WO2015113586A1 - Handover of subscriber terminal of mobile communications network - Google Patents

Handover of subscriber terminal of mobile communications network Download PDF

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Publication number
WO2015113586A1
WO2015113586A1 PCT/EP2014/051560 EP2014051560W WO2015113586A1 WO 2015113586 A1 WO2015113586 A1 WO 2015113586A1 EP 2014051560 W EP2014051560 W EP 2014051560W WO 2015113586 A1 WO2015113586 A1 WO 2015113586A1
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handover
subscriber terminal
switching center
mobile switching
subscriber
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PCT/EP2014/051560
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French (fr)
Inventor
Laszlo Tatrai
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Nokia Solutions And Networks Oy
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATIONS NETWORKS
    • H04W36/00Handoff or reselection arrangements
    • H04W36/12Reselecting a serving backbone network switching or routing node

Abstract

There is provided a method comprising, determining a need to perform a handover of a subscriber terminal in a mobile communications network, said subscriber terminal participating in a voice group call as a talker, obtaining a subscriber identifier of the subscriber terminal, causing to transmit a message towards a target mobile switching center, said message including the obtained subscriber identifier, for performing the hand- over from a source mobile switching center to a target mobile switching center in the communications network.

Description

DESCRIPTION TITLE

HANDOVER OF SUBSCRIBER TERMINAL OF MOBILE COMMUNICATIONS NETWORK FIELD

The present invention relates to a handover in a mobile communications network and more particularly to a handover between mobile switching centers during a voice group call.

BACKGROUND

The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.

Global System for Mobile Communications - Railway (GSM-R) is used by railway companies to operate their railway business which means in time control and safe working of trains. This encompasses ground-train voice and data communications, together with the ground-based mobile communications needs of shunting yards, trackside workers, station and depot staff and railway administrative and managerial persons.

European Integrated Railway Radio Enhanced Network (EIRENE) and Mobile

Radio for Railways Networks in Europe (MORANE) specifications are the binding standards, which describe the functional and system requirements for GSM-R networks including interoperability across borders.

The utmost part of the GSM-R features is described in 3GPP and Railway Standardization. GSM-R is a secure platform for voice and data communication between railway operational staff, including drivers, dispatchers, shunting team members, train engineers, and station controllers. It delivers features such as voice group call service (VGCS), voice broadcast service (VBS), location-based connections, and call pre-emption in case of an emergency. This will support applications such as cargo tracking, video sur- veillance in trains and at stations, and passenger information services.

GSM-R is typically implemented using dedicated base station towers close to the railway. The distance between the base stations is 7-15 km. This creates a high degree of redundancy and higher availability and reliability. VGCS allows a great number of users to participate in the same call. This feature imitates the analogue PMR (Private Mobile Radio) group call with the PTT key (Push- to-Talk).

VBS is a broadcast group call: this means that compared to VGCS, only the initiator of the call can speak. The others who join the call can only be listeners. This kind of call is mainly used to broadcast recorded messages or to make announcements.

In GSM-R, participants in a voice group call, e.g. the VGCS or VBS may be moving at a great speed when they are on board a train moving e.g. 200 km/h. Communications of the moving participants in the voice group call is facilitated by handovers of the participants' subscriber terminals in the GSM-R network. Typical handovers include handovers of the subscriber terminals from one base station to another and handovers of the subscriber terminals between mobile switching centers (MSC).

However if a subscriber that is currently a talker in the voice group call or the initiator of the voice group call makes a handover from a source MSC to a target MSC inside the group call service area, the subscriber does not receive the paging notification due to a point-to-point call as the location of the subscriber is maintained in the source MSC. This causes that point-to-point calls to the subscriber are routed to the last know location of the subscriber, which is the old MSC. The new location of the subscriber is updated in the GSM-R network only after the subscriber stops the talking in the voice group call and resources needed for the voice transmission are released.

The source MSC of the handover cannot transfer the paging message to the target MSC of the handover as connectionless messages are not transferred via the Mobile Application Part (MAP) E interface between MSCs. The MAP is specified in 3GPP TS 29.002 Mobile Application Part (MAP) specification, version 10.6.0.

BRIEF DESCRIPTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

An object of the present invention is to provide methods and apparatuses and computer program products for implementing the methods so as to alleviate at least part of the above problems. The objects of the invention are achieved by methods and apparatuses and computer program products which are characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.

According to an aspect there is provided a method comprising, determining a need to perform a handover of a subscriber terminal in a mobile communications network, said subscriber terminal participating in a voice group call as a talker, obtaining a subscriber identifier of the subscriber terminal, causing to transmit a message towards a target mobile switching center, said message including the obtained subscriber identifier, for performing the handover from a source mobile switching center to a target mobile switching center in the communications network.

According to an aspect there is provided a method comprising, obtaining a message indicating a request for a handover of a subscriber terminal in a mobile communications network, said subscriber terminal participating in a voice group call as a talker, from a source mobile switching center to a target mobile switching center in the mobile communications network, executing the handover, obtaining a message indicating a com- pletion of the handover, obtaining a subscriber identifier of the subscriber terminal from the message indicating the request for the handover or, requesting the subscriber identifier from the subscriber terminal in response to a completion of the handover.

According to an aspect there is provided an apparatus comprising an interfacing unit for communications of messages related to a handover of subscriber terminal from a source mobile switching center to a target mobile switching center in a communications network, and a handover unit operatively connected to the interfacing unit and configured to cause the apparatus to determine a need to perform a handover of a subscriber terminal in a mobile communications network, said subscriber terminal participating in a voice group call as a talker, to obtain a subscriber identifier of the subscriber terminal, to cause to transmit a message towards the target mobile switching center, said message including the obtained subscriber identifier, for performing the handover from the source mobile switching center to the target mobile switching center in the communications network.

According to an aspect there is provided an apparatus comprising an interfacing unit for communications of messages related to a handover subscriber terminal from a source mobile switching center to a target mobile switching center in a communications network, and a handover unit operatively connected to the interfacing unit and configured to cause the apparatus to obtain a message indicating a request for a handover of a subscriber terminal in the mobile communications network, said subscriber terminal participating in a voice group call as a talker, from the source mobile switching center to the target mobile switching center in the mobile communications network, to execute the handover, to obtain a message indicating a completion of the handover, to obtain a subscriber identifier of the subscriber terminal from the message indicating the request for the handover or, requesting the subscriber identifier from the subscriber terminal in response to a completion of the handover.

According to an aspect there is provided a computer program embodied on a non-transitory computer readable storage medium, the computer program being config- ured to control a processor to perform a method according to an aspect.

According to an aspect there is provided an apparatus according to any one of claim including means to perform a method according to an aspect.

According to an aspect there is provided a computer program product comprising executable code that when executed, cause execution of functions of a method according to an aspect.

Further aspects are described in the detailed description and the claims.

Some embodiments provide an improvement to updating the location of the subscriber terminal participating in a voice group call as a talker in case of handover of the subscriber terminal between mobile switching centers. BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Figure 1 illustrates architecture of a mobile communications network including mobile switching centers according to an embodiment;

Figure 2 illustrates radio network nodes connected to different mobile switching centers and a subscriber terminal participating in a group call as a talker moving between service areas of the radio network nodes;

Figures 3a and 3b illustrate message flows during handovers according to embodiments;

Figures 4a illustrates process for causing to transmit a message towards a target mobile switching center for performing a handover from a source mobile switching center to the target mobile switching center;

Figure 4b illustrates a process for obtaining a subscriber identifier of the subscriber terminal in connection with a handover of the subscriber terminal from a source mobile switching center to the target mobile switching center

Figure 5 illustrates an apparatus for carrying out an embodiment.

DETAILED DESCRIPTION

In various embodiments a subscriber terminal participating in a voice group call as a talker refers to a subscriber terminal that is allocated resources for communi- eating voice from the subscriber terminal to a mobile communications network. The sub- scriber terminal may be the initiator of the voice group call or any subscriber terminal that is in turn to talk in the voice group call. Typically, only one subscriber terminal is in turn to talk at a time. The allocated resources may comprise a traffic channel on a radio link between the subscriber terminal and a radio network node, e.g. a base station. The radio link is used to transmit voice from the subscriber terminal to the radio network node and the radio link may be referred to as an uplink connection.

Figure 1 illustrates an architecture of a mobile communications network 100 including Mobile Switching Centers (MSCs) 102, 104 according to an embodiment. The mobile communications network offers services to subscribers holding a subscription to the network. The services offered may include voice calls, voice group calls, data transmission and/or message transmission. A subscriber may obtain access to the mobile communications network via terminal 108 that is capable to communicate in the mobile communications network. This terminal may be referred to as a subscriber terminal. Typically the subscriber terminal includes a Subscriber Identity Module (SIM) that is used to authenticate the subscriber to the mobile communications network. In this way the mobile communication network can provide its services only to those subscribers who are subscribed to the mobile communications network.

The mobile communications network includes one or more radio network nodes connected to the MSC. The radio network nodes serve subscriber terminals 108 by providing radio access to the mobile communications network. The radio access may be provided by transmission of radio frequency signals between the radio network nodes and the subscriber terminal over an air interface Urn. The range of radio frequency transmissions is limited to the coverage area of each radio network node, whereby the coverage area may be used to define the service area of the radio network node 106. One radio network node may have one or more cells, where the radio frequency transmission is provided. A cell may be identified by a cell identifier.

The interface between the radio network node and the mobile switching center may be defined by an interface A and the MSCs may be interconnected by an interface E. The air interface may be provided a wireless radio connection according to a communica- tions standard, including the 3GPP GSM, GSM-R, 3G, LTE, LTE-A or IEEE 802.1 1 based wireless local area network connection. The A and E interfaces may be provided by wired or wireless connections according to any of the above defined communications standards.

In an embodiment, the radio network nodes are a part of a Base Station Subsystem (BSS), where the radio network nodes are base stations controlled by a base sta- tion controller (BSC) that performs the radio resource management functionality. This embodiment may be according to the GSM or GSM-R specifications. In various embodiments the radio network nodes may be referred to as NodeBs or evolved NodeBs or access points, and the base station controller may be referred to as a Radio Network Controller (RNC).

In an embodiment, the mobile communications network provides its subscrib- ers a voice group call as a service. The voice group call may be a voice call, where voice of at least one person is communicated from one subscriber terminal to a plurality of other subscriber terminals, as a service by the mobile communications network. It is possible that only one person can be talking during a voice group call. Also, more than one person can be talking in a voice group call, but in such a case the talkers should take turns. The mobile communications network may implement a service logic of the voice group call in a mobile switching center or a service control node, whereby the number of persons talking in a voice group call may be controlled.

When a person is talking in a voice group call, the subscriber terminal used by the person may receive the utterances of the person and transmits the received voice to the mobile communications network. The voice of the user is processed for transmission in the subscriber terminal and transmitted to the mobile communications network for delivery to the voice group call participants, and therefore it does not need to be discussed herein any further. Transmission of voice data in the group call from the subscriber terminal may be provide by a traffic channel allocated to the subscriber terminal in an uplink connection to the radio network node, e.g. a base station. In the context of GSM or GSM- R mobile communications network, the voice group call may be refer to VBS or VGCS.

A mobile communications network according to an embodiment may conform to some other technology than the GSM or GSM-R, whereby the specific terminology used or the parts of the mobile communications network and/or the services it provides may vary.

Figure 2 illustrates radio network nodes connected to different mobile switching centers 202, 204 and a subscriber terminal 210 participating in a group call as a talker moving between service areas of the radio network nodes 206a, 206b. The MSCs and the radio network nodes may be as described with Figure 1 .

The moving subscriber terminal may a passenger or railway personnel on board a train, or a transceiver module including a subscription or a transceiver module connected to a device including the subscription. The subscription may be implemented by a SIM card for example.

The MSCs provide the group call service to the subscriber terminal. The tasks of the MSC include connection management for group call e.g. connection establishment and tear down of connections. The group call service may be defined by a service logic that is executed by the MSC for providing the service. The MSC may include a combination of software and/or hardware elements to facilitate execution of the service logic.

In an embodiment a subscriber terminal may have various modes in a group call provided by the service logic. In a Receive Mode (RM), the subscriber terminal is only receiving communications, i.e. listening to the other participant in the group call. In the RM, the subscriber terminal listens to the downlink communication of a VBS channel or a VGCS channel. The channel may be allocated specific to each cell of the radio network nodes.

In a Transmit Mode, the subscriber terminal is both receiving and transmitting communications. In this mode, the subscriber terminal is allocated two dedicated control channels, one of them being a Slow Associated Control Channel (SACCH). Preferably, only one subscriber terminal is in TM at a time

Occasionally, as is conventional, the subscriber terminal has to listen to the Broadcast Control Channel (BCCH) of the serving cell, for example as defined in 3GPP TS 43.022 and 3GPP TS 45.008.

A plurality of users may be participating in the group call. Users participating in the group call are connected to the call by the service logic of the voice group call. The service logic may be executed by the MSC that is serving the subscriber terminal and/or the MSC under which the subscriber terminal is located. Preferably, in the group call, only one participant is talking at a time. This participant may be the initiator of the voice group call or the subsequent talker in the group call, who has obtained his turn to talk after the initiator or after a previous talker in the group call.

In the scenario of Figure 2, the subscriber terminal 210 is moving from the service area of the radio network node 206 to the service are of the radio network node 206b. The service areas of the radio network nodes are limited and the movement of the subscriber terminal causes a handover to take place from the radio network node 206a to the radio network node 206b. Since the radio network nodes are connected to different MSCs, the handover between the radio network nodes causes a handover from one MSC to another, i.e. an inter-MSC handover. In the inter-MSC handover the voice group call the subscriber terminal is participating is switched from the source MSC, MSC 102, to the target MSC, MSC 104. In this way the subscriber terminal may continue participating in the voice group call as a talker.

Figures 3a and 3b illustrate message flows during handovers according to embodiments. In the following the message flows of Figures 3a and 3b are explained with reference to Figure 4a illustrating a process for causing to transmit a message towards a target mobile switching center for performing a handover from a source mobile switching center to the target mobile switching center, and to Figure 4b illustrating a process for ob- taining a subscriber identifier of the subscriber terminal in connection with a handover of the subscriber terminal from a source mobile switching center to the target mobile switching center.

The process of Figure 4a may be performed by a radio network node or a subscriber terminal or the source MSC in the inter-MSC handover. The process of Figure 4b may be performed by the target MSC in the inter-MSC handover. In the processes, the subscriber terminal may be moving from the service area of one radio network node to the service area of another as illustrated in Figure 2. The service areas maybe provided by corresponding cells. In the handover, the subscriber terminal is moved from the service area of source radio network node to the service area of the target radio network node. The processes may start 402, 412, when the device performing the method is connected to the mobile communications network according to Figure 1 and capable of communicating handover related messages for executing the inter-MSC handover.

In Figure 3a and Figure 3b a location of the subscriber terminal participating in a voice group call as a talker is updated to the target mobile switching center in the handover. The mobile switching center may be provided in the mobile communications network according to Figure 1.

In the message flow of Figure 3a, the location is updated by a message 304 transmitted 408 from the source MSC to the target MSC and including the subscriber iden- tifier of the subscriber terminal. Preferably the message is transmitted in response to a determined 404 need to perform the handover.

In the message flow of Figure 3b, the location is updated in response to a completion 418 of the handover. The location is updated by a message that includes the subscriber identifier of the subscriber terminal and the message 324 is transmitted 420 from the subscriber terminal to the target mobile switching center of the handover. Preferably the message transmitted 420 immediately after competition of the handover.

When the location of the subscriber terminal is updated to the target MSC, a paging notification of an incoming point-to-point call to the subscriber terminal may be routed to the target MSC of the inter-MSC handover immediately after the handover is completed.

An embodiment is now referred to in more detail by reference to Figure 3a. The message flow involves a subscriber terminal (MS), one or more radio network nodes (BSS-A, BSS-B) and MSCs (MSC-A, MSC-B), which may a part of the mobile communications network illustrated in Figure 1 .

In 404 a message 302 is received from the radio network nodes, said message indicating that a handover of the subscriber terminal is required. The message may be received for example after the subscriber terminal and/or one or more of the radio net- work nodes have performed measurements of signal quality performed.

The MSC-A may determine 404 on the basis of the received message that a handover of the subscriber terminal is needed. The MSC-A is serving the subscriber terminal in the group voice call and knows the subscriber identifier of the subscriber terminal. The subscriber identifier of the subscriber terminal may have been obtained 406 by the MSC-A from a database storing subscriber identifiers served by the MSC-A. Examples of the databases comprise e.g. a Visitor Location Register (VLR) or a Home Location Register (HLR).

In 408 the MSC-A causes a message transmission 304, 414 towards the tar- get mobile switching center MSC-B, said message including the obtained subscriber identifier, for performing the handover from the source mobile switching center MSC-A to the target mobile switching center MSC-B in the communications network. Preferably the message is a handover request. In this way the MSC-B may obtain 420 the subscriber identifier.

The handover is executed in 316, 416, after which a message 318 indicating a completion of the handover is obtained from the radio network nodes. This message may follow a successful radio connection establishment of the subscriber terminal to the radio network node of the MSC-B.

The subscriber identifier included in the message to the target MSC-B allows implicit updating 320 of the location of the subscriber terminal to the MSC-B, whereby the subscriber terminal may be paged for point-to-point calls after the completion of the handover.

In an embodiment, the MSC-A maintains information of subscriber terminals that are served by the MSC-A and information of services it provides to the subscriber terminals. The maintaining may comprise obtaining from incoming service requests information that identifies the subscriber terminal served by the MSC-A and the associated service. This information may be used in executing the service logic of the voice group call.

Accordingly, when the subscriber terminal initiates a voice group call, it causes to transmit a request for the voice group call to the MSC-A. The MSC-A then stores the subscriber identifier and an identifier of the requested service, i.e. voice group call. The MSC-A also stores also information regarding, whether the subscriber terminal is in turn to talk in the group call. The stored information may be used to determine whether or not to include the subscriber identifier to the message 304. The subscriber identifier may be in- eluded to the message only, when the subscriber terminal has the turn to talk, i.e. is the current talker in the voice group call. And, if the subscriber terminal is not in turn to talk, the transmission of the subscriber identifier may be omitted. In this way sending unneces- sary information may be avoided in the inter-MSC handover.

In 410 the subscriber identifier has been transmitted to the MSC-B and the location of the subscriber terminal may be updated to the MSC-B, and the process may end.

An embodiment is now referred to in more detail by reference to Figure 3b. In 414, the MSC-B and MSC-B are executing the handover that is initiated by the message 302 to the MSC-A. The execution 317, 416 of the handover may comprise the MSC-A sending 414 a handover request to the MSC-B. The handover execution may include reserving resources in the radio network nodes BSS-B connected to the MSC-B and informing the MSC-B about the voice group call service to be provided to the subscriber termi- nal, for example.

In 418 a message 318 is obtained indicating a completion of the handover. In 420 the subscriber identifier of the subscriber terminal is determined. The subscriber identifier may be determined on the basis of an identity request procedure 324 between the MSC-B and the subscriber terminal. The identity request procedure allows implicit location update of the subscriber terminal to the MSC-B. The identity request is preferably initiated in response to the completion of the handover, e.g. in response to receiving the message 318. After completion of the handover, the subscriber terminal is served by the radio network node, e.g. the target cell, connected to the MSC-B. In this way the identity request procedure may be started immediately after the handover has been completed to obtain the subscriber identifier of the subscriber terminal. The identity request procedure may comprise a request from the MSC-B to the subscriber terminal for the subscriber identifier. The subscriber terminal responds to the request by a message including the requested subscriber identifier.

The subscriber identifier may be IMSI or TMSI. The TMSI serves as an identi- fier of the subscriber terminal only to one MSC that is preferably the MSC that has assigned the TMSI to the subscriber terminal. If the MSC-B receives the TMSI as subscriber identifier, the MSC-B may obtain the IMSI of the subscriber terminal from the MSC-A, where the IMSI is stored to a subscriber database, e.g. VLR or HLR, connected to the MSC-A. The obtaining may comprise sending a request for the IMSI. The request includes the TMSI and the MSC-A responds to the request by a message including the IMSI corresponding to the TMSI in the request. In this way the MSC-B may obtain the IMSI for uniquely identifying the subscriber terminal. The IMSI may be obtained from the MSC-A by employing a procedure, e.g. the MAP Send Identification service in the TS 29.002 Section 8.1.4.

It should be appreciated that in 420 the subscriber identifier may be transmitted to the MSC-B by the subscriber terminal after the subscriber terminal determines 404 a need to perform the handover the on the basis of the signal quality measurements for example. The subscriber terminal may be participating in the voice group call as a talker, whereby the subscriber terminal is allocated an uplink traffic channel for communications of voice in the voice group call. The subscriber terminal knows 406 its subscriber identifier from its SIM card and any identifier, e.g. a Temporary Mobile Subscriber Identity (TMSI), assigned to the subscriber terminal by the mobile communications network. After completion of the handover, preferably immediately after the completion, the subscriber terminal is caused to transmit a message towards the target mobile switching center, said message including the subscriber identifier, for performing the handover from the source mobile switching center to the target mobile switching center in the communications network. When the subscriber identifier fails to uniquely identify the subscriber terminal, the MSC-B may determine the unique identifier of the subscriber terminal by sending a request for the unique identifier of the subscriber terminal to the MSC-A, wherein the request includes the subscriber identifier obtained from the subscriber terminal, similar to explained above. Also the MAP Send Identification service may be employed, similar to explained above.

In an embodiment, a reception of the message 318 indicating a completion of the handover causes the MSC-B to determine whether the subscriber identifier of the subscriber terminal is needed and thus whether the identity request procedure should be executed. The determining may comprise determining whether the handover involves a voice group call and a subscriber terminal who is participating in the group call as a talker. This information may be determined from information obtained from the MSC-A during the handover execution 316. In one example the MSC-A may identify the MSC-B the one or more services of the moving subscriber terminal. The identifying may be provided by a service identifier that indicates the services, e.g. the voice group call. The MSC-A may further provide the MSC-B information regarding the resources needed in the radio net- work nodes for the subscriber terminal that is handed over from the MSC-A to the MSC-B. The resources needed for the subscriber terminal may be used to determine that the subscriber terminal is participating in the voice group call as a talker. In one example the resources needed for the subscriber terminal include a downlink dedicated control channel in the uplink direction and a dedicated control channel in the downlink direction. When the service is identified as voice group call the resource information may be used to determine that the subscriber terminal is participating the voice group call as a talker, e.g. in the TM of the voice group call, the identity request procedure is executed.

In 422 the subscriber identifier has been obtained and the location of the subscriber terminal may be updated to the MSC-B, and the process may end.

Figure 5 illustrates an apparatus 500 for carrying out an embodiment. The apparatus may be used to implement the functionalities described in the embodiments described herein. Figure 5 is a block diagram of the apparatus 500. Although the apparatus has been depicted as one entity, different modules and memory may be implemented in one or more physical or logical entities. The apparatus may be a subscriber terminal or a mobile switching center in a mobile communications network illustrated in Figure 1 , for example. Different functions may be performed by different blocks of the apparatus and/or execution of the functions may be shared between parts or between all of the blocks.

The apparatus 500 comprises an interfacing unit 502, a handover unit (HO) 508, and a memory (M) 510, that are all being electrically interconnected. The HO may comprise a single-core or a multi-core processor. The interfacing unit comprises an input 504 and an output unit 506 that provide, respectively, the input and output interfaces to the apparatus. The input and output units may be configured or arranged to send and receive data packets and/or transmissions according to one or more protocols according to communications standards and/or proprietary communications systems including but not limited to: ISA, PCI, Ethernet, SDH, SONET and IEEE 802.1 1 based Wireless Local Area Network and various cellular communications technologies mentioned above and any oth- er suitable standard/non-standard communication means. Preferably, the interfacing unit provides for communications of messages related to a handover from a source mobile switching center to a target mobile switching center in a communications network. In this way the HO may receive and transmit messages for execution of the handover. The memory may comprise one or more applications that are executable by the handover unit.

The handover unit is capable of performing tasks for executing a handover according to an embodiment. The tasks for executing the handover may comprise processing messages related to a handover procedure, preferably the inter-MSC handover procedure. The handover unit may be implemented by a central processing unit (CPU) capable of performing further tasks in addition to the tasks for executing the handover. The CPU may comprise a set of registers, an arithmetic logic unit, and a control unit. The handover unit may have dedicated parts of the CPU for performing the handover tasks. The control unit is controlled by a sequence of program instructions transferred to the CPU from the memory. The control unit may contain a number of microinstructions for basic operations. The implementation of micro-instructions may vary, depending on the CPU design. The program instructions may be coded by a programming language, which may be a high-level programming language, such as C, Java, etc., or a low-level programming language, such as a machine language, or an assembler. The electronic digital computer may also have an operating system, which may provide system services to a computer program written with the program instructions. The memory may be a volatile or a non-volatile memory, for example EEPROM, ROM, PROM, RAM, DRAM, SRAM, firmware, programmable logic, etc.

An embodiment provides a computer program embodied on a distribution me- dium, for example a non-transitory computer readable storage medium, comprising program instructions which, when loaded into an electronic apparatus, cause the CPU to perform according to an embodiment of the present invention.

The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers.

The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or processor or it may be distributed amongst a number of computers or processors.

The techniques described herein may be implemented by various means so that an apparatus implementing one or more functions described with an embodiment comprises not only prior art means, but also means for determining a need to perform a handover of a subscriber terminal in a mobile communications network, said subscriber terminal participating in a voice group call as a talker, obtaining a subscriber identifier of the subscriber terminal, causing to transmit a message towards a target mobile switching center, said message including the obtained subscriber identifier, for performing the hand- over from a source mobile switching center to a target mobile switching center in the communications network.

According to another aspect, an apparatus implementing one or more functions described with an embodiment comprises not only prior art means, but also means for obtaining a message indicating a request for a handover of a subscriber terminal in a mobile communications network, said subscriber terminal participating in a voice group call as a talker, from a source mobile switching center to a target mobile switching center in the mobile communications network, executing the handover, obtaining a message indicating a completion of the handover, obtaining a subscriber identifier of the subscriber terminal from the message indicating the request for the handover or, requesting the sub- scriber identifier from the subscriber terminal in response to a completion of the handover.

More precisely, the various means comprise means for implementing functionality of a corresponding apparatus described with an embodiment and it may comprise separate means for each separate function, or means may be configured to perform two or more functions. For example, these techniques may be implemented in hardware (one or more apparatuses), firmware (one or more apparatuses), software (one or more modules), or combinations thereof. For a firmware or software, implementation can be through modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in any suitable, processor/computer-readable data storage medium(s) or memory unit(s) or article(s) of manufacture and executed by one or more processors/computers. The data storage medium or the memory unit may be implemented within the processor/computer or external to the processor/computer, in which case it can be communicatively coupled to the processor/computer via various means as is known in the art.

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

Claims

1. A method comprising:
determining a need to perform a handover of a subscriber terminal in a mobile communications network, said subscriber terminal participating in a voice group call as a talker;
obtaining a subscriber identifier of the subscriber terminal;
causing to transmit a message towards a target mobile switching center, said message including the obtained subscriber identifier, for performing the handover from a source mobile switching center to a target mobile switching center in the communications network.
2. A method according to claim 1 , wherein the message is caused to be transmitted by the subscriber terminal in response to a completion of the handover.
3. A method according to claim 1 or 2, wherein the message is caused to be transmitted from a source mobile switching center to the target mobile switching center in response to the determined need to perform the handover.
4. A method according to any one of the preceding claims, wherein the mes- sage updates the location of the subscriber terminal to the target mobile switching center.
5. A method according to any one of the preceding claims, comprising:
receiving a paging notification of an incoming point-to-point call to the subscriber terminal after the handover is completed.
6. A method comprising:
obtaining a message indicating a request for a handover of a subscriber terminal in a mobile communications network, said subscriber terminal participating in a voice group call as a talker, from a source mobile switching center to a target mobile switching center in the mobile communications network;
executing the handover;
obtaining a message indicating a completion of the handover;
obtaining a subscriber identifier of the subscriber terminal from the message indicating the request for the handover or, requesting the subscriber identifier from the subscriber terminal in response to a completion of the handover.
7. A method according to claim 6, wherein the subscriber identifier updates the location of the subscriber terminal to the target mobile switching center.
8. A method according to any one of the preceding claims, wherein a mobile switching center is connected to one or more radio network nodes that serve subscriber terminals by providing radio access to the mobile communications network and after completion of the handover of the subscriber terminal, the subscriber terminal is served by the radio network nodes of the target mobile switching center of the handover:
receiving, after completion of the handover, a paging notification of an incom- ing point-to-point call to the subscriber terminal;
determining the radio network node serving the subscriber terminal, after completion of the handover; and
routing the paging notification to the determined radio network node.
9. A method according to any one of the preceding claims, comprising:
receiving from the source mobile switching center information regarding radio network resources and service for the subscriber terminal;
determining on the basis of the received information that the subscriber terminal is participating in the voice group call as a talker; and
requesting, the subscriber identifier from the subscriber terminal in response to a completion of the handover.
10. A method according to any one of the preceding claims, wherein the mobile communications network is a railway communications network, for example the Global System for Mobile Communications, providing the group call service to railway operational staff and trains.
1 1 . An apparatus according to any one of claim including means to perform a method according to any one of claims 1 to 10.
12. An apparatus according to claim 1 1 , comprising a subscriber terminal, a source mobile switching center or a target mobile switching center.
13. An apparatus comprising an interfacing unit for communications of mes- sages related to a handover of subscriber terminal from a source mobile switching center to a target mobile switching center in a communications network, and a handover unit op- eratively connected to the interfacing unit and configured to cause the apparatus to: determine a need to perform a handover of a subscriber terminal in a mobile communications network, said subscriber terminal participating in a voice group call as a talker;
obtain a subscriber identifier of the subscriber terminal;
cause to transmit a message towards the target mobile switching center, said message including the obtained subscriber identifier, for performing the handover from the source mobile switching center to the target mobile switching center in the communications network.
14. An apparatus according to claim 13, wherein the apparatus is the subscriber terminal or the source mobile switching center.
15. An apparatus comprising an interfacing unit for communications of messages related to a handover subscriber terminal from a source mobile switching center to a target mobile switching center in a communications network, and a handover unit opera- tively connected to the interfacing unit and configured to cause the apparatus to:
obtain a message indicating a request for a handover of a subscriber terminal in the mobile communications network, said subscriber terminal participating in a voice group call as a talker, from the source mobile switching center to the target mobile switch- ing center in the mobile communications network;
execute the handover;
obtain a message indicating a completion of the handover;
obtain a subscriber identifier of the subscriber terminal from the message indicating the request for the handover or, requesting the subscriber identifier from the sub- scriber terminal in response to a completion of the handover.
16. An apparatus according to claim 15, wherein the apparatus is the target mobile switching center.
17. A computer program product comprising executable code that when exe- cuted, cause execution of functions of a method according to any one of claims 1 to 5.
18. A computer program product comprising executable code that when executed, cause execution of functions of a method according to any one of claims 6 to 10.
PCT/EP2014/051560 2014-01-28 2014-01-28 Handover of subscriber terminal of mobile communications network WO2015113586A1 (en)

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EP20140704091 EP3100513A1 (en) 2014-01-28 2014-01-28 Handover of subscriber terminal of mobile communications network
CN 201480077642 CN106465213A (en) 2014-01-28 2014-01-28 Handover of subscriber terminal of mobile communications network

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WO2003049483A1 (en) * 2001-12-05 2003-06-12 Telefonaktiebolaget Lm Ericsson Optimization of circuit-switched call setup and call routing associated with inter-msc packet data handoff
EP1821557A1 (en) * 2004-10-26 2007-08-22 Huawei Technologies Co., Ltd. Method and device for implementing secret call service
US20100142488A1 (en) * 2007-08-19 2010-06-10 Jian Zhang Method, device and system of handover

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WO2001086975A2 (en) * 2000-05-11 2001-11-15 Telefonaktiebolaget L M Ericsson Handover method and apparatus for voice group calls in a mobile communications system
WO2003049483A1 (en) * 2001-12-05 2003-06-12 Telefonaktiebolaget Lm Ericsson Optimization of circuit-switched call setup and call routing associated with inter-msc packet data handoff
EP1821557A1 (en) * 2004-10-26 2007-08-22 Huawei Technologies Co., Ltd. Method and device for implementing secret call service
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