Method and wireless network for handling mission critical (MC) service user migration

Abstract

Embodiments herein disclose a method for handling a MC service user migration in a wireless network (100) by a first MC service server (108). The method includes receiving an ad hoc group call leave request from a first MC service client (114) during an ongoing ad hoc group call. The first MC service server (108) and the first MC service client (114) are in a first MC system (102). Further, the method includes sending an ad hoc group call leave response to the first MC service client (114) based on the ad hoc group call leave request. Further, the method includes maintaining the ongoing ad hoc group call by removing the first MC service client (114) and call continues with at least one remaining MC service client in the first MC system (102).

Description

METHOD AND WIRELESS NETWORK FOR HANDLING MISSION CRITICAL (MC) SERVICE USER MIGRATION

[0001] Embodiments disclosed herein relate to a wireless communication network, and more particularly to handling migration of a participating Mission Critical (MC) service user in the wireless communication network (or wireless network), when an ad hoc group call involving a user is ongoing.

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in "Sub 6GHz" bands such as 3.5GHz, but also in "Above 6GHz" bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] The principal object of embodiments herein is to disclose a method and a system (or wireless network) for handling a Mission Critical (MC) service user migration in the wireless network.

[0009] Another object of embodiments herein is to handle migration of a participating MC service user while an ongoing ad hoc group call and re-establishing an ad　hoc group call with a migrated MC service user from a partner MC system (e.g., migrated MC system) when an ad　hoc group call setup is initiated with a primary MC system assigned MC service ID of the targeted MC service user or criteria to determine the participant.

[0010] Another object of embodiments herein is to handle the migration of MC service user participating in the on-going ad hoc group call in the case where the participants list is provided by an originating MC service user of the on-going ad hoc group call.

[0011] Another object of embodiments herein is to handle the migration of MC service user participating in the on-going ad hoc group call in the case where the participants list is determined by a MC service server based on the criteria provided by the originating MC service user of the on-going ad hoc group call or based on the local policies configured at the MC service server.

[0012] The technical subjects pursued in the disclosure may not be limited to the above-mentioned technical subjects, and other technical subjects which are not mentioned may be clearly understood, through the following descriptions, by those skilled in the art to which the disclosure pertains.

[0013] Accordingly, the embodiments herein provide a method for handling a MC service user migration in a wireless network. The method includes receiving, by a first MC service server, an ad hoc group call leave request from a first MC service client during an ongoing ad hoc group call. The first MC service server and the first MC service client are in a first MC system. Further, the method includes sending, by the first MC service server, an ad hoc group call leave response to the first MC service client based on the ad hoc group call leave request. Further, the method includes maintaining, by the first MC service server, the ongoing ad hoc group call by removing the first MC service client and call continues with at least one remaining MC service client in the first MC system.

[0014] Accordingly, the embodiments herein provide a method for handling a MC service user migration in a wireless network. The method includes sending, by a first MC service client, an ad hoc group call leave request to a first MC service server during an ongoing ad hoc group call. The first MC service server and the first MC service client are in a first MC system. Further, the method includes receiving, by the first MC service client, an ad hoc group call leave response from the first MC service client based on the ad hoc group call leave request.

[0015] Accordingly, the embodiments herein provide a first MC service server including a MC service user migration handling controller coupled with a processor and a memory. The first MC service server is configured to receive an ad hoc group call leave request from a first MC service client during an ongoing ad hoc group call. The first MC service server and the first MC service client are in a first MC system. Further, the first MC service server is configured to send an ad hoc group call leave response to the first MC service client based on the ad hoc group call leave request. Further, the first MC service server is configured to maintain the ongoing ad hoc group call by removing the first MC service client and call continues with at least one remaining MC service client in the first MC system.

[0016] Accordingly, the embodiments herein provide a first MC service client including an MC service user migration handling controller coupled with a processor and a memory. Further, the first MC service client is configured to send an ad hoc group call leave request to a first MC service server during an ongoing ad hoc group call, where the first MC service server and the first MC service client are in a first MC system. Further, the first MC service client is configured to receive an ad hoc group call leave response from the first MC service client based on the ad hoc group call leave request.

[0017] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating at least one embodiment and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the scope thereof, and the embodiments herein include all such modifications.

[0018] An embodiment of the disclosure provides a method and a system (or wireless network) for handling a Mission Critical (MC) service user migration in the wireless network.

[0019] An embodiment of the disclosure provides method and apparatus to handle migration of a participating MC service user while an ongoing ad hoc group call and re-establishing an ad　hoc group call with a migrated MC service user from a partner MC system (e.g., migrated MC system) when an ad　hoc group call setup is initiated with a primary MC system assigned MC service ID of the targeted MC service user or criteria to determine the participant.

[0020] An embodiment of the disclosure provides method and apparatus to handle the migration of MC service user participating in the on-going ad hoc group call in the case where the participants list is provided by an originating MC service user of the on-going ad hoc group call.

[0021] An embodiment of the disclosure provides method and apparatus to handle the migration of MC service user participating in the on-going ad hoc group call in the case where the participants list is determined by a MC service server based on the criteria provided by the originating MC service user of the on-going ad hoc group call or based on the local policies configured at the MC service server.

[0022] Advantageous effects obtainable from the disclosure may not be limited to the above - mentioned effects, and other effects which are not mentioned may be clearly understood from the following descriptions by those skilled in the art to which the disclosure pertains.

[0023] Embodiments herein are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the following illustratory drawings. Embodiments herein are illustrated by way of examples in the accompanying drawings, and in which:

[0024] FIG. 1 illustrates a procedure for handling migration during an ongoing ad hoc group call based on a participant list and re-establishing the ad　hoc group call with a migrated MC service user in a migrated MC system (over a wireless network), according to embodiments as disclosed herein;

[0025] FIG. 2 illustrates a procedure for handling migration during ongoing ad hoc group call based on a criteria and re-establishing an ad　hoc group call with the migrated MC service user in the migrated MC system (over the wireless network), according to embodiments as disclosed herein;

[0026] FIG. 3 illustrates a procedure for handling migration information subscription request procedure in the wireless network, according to embodiments as disclosed herein;

[0027] FIG. 4 illustrates a procedure for handling notification of migration information to a MC service server in the wireless network, according to embodiments as disclosed herein;

[0028] FIG. 5 illustrates a procedure for handling migration during the ongoing ad hoc group call based on a participant list and re-establishing the ad　hoc group call with the migrated MC service user in the migrated MC system (over the wireless network), according to embodiments as disclosed herein;

[0029] FIG. 6 illustrates a procedure for handling migration information subscription request procedure in the wireless network, according to embodiments as disclosed herein;

[0030] FIG. 7 illustrates a procedure for handling notification of migration information to MC service server in the wireless network, according to embodiments as disclosed herein;

[0031] FIG. 8 illustrates a procedure for handling migration during the ongoing ad hoc group call based on the participant list and re-establishing the ad　hoc group call with the migrated MC service user in the migrated MC system (over the wireless network), according to embodiments as disclosed herein;

[0032] FIG. 9 shows various hardware components of a first MC service server, according to embodiments as disclosed herein;

[0033] FIG. 10 shows various hardware components of a first MC service client, according to embodiments as disclosed herein;

[0034] FIG. 11 is a flow chart illustrating a method, implemented by the first MC service server, for handling a MC service user migration in the wireless network, according to embodiments as disclosed herein; and

[0035] FIG. 12 is a flow chart illustrating a method, implemented by the first MC service client, for handling a MC service user migration in the wireless network, according to embodiments as disclosed herein.

[0036] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0037] The words / phrases "exemplary", "example", "illustration", "in an instance", "and the like", "and so on", "etc.", "etcetera", "e.g.,", "i.e.," are merely used herein to mean "serving as an example, instance, or illustration. Any embodiment or implementation of the present subject matter described herein using the words / phrases "exemplary", "example", "illustration", "in an instance", "and the like", "and so on", "etc.", "etcetera", "e.g.," , "i.e.," is not necessarily to be construed as preferred or advantageous over other embodiments.

[0038] Embodiments herein may be described and illustrated in terms of blocks which carry out a described function or functions.　These blocks, which may be referred to herein as managers, units, modules, hardware components or the like, are physically implemented by analog and / or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits and the like, and may optionally be driven by a firmware. The circuits may, for example, be embodied in one or more semiconductor chips, or on substrate supports such as printed circuit boards and the like.　The circuits constituting a block may be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware to perform some functions of the block and a processor to perform other functions of the block.　Each block of the embodiments may be physically separated into two or more interacting and discrete blocks without departing from the scope of the disclosure.　Likewise, the blocks of the embodiments may be physically combined into more complex blocks without departing from the scope of the disclosure.

[0039] It should be noted that elements in the drawings are illustrated for the purposes of this description and ease of understanding and may not have necessarily been drawn to scale. For example, the flowcharts / sequence diagrams illustrate the method in terms of the steps required for understanding of aspects of the embodiments as disclosed herein. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the present embodiments so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Furthermore, in terms of the system, one or more components / modules which comprise the system may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the present embodiments so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

[0040] The accompanying drawings are used to help easily understand various technical features and it should be understood that the embodiments presented herein are not limited by the accompanying drawings. As such, the present disclosure should be construed to extend to any modifications, equivalents, and substitutes in addition to those which are particularly set out in the accompanying drawings and the corresponding description. Usage of words such as first, second, third etc., to describe components / elements / steps is for the purposes of this description and should not be construed as sequential ordering / placement / occurrence unless specified otherwise.

[0041] The embodiments herein achieve methods and systems for handling migration of a participating MC service user while in an ongoing ad hoc group call.

[0042] Embodiments herein disclose methods and systems for handling migration of a participating MC service user while in an ongoing ad hoc group call and re-establishing an ad　hoc group call with the migrated MC service user from the partner MC system (e.g., migrated MC system) when an ad　hoc group call setup is initiated with the primary MC system assigned MC service ID of the targeted MC service user or criteria to determine the participant.

[0043] Referring now to the drawings, and more particularly to FIGS. 1 through 12, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments.

[0044] The ad hoc group call is a salient feature in both railways and public safety sectors. The ad hoc group call provides a mechanism to invite random set of users to participate in the group communication and this doesn't require the group document to be pre-configured. The migration is a mandatory feature for railways particularly in Europe since the train passes through multiple countries (for example). So it is inevitable that the participants of the ad hoc group call would have migrated to another MC service system and the ad hoc group call need to deliver to the participant who has migrated. Hence, the proposed method can be used to handle the participating MC service user migration while in the ongoing ad hoc group call and re-establish the ad hoc group call with the migrated MC service user in the partner MC system (e.g., migrated MC system) in an efficient manner without wasting the resource (e.g., bandwidth, CPU usage, signal usage or the like).

[0045] An ad　hoc group call can be initiated by using a participant list (e.g., MC service identifiers (IDs) of MC service users) or criteria (along with criteria or local policies at a MC service server) provided by an initiator of the call and the ad hoc group call will be hosted in a primary MC system of the initiator of the ad hoc group call. While the ad　hoc group call is ongoing, any of the participating MC service users can migrate to a partner MC system (i.e., migrated MC system) and get assigned with a new MC service ID from the partner MC system. During migration, the MC service user should be released from the ongoing ad hoc group call and re-establish the ad hoc group call once migrate to the partner MC system. The re-establishing of the ad　hoc group call with the migrated MC service user depends on whether the ad hoc group call has been initiated based on participant list or criteria, local policy at the MC service server etc.

[0046] The existing specification does not provide a way for handling migration of the participating MC service users while ongoing the ad hoc group call and re-establishing of the ad　hoc group call with the migrated MC service user in the partner MC system (e.g., migrated MC system)

[0047] Hence, there is a need in the art for solutions which will overcome the above mentioned drawback(s), among others.

[0048] Migration during Ad hoc group call procedure:

[0049] The following clauses specify the generic procedure for MC service user to continue to participate in ad hoc group call when migrating to a partner system that is utilized by all the MC services (i.e. Mission Critical Push-to-Talk (MCPTT), MCVideo and MCData) in conjunction with the procedures as specified in the respective MC services in Third Generation Partnership Project (3GPP) technical specification (TS) 23.379, 3GPP TS 23.281, and 3GPP TS 23.282.

[0050] The ad hoc group call can be initiated by using a participant list or criteria (along with criteria or local policies at a MC service server) provided by an initiator of the call and the ad hoc group call will be hosted in a primary MC system of the initiator of the ad hoc group call. During the ongoing call, the participating MC service user can migrate to the partner MC system. While migrating to the partner MC system, the MC service user will leave the ongoing ad hoc group call by providing the reason for leaving the ad hoc group call is due to migration. After successful migration, the MC service user will be invited again to continue the participation in an ongoing ad hoc group call. If the ad hoc group call is established using the participant list provided by the initiator of the call, then the MC service server where the ad hoc group call is hosted will invite the migrated MC service user using the partner MC system assigned MC service ID. If the ad hoc group call is established using the criteria provided by the initiator of the call, then the MC service server where the ad hoc group call is hosted will invite the migrated MC service user using the partner MC system assigned MC service ID only when it is informed about the migrated MC service user meeting the criteria and to be invited for ongoing ad hoc group call by partner MC system (migrated MC system).

[0051] Ad hoc group call leave request (MCPTT client - MCPTT server):Table　1 describes the information flow ad hoc group call leave request from the MCPTT client to the MCPTT server.

[0052] Information ElementStatusDescriptionMCPTT IDM (Mandatory)The MCPTT ID of the ad　hoc group call participant leaving the callMCPTT ad　hoc group IDMThe MCPTT group ID of ad　hoc group call on which call is on-goingReason to leaveMCarries the reason of why the MCPTT client is ongoing ad　hoc group call (e.g. Due to migration).

[0053] Ad hoc group call leave response (MCPTT server - MCPTT client):Table　2 describes the information flow Ad hoc group call leave response from the MCPTT server to the MCPTT client.

[0054] Information ElementStatusDescriptionMCPTT IDMThe MCPTT ID of the ad　hoc group call participant leaving the callMCPTT ad　hoc group IDMThe MCPTT group ID of ad　hoc group call on which call is on-going

[0055] Ad hoc group call redirection notify:Table　3 describes the information flow of an ad　hoc group call redirection notify, which is sent from the MC service server to the MC service server and the MC service server to an MC service client initiating an ad　hoc group call towards a migrated MC service user.

[0056] Information elementStatusDescriptionMC service IDMThe MC service ID of the MC service user initiating an ad　hoc group call, i.e., calling party. The MC service ID can either be MCPTT ID, MCVideo ID, or MCData ID.MC service IDMThe MC service ID of the target MC service user (i.e., called party), which the MC service user has obtained from its primary MC system before migration. The MC service ID can either be MCPTT ID, MCVideo ID, or MCData ID.MC service IDMThe MC service ID of the target MC service user, which the MC service user has obtained from its migrated MC system after Migration. The MC service ID can either be MCPTT ID, MCVideo ID, or MCData ID.Redirection reasonMThe called MC service user has migrated.

[0057] 1. Procedure for participants list provided by the initiator:

[0058] FIG. 1 illustrates a generic ad　hoc group call procedure in which a first MC service user using a first MC service client (114) and a second MC service user using a second MC service client (116) migrates during the call, where a first MC system (e.g., MC system A) (102) is the primary MC system of the first MC service user before migration, a second MC system (e.g., MC system B) is the primary MC system of the second MC service user before migration, the second MC system (104) is the MC system that the first MC service user has migrated and the third MC system (i.e. MC system C) (106) is the MC system that the second MC service user has migrated. After the migration, the migrated first MC service user and the second MC service user are re-invited to ongoing ad　hoc group call and successfully added to the call.

[0059] The procedure is based on the following existing procedures:

[0060] a) The ad　hoc group call setup procedures as described in clause　10.19.3.2.1 of 3GPP　TS　23.379, in clause　7.19.3.2.4 of 3GPP　TS　23.281, or in clause　7.17.3.2.1 of 3GPP　TS　23.282.

[0061] b) The migration of the MC service user to the partner MC system procedures as described in clause　10.6.3.

[0062] c) The inviting a MC service user and adding to the ongoing ad　hoc group call procedures steps (see steps 6 and 7) are as described in clause　10.19.3.2.1 of 3GPP　TS　23.379, in clause　7.19.3.2.4 of 3GPP　TS　23.281, or in clause　7.17.3.2.1 of 3GPP　TS　23.282.

[0063] The pre-conditions are as follows:

[0064] a) The first MC system (102), the second MC system (104) and the third MC system (106) are interconnected MC systems.

[0065] b) The first MC system (102) is the primary MC system of a third MC service user, a fourth MC service user and also the first MC service user before migration. The second MC system (104) is the MC system that first MC service user has migrated.

[0066] c) The second MC system (104) is the primary MC system of the second MC service user migration. The third MC system (106) is the MC system that the second MC service user has migrated.

[0067] d) The third MC service user, the fourth MC service user, and the first MC service user belongs to same home MC system i.e. primary MC system and the second MC service user belongs to another home MC system i.e. partner MC system (which is interconnected MC system).

[0068] e) The ad　hoc group call is ongoing among the MC service users at a third MC service client (118) (i.e., initiator), a fourth MC service client　(120), the first MC service client (114) and the second MC service client (116) using the MC service ID which are obtained from their primary MC system, and the participants list provided by the originating MC service user while initiating the ad　hoc group call.

[0069] f) The ad　hoc group call is hosted in the first MC service server (e.g., MC service server A) (108) of the first MC system (102).

[0070] As shown in FIG. 1, in step 1, the first MC service client (114) determines that there is a need to migrate to the second MC system (104) and the first MC service user is notified to be prepared for possible service interruption.

[0071] In steps 2a & 2b, the first MC service client (114) leaves the ad　hoc group call by sending an ad　hoc group call leave request towards the first MC service server (108) containing the ad　hoc group ID and reason for the leaving the call as user migration. That is, at step 2a, the first MC service client (114) sends the ad hoc group call leave request to the first MC service server (108). At step 2b, the first MC service server (108) sends the ad hoc group call leave response to the first MC service client (114) based on the ad hoc group call leave request.

[0072] In step 3, the ongoing ad　hoc group call is updated by removing the first MC service client (114) and the call continues with remaining MC service clients.

[0073] In step 4, the first MC service client (114) migrates to the second MC system (104) as described in the clause　10.6.3 and a new MC service ID is assigned by the second MC system (104). The first MC service server (108) of the first MC system (102), which is the primary MC system of the migrated first MC service user, is informed about migrated MC service user's MC service ID obtained from the second MC system (104) (i.e., a migrated MC system) along with successful MC service authorization at the second MC system (104).

[0074] In step 5, the first MC service server (108) of the first MC system (102) determines that the first MC service user has to be re-invited for ongoing ad　hoc group call. The first MC service server (108) of the first MC system (102) invites the first MC service client (114) to ad　hoc group call using MC service ID assigned by the second MC system (104) and successfully establishes the ad　hoc group call with the first MC service client (114).

[0075] Please note that how the MC service server determining to re-invite the migrated MC service user is left to the implementation (e.g. timer, policy, on migration completion with periodically querying for the migration status information etc.).

[0076] In step 6, the second MC service client (116) determines the need to migrate to the third MC system (106) and the second MC service user is notified to be prepared for possible service interruption.

[0077] In steps 7a, & 7b, the second MC service client (116) leaves the ad　hoc group call by sending ad　hoc group call leave request towards the first MC service server (108) containing the ad　hoc group ID and reason for the leaving the call as user migration. That is, at step 7a, the second MC service client (116) sends the ad hoc group call leave request to the first MC service server (108). At step 7b, the first MC service server (108) sends the ad hoc group call leave response to the second MC service client (116) based on the ad hoc group call leave request.

[0078] In step 8, the ongoing ad　hoc group call is updated by removing the second MC service client (116) and the call continues with remaining MC service clients.

[0079] In step 9, the second MC service client (116) migrates to the third MC system (106) as described in the clause　10.6.3 and a new MC service ID is assigned by the third MC system (106). The second service server (i.e., MC service server B) (110) of the second MC system (104), which is the primary MC system of the migrated second MC service user, is informed about migrated MC service user's MC service ID obtained from the third MC system (106) (i.e. a migrated MC system) along with successful MC service authorization at the third MC system (106).

[0080] In step 10, the first MC service server (108) of the first MC system (102) determines that the second MC service user has to be re-invited for ongoing ad　hoc group call. The first MC service server (108) of the first MC system (102) initiates an ad　hoc group call request towards the second MC service client (116) of the second MC system (104) (i.e. interconnected MC system) using MC service ID assigned by the second MC system (104) (i.e. primary MC system). The ad　hoc group call request is routed to the second MC service client (116) via the second service server (110) of the second MC system (104).

[0081] Please note that how the MC service server determining to re-invite the migrated MC service user is left to the implementation (e.g. timer, policy etc.).

[0082] In step 11, the second service server (110) of the second MC system (104) determines that the second MC service user has to be invited for ad　hoc group call is migrated to the third MC system (106) with a new MC service ID assigned by the third MC system (106).

[0083] In step 12, the second service server (110) informs the first MC service server (108) that initiation of ad　hoc group call towards the second MC service user has migrated and assigned with a new MC service ID by the third MC system (106) (migrated MC system) by sending ad　hoc group call redirection notify. The ad　hoc group call redirection notify contains the information about MC service ID of the target MC service user (i.e., second MC service user) assigned by both second MC system (104) and the third MC system (106), and reason for the call redirection notify as user migration.

[0084] In step 13, the first MC service server (108) further informs the third MC service client (118) that ad　hoc group call request towards the second MC service user is redirected to the third MC system (106) (i.e., migrated MC system) by sending ad　hoc group call redirection notify. The ad　hoc group call redirection contains the information about MC service ID of the target MC service user (e.g., second MC service user) assigned by both second MC system (104) and the third MC system (106), and reason for the call redirection as user migration.

[0085] In step 14, the first MC service server (108) of the first MC system (102) invites the second MC service client (116) to ad　hoc group call using MC service ID assigned by the third MC system (106) and successfully establishes the ad　hoc group call with the second MC service client (116).

[0086] Procedure for criteria provided by the initiator:

[0087] FIG. 2 illustrates a generic ad　hoc group call procedure in which first MC service user using the first MC service client (114) and the second MC service user using the second MC service client (116) migrates during the call, where the first MC system (102) is the primary MC system of the first MC service user before migration, the second MC system (104) is the primary MC system of the second MC service user before migration, the second MC system (104) is the MC system that the first MC service user has migrated and the third MC system (106) is the MC system that the second MC service user has migrated. After the migration, the migrated first MC service user and the second MC service user are re-invited to ongoing ad　hoc group call based on the criteria in the migrated MC system and successfully added to the call.

[0088] The procedure is based on the following existing procedures:

[0089] a) The ad　hoc group call setup procedures as described in clause　10.19.3.2.3 of 3GPP　TS　23.379, in clause　7.19.3.2.1 of 3GPP　TS　23.281, or in clause　7.17.3.2.3 of 3GPP　TS　23.282.

[0090] b) The migration of the MC service user to the partner MC system procedures as described in clause　10.6.3.

[0091] c) The inviting an MC service user meeting the criteria and adding to the ongoing ad　hoc group call procedure steps are as described in clause　10.19.3.2.4 of 3GPP　TS　23.379 (see steps 4 to 9), in clause　7.19.3.2.2 of 3GPP　TS　23.281 (see steps 4 to 9), or in clause　7.17.3.2.4 of 3GPP　TS　23.282 (see steps 3 to 8).

[0092] The pre-conditions are as follows:

[0093] a. The first MC system (102), the second MC system (104) and the third MC system (106) are interconnected MC systems.

[0094] b. The first MC system (102) is the primary MC system of the third MC service user, the fourth MC service user and also the first MC service user before migration. The second MC system (104) is the MC system that the first MC service user has migrated.

[0095] c. The second MC system (104) is the primary MC system of the second MC service user before migration. The third MC system (106) is the MC system that the second MC service user has migrated.

[0096] d. The third MC service user, the fourth MC service user, and the first MC service user belongs to same home MC system i.e. primary MC system and the second MC service user belongs to another home MC system i.e. partner MC system (which is interconnected MC system).

[0097] e. The ad　hoc group call is ongoing among the MC service users at the third MC service client (118) (i.e., initiator), the fourth MC service client　(120), the first MC service client (114) and the second MC service client (116) using the MC service ID which are obtained from their primary MC system, and the participants list determined using criteria provided by the originating MC service user while initiating the ad　hoc group call.

[0098] f. The ad　hoc group call is hosted in the first MC service server (108) of the first MC system (102).

[0099] The steps followed as illustrated in the FIG. 2 are as follows:

[0100] In step 1, the first MC service client (114) determines the need to migrate to the second MC system (104) and the first MC service user is notified to be prepared for possible service interruption.

[0101] In steps 2a & 2b, the first MC service client (114) leaves the ad　hoc group call by sending ad　hoc group call leave request towards the first MC service server (108) containing the ad　hoc group ID and reason for the leaving the call as user migration. That is, at step 2a, the first MC service client (114) sends the ad hoc group call leave request to the first MC service server (108). At step 2b, the first MC service server (108) sends the ad hoc group call leave response to the first MC service client (114) based on the ad hoc group call leave request.

[0102] In step 3, the ongoing ad　hoc group call is updated by removing the first MC service client (114) and call continues with remaining MC service clients.

[0103] In step 4, the first MC service client (114) migrates to the second MC system (104) as described in the clause　10.6.3 and new MC service ID is assigned by the second MC system (104). The first MC service server (108) of the first MC system (102), which is the primary MC system of the migrated first MC service user, is informed about migrated MC service user's MC service ID obtained from the second MC system (104) (i.e. a migrated MC system) along with successful MC service authorization at the second MC system (104).

[0104] In step 5, the second service server (110) of the second MC system (104) determines that newly migrated first MC service user meets the criteria and notify the first MC service server (108) of the first MC system (102) to add the first MC service user to an on-going ad　hoc group call. The first MC service server (108) of the first MC system (102) invites the first MC service client (114) to ad　hoc group call using MC service ID assigned by the second MC system (104) and successfully establishes the ad　hoc group call with the first MC service client (114).

[0105] In step 6, the second MC service client (116) determines the need to migrate to the third MC system (106) and the second MC service user is notified to be prepared for possible service interruption.

[0106] In steps 7a & 7b, the second MC service client (116) leaves the ad　hoc group call by sending ad　hoc group call leave request towards the first MC service server (108) containing the ad　hoc group ID and reason for the leaving the call as user migration. That is, at step 7a, the second MC service client (116) sends the ad hoc group call leave request to the first MC service server (108). At step 7b, the first MC service server (108) sends the ad hoc group call leave response to the second MC service client (116) based on the ad hoc group call leave request.

[0107] In step 8, the ongoing ad　hoc group call is updated by removing the second MC service client (116) and the call continues with remaining MC service clients.

[0108] In step 9 the second MC service client (116) migrates to the third MC system (106) as described in the clause　10.6.3 and new MC service ID is assigned by the third MC system (106). The second service server (110) of the second MC system (104), which is the primary MC system of the migrated second MC service user, is informed about migrated MC service user's MC service ID obtained from the third MC system (106) (i.e., a migrated MC system) along with successful MC service authorization at the third MC system (106).

[0109] In step 10, the third MC service server (i.e., MC service server C) (112) of the third MC system (106) determines that newly migrated second MC service user meets the criteria and notify the first MC service server (108) of the first MC system (102) to add the second MC service user to an on-going ad　hoc group call. The first MC service server (108) of the first MC system (102) invites the second MC service client (116) to ad　hoc group call using MC service ID assigned by the third MC system (106) and successfully establishes the ad　hoc group call with the second MC service client (116).

[0110] FIG. 3 illustrates a procedure for handling migration information subscription request procedure in the wireless network (100), according to embodiments as disclosed herein.

[0111] FIG. 4 illustrates a procedure for handling notification of migration information to a MC service server in the wireless network (100), according to embodiments as disclosed herein.

[0112] FIG. 5 illustrates a procedure for handling migration during the ongoing ad hoc group call based on the participant list and re-establishing the ad　hoc group call with the migrated MC service user in the migrated MC system (over the wireless network (100)), according to embodiments as disclosed herein. FIG. 5 is a sequence diagram that illustrates an alternate solution for the "procedure for participants list provided by the initiator", according to the embodiment as disclosed herein.

[0113] Migration information subscription request:Table　4 describes the information flow from the MC service server to another MC service server for migration information subscription request.

[0114] Information elementStatusDescriptionMC service IDMMC service user whose migration information is requested

[0115] Migration information subscription response:Table　5 describes the information flow from the MC service server to another MC service server for migration information subscription response.

[0116] Information elementStatusDescriptionMC service IDMMC service user whose migration information is requestedSubscription statusMIndicates the subscription result

[0117] Migration information notification:Table　6 describes the information flow from the MC service server to another MC service server for migration information notification.

[0118] Information elementStatusDescriptionMC service IDMMC service user whose migration information is being notifiedMigration information (see　NOTE)MMigration informationNOTE: This may contain multiple sets of elements for the MC service user. The following migration information elements shall be present: Migration status when the MC service user is migrated to partner MC system, service authorization status.

[0119] Subscription and notification for migration information procedure:

[0120] FIG. 3 illustrates the procedure of subscription for migration information is used by the MC service server (e.g., first MC service server 108) to indicate to the another MC service server (e.g., first MC service server 110) that it wishes to receive migration information of MC service user.

[0121] The pre-conditions are as follows:

[0122] a. The second service server (110) is the primary MC service server of the MC service user in the primary MC system, whose migration information is being subscribed to receive.

[0123] The steps followed as illustrated in the FIG. 3 are as follows:

[0124] In step 1, the first MC service server (108) sends a migration information subscription request to the second service server (110) to subscribe for the migration information of MC service user. In step 2, the second service server (110) replies with a migration information subscription response indicating the subscription status.

[0125] Please note that, as the MC service server is implicitly trusted, the authorization check for the MC service server is not needed.

[0126] The procedure for notification of migration information as described in FIG.　4 is used by the group management server to inform the MC service server that new group policy is available.

[0127] The pre-conditions are as follows:

[0128] a. The first MC service server (108) has subscribed to the migration information of MC service user in the second service server (110) of the MC service user's primary MC system.

[0129] In step 1, the second service server (110) provides the notification to the first MC service server (108), with migration status, and service authorization status.

[0130] Procedure for participants list provided by the initiator:

[0131] FIG. 5 illustrates another generic ad　hoc group call procedure in which first MC service user using the first MC service client (114) and the second MC service user using the second MC service client (116) migrates during the call, where the first MC system (102) is the primary MC system of the first MC service user before migration, second MC system (104) is the primary MC system of the second MC service user before migration, the second MC system (104) is the MC system that the first MC service user has migrated and the third MC system (106) is the MC system that the second MC service user has migrated. After the migration, the migrated first MC service user and the second MC service user are re-invited to ongoing ad　hoc group call and successfully added to the call.

[0132] The procedure is based on the following existing procedures:

[0133] a. The ad　hoc group call setup procedures as described in clause　10.19.3.2.1 of 3GPP　TS　23.379, in clause　7.19.3.2.4 of 3GPP　TS　23.281, or in clause　7.17.3.2.1 of 3GPP　TS　23.282.

[0134] b. The migration of the MC service user to the partner MC system procedures as described in clause　10.6.3.

[0135] c. The inviting a MC service user and adding to the ongoing ad　hoc group call procedures steps (see steps 6 and 7) are as described in clause　10.19.3.2.1 of 3GPP　TS　23.379, in clause　7.19.3.2.4 of 3GPP　TS　23.281, or in clause　7.17.3.2.1 of 3GPP　TS　23.282.

[0136] The pre-conditions are as follows:

[0137] a. The first MC system (102), the second MC system (104) and the third MC system (106) are interconnected MC systems.

[0138] b. The first MC system (102) is the primary MC system of the third MC service user, the fourth MC service user and also the first MC service user before migration. The second MC system (104) is the MC system that the first MC service user has migrated.

[0139] c. The second MC system (104) is the primary MC system of the second MC service user before migration. The third MC system (106) is the MC system that the second MC service user has migrated.

[0140] d. The third MC service user, the fourth MC service user, and the first MC service user belongs to same home MC system i.e. primary MC system and the second MC service user belongs to another home MC system i.e. partner MC system (which is interconnected MC system).

[0141] e. The ad　hoc group call is ongoing among the MC service users at the third MC service client (118) (i.e., initiator), the fourth MC service client　(120), the first MC service client (114) and the second MC service client (116) using the MC service ID which are obtained from their primary MC system, and the participants list provided by the originating MC service user while initiating the ad　hoc group call.

[0142] f. The ad　hoc group call is hosted in the first MC service server (108) of the first MC system (102).

[0143] The steps followed as illustrated in the FIG. 5 are as follows:

[0144] In step 1, the first MC service client (114) determines the need to migrate to the second MC system (104) and the first MC service user is notified to be prepared for possible service interruption.

[0145] In steps 2a & 2b, the first MC service client (114) leaves the ad　hoc group call by sending ad　hoc group call leave request towards the first MC service server (108) containing the ad　hoc group ID and reason for the leaving the call as user migration. That is, at step 2a, the first MC service client (114) sends the ad hoc group call leave request to the first MC service server (108). At step 2b, the first MC service server (108) sends the ad hoc group call leave response to the first MC service client (114) based on the ad hoc group call leave request.

[0146] In step 3, the ongoing ad　hoc group call is updated by removing the first MC service client (114) and the call continues with remaining MC service clients.

[0147] In step 4, the first MC service client (114) migrates to the second MC system (104) as described in the clause　10.6.3 and new MC service ID is assigned by the second MC system (104). The first MC service server (108) of the first MC system (102), which is the primary MC system of the migrated first MC service user, is informed about migrated MC service user's MC service ID obtained from the second MC system (104) (i.e. a migrated MC system) along with successful MC service authorization at the second MC system (104).

[0148] In step 5, the first MC service server (108) of the first MC system (102) determines that the first MC service user has to be re-invited for ongoing ad　hoc group call. The first MC service server (108) of the first MC system (102) invites the first MC service client (114) to ad　hoc group call using MC service ID assigned by the second MC system (104) and successfully establishes the ad　hoc group call with the first MC service client (114).

[0149] Please note that how the MC service server determining to re-invite the migrated MC service user is left to the implementation (e.g. timer, policy etc.).

[0150] In step 6, the second MC service client (116) determines the need to migrate to the third MC system (106) and the second MC service user is notified to be prepared for possible service interruption.

[0151] In steps 7a & 7b, the second MC service client (116) leaves the ad　hoc group call by sending ad　hoc group call leave request towards the first MC service server (108) containing the ad　hoc group ID and reason for the leaving the call as user migration. That is, at step 7a, the second MC service client (116) sends the ad hoc group call leave request to the first MC service server (108). At step 7b, the first MC service server (108) sends the ad hoc group call leave response to the second MC service client (116) based on the ad hoc group call leave request.

[0152] In step 8, the ongoing ad　hoc group call is updated by removing the second MC service client (116) and the call continues with remaining MC service clients.

[0153] In step 9, the first MC service server (108) of the first MC system (102) determines that the second MC service user has to be re-invited for ongoing ad　hoc group call. The first MC service server (108) of the first MC system (102) subscribe to the migration information of the second MC service user.

[0154] In step 10, the second MC service client (116) migrates to the third MC system (106) as described in the clause　10.6.3 and new MC service ID is assigned by the third MC system (106). The second service server (110) of the second MC system (104), which is the primary MC system of the migrated second MC service user, is informed about migrated MC service user's MC service ID obtained from the third MC system (106) (i.e., a migrated MC system) along with successful MC service authorization at the third MC system (106).

[0155] In step 11, the second service server (110) of the second MC system (104) determines that the second MC service user has migrated and the first MC service server (108) of the first MC system (102) has subscribed for the migration information. The second service server (110) of the second MC system (104) notifies the migration information of the second MC service user to the first MC service server (108) of the first MC system (102).

[0156] In step 12, the first MC service server (108) of the first MC system (102) initiates an ad　hoc group call request towards the second MC service client (116) of the second MC system (104) (i.e. interconnected MC system) using MC service ID assigned by the second MC system (104) (i.e. primary MC system). The ad　hoc group call request is routed to the second MC service client (116) via the second service server (110) of the second MC system (104).

[0157] In step 13, the second service server (110) of the second MC system (104) determines that the second MC service user has to be invited for ad　hoc group call is migrated to the third MC system (106) with a new MC service ID assigned by the third MC system (106).

[0158] In step 14, the second service server (110) informs the first MC service server (108) that initiation of ad　hoc group call towards the second MC service user has migrated and assigned with a new MC service ID by the third MC system (106) (migrated MC system) by sending ad　hoc group call redirection notify. The ad　hoc group call redirection notify contains the information about MC service ID of the target MC service user (e.g., second MC service user) assigned by both second MC system (104) and the third MC system (106), and reason for the call redirection notify as user migration. In step 15, the first MC service server (108) further informs the third MC service client (118) that ad　hoc group call request towards the second MC service user is redirected to the third MC system (106) (migrated MC system) by sending ad　hoc group call redirection notify. The ad　hoc group call redirection notify contains the information about MC service ID of the target MC service user (e.g., second MC service user) assigned by both second MC system (104) and the third MC system (106), and reason for the call redirection as user migration. In step 16, the first MC service server (108) of the first MC system (102) invites the second MC service client (116) to ad　hoc group call using MC service ID assigned by the third MC system (106) and successfully establishes the ad　hoc group call with the second MC service client (116).

[0159] FIG. 6 illustrates a procedure for handling migration information subscription request procedure in the wireless network (100), according to embodiments as disclosed herein.

[0160] FIG. 7 illustrates a procedure for handling notification of migration information to MC service server in the wireless network (100), according to embodiments as disclosed herein.

[0161] FIG. 8 illustrates a procedure for handling migration during the ongoing ad hoc group call based on the participant list and re-establishing the ad　hoc group call with the migrated MC service user in the migrated MC system (over the wireless network) (100), according to embodiments as disclosed herein.

[0162] Migration information subscription request:Table　7 describes the information flow from the MC service server to another MC service server for migration information subscription request.

[0163] Information elementStatusDescriptionMC service IDMMC service user whose migration information is requested

[0164] Migration information subscription response:Table　8 describes the information flow from the MC service server to another MC service server for migration information subscription response.

[0165] Information elementStatusDescriptionMC service IDMMC service user whose migration information is requestedSubscription statusMIndicates the subscription result

[0166] Migration information notification:Table　9 describes the information flow from the MC service server to another MC service server for migration information notification.

[0167] Information elementStatusDescriptionMC service IDMMC service user whose migration information is being notifiedMigration information (see　NOTE)MMigration informationNOTE: This may contain multiple sets of elements for the MC service user. The following migration information elements shall be present: MC service ID assigned by the migrated MC system to which the MC service user is migrated, migration status, service authorization status.

[0168] Subscription and notification for migration information procedure:

[0169] FIG.　6 illustrates the procedure of subscription for migration information is used by the MC service server to indicate to the another MC service server that it wishes to receive migration information of MC service user.

[0170] The pre-conditions are as follows:

[0171] a. The second service server (110) is the primary MC service server of the MC service user in the primary MC system, whose migration information is being subscribed to receive.

[0172] As shown in FIG. 6, In step 1, the first MC service server (108) sends a migration information subscription request to the second service server (110) to subscribe for the migration information of MC service user. In step 2, the second service server (110) replies with a migration information subscription response indicating the subscription status.

[0173] Please note that as the MC service server is implicitly trusted, the authorization check for the MC service server is not needed.

[0174] The procedure for notification of migration information as described in FIG.　7 is used by the group management server to inform the MC service server that new group policy is available.

[0175] The pre-conditions are as follows:

[0176] a. The first MC service server (108) has subscribed to the migration information of MC service user in the second service server (110) of the MC service user's primary MC system.

[0177] As shown in FIG. 7, In step 1, the second service server (110) provides the notification to the first MC service server (108), with MC service ID of the MC service user assigned by the migrated MC system to which the MC service user has migrated, migration status, service authorization status.

[0178] Procedure for participants list provided by the Initiator:

[0179] FIG.　8 illustrates a generic ad　hoc group call procedure in which the first MC service user using the first MC service client (114) and the second MC service user using the second MC service client (116) migrates during the call, where the first MC system (102) is the primary MC system of the first MC service user before migration, the second MC system (104) is the primary MC system of the second MC service user before migration, the second MC system (104) is the MC system that the first MC service user has migrated and the third MC system (106) is the MC system that the second MC service user has migrated. After the migration, the migrated first MC service user and the second MC service user are re-invited to ongoing ad　hoc group call and successfully added to the call.

[0180] The procedure is based on the following existing procedures:

[0181] a. The ad　hoc group call setup procedures as described in clause　10.19.3.2.1 of 3GPP　TS　23.379, in clause　7.19.3.2.4 of 3GPP　TS　23.281, or in clause　7.17.3.2.1 of 3GPP　TS　23.282.

[0182] b. The migration of the MC service user to the partner MC system procedures as described in clause　10.6.3.

[0183] c. The inviting a MC service user and adding to the ongoing ad　hoc group call procedures steps (see steps 6 and 7) are as described in clause　10.19.3.2.1 of 3GPP　TS　23.379, in clause　7.19.3.2.4 of 3GPP　TS　23.281, or in clause　7.17.3.2.1 of 3GPP　TS　23.282.

[0184] The pre-conditions are as follows:

[0185] a. The first MC system (102), the second MC system (104) and the third MC system (106) are interconnected MC systems.

[0186] b. The first MC system (102) is the primary MC system of the third MC service user, the fourth MC service user and also the first MC service user before migration. The second MC system (104) is the MC system that the first MC service user has migrated.

[0187] c. The second MC system (104) is the primary MC system of the second MC service user before migration. The third MC system (106) is the MC system that the second MC service user has migrated.

[0188] d. The third MC service user, the fourth MC service user, and the first MC service user belongs to same home MC system i.e. primary MC system and the second MC service user belongs to another home MC system i.e. partner MC system (which is interconnected MC system).

[0189] e. The ad　hoc group call is ongoing among the MC service users at the third MC service client (118) (i.e., initiator), the fourth MC service client　(120), the first MC service client (114) and the second MC service client (116) using the MC service ID which are obtained from their primary MC system, and the participants list provided by the originating MC service user while initiating the ad　hoc group call.

[0190] f. The ad　hoc group call is hosted in the first MC service server (108) of the first MC system (102).

[0191] The steps followed as illustrated in the FIG. 8 are as follows:

[0192] In step 1, the first MC service client (114) determines the need to migrate to the second MC system (104) and the first MC service user is notified to be prepared for possible service interruption.

[0193] In steps 2a & 2b, the first MC service client (114) leaves the ad　hoc group call by sending ad　hoc group call leave request towards the first MC service server (108) containing the ad　hoc group ID and reason for the leaving the call as user migration. That is, at step 2a, the first MC service client (114) sends the ad hoc group call leave request to the first MC service server (108). At step 2b, the first MC service server (108) sends the ad hoc group call leave response to the first MC service client (114) based on the ad hoc group call leave request.

[0194] In step 3, the ongoing ad　hoc group call is updated by removing the first MC service client (114) and the call continues with remaining MC service clients.

[0195] In step 4, the first MC service client (114) migrates to the second MC system (104) as described in the clause　10.6.3 and new MC service ID is assigned by the second MC system (104). The first MC service server (108) of the first MC system (102), which is the primary MC system of the migrated first MC service user, is informed about migrated MC service user's MC service ID obtained from the second MC system (104) (i.e. a migrated MC system) along with successful MC service authorization at the second MC system (104).

[0196] In step 5, the first MC service server (108) of the first MC system (102) determines that the first MC service user has to be re-invited for ongoing ad　hoc group call. The first MC service server (108) of the first MC system (102) invites the first MC service client (114) to ad　hoc group call using MC service ID assigned by the second MC system (104) and successfully establishes the ad　hoc group call with the first MC service client (114).

[0197] Please note that How the MC service server determining to re-invite the migrated MC service user is left to the implementation (e.g. timer, policy etc.).

[0198] In step 6, the second MC service client (116) determines the need to migrate to the third MC system (106) and the second MC service user is notified to be prepared for possible service interruption.

[0199] In steps 7a & 7b, the second MC service client (116) leaves the ad　hoc group call by sending ad　hoc group call leave request towards the first MC service server (108) containing the ad　hoc group ID and reason for the leaving the call as user migration. That is, at step 7a, the second MC service client (116) sends the ad hoc group call leave request to the first MC service server (108). At step 7b, the first MC service server (108) sends the ad hoc group call leave response to the second MC service client (116) based on the ad hoc group call leave request.

[0200] In step 8, the ongoing ad　hoc group call is updated by removing the second MC service client (116) and the call continues with remaining MC service clients.

[0201] In step 9, the first MC service server (108) of the first MC system (102) determines that the second MC service user has to be re-invited for ongoing ad　hoc group call. The first MC service server (108) of the first MC system (102) subscribe to the migration information of the second MC service user.

[0202] In step 10, the second MC service client (116) migrates to the third MC system (106) as described in the clause　10.6.3 and new MC service ID is assigned by the third MC system (106). The second service server (110) of the second MC system (104), which is the primary MC system of the migrated second MC service user, is informed about migrated MC service user's MC service ID obtained from the third MC system (106) (i.e. a migrated MC system) along with successful MC service authorization at the third MC system (106).

[0203] In step 11, the second service server (110) of the second MC system (104) determines that the second MC service user has migrated and the first MC service server (108) of the first MC system (102) has subscribed for the migration information. The second service server (110) of the second MC system (104) notifies the migration information of the second MC service user to the first MC service server (108) of the first MC system (102) with MC service ID obtained from the third MC system (106) (i.e. a migrated MC system) along with successful MC service authorization at the third MC system (106).

[0204] In step 12, the first MC service server (108) informs the third MC service client (118) that ad　hoc group call request towards the second MC service user is redirected to the third MC system (106) (migrated MC system) by sending ad　hoc group call redirection notify. The ad　hoc group call redirection notify contains the information about MC service ID of the target MC service user (e.g., second MC service user) assigned by both second MC system (104) and the third MC system (106), and reason for the call redirection as user migration.

[0205] In step 13, the first MC service server (108) of the first MC system (102) invites the second MC service client (116) to ad　hoc group call using MC service ID assigned by the third MC system (106) and successfully establishes the ad　hoc group call with the second MC service client (116).

[0206] FIG. 9 shows various hardware components of the first MC service server (108), according to embodiments as disclosed herein. In an embodiment, the first MC service server (108) includes a processor (910), a communicator (920), a memory (930), and a MC service user migration handling controller (940). The processor (910) is coupled with the communicator (920), the memory (930), the MC service user migration handling controller (940).

[0207] The MC service user migration handling controller (940) receives the ad hoc group call leave request from the first MC service client (114) during the ongoing ad hoc group call. In an embodiment, the MC service user migration handling controller (940) receives the ad hoc group call leave request from the first MC service client (114), when the first MC service client (114) determines the need to migrate to the second MC system (104) and the first MC service client (114) is notified to be prepared for the service interruption in the first MC system (102). Based on the ad hoc group call leave request, the MC service user migration handling controller (940) sends the ad hoc group call leave response to the first MC service client (114). Further, the MC service user migration handling controller (940) maintains the ongoing ad hoc group call by removing the first MC service client (114) and call continues with the at least one remaining MC service client (e.g., third MC service client, fourth MC service client or the like) in the first MC system (102).

[0208] Further, the MC service user migration handling controller (940) informs about the migrated MC service user MC service identifier (ID) obtained from the second MC system (104) along with the successful MC service authorization at the second MC system (104) to the first MC service client (114) when the first MC service client (114) migrates to the second MC system (104).

[0209] Further, the MC service user migration handling controller (940) invites the first MC service client (114) to ad hoc group call using the MC service ID assigned by the second MC system (104). In an embodiment, the MC service user migration handling controller (940) invites the first MC service client (114) to the ad hoc group call using the MC service ID assigned by the second MC system (104), when the second MC service server (110) of the second MC system (104) determines that the migrated first MC service user meets the criteria and notifies the first MC service server (108) of the first MC system (102) to add the first MC service user to the on-going ad hoc group call. In another embodiment, the MC service user migration handling controller (940) determines to re-invite the migrated MC service user associated with the first MC service client (114) based on at least one of: the timer, the policy, the migration completion with periodically querying for the migration status information. Further, the MC service user migration handling controller (940) establishes the ad hoc group call with the first MC service client (114) in the second MC system (104).

[0210] Further, the MC service user migration handling controller (940) receives the ad hoc group call leave request from the second MC service client (116) during the ongoing ad hoc group call. Further, the MC service user migration handling controller (940) sends the ad hoc group call leave response to the second MC service client (116) based on the ad hoc group call leave request. Further, the MC service user migration handling controller (940) maintains the ongoing ad hoc group call by removing the second MC service client (116) in the second MC system (104) and call continues with the at least one remaining MC service client in the first MC system (102) and the second MC system (104).

[0211] Further, the MC service user migration handling controller (940) invites the second MC service client (116) to ad hoc group call using the MC service ID assigned by the third MC system (106). In an embodiment, the MC service user migration handling controller (940) invites the second MC service client (116) to ad hoc group call using the MC service ID assigned by the third MC system (106), when the third MC service server (112) of the third MC system (106) determines that the migrated second MC service user meets the criteria and notifies the first MC service server (108) of the first MC system (102) to add the first MC service user to the on-going ad hoc group call. Further, the MC service user migration handling controller (940) establishes the ad hoc group call with the second MC service client (116) in the third MC system (106).

[0212] The MC service user migration handling controller (940) is implemented by analog and / or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits and the like, and may optionally be driven by firmware.

[0213] The processor (910) may include one or a plurality of processors. The one or the plurality of processors may be a general-purpose processor, such as a central processing unit (CPU), an application processor (AP), or the like, a graphics-only processing unit such as a graphics processing unit (GPU), a visual processing unit (VPU), and / or an AI-dedicated processor such as a neural processing unit (NPU). The processor (910) may include multiple cores and is configured to execute the instructions stored in the memory (930).

[0214] Further, the processor (910) is configured to execute instructions stored in the memory (930) and to perform various processes. The communicator (920) is configured for communicating internally between internal hardware components and with external devices via one or more networks. The memory (930) also stores instructions to be executed by the processor (910). The memory (930) may include non-volatile storage elements. Examples of such non-volatile storage elements may include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. In addition, the memory (930) may, in some examples, be considered a non-transitory storage medium. The term "non-transitory" may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. However, the term "non-transitory" should not be interpreted that the memory (930) is non-movable. In certain examples, a non-transitory storage medium may store data that can, over time, change (e.g., in Random Access Memory (RAM) or cache).

[0215] Although FIG. 9 shows various hardware components of the first MC service server (108) but it is to be understood that other embodiments are not limited thereon. In other embodiments, the first MC service server (108) may include less or more number of components. Further, the labels or names of the components are used only for illustrative purposes and does not limit the scope of the invention. One or more components can be combined together to perform the same or substantially similar function in the first MC service server (108).

[0216] FIG. 10 shows various hardware components of the first MC service client (114), according to embodiments as disclosed herein. In an embodiment, the first MC service client (114) includes a processor (1010), a communicator (1020), a memory (1030), and a controller (1040). The processor (1010) is coupled with the communicator (1020), the memory (1030), the controller (1040).

[0217] The MC service user migration handling controller (1040) sends the ad hoc group call leave request to the first MC service server (108) during the ongoing ad hoc group call. Based on the ad hoc group call leave request, the MC service user migration handling controller (1040) receives the ad hoc group call leave response from the first MC service client (114).

[0218] Further, the MC service user migration handling controller (1040) receives an invite from the first MC service server (108) of the first MC system (102) to establish the ad hoc group call using the MC service ID assigned by the second MC system (104). Further, the MC service user migration handling controller (1040) establishes the ad hoc group call with the second MC service server (110) in the second MC system (104).

[0219] The MC service user migration handling controller (1040) is implemented by analog and / or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits and the like, and may optionally be driven by firmware.

[0220] The processor (1010) may include one or a plurality of processors. The one or the plurality of processors may be a general-purpose processor, such as a central processing unit (CPU), an application processor (AP), or the like, a graphics-only processing unit such as a graphics processing unit (GPU), a visual processing unit (VPU), and / or an AI-dedicated processor such as a neural processing unit (NPU). The processor (1010) may include multiple cores and is configured to execute the instructions stored in the memory (1030).

[0221] Further, the processor (1010) is configured to execute instructions stored in the memory (1030) and to perform various processes. The communicator (1020) is configured for communicating internally between internal hardware components and with external devices via one or more networks. The memory (1030) also stores instructions to be executed by the processor (1010). The memory (1030) may include non-volatile storage elements. Examples of such non-volatile storage elements may include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. In addition, the memory (1030) may, in some examples, be considered a non-transitory storage medium. The term "non-transitory" may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. However, the term "non-transitory" should not be interpreted that the memory (1030) is non-movable. In certain examples, a non-transitory storage medium may store data that can, over time, change (e.g., in Random Access Memory (RAM) or cache).

[0222] Although FIG. 10 shows various hardware components of the first MC service client (114) but it is to be understood that other embodiments are not limited thereon. In other embodiments, the first MC service client (114) may include less or more number of components. Further, the labels or names of the components are used only for illustrative purposes and does not limit the scope of the invention. One or more components can be combined together to perform the same or substantially similar function in the first MC service client (114).

[0223] FIG. 11 is a flow chart (S1100) illustrating a method, implemented by the first MC service server (108), for handling the MC service user migration in the wireless network (100), according to embodiments as disclosed herein. The operations (S1102-S1106) are handled by the MC service user migration handling controller (940).

[0224] At S1102, the method includes receiving the ad hoc group call leave request from the first MC service client (114) during the ongoing ad hoc group call. The first MC service server (108) and the first MC service client (114) are in the first MC system (102). At S1104, the method includes sending the ad hoc group call leave response to the first MC service client (114) based on the ad hoc group call leave request. At S1106, the method includes maintaining the ongoing ad hoc group call by removing the first MC service client (114) and call continues with at least one remaining MC service client in the first MC system (102).

[0225] FIG. 12 is a flow chart (S1200) illustrating a method, implemented by the first MC service client (114), for handling the MC service user migration in the wireless network (100), according to embodiments as disclosed herein. The operations (S1202-S1204) are handled by the MC service user migration handling controller (1040).

[0226] At S1202, the method includes sending the ad hoc group call leave request to the first MC service server (108) during the ongoing ad hoc group call. The first MC service server (108) and the first MC service client (114) are in the first MC system (102). At S1204, the method includes receiving the ad hoc group call leave response from the first MC service client (114) based on the ad hoc group call leave request.

[0227] The various actions, acts, blocks, steps, or the like in the flow charts (S1100 and S1200) may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some of the actions, acts, blocks, steps, or the like may be omitted, added, modified, skipped, or the like without departing from the scope of the invention.

[0228] The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the network elements. The elements include blocks which can be at least one of a hardware device, or a combination of hardware device and software module.

[0229] The embodiments disclosed herein describe methods and systems for handling migration of a participating MC service user while in an ongoing ad hoc group call. Therefore, it is understood that the scope of the protection is extended to such a program and in addition to a computer readable means having a message therein, such computer readable storage means contain program code means for implementation of one or more steps of the method, when the program runs on a server or mobile device or any suitable programmable device. The method is implemented in at least one embodiment through or together with a software program written in e.g., Very high speed integrated circuit Hardware Description Language (VHDL) another programming language, or implemented by one or more VHDL or several software modules being executed on at least one hardware device. The hardware device can be any kind of portable device that can be programmed. The device may also include means which could be e.g., hardware means like e.g., an ASIC, or a combination of hardware and software means, e.g. an ASIC and an FPGA, or at least one microprocessor and at least one memory with software modules located therein. The method embodiments described herein could be implemented partly in hardware and partly in software. Alternatively, the invention may be implemented on different hardware devices, e.g., using a plurality of CPUs.

[0230] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and / or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the embodiments as described herein.

Claims

1.A method performed by a first mission critical (MC) service server of a first MC system in a communication system, the method comprising:receiving, from a first MC service client of the first MC system, an ad hoc group call leave request message during an ongoing ad hoc group call;transmitting, to the first MC service client, an ad hoc group call leave response message as a response to the ad hoc group call leave request message;receiving, from a second MC service server of a second MC system, a message including information on a first MC service identifier (ID) of the first MC service client assigned by the second MC system along with a successful MC service authorization at the second MC system;inviting the first MC service client to the ongoing ad hoc group call using the first MC service ID assigned by the second MC system; andestablishing the ongoing ad hoc group call with the first MC service client in the second MC system.2.The method of claim 1, further comprising:receiving, from a second MC service client of the second MC system, an ad hoc group call leave request message during the ongoing ad hoc group call;transmitting, to the second MC service client, an ad hoc group call leave response message as a response to the ad hoc group call leave request message;transmitting, to the second MC service server, an ad hoc group call request towards the second MC service client of the second MC system using a second MC service ID of the second MC service client assigned by the second MC system;receiving, from the second MC service server, an ad hoc group call redirection notify message including information indicating that an initiation of the ongoing ad hoc group call towards the second MC service client has migrated to a third MC system and information on a third MC service ID of the second MC service client assigned by the third MC system;inviting the second MC service client to the ongoing ad hoc group call using the third MC service ID assigned by the third MC system; andestablishing the ongoing ad hoc group call with the second MC service client in the third MC system.3.The method of claim 1, wherein the inviting the first MC service client comprises:receiving, from the second MC service server, a notification to add the first MC service client to the ongoing ad hoc group call, in case that the second MC service client meets a criteria; andinviting the first MC service client to ad hoc group call using the first MC service ID assigned by the second MC system.4.The method of claim 1, further comprising:receiving, from a second MC service client of the second MC system, an ad hoc group call leave request message during the ongoing ad hoc group call;transmitting, to the second MC service client, an ad hoc group call leave response message as a response to the ad hoc group call leave request message;receiving, from a third MC service server of a third MC system, a notification to add the second MC service client to the ongoing ad hoc group call, in case that the third MC service client meets a criteria;inviting the second MC service client to the ongoing ad hoc group call using a second MC service ID assigned by the third MC system; andestablishing the ongoing ad hoc group call with the second MC service client in the third MC system.5.The method of claim 1,wherein, in case that the ad hoc group call leave response message is transmitted to the first MC service client, the ongoing ad hoc group call is updated by removing the first MC service client and call continues with remaining MC service clients.6.The method of claim 1,wherein the ad hoc group call leave request message comprises at least one of a mission critical push to talk (MCPTT) ID, a MCPTT ad hoc group ID, or a reason to leave as a user migration, andwherein the hoc group call leave response message comprises at least one of the MCPTT ID or the MCPTT ad hoc group ID.7.A method performed by a mission critical (MC) service client in a communication system, the method comprising:transmitting, to a first MC service server of a first MC system, an ad hoc group call leave request message during an ongoing ad hoc group call;receiving, from the first MC service server, an ad hoc group call leave response message as a response to the ad hoc group call leave request message;receiving, from the first MC service server, an invite to the ongoing ad hoc group call using a first MC service identifier (ID) of the first MC service client assigned by a second MC system; andestablishing the ongoing ad hoc group call with the first MC service server of the first MC system.8.The method of claim 7,wherein the ad hoc group call leave request message comprises at least one of a mission critical push to talk (MCPTT) ID, a MCPTT ad hoc group ID, or a reason to leave as a user migration, andwherein the hoc group call leave response message comprises at least one of the MCPTT ID or the MCPTT ad hoc group ID.9.A first mission critical (MC) service server of a first MC system in a communication system, the first MC service server comprising:a transceiver; anda controller configured to:receive, from a first MC service client of the first MC system via the transceiver, an ad hoc group call leave request message during an ongoing ad hoc group call,transmit, to the first MC service client via the transceiver, an ad hoc group call leave response message as a response to the ad hoc group call leave request message,receive, from a second MC service server of a second MC system via the transceiver, a message including information on a first MC service identifier (ID) of the first MC service client assigned by the second MC system along with a successful MC service authorization at the second MC system,invite the first MC service client to the ongoing ad hoc group call using the first MC service ID assigned by the second MC system, andestablish the ongoing ad hoc group call with the first MC service client in the second MC system.10.The first MC service server of claim 9, wherein the controller is further configured to:receive, from a second MC service client of the second MC system via the transceiver, an ad hoc group call leave request message during the ongoing ad hoc group call,transmit, to the second MC service client via the transceiver, an ad hoc group call leave response message as a response to the ad hoc group call leave request message,transmit, to the second MC service server via the transceiver, an ad hoc group call request towards the second MC service client of the second MC system using a second MC service ID of the second MC service client assigned by the second MC system,receive, from the second MC service server via the transceiver, an ad hoc group call redirection notify message including information indicating that an initiation of the ongoing ad hoc group call towards the second MC service client has migrated to a third MC system and information on a third MC service ID of the second MC service client assigned by the third MC system,invite the second MC service client to the ongoing ad hoc group call using the third MC service ID assigned by the third MC system, andestablish the ongoing ad hoc group call with the second MC service client in the third MC system.11.The first MC service server of claim 9, wherein the controller is further configured to:receive, from the second MC service server via the transceiver, a notification to add the first MC service client to the ongoing ad hoc group call, in case that the second MC service client meets a criteria, andinvite the first MC service client to ad hoc group call using the first MC service ID assigned by the second MC system.12.The first MC service server of claim 9, wherein the controller is further configured to:receive, from a second MC service client of the second MC system via the transceiver, an ad hoc group call leave request message during the ongoing ad hoc group call,transmit, to the second MC service client via the transceiver, an ad hoc group call leave response message as a response to the ad hoc group call leave request message,receive, from a third MC service server of a third MC system via the transceiver, a notification to add the second MC service client to the ongoing ad hoc group call, in case that the third MC service client meets a criteria,invite the second MC service client to the ongoing ad hoc group call using a second MC service ID assigned by the third MC system, andestablish the ongoing ad hoc group call with the second MC service client in the third MC system.13.The first MC service server of claim 9,wherein, in case that the ad hoc group call leave response message is transmitted to the first MC service client, the ongoing ad hoc group call is updated by removing the first MC service client and call continues with remaining MC service clients,wherein the ad hoc group call leave request message comprises at least one of a mission critical push to talk (MCPTT) ID, a MCPTT ad hoc group ID, or a reason to leave as a user migration, andwherein the hoc group call leave response message comprises at least one of the MCPTT ID or the MCPTT ad hoc group ID.14.A mission critical (MC) service client in a communication system, the MC service client comprising:a transceiver; anda controller configured to:transmit, to a first MC service server of a first MC system via the transceiver, an ad hoc group call leave request message during an ongoing ad hoc group call,receive, from the first MC service server via the transceiver, an ad hoc group call leave response message as a response to the ad hoc group call leave request message,receive, from the first MC service server via the transceiver, an invite to the ongoing ad hoc group call using a first MC service identifier (ID) of the first MC service client assigned by a second MC system, andestablish the ongoing ad hoc group call with the first MC service server of the first MC system.15.The MC service client of claim 14,wherein the ad hoc group call leave request message comprises at least one of a mission critical push to talk (MCPTT) ID, a MCPTT ad hoc group ID, or a reason to leave as a user migration, andwherein the hoc group call leave response message comprises at least one of the MCPTT ID or the MCPTT ad hoc group ID.

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