may request a MME, in case of GERAN / UMTS radio access network (UTRAN), to perform the CSFB procedures whenever the MS 102 requests for the CS domain 30 services.

Referring to Figure 1, some MSs, such as the MS 102, support a communication mode in which the CS capability is disabled, and the MS 102 operates in a mode where it is configured to use only the packet switched (PS) connections. The MS 102 may have the capability for the CS connection as well, but the CS connections 35 may be temporarily disabled in this "PS only" communication mode. In "PS only" mode, the cellular communication network may see the MS 102 as a terminal device

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that has no support for the CS connections, e.g. as a dongle providing only PS connections. This may cause problems with establishing an emergency call initiated in the MS 102, for example.

Let us now consider an embodiment of the invention for configuring 5 support for voice calls in a terminal device, e.g. the MS 102, and in a network element, e.g. the base station 100 or another network element such as a MME. Figure 2 illustrates a signalling diagram comprising steps carried out in the network element and in the MS 102 and their communication in this respect. Referring to Figure 2, the MS 102 initiates in SI a packet communication mode (PS only mode) in which the 10 terminal device is configured to operate solely in a packet switched connection mode. This communication mode may be triggered by a user input through a user interface of the MS 102. In block S2, the MS 102 operating in the packet communication mode is configured to register into a cellular communication network, wherein the registration comprises indicating to the cellular communication network that the MS 102 supports 15 only a PS connection type and indicating to the cellular communication network that the MS 102 supports fallback to a circuit-switched connection in case a voice call is triggered. The network element acquires this registration information in at least one registration message in S2 and determines from this registration information that the MS 102 operates in the PS only mode but that voice calls shall still be allowed to the 20 MS 102. Therefore, the network element enables the CSFB for the voice calls for the MS 102 in S3. In optional step S4, PS data may be transferred between the MS 102 and the cellular communication network.

In S5, a voice call is triggered in the MS. S5 may comprise receiving a dialling input from the user interface, wherein the dialling input indicates a call to a 25 telephone number which may be an emergency telephone number, e.g. "911" or "112", or it may be another telephone number. Upon triggering the voice call, the MS 102 is configured in S6 to transmit to the network element a service request related to the fallback to the circuit switched connection for the voice call. The network element acquires the service request in S2 and, in response to the service request, the network 30 element carries out the fallback of the MS 102 from the packet switched connection type to the circuit switched connection for the voice call in S7. The MS 102 also carries out the CSFB procedures in S7, wherein S7 may comprise handing the MS 102 over from the cellular communication network to another cellular communication network, e.g. from a packet switched cellular communication network (LTE) to a 35 circuit switched cellular communication network (GSM or UMTS).

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It should be appreciated that all the steps of the network element may be carried out by the same network entity, or the steps may be distributed between a plurality of network entities, e.g. between the base station 102 and the MME 104. The same applies to Figures 3 to 6 described below.

5 An advantage of the above-described embodiment is that it provides the

MS 102 with the capability of carrying out the voice calls even in the PS only communication mode. It also enables the cellular communication network to distinguish the MS 102 from a MS that is not configured for CS connections and, thus, enables the CSFB for the MS 102 on the network side.

10 In an embodiment, the indication to the cellular communication network that the MS 102 supports the fallback to the circuit-switched connection indicates the CSFB support for only emergency calls, while in another embodiment, the indication defines the CSFB support for all voice calls. The indication may comprise transmission of a code word that explicitly indicates the support for the fallback to a CS connection 15 for the emergency/voice call. In an embodiment, the code word is a one-bit indicator. In an embodiment, the code word is included in an attach request message used to register the terminal device into the cellular communication network. Table 1 below illustrates some of the contents of the attach request according to LTE specifications designed within the 3GPP. The whole contents of the attach request are not shown to 20 maintain the conciseness of the description.

IEI

Information Element

Type/Reference

Presence

Format

Length

Protocol discriminator

M

V

1/2

31

MS Network Capability

O

TLV

4-10

11

MS classmark 2

O

TLV

5

20

MS classmark 3

O

TLV

2-34

F-

Additional Update Type

O

TV

1

Table 1

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In an embodiment, a new bit is added to the Additional Update Type information element (IE) to indicate the support for the CSFB for the emergency calls. The Additional Update Type IE may have the following structure:

Additional Update Type

IE

Length

SMS only

1 bit

Emergency calls only

1 bit

All voice calls

1 bit

Table 2

The short message system (SMS) only field may indicate whether or not the MS 102 is registered for SMS services, while the Emergency calls only field may indicate whether or not the CSFB is supported for the emergency calls. The all voice 10 calls information element may indicate whether the CSFB support is for all voice calls. It should be appreciated one of the Emergency calls only and All voice calls IEs may be omitted in some embodiments. In yet another embodiment, All voice calls IE may be expanded to separately define support for MS originated and MS terminated calls. In such an embodiment, All voice calls IE may comprise two bits to indicate the 15 following four states: no voice calls supported, only MS originated voice calls supported, only MS terminated voice calls supported, and both MS originated and MS terminated voice calls supported.

In another embodiment, the code word is inserted into a tracking area update request message. The tracking area update request message also comprises the 20 Additional Update Type IE, and it may be modified into the format of Table 2 in this embodiment.

The Emergency calls only IE and the All voice calls IE may inherently indicate also the PS only communication mode of the MS 102.

In an embodiment, the MS 102 indicates to the network element any 25 capability information needed for the handover of the MS 102 during the CSFB. For example, the attach request and the tracking area update request comprise such capability information in IEs MS Network capability, MS classmark 2, and MS classmark 3 shown in Table 1. Other capability information or equivalent capability information may be used in other embodiments. Figures 3 to 5 illustrate some 30 embodiments for providing the network element with the capability information to

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enable the CSFB. The same reference signs as in Figure 2 denote the same or essentially similar functions.

Referring to Figure 3, in response to triggering the PS only mode in the MS 102 (SI), the MS 102 is configured to prepare the above-mentioned attach request 5 message in S10. The attach request message may be a NAS attach request message. The MS 102 inserts in S2 the IE indicating the support for the CSFB for the emergency/voice calls into the attach request message, and the MS 102 inserts the capability information into the attach request message in S10. Then, the MS 102 is configured to transmit the attach request message in SI 1. In S12, the network element 10 acquires and processes the attach request message, determines the capability of the MS 102 for the CSFB for the emergency/voice calls and related CSFB parameters defined by the capability information from the attach request. Then, the network element may enable the CSFB procedures for the MS 102 in case the MS 102 requests for the emergency/voice call from the network element. In S6 and S7, the emergency/voice 15 call procedures are triggered and executed.

In the embodiments described below, the emergency calls are used as an example, but it should be appreciated that the same embodiments are equally applicable to all voice calls.

Referring to Figure 4, in response to triggering the PS only mode in the 20 MS 102 (SI), the MS 102 is configured to prepare the above-mentioned attach request message in S20. The MS 102 inserts in S20 the IE indicating the support for the CSFB for the emergency calls into the attach request message, but it omits at least some of the capability information from the attach request message in S20. Then, the MS 102 is configured to transmit the attach request message in S21. In S22, the network element 25 acquires and processes the attach request message, determines the capability of the MS 102 for the CSFB for the emergency calls. Then, the network element may enable the CSFB procedures for the MS 102 in case the MS 102 requests for the emergency call from the network element. When the emergency call is triggered in the MS 102, the MS 102 prepares an extended service request in S23. The MS 102 inserts the capability 30 information, e.g. at least some of the MS Network Capability, Classmark 2, and Classmark 3 IEs, omitted from the attach request to the extended service request. The MS 102 then transmits the extended service request to the network element in S24 to request for the CSFB for the emergency call. Upon receiving the capability information from the extended service request, the network element acquires the 35 necessary parameters for the CSFB, e.g. for handing the MS 102 from the PS network to a CS network. In S7, the emergency call procedures are executed.

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Referring to Figure 5, in response to triggering the PS only mode in the MS 102, the MS 102 is configured to prepare the above-mentioned attach request message in S30. The MS 102 inserts in S30 the IE indicating the support for the CSFB for the emergency calls into the attach request message, but it omits at least some of 5 the capability information from the attach request message in S30. Then, the MS 102 is configured to transmit the attach request message in S31. In S32, the network element acquires and processes the attach request message, determines the capability of the MS 102 for the CSFB for the emergency calls. Then, the network element may enable the CSFB procedures for the MS 102 in case the MS 102 requests for the emergency call 10 from the network element (S32). In S33, the MS 102 triggers transmission of a tracking area update request The tracking area update message may be triggered when the MS changes at least some of the communication parameters, when the MS 102 enters a new tracking area comprising a set of base stations, or in response to a determined event in the registration or in the communication properties. In S33, the 15 MS 102 prepares a tracking area update request message and inserts into the tracking area update request message the capability information needed for the CSFB. In S34, the MS 102 transmits the tracking area update request message to the network element, e.g. the MME 104, and the network element acquires the message in S34. In S35, the network element processes the request, extracts the capability information related to 20 the CSFB from the message, and stores the capability information as linked to the CSFB for the MS 102. In S6 and S7, the emergency call procedures are triggered and executed.

In the embodiments, of Figures 3 to 5, the MS 102 indicates the support for the CSFB for the emergency/voice calls explicitly in the form of the code word. Figure 25 6 illustrates another embodiment in which the MS 102 indicates the support for the CSFB for the emergency calls to the network element implicitly. In this embodiment, the indication to the cellular communication network that the MS 102 supports the CSFB for the emergency call comprises registering the terminal device to a CSFB for all circuit switched connections and indicating that the terminal device supports only 30 the packet switched connection type. As a consequence, the specific combination of registering to the CSFB for all circuit switched connections and indicating the support for only the packet switched connection type indicates to the cellular communication network that the circuit switched fallback shall be applied only to the emergency calls.

Referring to Figure 6, in response to triggering the PS only mode in the 35 MS 102 (SI), the MS 102 is configured to register to the CS domain of the EPS with respect to all voice calls (S41). This may be understood as a conventional registration

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to the CS domain. However, in connection with the registration in S41, the MS 102 indicates to the network element that it supports the PS only mode. This may be indicated by disabling at least some of the above-mentioned capability information, e.g. the classmark information. As separate, these two indications may be seen as 5 contradicting each other but the network element is configured to determine this specific combination as an indication that the CSFB is enabled only for the emergency calls. The CSFB for the other calls may be disabled. As a consequence, the network element enables the CSFB for only the emergency calls in S42.

In another embodiment, this implicit indication is applied to all voice calls 10 instead of the emergency voice calls. Accordingly, the specific combination of registering to the CSFB for all circuit switched connections and indicating the support for only the packet switched connection type indicates to the cellular communication network that the circuit switched fallback shall be applied to all voice calls.

As the capability information was disabled in S41 to indicate the PS only 15 mode of the MS 102, the capability information may be transmitted to the network element after the registration (after S41). The MS 102 may insert the capability information into the extended service request when the emergency call is triggered (S23), as in the embodiment of Figure 4. In another embodiment, the capability information is inserted into the tracking area update request message, as in the 20 embodiment of Figure 5 (S33). As a consequence, the network element is able to acquire the remaining CSFB parameters, e.g. the classmark information, from the extended service request or from the tracking area update request message. Then, the CSFB may be carried when the emergency call is triggered (S6 and S7).

Figure 7 illustrates an embodiment of an apparatus comprising means for 25 carrying out the above-mentioned functionalities of the network element of the cellular communication network. The apparatus may be the base station 100, the MME 104, or another network element of the cellular communication system. In another embodiment, the apparatus is comprised in such a network element, e.g. the apparatus may comprise a physical circuitry, e.g. a chip, a processor, a micro controller, or a 30 combination of such circuitries in the communication apparatus.

The apparatus may comprise a communication controller circuitry 10 configured to control the communications in the apparatus. The communication controller circuitry 10 may comprise a control part 12 handling control signalling communication with respect to transmission, reception, and extraction of control 35 messages, e.g. registration messages related to registering the MSs in the cellular communication system, handover messages, and NAS messages. The communication

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controller circuitry 10 may further comprise a data part 16 that handles transmission and reception of payload data with the terminal devices, e.g. PS data. If the network element is the MME 104 or another purely control element of the cellular communication network, the data part 16 may be omitted. The communication 5 controller circuitry 10 may further comprise a registration controller circuitry 18 configured to carry out registration of the MSs in the cellular communication system. The registration controller circuitry 18 may be configured to carry out the communication with the MS 102 in connection with registering the MS 102 to the cellular communication network and identifying that the MS 102 operates in the PS 10 network but is provided with the capability of CSFB for the emergency/voice calls, as described above. The registration controller circuitry 18 may then output to a CSFB processor circuitry 14 a message that the CSFB is enabled for the MS 102 for the emergency calls only or to all voice calls, as described above. The CSFB processor circuitry 14 handles at least some of the CSFB functions. The CSFB processor 15 circuitry 14 may, for example, acquire any CSFB related capability parameters of the MS 102 from the control part 12 and/or from the registration controller circuitry 18, e.g. the above-mentioned capability information needed for handing the MS 102 over to a CS network. Such information may be stored in a memory 20. When the control part 12 receives the extended service request requesting for the emergency call, the 20 control part 12 may forward the request to the CSFB processor circuitry 14, and the CSFB processor circuitry may then retrieve the CSFB parameters from the memory 20 and initiate the CSFB procedure to hand the MS 102 to the CS network.

The circuitries 12 to 18 of the communication controller circuitry 10 may be carried out by the one or more physical circuitries or processors. In practice, the 25 different circuitries may be realized by different computer program modules. Depending on the specifications and the design of the apparatus, the apparatus may comprise some of the circuitries 12 to 18 or all of them.

The memory 20 may further store computer programs (software) configuring the apparatus to perform the above-described functionalities of the 30 apparatus. The memory 20 may also store communication parameters and other information needed for the registration of the MSs and for the CSFB procedures. The apparatus may further comprise input/output (I/O) components 22 providing the apparatus with communication capabilities with the MS 102 and with other network elements of the cellular communication system and/or with other wireless networks. 35 The I/O components 22 may comprise radio interface components such as amplifier, filter, switch, isolator, coupler, antenna tuner, frequency-converter, (de)modulator, and

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encoder/decoder circuitries and one or more antennas. The I/O components 22 may additionally or alternatively comprise I/O components needed for realizing wired connections such as internet protocol (IP) connections and/or system-specific wired connections, e.g. SI connection of the LTE.

5 In an embodiment, the apparatus carrying out the embodiments of the invention in the network element comprises at least one processor and at least one special purpose memory or/and one special purpose software (SW) executable memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the 10 apparatus to carry out the functionality of the network element in any one of the processes of Figures 2 to 6. Accordingly, the at least one processor, the memory, and the computer program code form processing means for carrying out embodiments of the present invention in the network element.

Figure 8 illustrates an embodiment of an apparatus comprising means for 15 carrying out the above-mentioned functionalities of the MS 102 configured to operate in at least in the PS only mode in which the CS capability is disabled. The apparatus may be a computer (PC), a laptop, a tablet computer, a cellular phone, a palm computer, a dongle, or any other apparatus provided with radio communication capability. In another embodiment, the apparatus is comprised in such a 20 communication apparatus, e.g. the apparatus may comprise a physical circuitry, e.g. a chip, a processor, a micro controller, or a combination of such circuitries in the communication apparatus.

The apparatus may comprise a communication controller circuitry 50 configured to control the communications in the communication apparatus. The 25 communication controller circuitry 50 may comprise a control part 52 handling transmission, reception, and extraction of control messages, e.g. registration messages related to registering the MS 102 in the cellular communication system, handover messages, and NAS messages exchanged with a serving BS 100, the MME 104, and/or another network element. The communication controller circuitry 50 may further 30 comprise a data part 56 that handles transmission and reception of payload data with the terminal devices, e.g. PS data and/or CS data.

The apparatus may further comprise radio interface components 62 providing the apparatus with radio communication capabilities with the cellular communication network. The radio interface components 62 may comprise standard 35 well-known components such as amplifier, filter such as the above-mentioned RF filter(s), frequency-converter comprising a frequency synthesizer, (de)modulator, and

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encoder/decoder circuitries, switch, isolator, antenna connector, other special purposes RF component(s) and / or modules and one or more antennas / antenna systems and antenna system control signals to set antennas for selected configuration. The apparatus may further comprise a user interface (not shown) or an interface to 5 communicate with an external user interface so as to provide interaction with a user of the apparatus, e.g. in connection with the selection of the communication mode. The user interface may comprise a display, a keypad or a keyboard, a loudspeaker, mouse, touch screen, voice, gestures etc.

The communication controller circuitry 50 may further comprise a mode 10 selector circuitry 54 configured to select the communication mode of the MS 102 according to a user input or by other means. The available communication modes may include the PS only mode in which the CS connections are disabled and a CS/PS mode in which both CS and PS connections are enabled. With respect to the PS only communication mode, the mode selector circuitry 54 may use the initiation of the 15 emergency call as a trigger to transit to a communication mode in which the CS connection is allowed so as to initiate the CSFB. The control part 52 may be configured in the PS only communication mode to indicate to the cellular communication network that the CSFB is supported for the emergency calls (see the above-described embodiments). The control part 52 may also carry out the preparation 20 of the control messages such as the attach request, the tracking area update request, the extended service request, any other registration messages, etc.

The circuitries 52 to 56 of the communication controller circuitry 50 may be carried out by the one or more physical circuitries or processors. In practice, the different circuitries may be realized by different computer program modules. 25 Depending on the specifications and the design of the apparatus, the apparatus may comprise some of the circuitries 52 to 56 or all of them.

The apparatus may further comprise a memory 60 to store computer programs (software) configuring the apparatus to perform the above-described functionalities of the communication apparatus. The memory 60 may also store 30 communication parameters and other information needed for the wireless communications, e.g. configurations for the different communication modes, the rules for indicating the support for the CSFB for the emergency calls, the rules for the CSFB procedures, etc.

In an embodiment, the apparatus carrying out the embodiments of the 35 invention in the communication apparatus comprises at least one processor and at least one memory including a computer program code, wherein the at least one memory and

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the computer program code are configured, with the at least one processor, to cause the apparatus to carry out the functionality of the MS 102 in any one of the processes of Figures 2 to 6. Accordingly, the at least one processor, the memory, and the computer program code form processing means for carrying out embodiments of the present 5 invention in the apparatus functioning in the MS 102.

As used in this application, the term 'circuitry' refers to all of the following: (a) hardware-only circuit implementations such as implementations in only analog and/or digital circuitry; (b) combinations of circuits and software and/or firmware, such as (as applicable): (i) a combination of processor(s) or processor cores; 10 or (ii) portions of processor(s)/software including digital signal processor(s), software, and at least one memory that work together to cause an apparatus to perform specific functions; and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

15 This definition of 'circuitry' applies to all uses of this term in this application. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor, e.g. one core of a multi-core processor, and its (or their) accompanying software and/or firmware. The term "circuitry" would also cover, for 20 example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit (ASIC) for the apparatus according to an embodiment of the invention.

The processes or methods described in Figures 4 to 8 may also be carried out in the form of a computer process defined by a computer program. The computer 25 program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. Such carriers include transitory and/or non-transitory computer media, e.g. a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package. 30 Depending on the processing power needed, the computer program may be executed in a single electronic digital processing unit or it may be distributed amongst a number of processing units.

The present invention is applicable to cellular or mobile telecommunication systems defined above but also to other suitable telecommunication 35 systems. The protocols used, the specifications of mobile telecommunication systems, their network elements and subscriber terminals, develop rapidly. Such development

16

may require extra changes to the described embodiments. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The 5 invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

17

Claims

Claims

1. A method of configuring support for emergency calls in a terminal device, the method comprising:

initiating in the terminal device a packet communication mode in which the 5 terminal device is configured to operate solely in a packet switched connection mode;

causing the terminal device in the packet communication mode to register into a cellular communication network, wherein the registration comprises indicating to the cellular communication network that the terminal device supports only a packet switched connection type and indicating to the cellular communication network that 10 the terminal device supports fallback to a circuit-switched connection in case a voice call is triggered;

triggering a voice call in the terminal device; and upon triggering the voice call, causing the terminal device to transmit a service request related to the fallback to the circuit switched connection for the voice 15 call.

2. The method of claim 1, wherein the indication to the cellular communication network that the terminal device supports the fallback to a circuit-switched connection for the voice call comprises causing transmission of a code word that explicitly indicates the support for the fallback to a circuit-switched connection for

20 the voice call.

3. The method of claim 2, wherein, the code word comprises an information element indicating whether or not the terminal device supports the fallback to the circuit-switched connection only for emergency voice calls.

4. The method of claim 2 or 3, wherein the code word comprises an 25 information element indicating whether or not the terminal device supports the fallback to the circuit-switched connection for all voice calls.

5. The method of any one of claims 2 to 4, wherein the code word is a one-bit indicator.

6. The method of any one of claims 2 to 5, wherein the code word is 30 comprised in an attach request and/or a tracking area update request message.

7. The method of any preceding claim, further comprising causing the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network during the registration.

8. The method of any preceding claim, further comprising causing the 35 terminal device to transmit capability information related to the fallback to the circuit

18

switched connection to the cellular communication network in an attach request requesting registration of the terminal device in the cellular communication network.

9. The method of any preceding claim, further comprising causing the terminal device to transmit capability information related to the fallback to the circuit

5 switched connection to the cellular communication network in a tracking area update request requesting for update of at least some of tracking area parameters.

10. The method of any preceding claim, further comprising causing the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network in a service request

10 requesting for the establishment of the voice call.

11. The method of claim 1, wherein the indication to the cellular communication network that the terminal device supports the fallback to a circuit-switched connection for the voice call comprises registering the terminal device to a circuit switched fallback for all circuit switched connections and indicating that the

15 terminal device supports only the packet switched connection type, wherein the combination of registering to the circuit switched fallback for all circuit switched connections and indicating the support for only the packet switched connection type indicates to the cellular communication network that the circuit switched fallback shall be applied only to the voice calls.

20 12. The method of claim 11, further comprising excluding transmission of at least some of circuit switched fallback parameters in connection with registering and causing transmission of the excluded circuit switched fallback parameters in the service request.

13. The method of claim 11, wherein the terminal device is configured for

25 use in a Universal Mobile Telecommunication System Long-Term Evolution network and/or in a Universal Mobile Telecommunication System Long-Term Evolution Advanced network.

14. A method of determining support for voice calls in a network apparatus of a cellular communication network, the method comprising:

30 acquiring from a terminal device a registration message to register the terminal device into a cellular communication network, wherein the registration comprises an indication from the terminal device that the terminal device supports only a packet switched connection type and an indication from the terminal device that the terminal device supports fallback to a circuit-switched connection in case a voice call

35 is triggered;

19

acquiring a service request related to a voice call from the terminal device;

and in response to the service request, preparing the fallback of the terminal device from the packet switched connection type to the circuit switched connection for 5 the voice call.

15. The method of claim 14, wherein the indication that the terminal device supports the fallback to a circuit-switched connection for the voice call comprises a code word that explicitly indicates the support for the fallback to a circuit-switched connection for only an emergency call, the method further comprising determining

10 from the code word that the terminal device supports the fallback to the circuit switched connection only in case of an emergency call and preventing the fallback to the circuit switched connection for any other circuit switched call type.

16. The method of claim 14, wherein the indication that the terminal device supports the fallback to a circuit-switched connection for the voice call comprises a

15 code word that explicitly indicates the support for the fallback to a circuit-switched connection for all voice calls, the method further comprising determining from the code word that the terminal device supports the fallback to the circuit switched connection for all voice calls and enabling the fallback to the circuit switched connection for any voice call type.

20 17. The method of claim 15 or 16, wherein the code word is a one-bit indicator.

18. The method of any one of claims 15 to 17, wherein the code word is comprised in an attach request and/or a tracking area update request message originated from the terminal device.

25 19. The method of any one of claims 14 to 18, further comprising acquiring capability information related to the fallback to the circuit switched connection from the terminal device during the registration of the terminal device.

20. The method of any one of claims 14 to 19, further comprising acquiring capability information related to the fallback to the circuit switched connection from

30 the terminal device in a service request requesting for the establishment of the voice call.

21. The method of claim 14, wherein the indication that the terminal device supports the fallback to a circuit-switched connection for the voice call comprises registering the terminal device to a circuit switched fallback for all circuit switched

35 connections and acquiring from the terminal device an indication that the terminal device supports only the packet switched connection type, the method further

20

comprising determining from the combination of registering the terminal device to the circuit switched fallback for all circuit switched connection and acquiring the indication of the support for only the packet switched connection type that the circuit switched fallback shall be applied only to the voice calls.

5 22. The method of claim 21, wherein the at least some of circuit switched fallback parameters of the terminal device are received in the service request.

23. The method of any preceding claim 14 to 22, further comprising determining the capability of the terminal device for the circuit switched fallback from the indication that the terminal device supports only a packet switched connection type

10 and the indication that the terminal device supports fallback to a circuit-switched connection in case a voice call is triggered, thereby discriminating the terminal device from terminal devices that do not have the capability for the circuit switched fallback.

24. The method of any preceding claim 14 to 23, wherein the network apparatus is configured for use in a Universal Mobile Telecommunication System

15 Long-Term Evolution network and/or in a Universal Mobile Telecommunication System Long-Term Evolution Advanced network.

25. An apparatus for configuring support for emergency calls, the apparatus comprising:

a processing system arranged to:

20 cause a terminal device to initiate a packet communication mode in which the terminal device is arranged to operate solely in a packet switched connection mode;

cause the terminal device in the packet communication mode to register into a cellular communication network, wherein the registration comprises indicating to the cellular communication network that the terminal device supports only a packet 25 switched connection type and indicating to the cellular communication network that the terminal device supports fallback to a circuit-switched connection in case a voice call is triggered;

trigger a voice call in the terminal device; and upon triggering the voice call, cause the terminal device to transmit a 30 service request related to the fallback to the circuit switched connection for the voice call.

26. The apparatus of claim 25, wherein processing system is arranged to cause the terminal device to transmit of a code word that explicitly indicates the support for the fallback to a circuit-switched connection for the voice call, thus

35 indicating to the cellular communication network that the terminal device supports the fallback to a circuit-switched connection for the voice call.

21

27. The apparatus of claim 26, wherein, the code word comprises an information element indicating whether or not the terminal device supports the fallback to the circuit-switched connection only for emergency voice calls.

28. The apparatus of claim 26 or 27, wherein the code word comprises an 5 information element indicating whether or not the terminal device supports the fallback to the circuit-switched connection for all voice calls.

29. The apparatus of claim 26, wherein the code word is a one-bit indicator.

30. The apparatus of any one of claims 26 to 29, wherein the processing system is arranged to cause the terminal device to insert the code word into an attach

10 request and/or a tracking area update request message.

31. The apparatus of any one of claims 25 to 30, wherein the processing system is further arranged to cause the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network during the registration.

15 32. The apparatus of any one of claims 25 to 31, wherein the processing system is further arranged to cause the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network in an attach request requesting registration of the terminal device in the cellular communication network.

20 33. The apparatus of any one of claims 25 to 32, wherein the processing system is further arranged to cause the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network in a tracking area update request requesting for update of at least some of tracking area parameters.

25 34. The apparatus of any one of claims 25 to 33, wherein the processing system is further arranged to cause the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network in a service request requesting for the establishment of the voice call.

30 35. The apparatus of claim 25, wherein the processing system is further arranged to cause the terminal device to register the terminal device to a circuit switched fallback for all circuit switched connections and to indicate that the terminal device supports only the packet switched connection type, wherein the combination of registering to the circuit switched fallback for all circuit switched connection and

35 indicating the support for only the packet switched connection type indicates to the

22

cellular communication network that the circuit switched fallback shall be applied only to the voice calls.

36. The apparatus of claim 35, wherein the processing system is further arranged to cause the terminal device to exclude transmission of at least some of

5 circuit switched fallback parameters in connection with registering, and to cause the terminal device to transmit the excluded circuit switched fallback parameters in the service request.

37. The apparatus of any preceding claim 25 to 36, wherein the apparatus is the terminal device, and wherein the apparatus further comprises radio interface

10 components providing the apparatus with radio communication capability.

38. The apparatus of any preceding claim 25 to 37, wherein processing system is arranged to configure the terminal device to operate in a Universal Mobile Telecommunication System Long-Term Evolution network and/or in a Universal Mobile Telecommunication System Long-Term Evolution Advanced network.

15 39. An apparatus for determining support for voice calls in a network apparatus of a cellular communication network, the apparatus comprising:

a processing system arranged to:

acquire from a terminal device a registration message to register the terminal device into a cellular communication network, wherein the registration 20 comprises an indication from the terminal device that the terminal device supports only a packet switched connection type and an indication from the terminal device that the terminal device supports fallback to a circuit-switched connection in case a voice call is triggered;

acquire a service request related to a voice call from the terminal device;

25 and in response to the service request, prepare the fallback of the terminal device from the packet switched connection type to the circuit switched connection for the voice call.

40. The apparatus of claim 39, wherein the indication that the terminal 30 device supports the fallback to a circuit-switched connection for the voice call comprises a code word that explicitly indicates the support for the fallback to a circuit-switched connection for only an emergency call, and wherein the processing system is further arranged to determine from the code word that the terminal device supports the fallback to the circuit switched connection only in case of an emergency call and 35 preventing the fallback to the circuit switched connection for any other circuit switched call type.

23

41. The apparatus of claim 39, wherein the indication that the terminal device supports the fallback to a circuit-switched connection for the voice call comprises a code word that explicitly indicates the support for the fallback to a circuit-switched connection for all voice calls, and wherein the processing system is further

5 arranged to determine from the code word that the terminal device supports the fallback to the circuit switched connection for all voice calls and to enable the fallback to the circuit switched connection for any voice call type.

42. The apparatus of claim 40 or 41, wherein the code word is a one-bit indicator.

10 43. The apparatus of any one of claims 39 to 42, wherein the code word is comprised in an attach request and/or a tracking area update request message originated from the terminal device.

44. The apparatus of any one of claims 39 to 43, wherein the processing system is further arranged to acquire capability information related to the fallback to

15 the circuit switched connection from the terminal device during the registration of the terminal device.

45. The apparatus of any one of claims 36 to 44, wherein the processing system is further arranged to acquire capability information related to the fallback to the circuit switched connection from the terminal device in a service request requesting

20 for the establishment of the voice call.

46. The apparatus of claim 39, wherein the processing system is further arranged to register the terminal device to a circuit switched fallback for all circuit switched connections, to acquire from the terminal device an indication that the terminal device supports only the packet switched connection type, and to determine

25 that the circuit switched fallback shall be applied only to the voice calls from the combination that the terminal device is registered to the circuit switched fallback for all circuit switched connection and that the processing system has acquired the indication of the support for only the packet switched connection type.

47. The apparatus of claim 46, wherein the at least some of circuit switched

30 fallback parameters of the terminal device are acquired in the service request.

48. The apparatus of any one of claims 39 to 47, wherein the processing system is further arranged to determine the capability of the terminal device for the circuit switched fallback from the indication that the terminal device supports only a packet switched connection type and the indication that the terminal device supports

35 fallback to a circuit-switched connection in case a voice call is triggered, thereby

24

discriminating the terminal device from terminal devices that do not have the capability for the circuit switched fallback.

49. The apparatus of any one of claims 39 to 48, wherein the apparatus is the network apparatus further comprising input/output components providing the

5 apparatus with communication capability with the terminal device.

50. The apparatus of any one of claims 25 to 37, wherein processing system is arranged to configure the apparatus to operate in a Universal Mobile Telecommunication System Long-Term Evolution network and/or in a Universal Mobile Telecommunication System Long-Term Evolution Advanced network.

10 51. An apparatus comprising means for configuring a terminal device to carry out the method according to any one of claims 1 to 13.

52. An apparatus comprising means for configuring a network element of a cellular communication network to carry out the method according to any one of claims 14 to 24.

15 53. A computer readable medium comprising a set of instructions, which,

when executed on a terminal device, causes the terminal device to perform the steps of any one of claims 1 to 13.

54. A computer readable medium comprising a set of instructions, which, when executed on a network element of a cellular communication network, causes the

20 network element to perform the steps of any one of claims 14 to 24.

25

Amendments to the Claims have been filed as follows Claims

1. A method of configuring support for emergency calls in a terminal device that supports a packet communication mode and a circuit-switched communication mode, the method comprising:

initiating in the terminal device a packet communication mode in which the terminal device is configured to operate solely in a packet switched connection mode;

causing the terminal device in the packet communication mode to register into a cellular communication network, wherein the registration comprises indicating to the cellular communication network that the terminal device supports only a packet switched connection type and indicating to the cellular communication network that the terminal device supports fallback to a circuit-switched connection in case a voice call is triggered by the terminal device;

triggering a voice call in the terminal device; and upon triggering the voice call, causing the terminal device to transmit a service request related to the fallback to the circuit switched connection for the voice call.

2. The method of claim 1, wherein the indication to the cellular communication network that the terminal device supports the fallback to a circuit-switched connection for the voice call comprises causing transmission of a code word that explicitly indicates the support for the fallback to a circuit-switched connection for the voice call.

3. The method of claim 2, wherein, the code word comprises an information element indicating whether or not the terminal device supports the fallback to the circuit-switched connection only for emergency voice calls.

4. The method of claim 2 or 3, wherein the code word comprises an information element indicating whether or not the terminal device supports the fallback to the circuit-switched connection for all voice calls.

5. The method of any one of claims 2 to 4, wherein the code word is a one-bit indicator.

6. The method of any one of claims 2 to 5, wherein the code word is comprised in an attach request and/or a tracking area update request message.

7. The method of any preceding claim, further comprising causing the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network during the registration.

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8. The method of any preceding claim, further comprising causing the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network in an attach request requesting registration of the terminal device in the cellular communication network.

5 9. The method of any preceding claim, further comprising causing the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network in a tracking area update request requesting for update of at least some of tracking area parameters.

10. The method of any preceding claim, further comprising causing the 10 terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network in a service request requesting for the establishment of the voice call.

11. The method of claim 1, wherein the indication to the cellular communication network that the terminal device supports the fallback to a circuit-

15 switched connection for the voice call comprises registering the terminal device to a circuit switched fallback for all circuit switched connections and indicating that the terminal device supports only the packet switched connection type, wherein the combination of registering to the circuit switched fallback for all circuit switched connections and indicating the support for only the packet switched connection type 20 indicates to the cellular communication network that the circuit switched fallback shall be applied only to the voice calls.

12. The method of claim 11, further comprising excluding transmission of at least some of circuit switched fallback parameters in connection with registering and causing transmission of the excluded circuit switched fallback parameters in the

25 service request.

13. The method of claim 11, wherein the terminal device is configured for use in a Universal Mobile Telecommunication System Long-Term Evolution network and/or in a Universal Mobile Telecommunication System Long-Term Evolution Advanced network.

30 14. A method of determining support for voice calls in a network apparatus of a cellular communication network, the method comprising:

acquiring from a terminal device, which supports a packet communication mode and a circuit-switched communication mode, a registration message to register the terminal device into a cellular communication network, wherein the registration 35 comprises an indication from the terminal device that the terminal device supports only a packet switched connection type and an indication from the terminal device that the

27

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terminal device supports fallback to a circuit-switched connection in case a voice call is triggered by the terminal device;

acquiring a service request related to a voice call from the terminal device;

and

5 in response to the service request, preparing the fallback of the terminal device from the packet switched connection type to the circuit switched connection for the voice call.

15. The method of claim 14, wherein the indication that the terminal device supports the fallback to a circuit-switched connection for the voice call comprises a 10 code word that explicitly indicates the support for the fallback to a circuit-switched connection for only an emergency call, the method further comprising determining from the code word that the terminal device supports the fallback to the circuit switched connection only in case of an emergency call and preventing the fallback to the circuit switched connection for any other circuit switched call type. 15 16. The method of claim 14, wherein the indication that the terminal device supports the fallback to a circuit-switched connection for the voice call comprises a code word that explicitly indicates the support for the fallback to a circuit-switched connection for all voice calls, the method further comprising determining from the code word that the terminal device supports the fallback to the circuit switched 20 connection for all voice calls and enabling the fallback to the circuit switched connection for any voice call type.

17. The method of claim 15 or 16, wherein the code word is a one-bit indicator.

18. The method of any one of claims 15 to 17, wherein the code word is 25 comprised in an attach request and/or a tracking area update request message originated from the terminal device.

19. The method of any one of claims 14 to 18, further comprising acquiring capability information related to the fallback to the circuit switched connection from the terminal device during the registration of the terminal device.

30 20. The method of any one of claims 14 to 19, further comprising acquiring capability information related to the fallback to the circuit switched connection from the terminal device in a service request requesting for the establishment of the voice call.

21. The method of claim 14, wherein the indication that the terminal device 35 supports the fallback to a circuit-switched connection for the voice call comprises registering the terminal device to a circuit switched fallback for all circuit switched

28

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connections and acquiring from the terminal device an indication that the terminal device supports only the packet switched connection type, the method further comprising determining from the combination of registering the terminal device to the circuit switched fallback for all circuit switched connection and acquiring the 5 indication of the support for only the packet switched connection type that the circuit switched fallback shall be applied only to the voice calls.

22. The method of claim 21, wherein the at least some of circuit switched fallback parameters of the terminal device are received in the service request.

23. The method of any preceding claim 14 to 22, further comprising 10 determining the capability of the terminal device for the circuit switched fallback from the indication that the terminal device supports only a packet switched connection type and the indication that the terminal device supports fallback to a circuit-switched connection in case a voice call is triggered, thereby discriminating the terminal device from terminal devices that do not have the capability for the circuit switched fallback. 15 24. The method of any preceding claim 14 to 23, wherein the network apparatus is configured for use in a Universal Mobile Telecommunication System Long-Term Evolution network and/or in a Universal Mobile Telecommunication System Long-Term Evolution Advanced network.

25. An apparatus for configuring support for emergency calls, the apparatus 20 comprising:

a processing system arranged to:

cause a terminal device, which supports a packet communication mode and a circuit-switched communication mode, to initiate a packet communication mode in which the terminal device is arranged to operate solely in a packet switched connection 25 mode;

cause the terminal device in the packet communication mode to register into a cellular communication network, wherein the registration comprises indicating to the cellular communication network that the terminal device supports only a packet switched connection type and indicating to the cellular communication network that 30 the terminal device supports fallback to a circuit-switched connection in case a voice call is triggered by the terminal device;

trigger a voice call in the terminal device; and upon triggering the voice call, cause the terminal device to transmit a service request related to the fallback to the circuit switched connection for the voice 35 call.

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26. The apparatus of claim 25, wherein processing system is arranged to cause the terminal device to transmit of a code word that explicitly indicates the support for the fallback to a circuit-switched connection for the voice call, thus indicating to the cellular communication network that the terminal device supports the

5 fallback to a circuit-switched connection for the voice call.

27. The apparatus of claim 26, wherein, the code word comprises an information element indicating whether or not the terminal device supports the fallback to the circuit-switched connection only for emergency voice calls.

28. The apparatus of claim 26 or 27, wherein the code word comprises an

10 information element indicating whether or not the terminal device supports the fallback to the circuit-switched connection for all voice calls.

29. The apparatus of claim 26, wherein the code word is a one-bit indicator.

30. The apparatus of any one of claims 26 to 29, wherein the processing system is arranged to cause the terminal device to insert the code word into an attach

15 request and/or a tracking area update request message.

31. The apparatus of any one of claims 25 to 30, wherein the processing system is further arranged to cause the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network during the registration.

20 32. The apparatus of any one of claims 25 to 31, wherein the processing system is further arranged to cause the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network in an attach request requesting registration of the terminal device in the cellular communication network.

25 33. The apparatus of any one of claims 25 to 32, wherein the processing system is further arranged to cause the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network in a tracking area update request requesting for update of at least some of tracking area parameters.

30 34. The apparatus of any one of claims 25 to 33, wherein the processing system is further arranged to cause the terminal device to transmit capability information related to the fallback to the circuit switched connection to the cellular communication network in a service request requesting for the establishment of the voice call.

35 35. The apparatus of claim 25, wherein the processing system is further arranged to cause the terminal device to register the terminal device to a circuit

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switched fallback for all circuit switched connections and to indicate that the terminal device supports only the packet switched connection type, wherein the combination of registering to the circuit switched fallback for all circuit switched connection and indicating the support for only the packet switched connection type indicates to the 5 cellular communication network that the circuit switched fallback shall be applied only to the voice calls.

36. The apparatus of claim 35, wherein the processing system is further arranged to cause the terminal device to exclude transmission of at least some of circuit switched fallback parameters in connection with registering, and to cause the

10 terminal device to transmit the excluded circuit switched fallback parameters in the service request.

37. The apparatus of any preceding claim 25 to 36, wherein the apparatus is the terminal device, and wherein the apparatus further comprises radio interface components providing the apparatus with radio communication capability.

15 38. The apparatus of any preceding claim 25 to 37, wherein processing system is arranged to configure the terminal device to operate in a Universal Mobile Telecommunication System Long-Term Evolution network and/or in a Universal Mobile Telecommunication System Long-Term Evolution Advanced network.

39. An apparatus for determining support for voice calls in a network 20 apparatus of a cellular communication network, the apparatus comprising:

a processing system arranged to:

acquire from a terminal device, which supports a packet communication mode and a circuit-switched communication mode, a registration message to register the terminal device into a cellular communication network, wherein the registration 25 comprises an indication from the terminal device that the terminal device supports only a packet switched connection type and an indication from the terminal device that the terminal device supports fallback to a circuit-switched connection in case a voice call is triggered by the terminal device;

acquire a service request related to a voice call from the terminal device;

30 and in response to the service request, prepare the fallback of the terminal device from the packet switched connection type to the circuit switched connection for the voice call.

40. The apparatus of claim 39, wherein the indication that the terminal 35 device supports the fallback to a circuit-switched connection for the voice call comprises a code word that explicitly indicates the support for the fallback to a circuit-

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switched connection for only an emergency call, and wherein the processing system is further arranged to determine from the code word that the terminal device supports the fallback to the circuit switched connection only in case of an emergency call and preventing the fallback to the circuit switched connection for any other circuit 5 switched call type.

41. The apparatus of claim 39, wherein the indication that the terminal device supports the fallback to a circuit-switched connection for the voice call comprises a code word that explicitly indicates the support for the fallback to a circuit-switched connection for all voice calls, and wherein the processing system is further

10 arranged to determine from the code word that the terminal device supports the fallback to the circuit switched connection for all voice calls and to enable the fallback to the circuit switched connection for any voice call type.

42. The apparatus of claim 40 or 41, wherein the code word is a one-bit indicator.

15 43. The apparatus of any one of claims 39 to 42, wherein the code word is comprised in an attach request and/or a tracking area update request message originated from the terminal device.

44. The apparatus of any one of claims 39 to 43, wherein the processing system is further arranged to acquire capability information related to the fallback to

20 the circuit switched connection from the terminal device during the registration of the terminal device.

45. The apparatus of any one of claims 36 to 44, wherein the processing system is further arranged to acquire capability information related to the fallback to the circuit switched connection from the terminal device in a service request requesting

25 for the establishment of the voice call.

46. The apparatus of claim 39, wherein the processing system is further arranged to register the terminal device to a circuit switched fallback for all circuit switched connections, to acquire from the terminal device an indication that the terminal device supports only the packet switched connection type, and to determine

30 that the circuit switched fallback shall be applied only to the voice calls from the combination that the terminal device is registered to the circuit switched fallback for all circuit switched connection and that the processing system has acquired the indication of the support for only the packet switched connection type.

47. The apparatus of claim 46, wherein the at least some of circuit switched

35 fallback parameters of the terminal device are acquired in the service request.

32

48. The apparatus of any one of claims 39 to 47, wherein the processing system is further arranged to determine the capability of the terminal device for the circuit switched fallback from the indication that the terminal device supports only a packet switched connection type and the indication that the terminal device supports fallback to a circuit-switched connection in case a voice call is triggered, thereby discriminating the terminal device from terminal devices that do not have the capability for the circuit switched fallback.

49. The apparatus of any one of claims 39 to 48, wherein the apparatus is the network apparatus further comprising input/output components providing the apparatus with communication capability with the terminal device.

50. The apparatus of any one of claims 25 to 37, wherein processing system is arranged to configure the apparatus to operate in a Universal Mobile Telecommunication System Long-Term Evolution network and/or in a Universal Mobile Telecommunication System Long-Term Evolution Advanced network.

51. An apparatus comprising means for configuring a terminal device to carry out the method according to any one of claims 1 to 13.

52. An apparatus comprising means for configuring a network element of a cellular communication network to carry out the method according to any one of claims 14 to 24.

53. A computer readable medium comprising a set of instructions, which, when executed on a terminal device, causes the terminal device to perform the steps of any one of claims 1 to 13.

54. A computer readable medium comprising a set of instructions, which, when executed on a network element of a cellular communication network, causes the network element to perform the steps of any one of claims 14 to 24.