Optimized multicast and broadcast systems data forwarding with split gnb

Abstract

Embodiments of the present disclosure relate to methods, devices, apparatuses and computer readable storage medium for optimized Multicast and Broadcast Systems (MBS) data forwarding with split gNodeB (gNB). A method comprising: at a first apparatus, receiving, from a second apparatus, a request of an Xn Handover related to a user equipment (UE); obtaining, from a third apparatus, in a MBS session establishment or modification, an Xn forwarding address related to the Xn handover before an F1 UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers an F1-U forwarding tunnel setup for the Xn handover; and delivering the Xn forwarding address to at least one of: the fourth apparatus before the fourth apparatus triggers an F1-U forwarding tunnel setup for the Xn handover; or second apparatus in an acknowledge message for the request of the Xn handover before the fourth apparatus triggers an F1-U forwarding tunnel for the Xn handover and / or before F1 the UE context is setup between the first apparatus and the fourth apparatus.

Description

OPTIMIZED MULTICAST AND BROADCAST SYSTEMS DATA FORWARDING WITH SPLIT GNBFIELDS

[0001] Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for optimized Multicast and Broadcast Systems (MBS) data forwarding with split gNodeB (gNB).BACKGROUND

[0002] The 3rd Generation Partnership Project (3GPP) finalized a work item for support of MBS in New Radio (NR). Herein, Point to Multi-Point (PTM) transmission is expected to efficiently provision MBS services to multiple users by using the same radio framework as unicast transmission. The reception of a multicast service by the UEs is enabled in a radio resource control (RRC) connected (RRC CONNECTED) state, only. In addition, the broadcast reception in all RRC states has been specified.

[0003] A gNB can be split between a centralized unit (CU) containing higher layer protocol and a distributed unit (DU) containing lower layer protocol. Furthermore, the CU can be itself split in a control plane (CP) part named CU-CP and a user plane (UP) part named CU-UP.

[0004] Data forwarding was also added for MBS. It is supported for both monolithic gNB and for split gNB. Data can be forwarded from source gNB to target gNB over one or more Xn-U forwarding tunnels.SUMMARY

[0005] In a first aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: receive, from a second apparatus, a request of an Xn Handover related to a userequipment (UE); obtain, from a third apparatus, in an MBS session establishment or modification, an Xn forwarding address related to the Xn handover before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; and deliver the Xn forwarding address to at least one of the fourth apparatus before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; or second apparatus in an acknowledge message for the request of the Xn handover before the fourth apparatus triggers an Fl-U forwarding tunnel for the Xn handover and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

[0006] In a second aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: transmit, to a first apparatus, a request of an Xn Handover related to a UE; and receive, from the first apparatus in an acknowledge message for the request of the Xn handover, an Xn forwarding address related to the Xn handover before a fourth apparatus triggers an Fl-U forwarding tunnel and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

[0007] In a third aspect of the present disclosure, there is provided a third apparatus. The third apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: transmit, to a first apparatus, in an MBS session establishment or modification, an Xn forwarding address for an Xn handover related to a UE before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers the setup of an F 1 -U forwarding tunnel for the Xn handover.

[0008] In a fourth aspect of the present disclosure, there is provided a fourth apparatus. The fourth apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the fourth apparatus at least to: receive, from a first apparatus, an Xn forwarding address for an Xn handover related to a UE before the fourth apparatus triggers an Fl-U forwarding tunnel setup for this handover; and transmit, to the first apparatus, an Fl-U DU address of the fourth apparatus for the Fl-U forwarding tunnel setup for the Xn handover along with the Xn forwarding address.

[0009] In a fifth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a second apparatus, a request of an Xn Handover related to a UE; obtaining, from a third apparatus, in an MBS session establishment or modification, an Xn forwarding address related to the Xn handover before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; and delivering the Xn forwarding address to at least one of: the fourth apparatus before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; or second apparatus in an acknowledge message for the request of the Xn handover before the fourth apparatus triggers an Fl-U forwarding tunnel for the Xn handover and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

[0010] In a sixth aspect of the present disclosure, there is provided a method. The method comprises: transmitting, to a first apparatus, a request of an Xn Handover related to a UE; and receiving, from the first apparatus in an acknowledge message for the request of the Xn handover, an Xn forwarding address related to the Xn handover before a fourth apparatus triggers an Fl-U forwarding tunnel and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

[0011] In a seventh aspect of the present disclosure, there is provided a method. The method comprises: transmitting, to a first apparatus, in an MBS session establishment or modification, an Xn forwarding address for an Xn handover related to a UE before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers the setup of an Fl-U forwarding tunnel for the Xn handover.

[0012] In an eighth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a first apparatus, an Xn forwarding address for an Xn handover related to a UE before the fourth apparatus triggers an Fl-U forwarding tunnel setup for this handover; and transmitting, to the first apparatus, an Fl-U DU address of the fourth apparatus for the Fl-U forwarding tunnel setup for the Xn handover along with the Xn forwarding address.

[0013] In a ninth aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for receiving, from a second apparatus, a request of an Xn Handover related to a UE; means for obtaining, from a third apparatus, in an MBS session establishment or modification, an Xn forwarding address related to the Xnhandover before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; and means for delivering the Xn forwarding address to at least one of: the fourth apparatus before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; or second apparatus in an acknowledge message for the request of the Xn handover before the fourth apparatus triggers an Fl-U forwarding tunnel for the Xn handover and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

[0014] In a tenth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for transmitting, to a first apparatus, a request of an Xn Handover related to a UE; and means for receiving, from the first apparatus in an acknowledge message for the request of the Xn handover, an Xn forwarding address related to the Xn handover before a fourth apparatus triggers an Fl-U forwarding tunnel and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

[0015] In an eleventh aspect of the present disclosure, there is provided a third apparatus. The third apparatus comprises means for transmitting, to a first apparatus, in an MBS session establishment or modification, an Xn forwarding address for an Xn handover related to a UE before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers the setup of an Fl-U forwarding tunnel for the Xn handover.

[0016] In a twelfth aspect of the present disclosure, there is provided a fourth apparatus. The fourth apparatus comprises means for receiving, from a first apparatus, an Xn forwarding address for an Xn handover related to a UE before the fourth apparatus triggers an Fl-U forwarding tunnel setup for this handover; and means for transmitting, to the first apparatus, an Fl-U DU address of the fourth apparatus for the Fl-U forwarding tunnel setup for the Xn handover along with the Xn forwarding address.

[0017] In a thirteenth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fifth aspect.

[0018] In a fourteenth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereonfor causing an apparatus to perform at least the method according to the sixth aspect.

[0019] In a fifteenth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the seventh aspect.

[0020] In a sixteenth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the eighth aspect.

[0021] It is to be understood that the Summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0023] FIG. 1 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

[0024] FIG. 2 illustrates a signaling chart illustrating an example of process according to some example embodiments of the present disclosure;

[0025] FIG. 3 illustrates a flowchart of a method implemented at a first device according to some example embodiments of the present disclosure;

[0026] FIG. 4 illustrates a flowchart of a method implemented at a second device according to some example embodiments of the present disclosure;

[0027] FIG. 5 illustrates a flowchart of a method implemented at a third device according to some example embodiments of the present disclosure;

[0028] FIG. 6 illustrates a flowchart of a method implemented at a fourth device according to some example embodiments of the present disclosure;

[0029] FIG. 7 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0030] FIG. 8 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0031] Throughout the drawings, the same or similar reference numerals represent the same or similar element.DETAILED DESCRIPTION

[0032] Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. Embodiments described herein can be implemented in various manners other than the ones described below.

[0033] In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

[0034] References in the present disclosure to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0035] It shall be understood that although the terms “first,” “second,”..., etc. in front of noun(s) and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another and they do not limit the order of the noun(s). For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the listed terms.

[0036] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0037] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and / or “including”, when used herein, specify the presence of stated features, elements, and / or components etc., but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof.

[0039] As used in this application, the term “circuitry” may refer to one or more or all of the following:(a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and(b) combinations of hardware circuits and software, such as (as applicable):(i) a combination of analog and / or digital hardware circuit(s) with software / firmware and(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0040] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0041] As used herein, the term “communication network” refers to a network following any suitable communication standards, such as New Radio (NR), Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), Narrow Band Internet of Things (NB-IoT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G), the sixth generation (6G) communication protocols, and / or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

[0042] As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN)split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0043] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0044] As used herein, the term “resource,” “transmission resource,” “resource block,” “physical resource block” (PRB), “uplink resource,” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other combination of the time, frequency, space and / or code domain resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted thatexample embodiments of the present disclosure are equally applicable to other resources in other domains.

[0045] As discussed above, data forwarding was added for MBS. It is supported for both monolithic gNB and for split gNB. Data can be forwarded from source gNB to target gNB over one or more Xn-U forwarding tunnels.

[0046] At the target gNB, if the target gNB is a split gNB, for each UE being handed over, an Fl-U forwarding dedicated tunnel can be setup between the target CU UP and the target DU to forward the missing packets to a first UE via the target DU, if any. The first UE may be missing packets in case the MBS delivery at the source gNB was behind the MBS delivery at the target gNB. For example, at the time of first UE hand-over the source gNB is still transmitting packet sequence number (SN) 100 while the target gNB is already transmitting packet SN 110, then when the first UE arrives it is missing packets SN 101 to SN 109.

[0047] In an 3GPP solution, there is no one-to-one mapping between Xn forwarding tunnel and the Fl-U forwarding tunnel. This is because the packets to be forwarded over the Fl-U forwarding tunnel by the target CU UP for the given first UE are determined instead by using a first UE “MRB progress information”.

[0048] The first UE MRB progress information is the current SN used at the source gNB which the source gNB includes in the Xn handover request to the target gNB CU CP. For example, a first UE MRB progress information would correspond to SN=100. The target CU CP request the Fl-U forwarding tunnel to the target DU including the first UE MRB progress information (SN=100). Then when the target DU triggers the setup of the Fl-U forwarding tunnel, it forwards the received first UE MRB progress information (SN=100) towards the target CU UP via the target CU CP. Based on the received first UE MRB progress information (SN=100), the target CU UP may remember that the packets to be delivered over that Fl-U forwarding tunnel destined to the first UE need to start at SN 101.

[0049] Assuming the target CU is ahead of the source gNB and currently delivering packets at SN 110 when receiving the Xn handover request for the first UE, the target CU UP may decide to not allocate an Xn forwarding tunnel if it still has in its buffer the packets to be delivered over the Fl-U forwarding tunnel for the first UE (i.e. the packets from SN 101 to SN 109).

[0050] It may also decide to not allocate an Xn forwarding tunnel for this first UE if it has just before already setup and Xn forwarding tunnel for the incoming handover of a second UE which will already provide the needed packets for the UE Fl-U forwarding tunnel (i.e., packets from SN 101 to SN 109).

[0051] As a result, in the first case the first UE will have an Fl-U forwarding tunnel without having an Xn forwarding tunnel, or in the second case it could be that the Fl-U forwarding tunnel of the first UE will be delivered packets coming from the the Xn forwarding tunnel of the second UE, which is quite unusual so far in the 3 GPP state.

[0052] In summary, with the current MBS data forwarding scheme, when there is Xn handover of the first UE, there is no need of one-to-one mapping between an Xn forwarding tunnel and the Fl-U forwarding tunnel of this first UE because the packets to be forwarded over the Fl-U forwarding tunnel for the first UE are determined based on the UE MRB information (the SN of last packet delivered to the first UE at the source gNB).

[0053] An alternative scheme has been proposed to avoid relying on the UE MRB progress information for CU UP to determine which packets to send over the Fl-U forwarding tunnel. Instead that the target DU newly includes the Fl UE Context Setup Response the Fl-U context reference that the target DU will further use when setting up the Fl-U forwarding tunnel. The target CU CP then stores this Fl-U context reference in the target CU CP UE context.

[0054] Then the target DU triggers the setup of the Fl-U forwarding tunnel towards the target CU UP via the target CU CP including this Fl-U context reference. Then the target CU CP further request an Xn forwarding address to target CU UP. The target CU CP receives the Xn forwarding address from target CU UP. Then the target CU CP needs to identify which of the UE contexts had earlier received the Fl-U context reference at step 8. Once identified, the target CU CP can store the received Xn forwarding address into this identified UE context as well. When target CU CP sends back the Xn handover request acknowledge associated to this UE context to the source gNB, it can thus include the Xn forwarding tunnel address. The target CU UP can bind the Xn forwarding tunnel and the Fl-U forwarding tunnel for the UE.

[0055] The MBS data forwarding for split gNB in 3GPP solution may have the following main problems.

[0056] First, it delays the handover because the forwarding process relies on the UE MBR progress information to be sent from the source gNB to the target gNB. The problem is that when source gNB is a split gNB, this induces the additional operations for the source CU CP to fetch the UE MBR progress information from the source CU UP (i.e., the current packet SN being delivered by the source CU UP), which may degrade the handover performance.

[0057] Second, the 3GPP solution does not use a one-one mapping between an Xn forwarding tunnel of a first UE and an Fl-U forwarding tunnel of the same first UE. This requires a complicated and new processing in the target CU UP to memorize which packets must be delivered over which the Fl-U forwarding tunnel, and whether these packets are already expected to be received from a second UE’s Xn forwarding tunnel. This is more complicated logic than a systematic simple one-to-one mapping / binding between the Xn forwarding tunnel of a first UE and its Fl-U forwarding tunnel, where all packets received over the Xn forwarding tunnel would be blindly forwarded by the target CU UP to the target DU without any further logic or processing.

[0058] For the alternative scheme proposed to avoid relying on the UE MRB progress information, although it solves part of the issues of the 3GPP solution, there are still some other drawbacks, for example, it removes the delay due the additional operation in the 3 GPP solution but the sending of the Xn handover request acknowledge to the source gNB is still late and therefore not fully optimized.

[0059] Moreover, it introduces a complex parsing in the target CU CP whereby the target CU CP receiving the Xn forwarding address from CU UP together with an Fl-U context reference needs to parse all its UE contexts to find the one which had received in the Fl UE context setup response message the same Fl-U context reference. This is because the process of setting up the Fl-U forwarding tunnel uses a non-UE associated procedure while the Fl UE context setup response uses a UE-associated procedure, therefore the need of identifying the right UE context through parsing of all UE contexts.

[0060] FIG. 1 illustrates an example communication environment 100 in which example embodiments of the present disclosure can be implemented. As shown in FIG. 1, the communication environment 100 comprises a first apparatus 110, a second apparatus 120 and a third apparatus 130 and a fourth apparatus 140. The first apparatus 110 may communication with the second apparatus 120, the third apparatus 130 and the fourthapparatus 140 with each other, respectively.

[0061] The first apparatus 110, the second apparatus 120, the third apparatus 130 and the fourth apparatus 140 each may be a network device in RAN, for example, a gNB. In some example embodiments, the first apparatus 110 the third apparatus 130 and the fourth apparatus 140 may be implemented as discrete components of a RAN network device, either logically or physically.

[0062] In the example shown in FIG. 1, the first apparatus 110 may be referred to as a gNB CU CP, the third apparatus 130 may be referred to as a gNB CU UP and the fourth apparatus 140 may be referred to as a gNB DU. In particular, a gNB CU CP may be connected to a gNB DU via an Fl-C interface, while a gNB CU UP may be connected to a gNB DU via an Fl-U interface. The second apparatus 120 may be referred to as a further gNB. The second apparatus 120 may be connected to the first apparatus 110 via an Xn interface.

[0063] Furthermore, the communication environment 100 may also comprises a terminal device 150 (e.g., UE). In some scenarios, the terminal device 150 may be served by the second apparatus 120. As radio conditions between the second apparatus 120 and the terminal device 150 have changed, a handover procedure of the terminal device 150 may be initiated, e.g., a handover to the first apparatus 110. In this situation, the second apparatus 120 may act as a source gNB of the terminal device 150 in this handover procedure. The first apparatus 110, the third apparatus 130 and the fourth apparatus 140 may act as a target gNB CU CP, a target gNB CU UP and a target gNB DU, respectively.

[0064] In some example embodiments, a link from a network device to a terminal device is referred to as a downlink (DL), and a link from a terminal device to a network device is referred to as an uplink (UL). In DL, the network device is a transmitting (TX) device (or a transmitter) and the terminal device is a receiving (RX) device (or a receiver). In UL, the terminal device is a TX device (or a transmitter) and the network device is a RX device (or a receiver).

[0065] Communications in the communication environment 100 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (1G), the second generation (2G), the third generation (3G), the fourth generation (4G), the fifth generation (5G), the sixth generation (6G), and the like, wireless local network communication protocols such asInstitute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and / or any other technologies currently known or to be developed in the future.

[0066] According to some example embodiments of the present disclosure, there is provided a solution for optimized MBS data forwarding with split gNB. In this solution, a source gNB transmits to a target CU CP a request of an Xn Handover related to a UE. The target CU CP obtains, from a target CU UP, in an MBS session establishment or modification, an Xn forwarding address related to the Xn handover before an Fl UE context is setup between the target CU CP and a target DU or before the target DU triggers an Fl-U forwarding tunnel setup for the Xn handover. Then the target CU CP deliver the obtained Xn forwarding address to the target DU before the target DU triggers an Fl-U forwarding tunnel setup and / or to the source gNB before the target DU triggers an Fl-U forwarding tunnel setup for the Xn handover or before the Fl UE context is setup between the target CU CP and a target DU.

[0067] In this way, the delay of handover may be optimized and simple logic in target CU UP with one-to-one mapping in target CU UP between the Xn forwarding tunnel of a UE and the Fl-U forwarding tunnel setup for the same UE can be established. The delay for the handover may be optimized because the source gNB can trigger the handover execution towards the UE as soon as it receives the handover request acknowledge message containing the Xn forwarding address.

[0068] Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0069] Reference is now made to FIG. 2, which illustrates a signaling chart 200 of an example process based on normal handover according to some example embodiments of the present disclosure. As shown in FIG. 2, the signaling chart 200 involves the first apparatus 110, the second apparatus 120, the third apparatus 130 and the fourth apparatus140. For the purposes of discussion, the signaling chart 200 will be discussed with reference to FIG. 1.

[0070] As shown in FIG. 2, if a Xn handover associated with a UE (e.g., the terminal device 150 in FIG. 5) is to be initiated, the second apparatus 120 may send (205), to the first apparatus 110, an Xn Handover request message.

[0071] Then the first apparatus 110 may establish the multicast MBS context in the third apparatus 130.

[0072] For example, if no MBS context exists yet for this multicast MBS session, the first apparatus 110 perform the multicast MBS context establishment procedure with third apparatus 130, otherwise it performs the MBS context modification procedure towards the third apparatus 130.

[0073] As part of the multicast MBS context establishment or modification procedure, the first apparatus 110 may request (210), to the third apparatus 130, for example, via a El BC bearer context setup / modification request message for an Xn forwarding address related to the Xn handover.

[0074] In some embodiments, the first apparatus 110 may request (210), to the third apparatus 130, the Xn forwarding address related to the Xn handover before an Fl UE context is setup between the first apparatus 110 and the fourth apparatus 140. In some other embodiments, the first apparatus 110 may request (210), to the third apparatus 130, the Xn forwarding address related to the Xn handover before the fourth apparatus 140 triggers an F 1 -U forwarding tunnel setup for the Xn handover.

[0075] After receiving the request of the Xn forwarding address related to the Xn handover, the third apparatus 130 may allocate the Xn forwarding address and send (215) it back to the first apparatus 110, for example, via an El BC Bearer Context modification response message. That is, the first apparatus 110 may obtain the Xn forwarding address related to the Xn handover before an Fl UE context is setup between the first apparatus 110 and the fourth apparatus 140 and / or before the fourth apparatus 140 triggers an Fl-U forwarding tunnel setup for the Xn handover.

[0076] Upon receiving the Xn forwarding address related to the Xn handover from the third apparatus 130, the first apparatus 110 may deliver (220) the obtained the Xn forwarding address immediately to the second apparatus 120, e.g., via an Xn handoverrequest acknowledge message. The first apparatus 110 may send the Xn handover request acknowledge message along with the obtained the Xn forwarding address before the fourth apparatus 140 triggers an Fl-U forwarding tunnel for the Xn handover and / or before the UE context is setup between the first apparatus 110 and the fourth apparatus 140.

[0077] Furthermore, the first apparatus 110 may deliver (225) the obtained the Xn forwarding address to the fourth apparatus 140 in a procedure of an Fl UE context setup. For example, the first apparatus 110 may deliver (225) the obtained the Xn forwarding address to the fourth apparatus 140 via an Fl UE context setup request message.

[0078] Upon receiving the F 1 UE context setup request message from the first apparatus 110, the fourth apparatus 140 may trigger the setting up of the Fl-U forwarding tunnel. In this process, the fourth apparatus 140 may send (230), to the first apparatus 110, an Fl distribution setup request message including its Fl-U DU address for an Fl-U forwarding tunnel and the Xn forwarding address received from the first apparatus 110 in the action 225.

[0079] Since the first apparatus 110 newly receives both the Xn forwarding address and the Fl-U DU address for the Fl-U forwarding tunnel setup sent by the fourth apparatus 140, the first apparatus 110 may send (235) the Fl-U DU address for the Fl-U forwarding tunnel setup along with the Xn forwarding address to the third apparatus 130, e.g., within a the El BC Bearer Context Modification request message.

[0080] Upon receiving both Fl-U DU address and Xn forwarding address, the third apparatus 130 may bind (240) this Xn forwarding address with the Fl-U DU address. That is, a one-to-one mapping between the Xn forwarding address and the Fl-U DU address of the fourth apparatus 140 for the Fl-U forwarding tunnel setup is established.

[0081] Then the third apparatus 130 may send (245) the El BC Bearer context modification response message to first apparatus 110. The first apparatus 110 then sends (250) the Fl distribution setup response message to the fourth apparatus 140, both including the target CU UP Fl-U address to complete the distribution setup procedure, i.e., the Fl-U tunnel setup procedure.

[0082] With the solution proposed in the present disclosure, comparing to the 3 GPP solution, the delay for the handover may be optimized. A source CU CP does not need to fetch information from the source CU UP before sending the Xn Handover request. Also,the Xn handover request acknowledge is sent very early to the source gNB (before the target DU setting up the Fl -U forwarding tunnel) which enables the source gNB to receive the Xn handover request acknowledge early and to send an early RRC reconfiguration message (handover command) to the UE to execute the handover faster.

[0083] Furthermore, a simple logic in a target CU UP with one-to-one mapping in the target CU UP between the Xn forwarding tunnel of a UE and the Fl-U forwarding tunnel setup for the same UE may be achieved. The mapping / binding may further be simplified by the target CU UP receiving in the same El BC bearer context modification request message both addresses together (i.e., the Xn forwarding address, and the Fl-U DU address).

[0084] Comparing to the other conventional approach, on the one hand, the delay for the handover may be optimized. The Xn handover request acknowledge may be sent very early to the source gNB (before the Fl setting up the Fl-U forwarding tunnel) which enables the source gNB to receive the Xn handover request acknowledge early and to send an early RRC reconfiguration (handover command) to the UE to execute the handover faster.

[0085] On the other hand, a simpler logic in target CU CP which blindly relays the two addresses included by target DU during the setup of the Fl-U forwarding tunnel (i.e., in the Fl Distribution setup request procedure triggered by target DU) towards the target CU UP. This avoids the need for the target DU to include the Fl-U context reference in the Fl UE context response and the associated drawback for target CU CP to parse UE contexts to retrieve the UE context which has received earlier this Fl-U reference.

[0086] FIG. 3 shows a flowchart of an example method 300 implemented at a first device in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 300 will be described from the perspective of the first apparatus 110 in FIG. 1.

[0087] At block 310, the first apparatus 110 receives, from a second apparatus, a request of an Xn Handover related to a UE.

[0088] At block 320, the first apparatus 110 obtains, from a third apparatus, in an MBS session establishment or modification, an Xn forwarding address related to the Xn handover before an Fl UE context is setup between the first apparatus and a fourthapparatus or before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover.

[0089] At block 330, the first apparatus 110 delivers the Xn forwarding address to at least one of: the fourth apparatus before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; or second apparatus in an acknowledge message for the request of the Xn handover before the fourth apparatus triggers an Fl-U forwarding tunnel for the Xn handover and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

[0090] In some example embodiments, the method 300 further comprises: in response to receiving from the fourth apparatus, an Fl-U DU address of the fourth apparatus for the Fl-U forwarding tunnel setup along with the Xn forwarding address, transmit, to third apparatus, the Fl-U DU address along with the Xn forwarding address.

[0091] In some example embodiments, the method 300 further comprises: transmitting, to the third apparatus as part of an MBS session establishment or modification process, an El BC bearer context setup or modification request message indicating a request of the Xn forwarding address before the Fl UE context setup or before the fourth apparatus triggers the Fl-U forwarding tunnel setup; and receiving, from the third apparatus, the Xn forwarding address via an El BC bearer context setup / modification response message before the Fl UE context setup or before the fourth apparatus triggers the Fl-U forwarding tunnel setup.

[0092] In some example embodiments, the method 300 further comprises: delivering the Xn forwarding address to the fourth apparatus via an Fl UE context setup request message.

[0093] In some example embodiments, the method 300 further comprises: delivering the Xn forwarding address to the fourth apparatus via the Fl UE context setup request message together with a request to setup an Fl-U forwarding tunnel; and receiving, from the fourth apparatus, the Fl-U DU address for the Fl-U forwarding tunnel along with the Xn forwarding address via a Fl multicast distribution setup request message.

[0094] In some example embodiments, the method 300 further comprises: transmitting, to the third apparatus, the Fl-U DU address along with the Xn forwarding address via a further El BC bearer context modification request message.

[0095] In some example embodiments, the first apparatus comprises a CU control plane of a network device, the second apparatus comprises a further network device, the third apparatus comprises a CU user plane of the network device, and the fourth apparatus comprises a DU of the network device.

[0096] FIG. 4 shows a flowchart of an example method 400 implemented at a second device in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 400 will be described from the perspective of the second apparatus 120 in FIG. 1.

[0097] At block 410, the second apparatus 120 transmits, to a first apparatus, a request of an Xn Handover related to a UE.

[0098] At block 420, the second apparatus 120 receives, from the first apparatus in an acknowledge message for the request of the Xn handover, an Xn forwarding address related to the Xn handover before a fourth apparatus triggers an Fl-U forwarding tunnel and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

[0099] In some example embodiments, the first apparatus comprises a CU control plane of a network device, the second apparatus comprises a further network device, and the fourth apparatus comprises a DU of the network device.

[0100] FIG. 5 shows a flowchart of an example method 500 implemented at a third device in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 500 will be described from the perspective of the third apparatus 130 in FIG. 1.

[0101] At block 510, the third apparatus 130 transmits, to a first apparatus, in an MBS session establishment or modification, an Xn forwarding address for an Xn handover related to a UE before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers the setup of an Fl-U forwarding tunnel for the Xn handover.

[0102] In some example embodiments, the method 500 further comprises: receiving, from the first apparatus, the Fl-U DU address for an Fl-U forwarding tunnel along with the Xn forwarding address; and associating the Xn forwarding address to the Fl-U DU address.

[0103] In some example embodiments, associating the Xn forwarding address and the Fl-U DU address consists of forwarding packets received over the Xn forwarding address towards the received Fl-U DU address.

[0104] In some example embodiments, the method 500 further comprises: receiving, from the first apparatus in the MBS session establishment or modification, an El BC bearer context modification request message indicating a request for the Xn forwarding address for the Xn handover before the Fl UE context setup or before the fourth apparatus triggers the Fl-U forwarding tunnel setup for the Xn handover; and transmitting, to the first apparatus, the Xn forwarding address via an El BC bearer context modification response message before the Fl UE context setup or before the fourth apparatus triggers the Fl-U forwarding tunnel setup for the Xn handover.

[0105] In some example embodiments, the method 500 further comprises: receiving, from the first apparatus, a further El BC bearer context modification request message containing both the Fl-U DU address and the Xn forwarding address.

[0106] In some example embodiments, the first apparatus comprises a CU control plane of a network device, the third apparatus comprises a CU user plane of the network device, and the fourth apparatus comprises a DU of the network device.

[0107] FIG. 6 shows a flowchart of an example method 600 implemented at a fourth device in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 600 will be described from the perspective of the fourth apparatus 140 in FIG. 1.

[0108] At block 610, the fourth apparatus 140 receives, from a first apparatus, an Xn forwarding address for an Xn handover related to a UE before the fourth apparatus triggers an Fl-U forwarding tunnel setup for this handover.

[0109] At block 620, the fourth apparatus 140 transmits, to the first apparatus, an Fl-U DU address of the fourth apparatus for the Fl-U forwarding tunnel setup for the Xn handover along with the Xn forwarding address.

[0110] In some example embodiments, the method 600 further comprises: receiving, from the first apparatus, an Fl UE context setup request message containing an Xn forwarding address together with a request to setup an Fl-U forwarding tunnel; determining an Fl-U DU address for the Fl-U forwarding tunnel; and transmitting, to thefirst apparatus, an Fl multicast distribution setup request message containing both the Fill DU address along with the Xn forwarding address.

[0111] In some example embodiments, the first apparatus comprises a CU control plane of a network device and the fourth apparatus comprises a DU of the network device.

[0112] In some example embodiments, a first apparatus capable of performing any of the method 300 (for example, the first apparatus 110 in FIG. 1) may comprise means for performing the respective operations of the method 300. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the first apparatus 110 in FIG. 1.

[0113] In some example embodiments, the first apparatus comprises means for receiving, from a second apparatus, a request of an Xn Handover related to a UE; means for obtaining, from a third apparatus, in an MBS session establishment or modification, an Xn forwarding address related to the Xn handover before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; and means for delivering the Xn forwarding address to at least one of the fourth apparatus before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; or second apparatus in an acknowledge message for the request of the Xn handover before the fourth apparatus triggers an Fl-U forwarding tunnel for the Xn handover and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

[0114] In some example embodiments, the first apparatus further comprises: means for in response to receiving from the fourth apparatus, an Fl-U DU address of the fourth apparatus for the Fl-U forwarding tunnel setup along with the Xn forwarding address, transmit, to third apparatus, the Fl-U DU address along with the Xn forwarding address.

[0115] In some example embodiments, the first apparatus further comprises: means for transmitting, to the third apparatus as part of an MBS session establishment or modification process, an El BC bearer context modification request message indicating a request of the Xn forwarding address before the Fl UE context setup or before the fourth apparatus triggers the Fl-U forwarding tunnel setup; and means for receiving, from the third apparatus, the Xn forwarding address via an El BC bearer context modification response message before the Fl UE context setup or before the fourth apparatus triggersthe Fl-U forwarding tunnel setup.

[0116] In some example embodiments, the first apparatus further comprises: means for delivering the Xn forwarding address to the fourth apparatus via an Fl UE context setup request message.

[0117] In some example embodiments, the first apparatus further comprises: means for delivering the Xn forwarding address to the fourth apparatus via the Fl UE context setup request message together with a request to setup an Fl-U forwarding tunnel; and means for receiving, from the fourth apparatus, the Fl-U DU address for the Fl-U forwarding tunnel along with the Xn forwarding address via a Fl multicast distribution setup request message.

[0118] In some example embodiments, the first apparatus further comprises: means for transmitting, to the third apparatus, the Fl-U DU address along with the Xn forwarding address via a further El BC bearer context modification request message.

[0119] In some example embodiments, the first apparatus comprises a CU control plane of a network device, the second apparatus comprises a further network device, the third apparatus comprises a CU user plane of the network device, and the fourth apparatus comprises a DU of the network device.

[0120] In some example embodiments, the first apparatus further comprises means for performing other operations in some example embodiments of the method 300 or the first apparatus 110. In some example embodiments, the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the first apparatus.

[0121] In some example embodiments, a second apparatus capable of performing any of the method 400 (for example, the second apparatus 120 in FIG. 1) may comprise means for performing the respective operations of the method 400. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the second apparatus 120 in FIG. 1.

[0122] In some example embodiments, the second apparatus comprises means for transmitting, to a first apparatus, a request of an Xn Handover related to a UE; and means for receiving, from the first apparatus in an acknowledge message for the request of theXn handover, an Xn forwarding address related to the Xn handover before a fourth apparatus triggers an Fl-U forwarding tunnel and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

[0123] In some example embodiments, the first apparatus comprises a CU control plane of a network device, the second apparatus comprises a further network device, and the fourth apparatus comprises a DU of the network device.

[0124] In some example embodiments, the second apparatus further comprises means for performing other operations in some example embodiments of the method 400 or the second apparatus 120. In some example embodiments, the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the second apparatus.

[0125] In some example embodiments, a third apparatus capable of performing any of the method 500 (for example, the third apparatus 130 in FIG. 1) may comprise means for performing the respective operations of the method 500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The third apparatus may be implemented as or included in the third apparatus 130 in FIG. 1.

[0126] In some example embodiments, the third apparatus comprises means for transmitting, to a first apparatus, in an MBS session establishment or modification, an Xn forwarding address for an Xn handover related to a UE before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers the setup of an F 1 -U forwarding tunnel for the Xn handover.

[0127] In some example embodiments, the third apparatus further comprises: means for receiving, from the first apparatus, the Fl-U DU address for an Fl-U forwarding tunnel along with the Xn forwarding address; and means for associating the Xn forwarding address to the Fl-U DU address.

[0128] In some example embodiments, associating the Xn forwarding address and the Fl-U DU address consists of forwarding packets received at the Xn forwarding address towards the received Fl-U DU address.

[0129] In some example embodiments, the third apparatus further comprises: means for receiving, from the first apparatus in the MBS session establishment or modification, anEl BC bearer context modification request message indicating a request for the Xn forwarding address for the Xn handover before the Fl UE context setup or before the fourth apparatus triggers the Fl-U forwarding tunnel setup for the Xn handover; and means for transmitting, to the first apparatus, the Xn forwarding address via an El BC bearer context modification response message before the Fl UE context setup or before the fourth apparatus triggers the Fl-U forwarding tunnel setup for the Xn handover.

[0130] In some example embodiments, the third apparatus further comprises: means for receiving, from the first apparatus, a further El BC bearer context modification request message containing both the Fl-U DU address and the Xn forwarding address.

[0131] In some example embodiments, the first apparatus comprises a CU control plane of a network device, the third apparatus comprises a CU user plane of the network device, and the fourth apparatus comprises a DU of the network device.

[0132] In some example embodiments, the third apparatus further comprises means for performing other operations in some example embodiments of the method 500 or the third apparatus 130. In some example embodiments, the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the third apparatus.

[0133] In some example embodiments, a fourth apparatus capable of performing any of the method 600 (for example, the fourth apparatus 140 in FIG. 1) may comprise means for performing the respective operations of the method 600. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The fourth apparatus may be implemented as or included in the fourth apparatus 140 in FIG. 1.

[0134] In some example embodiments, the fourth apparatus comprises means for receiving, from a first apparatus, an Xn forwarding address for an Xn handover related to a UE before the fourth apparatus triggers an Fl-U forwarding tunnel setup for this handover; and means for transmitting, to the first apparatus, an Fl-U DU address of the fourth apparatus for the Fl-U forwarding tunnel setup for the Xn handover along with the Xn forwarding address.

[0135] In some example embodiments, the fourth apparatus further comprises: means for receiving, from the first apparatus, an F 1 UE context setup request message containingan Xn forwarding address together with a request to setup an Fl-U forwarding tunnel; means for determining an Fl-U DU address for the Fl-U forwarding tunnel; and means for transmitting, to the first apparatus, an Fl multicast distribution setup request message containing both the Fl-U DU address along with the Xn forwarding address.

[0136] In some example embodiments, the first apparatus comprises a CU control plane of a network device and the fourth apparatus comprises a DU of the network device.

[0137] In some example embodiments, the fourth apparatus further comprises means for performing other operations in some example embodiments of the method 600 or the fourth apparatus 140. In some example embodiments, the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the fourth apparatus.

[0138] FIG. 7 is a simplified block diagram of a device 700 that is suitable for implementing example embodiments of the present disclosure. The device 700 may be provided to implement a communication device, for example, the first apparatus 110, the second apparatus 120, the third apparatus 130 or the fourth apparatus 140 as shown in FIG. 1. As shown, the device 700 includes one or more processors 710, one or more memories 720 coupled to the processor 710, and one or more communication modules 740 coupled to the processor 710.

[0139] The communication module 740 is for bidirectional communications. The communication module 740 has one or more communication interfaces to facilitate communication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 740 may include at least one antenna.

[0140] The processor 710 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 700 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

[0141] The memory 720 may include one or more non-volatile memories and one ormore volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 724, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), an optical disk, a laser disk, and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 722 and other volatile memories that will not last in the power-down duration.

[0142] A computer program 730 includes computer executable instructions that are executed by the associated processor 710. The instructions of the program 730 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 730 may be stored in the memory, e.g., the ROM 724. The processor 710 may perform any suitable actions and processing by loading the program 730 into the RAM 722.

[0143] The example embodiments of the present disclosure may be implemented by means of the program 730 so that the device 700 may perform any process of the disclosure as discussed with reference to FIG. 2 to FIG. 6. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0144] In some example embodiments, the program 730 may be tangibly contained in a computer readable medium which may be included in the device 700 (such as in the memory 720) or other storage devices that are accessible by the device 700. The device 700 may load the program 730 from the computer readable medium to the RAM 722 for execution. In some example embodiments, the computer readable medium may include any types of non-transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0145] FIG. 8 shows an example of the computer readable medium 800 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 800 has the program 730 stored thereon.

[0146] Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Someaspects may be implemented in hardware, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0147] Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non- transitory computer readable medium. The computer program product includes computerexecutable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

[0148] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. The program code may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program code, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

[0149] In the context of the present disclosure, the computer program code or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

[0150] The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0151] Further, although operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, although several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable sub-combination.

[0152] Although the present disclosure has been described in languages specific to structural features and / or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

WHAT IS CLAIMED IS:

1. A first apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: receive, from a second apparatus, a request of an Xn Handover related to a user equipment, UE; obtain, from a third apparatus, in a multicast and broadcast systems, MBS, session establishment or modification, an Xn forwarding address related to the Xn handover before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; and deliver the Xn forwarding address to at least one of: the fourth apparatus before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; or second apparatus in an acknowledge message for the request of the Xn handover before the fourth apparatus triggers the Fl-U forwarding tunnel for the Xn handover and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

2. The first apparatus of claim 1, wherein the first apparatus is caused to: in response to receiving from the fourth apparatus, a Fl-U distributed unit, DU, address of the fourth apparatus for the Fl-U forwarding tunnel setup along with the Xn forwarding address, transmit, to third apparatus, the Fl-U DU address along with the Xn forwarding address.

3. The first apparatus of claim 1 or 2, wherein the first apparatus is caused to: transmit, to the third apparatus as part of an MBS session establishment ormodification process, an El BC bearer context modification request message indicating a request of the Xn forwarding address before the Fl UE context setup or before the fourth apparatus triggers the Fl-U forwarding tunnel setup; and receive, from the third apparatus, the Xn forwarding address via an El BC bearer context modification response message before the Fl UE context setup or before the fourth apparatus triggers the Fl-U forwarding tunnel setup.

4. The first apparatus of any of claims 1-3, wherein the first apparatus is caused to: deliver the Xn forwarding address to the fourth apparatus via an Fl UE context setup request message.

5. The first apparatus of any of claims 1-4, wherein the first apparatus is caused to: deliver the Xn forwarding address to the fourth apparatus via the Fl UE context setup request message together with a request to setup an Fl-U forwarding tunnel; and receive, from the fourth apparatus, the Fl-U DU address for the Fl-U forwarding tunnel along with the Xn forwarding address via a Fl distribution setup request message.

6. The first apparatus of claim 5, wherein the first apparatus is caused to: transmit, to the third apparatus, the Fl-U DU address along with the Xn forwarding address via a further El BC bearer context modification request message.

7. The first apparatus of any of claim 1-6, wherein the first apparatus comprises a centralized unit, CU, control plane of a network device, the second apparatus comprises a further network device, the third apparatus comprises a CU user plane of the network device, and the fourth apparatus comprises a DU of the network device.

8. A second apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least oneprocessor, cause the second apparatus at least to: transmit, to a first apparatus, a request of an Xn Handover related to a user equipment, UE; and receive, from the first apparatus in an acknowledge message for the request of the Xn handover, an Xn forwarding address related to the Xn handover before a fourth apparatus triggers an Fl-U forwarding tunnel and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

9. The second apparatus of claim 8, wherein the first apparatus comprises a centralized unit, CU, control plane of a network device, the second apparatus comprises a further network device, and the fourth apparatus comprises a DU of the network device.

10. A third apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: transmit, to a first apparatus, in a multicast and broadcast systems, MBS, session establishment or modification, an Xn forwarding address for an Xn handover related to a user equipment, UE, before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers the setup of an Fl-U forwarding tunnel for the Xn handover.

11. The third apparatus of claim 10, wherein the third apparatus is caused to: receive, from the first apparatus, the Fl-U distributed unit, DU, address for an Fl-U forwarding tunnel along with the Xn forwarding address; and associate the Xn forwarding address to the Fl-U DU address.

12. The third apparatus of claim 10 or 11, wherein associating the Xn forwarding address and the Fl-U address consists of forwarding packets received over the Xnforwarding address towards the received Fl-U DU address.

13. The third apparatus of any of claims 10-12, wherein the third apparatus is caused to: receive, from the first apparatus in the MBS session establishment or modification, an El BC bearer context modification request message indicating a request for the Xn forwarding address for the Xn handover before the Fl UE context setup or before the fourth apparatus triggers the Fl-U forwarding tunnel setup for the Xn handover; and transmit, to the first apparatus, the Xn forwarding address via an El BC bearer context modification response message before the Fl UE context setup or before the fourth apparatus triggers the Fl-U forwarding tunnel setup for the Xn handover.

14. The third apparatus of any of claims 10-13, wherein the third apparatus is caused to: receive, from the first apparatus, a further El BC bearer context modification request message containing both the Fl-U DU address and the Xn forwarding address.

15. The third apparatus of any of claims 10-14, wherein the first apparatus comprises a centralized unit, CU, control plane of a network device, the third apparatus comprises a CU user plane of the network device, and the fourth apparatus comprises a DU of the network device.

16. A fourth apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the fourth apparatus at least to: receive, from a first apparatus, an Xn forwarding address for an Xn handover related to a user equipment, UE, before the fourth apparatus triggers an Fl-U forwarding tunnel setup for this handover; andtransmit, to the first apparatus, an Fl-U distributed unit, DU, address of the fourth apparatus for the Fl-U forwarding tunnel setup for the Xn handover along with the Xn forwarding address.

17. The fourth apparatus of claim 16, wherein the fourth apparatus is caused to: receive, from the first apparatus, an Fl UE context setup request message containing an Xn forwarding address together with a request to setup an Fl-U forwarding tunnel; determine an Fl-U DU address for the Fl-U forwarding tunnel; and transmit, to the first apparatus, an Fl distribution setup request message containing both the Fl-U DU address along with the Xn forwarding address.

18. The fourth apparatus of claim 16 or 17, wherein the first apparatus comprises a centralized unit, CU, control plane of a network device and the fourth apparatus comprises a DU of the network device.

19. A method comprising: receiving, at a first apparatus and from a second apparatus, a request of an Xn Handover related to a user equipment, UE; obtaining, from a third apparatus, in a multicast and broadcast systems, MBS, session establishment or modification, an Xn forwarding address related to the Xn handover before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; and delivering the Xn forwarding address to at least one of: the fourth apparatus before the fourth apparatus triggers an Fl-U forwarding tunnel setup for the Xn handover; or second apparatus in an acknowledge message for the request of the Xn handover before the fourth apparatus triggers an Fl-U forwarding tunnel for the Xn handover and / or before the Fl UE context is setup between the first apparatus and thefourth apparatus.

20. A method comprising: transmitting, from a second apparatus to a first apparatus, a request of an XnHandover related to a user equipment, UE; and receiving, from the first apparatus in an acknowledge message for the request of the Xn handover, an Xn forwarding address related to the Xn handover before a fourth apparatus triggers an Fl-U forwarding tunnel and / or before the Fl UE context is setup between the first apparatus and the fourth apparatus.

21. A method comprising: transmitting, from a third apparatus to a first apparatus, in a multicast and broadcast systems, MBS, session establishment or modification, an Xn forwarding address for an Xn handover related to a user equipment, UE, before an Fl UE context is setup between the first apparatus and a fourth apparatus or before the fourth apparatus triggers the setup of an F 1 -U forwarding tunnel for the Xn handover.

22. A method comprising: receiving, at a fourth apparatus and from a first apparatus, an Xn forwarding address for an Xn handover related to a user equipment, UE, before the fourth apparatus triggers an Fl-U forwarding tunnel setup for this handover; and transmitting, to the first apparatus, an Fl-U distributed unit, DU, address of the fourth apparatus for the Fl-U forwarding tunnel setup for the Xn handover along with the Xn forwarding address.

23. A computer readable medium comprising instructions stored thereon for causing an apparatus at least to perform the method of claim 19 or the method of claim 20 or the method of claim 21 or the method of claim 22.

Images