WO2022223178A1

WO2022223178A1 - Handling temporary f1-u tunnel for multicast broadcast service (mbs) mobility

Info

Publication number: WO2022223178A1
Application number: PCT/EP2022/054502
Authority: WO
Inventors: Philippe Godin; David NAVRÁTIL; Esa Mikael MALKAMÄKI
Original assignee: Nokia Technologies Oy
Priority date: 2021-04-19
Filing date: 2022-02-23
Publication date: 2022-10-27

Abstract

Systems, methods, apparatuses, and computer program products for handling temporary Fl-U tunnel for multicast broadcast service (MBS) mobility are provided.

Description

TITLE:

HANDLING TEMPORARY Fl-U TUNNEL FOR MULTICAST BROADCAST SERVICE (MBS) MOBILITY

FIELD:

[0001] Some example embodiments may generally relate to communications including mobile or wireless telecommunication systems, such as Long Term Evolution (LTE) or fifth generation (5G) radio access technology or new radio (NR) access technology, or other communications systems. For example, certain example embodiments may generally relate to systems and/or methods for handling temporary Fl-U tunnel for multicast broadcast service (MBS) mobility.

BACKGROUND:

[0002] Examples of mobile or wireless telecommunication systems may include the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN), Long Term Evolution (LTE) Evolved UTRAN (E-UTRAN), LTE- Advanced (LTE- A), MulteFire, LTE-A Pro, and/or fifth generation (5G) radio access technology or new radio (NR) access technology. 5G wireless systems refer to the next generation (NG) of radio systems and network architecture. A 5G system is mostly built on a 5G new radio (NR), but a 5G (or NG) network can also build on the E-UTRA radio. It is estimated that NR provides bitrates on the order of 10-20 Gbit/s or higher, and can support at least service categories such as enhanced mobile broadband (eMBB) and ultra-reliable low-latency-communication (URLLC) as well as massive machine type communication (mMTC). NR is expected to deliver extreme broadband and ultra-robust, low latency connectivity and massive networking to support the Internet of Things (IoT). With IoT and machine-to-machine (M2M) communication becoming more widespread, there will be a growing need for networks that meet the needs of lower power, low data rate, and long battery life. The next generation radio access network (NG-RAN) represents the RAN for 5G, which can provide both NR and LTE (and LTE-Advanced) radio accesses. It is noted that, in 5G, the nodes that can provide radio access functionality to a user equipment (i.e., similar to the Node B, NB, in UTRAN or the evolved NB, eNB, in LTE) may be named next-generation NB (gNB) when built on NR radio and may be named next-generation eNB (NG-eNB) when built on E-UTRA radio.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0003] For proper understanding of example embodiments, reference should be made to the accompanying drawings, wherein:

[0004] Fig. 1 illustrates an example signaling diagram, according to an embodiment;

[0005] Fig. 2 illustrates an example signaling diagram, according to an embodiment;

[0006] Fig. 3 illustrates an example signaling diagram, according to an embodiment;

[0007] Fig. 4 illustrates an example signaling diagram, according to an embodiment;

[0008] Fig. 5A illustrates an example flow diagram of a method, according to an embodiment;

[0009] Fig. 5B illustrates an example flow diagram of a method, according to an embodiment;

[0010] Fig. 6A illustrates an example flow diagram of a method, according to an embodiment;

[0011] Fig. 6B illustrates an example flow diagram of a method, according to an embodiment; [0012] Fig. 7 A illustrates an example flow diagram of a method, according to an embodiment;

[0013] Fig. 7B illustrates an example flow diagram of a method, according to an embodiment;

[0014] Fig. 8A illustrates an example block diagram of an apparatus, according to an embodiment; and

[0015] Fig. 8B illustrates an example block diagram of an apparatus, according to an embodiment.

DETAILED DESCRIPTION:

[0016] It will be readily understood that the components of certain example embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of some example embodiments of systems, methods, apparatuses, and computer program products for handling temporary Fl-U tunnel for multicast broadcast service (MBS) mobility, is not intended to limit the scope of certain embodiments but is representative of selected example embodiments.

[0017] The features, structures, or characteristics of example embodiments described throughout this specification may be combined in any suitable manner in one or more example embodiments. For example, the usage of the phrases “certain embodiments,” “some embodiments,” or other similar language, throughout this specification refers to the fact that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment. Thus, appearances of the phrases “in certain embodiments,” “in some embodiments,” “in other embodiments,” or other similar language, throughout this specification do not necessarily all refer to the same group of embodiments, and the described features, structures, or characteristics may be combined in any suitable manner in one or more example embodiments.

[0018] Additionally, if desired, the different functions or procedures discussed below may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the described functions or procedures may be optional or may be combined. As such, the following description should be considered as illustrative of the principles and teachings of certain example embodiments, and not in limitation thereof [0019] For mobility from a MBS supporting node to a MBS supporting node, it has been determined to use Point-to-Point (PtP) mode at the target cell to start with. It has also been decided to minimize data loss during the handover (HO) using data forwarding.

[0020] A target central unit (CU) user plane (UP) can deliver MBS data received from a core network to a distributed unit (DU) for Point-to- Multipoint (PtM) delivery over a shared Fl-U tunnel· The target gNB starts buffering during HO preparation when the sequence number (SN)=SN0 for packet data convergence protocol (PDCP) multicast radio bearer (MRB) and replies back SN0 to the source gNB for data forwarding until SN0. The target DU PtP leg needs to deliver the data forwarded from the source gNB and the data buffered at the target gNB until traffic over the DU PtP leg catches up with the traffic over the DU PtM leg. However, a problem arises in determining how to send the forwarded and buffered data to the DU PtP leg, since sending this data over the shared Fl-U tunnel mixed with other traffic is complicated.

[0021] Fig. 1 illustrates an example signaling diagram of a method for a target gNB (T-gNB) to receive forwarded data from a source gNB (S-gNB). As illustrated in the example of Fig. 1, at 110, the S-gNB may transmit a HO request including an UL tunnel endpoint identifier (TEID) to the T-gNB. The T-gNB may determine the current SN delivered over the shared tunnel = SNO, start buffering data at SNO and, at 120, send back SNO to the S-gNB in a HO request acknowledgement. Then, at 130, the s-gNB may send and the T-gNB may receive forwarded data until SNO. The T-gNB may send, to the UE, the forwarded and buffered data over radio PtP leg of UE until this leg has caught up with the PtM leg of UE. However, there is no solution yet provided for how to solve the problem in the case of a disaggregated gNB, i.e., a gNB with a CU and DU split. For example, there is currently no solution for how this can be accomplished when the target gNB is split between CU and DU in a multi-vendor scenario, i.e., with the CU and DU which are separate nodes owned by different vendors and connected through an FI interface.

[0022] Certain example embodiments may provide several solutions for addressing the issue of minimizing packet loss during mobility when the target gNB is split into a CU node and DU node, which may or may not be owned by different vendors. More precisely, some example embodiments can provide methods for sending, to the UE, the forwarded and buffered data over the radio PtP leg of the UE until this leg has caught up with the PtM leg of the UE, e.g., when the target gNB is split between CU and DU. The PtP leg catches up to the PtM leg when the forwarded, i.e. data with corresponding SN lower than SNO, and buffered data, i.e. data with corresponding SN equal and larger than SNO and lower than SN1, wherein the target gNB determines data with SN1 to correspond to the first data transmitted on the PtM leg, which the UE may receive. For example, SN1 may be the SN associated with the first data transmitted over the PtM leg after the completion of HO in the target, i.e. after the target gNB received the RRCReconfigurationComplete message from the UE. Alternatively, the target gNB could determine the SN1 from a status message, e.g. PDCP status report. [0023] An embodiment may be configured to allow the DU to manage a temporary tunnel with the CU UP. The timing for setting up and/or releasing this tunnel can vary according to the solutions provided, as well as the type of data that is transmitted over that temporary tunnel. Certain embodiments may also depend on whether or not target gNB wants to process the forwarded data at PDCP, e.g. to cipher or compress the header. For example, some embodiments may be applicable if the target gNB does not want to process the forwarded data at PDCP.

[0024] One embodiment may be configured to forward data via a CU UP and to buffer incoming data from a core network (and referred to as “fresh data” in the drawings) at the CU UP. Fig. 2 illustrates an example signaling diagram, according to this embodiment. As illustrated in the example of Fig. 2, at 210, the target CU UP may start buffering new incoming data, e.g., from a user plane function (UPF) starting from sequence number NO (SN NO). For instance, when the CU UP is notified of a handover request, the CU UP may start buffering the packets or data that it receives from a UPF, where the first buffered packet may have a sequence number labeled as NO. At 215, the target CU UP may start buffering data forwarded from the source gNB. In an embodiment, the SN NO may be indicated in a HO request acknowledgement to the source gNB.

[0025] As further illustrated in the example of Fig. 2, at 217, the target CU CP may set up a temporary Fl-U tunnel from the target CU UP to the target DU in order to feed, at 220, the DU PtP leg at the target side with the forwarded data followed by the incoming data buffered at the target CU UP after the CU UP has PDCP processed the incoming data. Hence, in one embodiment, PDCP processing of the forwarded and incoming data may occur in the target CU UP. According to an embodiment, at 225, the DU may deliver the buffered forward data and the buffered incoming data to one or more UE(s) over the PtP leg. In an embodiment, the target DU may detect, at 230, that data delivery over the PtP leg is caught up with the delivery over the PtM leg. The target DU may then, at 235, request to release the temporary Fl-U tunnel when the DU detects that the data delivery over the PtP leg has caught up with the delivery of data over the PtM leg. In an embodiment, at 240, the target CU CP may release the temporary Fl-U tunnel from the target CU UP to the target DU.

[0026] As discussed above, Fig. 2 is provided as one example. Other examples or modifications are possible according to certain embodiments. [0027] An embodiment may be configured to forward data via a CU UP and to buffer incoming data from a core network received via the CU UP over a shared tunnel at a DU. Fig. 3 illustrates an example signaling diagram, according to this embodiment. In this example, the target DU may itself buffer the data forwarded from the source gNB via the CU UP and the incoming data from the core network received via the target CU UP (e.g., over a separate shared Fl-U tunnel). As illustrated in the example of Fig. 3, at 305, the target CU CP may setup a temporary Fl-U tunnel from the target CU UP to the DU and, at 307, may setup a forwarding tunnel from the source gNB to the target CU UP. At 310, the DU may start buffering incoming data received from the target CU UP over a shared Fl-U tunnel, e.g., starting at sequence number NO (SN NO). In an embodiment, the CU CP may receive an indication of the SN NO from the DU when the temporary Fl-U tunnel is created at step 305, e.g., in an F1AP message, such as a UE context setup response message. According to one example, the SN NO may be indicated in a HO request acknowledgement to the source gNB. As further illustrated in the example of Fig. 3, at 315, the target CU UP may perform PDCP processing of data forwarded from the source gNB before delivery to the DU. At 320, the PDCP processed forwarded data may be transmitted to the DU over the temporary Fl-U tunnel. At 325, the DU may deliver the forwarded data to at least one UE over a PtP leg together with and/or followed by the buffered incoming data (e.g., until DU detects that data delivery over the PtP leg has caught up with delivery of data over PtM leg such as 345). At 330, the DU may detect or determine that the data forwarding has ended. For example, the end of the forwarded data may be detected when the forwarded data reaches SN NO. As also illustrated in the example of Fig. 3, at 335, the DU may request release of the temporary forwarding Fl-U tunnel (e.g., requesting to release the Fl-U DL TEID of the forwarding tunnel) when an end of the forwarded data is detected and, at 340, the target CU CP may release the temporary forwarding Fl-U tunnel after the PDCP processed data have been sent to the DU or after receiving the above release request from the DU. Then, at 345, the DU may deliver, to the at least one UE, the buffered forwarded data and the buffered incoming data until it is detected that delivery of data over the point-to-point (PtP) leg has caught up with delivery of data over a point-to-multipoint (PtM) leg.

[0028] As discussed above, Fig. 3 is provided as one example. Other examples or modifications to Fig. 3 are possible according to certain embodiments.

[0029] Another embodiment may be configured to directly forward data from the source gNB to the DU and to buffer incoming data from a core network received via CU UP over a shared tunnel at the DU. Fig. 4 illustrates an example signaling diagram, according to this embodiment. In this example, the target DU may itself buffer the data which is directly forwarded from the source gNB and may buffer the incoming data from the core network received via a CU UP, e.g., over shared Fl-U tunnel starting from SN NO. As illustrated in the example of Fig. 4, at 405, the target CU CP may set up a temporary Fl-U forwarding tunnel directly from the source gNB to target DU. In one example, the Fl-U DL TEID and/or SN NO may be sent back to the source gNB in a HO request acknowledgement. At 410, the DU may start buffering incoming data from CU UP received over a separate shared tunnel, e.g., starting at SN NO. At 415, the DU may receive forwarded data directly from the source gNB over the temporary forwarding tunnel. At 425, the DU may deliver the forwarded data to at least one UE over a PtP leg together with and/or followed by the buffered incoming data (e.g., until DU detects that data delivery over the PtP leg has caught up with delivery of data over PtM leg). At 430, the DU may detect or determine that the data forwarding has ended. For example, the end of the forwarded data may be detected when the forwarded data reaches SN NO. As also illustrated in the example of Fig. 4, at 435, the DU may request release of the temporary forwarding Fl-U tunnel (e.g., requesting to release the Fl-U DF TEID of the forwarding tunnel) when all of the data has been forwarded. Alternatively, the source gNB may request release of the temporary forwarding Fl-U tunnel. At 440, e.g., responsive to receiving a request to release the temporary tunnel, the target CU CP may release the temporary forwarding Fl-U tunnel. Then, at 445, the DU may deliver, to the at least one UE, the buffered forwarded data and the buffered incoming data until it is detected that delivery of data over the point-to-point (PtP) leg has caught up with delivery of data over a point-to- multipoint (PtM) leg.

[0030] In some embodiments, PDCP COUNT can be used instead of PDCP SN and thus PDCP COUNT NO may be used instead of SN NO. It should be noted, however, that PDCP COUNT may be known by just the CU UP, since DU sees just PDCP SN. As such, SN NO can be used towards the target DU.

[0031] In the example of Fig. 4, the PDCP processing for the forwarded data may occur in the source gNB. In this case, it may be assumed that PDCP processing just adds the PDCP header with SN (no ciphering or integrity protection, and possibly no header compression). Additionally, PDCP COUNT of multicast radio bearer may be assumed to be synchronized between gNBs. [0032] As discussed above, Fig. 4 is provided as one example. Other examples or modifications to Fig. 4 are possible according to certain embodiments.

[0033] It should be noted that the example embodiments depicted in Figs. 2-4 or the individual procedures depicted therein may be combined in any suitable manner or may be performed in a different order. As such, Figs. 2-4 are provided to illustrate some, but not necessarily all, example embodiments.

[0034] Fig. 5A illustrates an example flow diagram of a method for handling temporary Fl-U tunnel for MBS mobility, according to an example embodiment. In certain example embodiments, the flow diagram of Fig. 5 A may be performed by a network entity or network node in a communications system, such as LTE or 5G NR. In some example embodiments, the network entity performing the method of Fig. 5 A may include or be included in a base station, access node, node B, eNB, gNB, NG-RAN node, transmission- reception points (TRPs), high altitude platform stations (HAPS), relay station or the like. In one embodiment, the network node performing the method of Fig. 5A may include a CU (e.g., CU UP and/or CU CP) of a network node, such as the CU CP or CU UP of the target node illustrated in the examples of Figs. 2-4, or a similar radio node or unit.

[0035] As illustrated in the example of Fig. 5 A, the method may include, 500, buffering, at the CU UP of the target network node (e.g., target gNB), data forwarded from a source network node (e.g., source gNB) and buffering new incoming data from a core network (e.g. UPF). In an embodiment, the method may include, at 505, setting up, by the CU CP of the target network node, a temporary Fl-U tunnel from the CU UP of the target network node to a DU of the target network node to feed the DU point-to-point (PtP) leg with the forwarded data together with and/or followed by the incoming data buffered at the CU UP of the target network node after the CU UP has PDCP processed the data. According to one embodiment, the method may include, at 510, receiving a request from the DU to release the temporary Fl-U tunnel when data delivery over the point-to-point (PtP) leg has caught up with data delivery over a point-to-multipoint (PtM) leg and, at 515, releasing the temporary Fl-U tunnel. In an embodiment, the buffering of the incoming data may include buffering incoming data from a UPF starting from sequence number NO (SN NO) or packet data convergence protocol (PDCP) count NO (COUNT NO). According to some embodiments, the method may include indicating the sequence number NO (SN NO) or the packet data convergence protocol (PDCP) count NO (COUNT NO) in a handover request acknowledgement to the source network node.

[0036] Fig. 5B illustrates an example flow diagram of a method for handling temporary Fl-U tunnel for MBS mobility, according to an example embodiment. In certain example embodiments, the flow diagram of Fig. 5B may be performed by a network entity or network node in a communications system, such as LTE or 5G NR. In some example embodiments, the network entity performing the method of Fig. 5B may include or be included in a base station, access node, node B, eNB, gNB, NG-RAN node, transmission- reception points (TRPs), high altitude platform stations (HAPS), relay station or the like. In one embodiment, the network node performing the method of Fig. 5B may include a DU of a network node, such as the DU of the target node illustrated in the examples of Figs. 2-4, or a similar radio node or unit.

[0037] As illustrated in the example of Fig. 5B, the method may include, 550, receiving, at a DU of a target network node (e.g., target gNB), data forwarded from a source network node (e.g., source gNB) and new incoming data over a temporary Fl-U tunnel setup from a CU UP of the target network node to the DU of the target network node. In an embodiment, the method may include, at 555, transmitting or forwarding the forwarded data and the incoming data to at least one user equipment over a point-to-point (PtP) leg. [0038] According to an embodiment, the method of Fig. 5B may include, at 560, detecting when delivery of data over the point-to-point (PtP) leg has caught up with the delivery of data over a point-to-multipoint (PtM) leg. In one embodiment, the method may include, at 565, based on the detecting, requesting a CU CP to release the temporary Fl-U tunnel from the CU UP of the target network node.

[0039] Fig. 6A illustrates an example flow diagram of a method for handling temporary Fl-U tunnel for MBS mobility, according to an example embodiment. In certain example embodiments, the flow diagram of Fig. 6 A may be performed by a network entity or network node in a communications system, such as LTE or 5G NR. In some example embodiments, the network entity performing the method of Fig. 6 A may include or be included in a base station, access node, node B, eNB, gNB, NG-RAN node, transmission- reception points (TRPs), high altitude platform stations (HAPS), relay station or the like. In one embodiment, the network node performing the method of Fig. 6A may include a CU (e.g., CU UP and/or CU CP) of a network node, such as the CU CP or CU UP or the target node illustrated in the examples of Figs. 2-4, or a similar radio node or unit.

[0040] As illustrated in the example of Fig. 6 A, the method may include, 600, setting up, by a CU CP of a target network node (e.g., a target gNB), a forwarding tunnel (e.g., an Xn-U tunnel) from a source network node (e.g., a source gNB) to a CU UP of the target network node and a temporary Fl-U tunnel from the CU UP of the target network node to a DU of the target network node. The method may also include, at 605, processing (e.g., PDCP processing) data received from the source network node over the forwarding tunnel and, at 610, transmitting the processed forwarded data to the DU of the target network node over the temporary Fl-U tunnel. In an embodiment, the processing 605 may include PDCP processing the data received from the source network node and the transmitting 610 may include transmitting the PDCP processed forwarded data to the DU. The method may then include, at 615, releasing the temporary Fl-U tunnel after all of the processed forwarded data have been sent to the DU. For example, in one embodiment, the method may include receiving, at the CU CP, a request from the DU to release the temporary Fl-U tunnel after the processed forwarded data have been sent over the temporary Fl-U tunnel, and releasing the temporary Fl-U tunnel in response to the request. In some embodiments, the release request from the DU may be received when an end of the forwarded data is detected and the detection may happen when the forwarded data reaches sequence number NO (SN NO) or packet convergence protocol count NO (COUNT NO). According to certain embodiments, the sequence number NO (SN NO) or PDCP count NO (COUNT NO) may be received by CU CP from the DU when the temporary Fl-U tunnel is created. In one example, the sequence number NO (SN NO) or PDCP count NO (COUNT NO) may be sent to the source network node in a handover request acknowledgement message.

[0041] Fig. 6B illustrates an example flow diagram of a method for handling temporary Fl-U tunnel for MBS mobility, according to an example embodiment. In certain example embodiments, the flow diagram of Fig. 6B may be performed by a network entity or network node in a communications system, such as LTE or 5G NR. In some example embodiments, the network entity performing the method of Fig. 6B may include or be included in a base station, access node, node B, eNB, gNB, NG-RAN node, transmission- reception points (TRPs), high altitude platform stations (HAPS), relay station or the like. In one embodiment, the network node performing the method of Fig. 6B may include a DU of a network node, such as the DU of the target node illustrated in the examples of Figs. 2-4, or a similar radio node or unit. [0042] As illustrated in the example of Fig. 6B, the method may include, 650, receiving, at a DU of a target network node (e.g., target gNB), data forwarded from a source network node (e.g., source gNB) over a first temporary Fl-U tunnel from a CU UP of the target network node and buffering incoming data received from the CU UP over a different second shared Fl-U tunnel. For instance, the buffering of the incoming data may include buffering incoming data starting from sequence number NO (SN NO) or PDCP count NO (COUNT NO).

[0043] The method of Fig. 6B may include, at 655, transmitting, to at least one user equipment, over a point-to-point (PtP) leg the forwarded data received over the first temporary Fl-U tunnel together with and/or followed by the buffered incoming data received over the second shared Fl-U tunnel until it is detected that delivery of data over the point-to-point (PtP) leg has caught up with the delivery of data over a point-to-multipoint (PtM) leg. In other words, the transmitting 655 of the buffered incoming data may include transmitting the buffered incoming data after the transmitting of the forwarded data to the at least one user equipment. In an embodiment, the method may include, at 660, requesting release of the first temporary Fl-U tunnel after all of the forwarded data has been received over the first temporary Fl-U tunnel. For example, the end of the forwarded data may be detected when the forwarded data reaches sequence number NO (SN NO) or PDCP count NO (COUNT NO). In one embodiment, the method may include indicating the sequence number NO (SN NO) or the PDCP count NO (COUNT NO) to the CU CP when the first temporary Fl-U tunnel is created in an F1AP message, such as a UE context setup response message. According to some embodiments, the method may also include indicating the sequence number NO (SN NO) or the PDCP count NO (COUNT NO) received by the CU CP in a handover request acknowledgement to the source network node. [0044] Fig. 7A illustrates an example flow diagram of a method for handling temporary Fl-U tunnel for MBS mobility, according to an example embodiment. In certain example embodiments, the flow diagram of Fig. 7 A may be performed by a network entity or network node in a communications system, such as LTE or 5G NR. In some example embodiments, the network entity performing the method of Fig. 7 A may include or be included in a base station, access node, node B, eNB, gNB, NG-RAN node, transmission- reception points (TRPs), high altitude platform stations (HAPS), relay station or the like. In one embodiment, the network node performing the method of Fig. 7A may include a CU (e.g., CU UP and/or CU CP) of a network node, such as the CU CP or CU UP or the target node illustrated in the examples of Figs. 2-4, or a similar radio node or unit.

[0045] As illustrated in the example of Fig. 7 A, the method may include, 700, setting up, by a CU CP of a target network node (e.g., a target gNB), a temporary Fl-U forwarding tunnel directly from a source network node (e.g., a source gNB) to a DU of the target network node. The method of Fig. 7A may include, at 705, receiving a request to release the temporary Fl-U forwarding tunnel after all of the data have been forwarded and, at 710, releasing the temporary Fl-U forwarding tunnel. In certain embodiments, the receiving 705 may include receiving the request to release the temporary Fl-U forwarding tunnel from the distributed unit (DU) and/or from the source network node. According to some embodiments, it may be determined that all of the data has been forwarded when the forwarded data reaches sequence number NO (SN NO) or PDCP count NO (COUNT NO). In an embodiment, the sequence number NO (SN NO) may be received by the CU CP from the DU when the Fl-U forwarding tunnel is created or when the DU starts to buffer incoming data.

[0046] According to some embodiments, the method may include indicating at least one of the sequence number NO (SN NO) or the PDCP count NO (COUNT NO) or a tunnel endpoint identifier (TEID) of the temporary Fl-U forwarding tunnel in a handover request acknowledgement to the source network node. In one example, the tunnel endpoint identifier (TEID) of the temporary Fl-U forwarding tunnel is a downlink tunnel endpoint identifier of the DU which is received by the CU CP from the DU when the Fl-U forwarding tunnel is created.

[0047] Fig. 7B illustrates an example flow diagram of a method for handling temporary Fl-U tunnel for MBS mobility, according to an example embodiment. In certain example embodiments, the flow diagram of Fig. 7B may be performed by a network entity or network node in a communications system, such as FTE or 5G NR. In some example embodiments, the network entity performing the method of Fig. 7B may include or be included in a base station, access node, node B, eNB, gNB, NG-RAN node, transmission- reception points (TRPs), high altitude platform stations (HAPS), relay station or the like. In one embodiment, the network node performing the method of Fig. 7B may include a DU of a network node, such as the DU of the target node illustrated in the examples of Figs. 2-4, or a similar radio node or unit.

[0048] As illustrated in the example of Fig. 7B, the method may include, 750, receiving, at a DU of a target network node (e.g., target gNB), data that is directly forwarded from a source network node (e.g., source gNB) over a first Fl-U forwarding tunnel and buffering incoming data from a CU UP of the target network node received over a second shared Fl-U tunnel. The method may include, at 755, transmitting the forwarded data to at least one user equipment over a point-to-point (PtP) leg until an end of the forwarded data is detected. In an embodiment, the method may include, at 760, requesting the release of the first Fl-U forwarding tunnel after all the forwarded data has been sent over the PtP leg. The method may also include, at 765, transmitting the buffered incoming data to at least one user equipment over the point-to- point (PtP) leg after and/or together with the forwarded data until it is detected that delivery of data over the point-to-point (PtP) leg has caught up with the delivery of data over a point-to-multipoint (PtM) leg. In other words, in an embodiment, the transmitting 765 of the buffered incoming data may include transmitting the buffered incoming data after transmission of the forwarded data to the at least one user equipment.

[0049] In certain embodiments, the buffering of the incoming data may include buffering incoming data starting from sequence number NO (SN NO) or PDCP count NO (COUNT NO). In an embodiment, the end of the forwarded data may be detected when the forwarded data reaches sequence number NO (SN NO) or packet convergence protocol count NO (COUNT NO). According to some embodiments, the sequence number NO (SN NO) may be sent to a CU CP of the target network node, and to the source network node via the CU CP, when the first Fl-U forwarding tunnel is created.

[0050] Fig. 8A illustrates an example of an apparatus 10 according to an embodiment. In an embodiment, apparatus 10 may be a node, host, or server in a communications network or serving such a network. For example, apparatus 10 may be a network node, a sensing node, satellite, base station, a Node B, an evolved Node B (eNB), 5G Node B or access point, next generation Node B (NG-NB or gNB), TRP, HAPS, integrated access and backhaul (IAB) node, and/or a WLAN access point, associated with a radio access network, such as a LTE network, 5G or NR. In some example embodiments, apparatus 10 may be gNB or other similar radio node, for instance.

[0051] It should be understood that, in some example embodiments, apparatus 10 may be comprised of an edge cloud server as a distributed computing system where the server and the radio node may be stand-alone apparatuses communicating with each other via a radio path or via a wired connection, or they may be located in a same entity communicating via a wired connection. For instance, in certain example embodiments where apparatus 10 represents a gNB, it may be configured in a central unit (CU) and distributed unit (DU) architecture that divides the gNB functionality. In such an architecture, the CU may be a logical node that includes gNB functions such as transfer of user data, mobility control, radio access network sharing, positioning, and/or session management, etc. The CU may control the operation of DU(s) over a front-haul interface. The DU may be a logical node that includes a subset of the gNB functions, depending on the functional split option. It should be noted that one of ordinary skill in the art would understand that apparatus 10 may include components or features not shown in Fig. 8 A.

[0052] As illustrated in the example of Fig. 8A, apparatus 10 may include a processor 12 for processing information and executing instructions or operations. Processor 12 may be any type of general or specific purpose processor. In fact, processor 12 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application- specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, or any other processing means, as examples. While a single processor 12 is shown in Fig. 8A, multiple processors may be utilized according to other embodiments. For example, it should be understood that, in certain embodiments, apparatus 10 may include two or more processors that may form a multiprocessor system (e.g., in this case processor 12 may represent a multiprocessor) that may support multiprocessing. In certain embodiments, the multiprocessor system may be tightly coupled or loosely coupled (e.g., to form a computer cluster).

[0053] Processor 12 may perform functions associated with the operation of apparatus 10, which may include, for example, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 10, including processes related to management of communication or communication resources.

[0054] Apparatus 10 may further include or be coupled to a memory 14 (internal or external), which may be coupled to processor 12, for storing information and instructions that may be executed by processor 12. Memory 14 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor- based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and/or removable memory. For example, memory 14 can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, hard disk drive (HDD), or any other type of non- transitory machine or computer readable media, or other appropriate storing means. The instructions stored in memory 14 may include program instructions or computer program code that, when executed by processor 12, enable the apparatus 10 to perform tasks as described herein.

[0055] In an embodiment, apparatus 10 may further include or be coupled to (internal or external) a drive or port that is configured to accept and read an external computer readable storage medium, such as an optical disc, USB drive, flash drive, or any other storage medium. For example, the external computer readable storage medium may store a computer program or software for execution by processor 12 and/or apparatus 10.

[0056] In some embodiments, apparatus 10 may also include or be coupled to one or more antennas 15 for transmitting and receiving signals and/or data to and from apparatus 10. Apparatus 10 may further include or be coupled to a transceiver 18 configured to transmit and receive information. The transceiver 18 may include, for example, a plurality of radio interfaces that may be coupled to the antemia(s) 15, or may include any other appropriate transceiving means. The radio interfaces may correspond to a plurality of radio access technologies including one or more of GSM, NB-IoT, LTE, 5G, WLAN, Bluetooth, BT-LE, NFC, radio frequency identifier (RFID), ultrawideband (UWB), MulteFire, and the like. The radio interface may include components, such as filters, converters (for example, digital-to-analog converters and the like), mappers, a Fast Fourier Transform (FFT) module, and the like, to generate symbols for a transmission via one or more downlinks and to receive symbols (via an uplink, for example).

[0057] As such, transceiver 18 may be configured to modulate information on to a carrier waveform for transmission by the antenna(s) 15 and demodulate information received via the antenna(s) 15 for further processing by other elements of apparatus 10. In other embodiments, transceiver 18 may be capable of transmitting and receiving signals or data directly. Additionally or alternatively, in some embodiments, apparatus 10 may include an input and/or output device (I/O device), or an input/output means.

[0058] In an embodiment, memory 14 may store software modules that provide functionality when executed by processor 12. The modules may include, for example, an operating system that provides operating system functionality for apparatus 10. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatus 10. The components of apparatus 10 may be implemented in hardware, or as any suitable combination of hardware and software.

[0059] According to some embodiments, processor 12 and memory 14 may be included in or may form a part of processing circuitry/means or control circuitry/means. In addition, in some embodiments, transceiver 18 may be included in or may form a part of transceiver circuitry /means.

[0060] As used herein, the term “circuitry” may refer to hardware-only circuitry implementations (e.g., analog and/or digital circuitry), combinations of hardware circuits and software, combinations of analog and/or digital hardware circuits with software/firmware, any portions of hardware processor(s) with software (including digital signal processors) that work together to cause an apparatus (e.g., apparatus 10) to perform various functions, and/or hardware circuit(s) and/or processor(s), or portions thereof, that use software for operation but where the software may not be present when it is not needed for operation. As a further example, as used herein, the term “circuitry” may also cover an implementation of merely a hardware circuit or processor (or multiple processors), or portion of a hardware circuit or processor, and its accompanying software and/or firmware. The term circuitry may also cover, for example, a baseband integrated circuit in a server, cellular network node or device, or other computing or network device.

[0061] As introduced above, in certain embodiments, apparatus 10 may be or may be a part of a network element or RAN node, such as a base station, access point, Node B, eNB, gNB, TRP, HAPS, IAB node, WLAN access point, or the like. In one example embodiment, apparatus 10 may be a gNB or other radio node, or may be a CU and/or DU of a gNB. According to certain embodiments, apparatus 10 may be controlled by memory 14 and processor 12 to perform the functions associated with any of the embodiments described herein. For example, in some embodiments, apparatus 10 may be configured to perform one or more of the processes depicted in any of the flow charts or signaling diagrams described herein, such as those illustrated in Figs. 2-4, 5A, 5B, 6A, 6B, 7A or 7C, or any other method described herein. In some embodiments, as discussed herein, apparatus 10 may be configured to perform a procedure relating to handling temporary Fl-U tunnel for MBS mobility, as discussed elsewhere herein, for example.

[0062] Fig. 8B illustrates an example of an apparatus 20 according to another embodiment. In an embodiment, apparatus 20 may be a node or element in a communications network or associated with such a network, such as a UE, communication node, mobile equipment (ME), mobile station, mobile device, stationary device, IoT device, or other device. As described herein, a UE may alternatively be referred to as, for example, a mobile station, mobile equipment, mobile unit, mobile device, user device, subscriber station, wireless terminal, tablet, smart phone, IoT device, sensor or NB-IoT device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications thereof (e.g., remote surgery), an industrial device and applications thereof (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain context), a consumer electronics device, a device operating on commercial and/or industrial wireless networks, or the like. As one example, apparatus 20 may be implemented in, for instance, a wireless handheld device, a wireless plug-in accessory, or the like.

[0063] In some example embodiments, apparatus 20 may include one or more processors, one or more computer-readable storage medium (for example, memory, storage, or the like), one or more radio access components (for example, a modem, a transceiver, or the like), and/or a user interface. In some embodiments, apparatus 20 may be configured to operate using one or more radio access technologies, such as GSM, LTE, LTE-A, NR, 5G, WLAN, WiFi, NB-IoT, Bluetooth, NFC, MulteFire, and/or any other radio access technologies. It should be noted that one of ordinary skill in the art would understand that apparatus 20 may include components or features not shown in Fig. 8B. [0064] As illustrated in the example of Fig. 8B, apparatus 20 may include or be coupled to a processor 22 for processing information and executing instructions or operations. Processor 22 may be any type of general or specific purpose processor. In fact, processor 22 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples. While a single processor 22 is shown in Fig. 8B, multiple processors may be utilized according to other embodiments. For example, it should be understood that, in certain embodiments, apparatus 20 may include two or more processors that may form a multiprocessor system (e.g., in this case processor 22 may represent a multiprocessor) that may support multiprocessing. In certain embodiments, the multiprocessor system may be tightly coupled or loosely coupled (e.g., to form a computer cluster).

[0065] Processor 22 may perform functions associated with the operation of apparatus 20 including, as some examples, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 20, including processes related to management of communication resources.

[0066] Apparatus 20 may further include or be coupled to a memory 24 (internal or external), which may be coupled to processor 22, for storing information and instructions that may be executed by processor 22. Memory 24 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor- based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and/or removable memory. For example, memory 24 can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, hard disk drive (HDD), or any other type of non- transitory machine or computer readable media. The instructions stored in memory 24 may include program instructions or computer program code that, when executed by processor 22, enable the apparatus 20 to perform tasks as described herein.

[0067] In an embodiment, apparatus 20 may further include or be coupled to (internal or external) a drive or port that is configured to accept and read an external computer readable storage medium, such as an optical disc, USB drive, flash drive, or any other storage medium. For example, the external computer readable storage medium may store a computer program or software for execution by processor 22 and/or apparatus 20.

[0068] In some embodiments, apparatus 20 may also include or be coupled to one or more antennas 25 for receiving a downlink signal and for transmitting via an uplink from apparatus 20. Apparatus 20 may further include a transceiver 28 configured to transmit and receive information. The transceiver 28 may also include a radio interface (e.g., a modem) coupled to the antenna 25. The radio interface may correspond to a plurality of radio access technologies including one or more of GSM, LTE, LTE-A, 5G, NR, WLAN, NB-IoT, Bluetooth, BT-LE, NFC, RFID, UWB, and the like. The radio interface may include other components, such as filters, converters (for example, digital-to-analog converters and the like), symbol demappers, signal shaping components, an Inverse Fast Fourier Transform (IFFT) module, and the like, to process symbols, such as OFDMA symbols, carried by a downlink or an uplink.

[0069] For instance, transceiver 28 may be configured to modulate information on to a carrier waveform for transmission by the antenna(s) 25 and demodulate information received via the antenna(s) 25 for further processing by other elements of apparatus 20. In other embodiments, transceiver 28 may be capable of transmitting and receiving signals or data directly. Additionally or alternatively, in some embodiments, apparatus 20 may include an input and/or output device (I/O device). In certain embodiments, apparatus 20 may further include a user interface, such as a graphical user interface or touchscreen.

[0070] In an embodiment, memory 24 stores software modules that provide functionality when executed by processor 22. The modules may include, for example, an operating system that provides operating system functionality for apparatus 20. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatus 20. The components of apparatus 20 may be implemented in hardware, or as any suitable combination of hardware and software. According to an example embodiment, apparatus 20 may optionally be configured to communicate with apparatus 10 via a wireless or wired communications link 70 according to any radio access technology, such as NR.

[0071] According to some embodiments, processor 22 and memory 24 may be included in or may form a part of processing circuitry or control circuitry. In addition, in some embodiments, transceiver 28 may be included in or may form a part of transceiving circuitry.

[0072] As discussed above, according to some embodiments, apparatus 20 may be a UE, SL UE, relay UE, mobile device, mobile station, ME, IoT device and/or NB-IoT device, or the like, for example. According to certain embodiments, apparatus 20 may be controlled by memory 24 and processor 22 to perform the functions associated with any of the embodiments described herein, such as one or more of the operations illustrated in, or described with respect to, Figs. 2-4, 5A, 5B, 6A, 6B, 7A, or any other method described herein. For example, in an embodiment, apparatus 20 may be controlled to perform a process relating to handling temporary Fl-U tunnel for MBS mobility, as described in detail elsewhere herein.

[0073] In some embodiments, an apparatus (e.g., apparatus 10 and/or apparatus 20) may include means for performing a method, a process, or any of the variants discussed herein. Examples of the means may include one or more processors, memory, controllers, transmitters, receivers, and/or computer program code for causing the performance of the operations.

[0074] In view of the foregoing, certain example embodiments provide several technological improvements, enhancements, and/or advantages over existing technological processes and constitute an improvement at least to the technological field of wireless network control and/or management. For example, as discussed in detail above, certain embodiments provide an approach for transmitting forwarded and buffered data to the DU PtP leg. For example, certain embodiments provide a solution for transmitting the forwarded and buffered data in a case where the target network node (e.g., gNB) is split between CU and DU, such as, but not limited to, in a multi vendor scenario. Example embodiments avoid the complexity of mixing traffic over the shared Fl-U tunnel. Further, some example embodiments minimize packet loss during mobility when the target network node is split into a CU node and DU node, which may or may not be owned by different vendors. For instance, some example embodiments can provide methods for sending, to the UE, the forwarded and buffered data over the radio PtP leg of the UE until this leg has caught up to the PtM leg of the UE, e.g., when the target gNB is split between CU and DU. Accordingly, the use of certain example embodiments results in improved functioning of communications networks and their nodes, such as base stations, eNBs, gNBs, and/or IoT devices, UEs or mobile stations.

[0075] In some example embodiments, the functionality of any of the methods, processes, signaling diagrams, algorithms or flow charts described herein may be implemented by software and/or computer program code or portions of code stored in memory or other computer readable or tangible media, and may be executed by a processor.

[0076] In some example embodiments, an apparatus may include or be associated with at least one software application, module, unit or entity configured as arithmetic operation(s), or as a program or portions of programs (including an added or updated software routine), which may be executed by at least one operation processor or controller. Programs, also called program products or computer programs, including software routines, applets and macros, may be stored in any apparatus-readable data storage medium and may include program instructions to perform particular tasks. A computer program product may include one or more computer-executable components which, when the program is run, are configured to carry out some example embodiments. The one or more computer-executable components may be at least one software code or portions of code. Modifications and configurations required for implementing the functionality of an example embodiment may be performed as routine(s), which may be implemented as added or updated software routine(s). In one example, software routine(s) may be downloaded into the apparatus.

[0077] As an example, software or computer program code or portions of code may be in source code form, object code form, or in some intermediate form, and may be stored in some sort of carrier, distribution medium, or computer readable medium, which may be any entity or device capable of carrying the program. Such carriers may include a record medium, computer memory, read-only memory, photoelectrical and/or electrical carrier signal, telecommunications signal, and/or software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers. The computer readable medium or computer readable storage medium may be a non-transitory medium. [0078] In other example embodiments, the functionality of example embodiments may be performed by hardware or circuitry included in an apparatus, for example through the use of an application specific integrated circuit (ASIC), a programmable gate array (PGA), a field programmable gate array (FPGA), or any other combination of hardware and software. In yet another example embodiment, the functionality of example embodiments may be implemented as a signal, such as a non-tangible means, that can be carried by an electromagnetic signal downloaded from the Internet or other network.

[0079] According to an example embodiment, an apparatus, such as a node, device, or a corresponding component, may be configured as circuitry, a computer or a microprocessor, such as single-chip computer element, or as a chipset, which may include at least a memory for providing storage capacity used for arithmetic operation(s) and/or an operation processor for executing the arithmetic operation(s).

[0080] Example embodiments described herein may apply to both singular and plural implementations, regardless of whether singular or plural language is used in connection with describing certain embodiments. For example, an embodiment that describes operations of a single network node may also apply to embodiments that include multiple instances of the network node, and vice versa.

[0081] One having ordinary skill in the art will readily understand that the example embodiments as discussed above may be practiced with procedures in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although some embodiments have been described based upon these example embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of example embodiments.

Claims

We Claim:

1. A method, comprising: buffering, at a central unit (CU) user plane (UP) of a target network node, data forwarded from a source network node and buffering new incoming data; and setting up, by the central unit (CU) control plane (CP) of the target network node, a temporary Fl-U tunnel from the central unit (CU) user plane (UP) of the target network node to a distributed unit (DU) of the target network node to feed the distributed unit (DU) point-to-point (PtP) leg with the forwarded data and the incoming data buffered at the central unit (CU) user plane (UP) of the target network node after the CU UP has PDCP processed them.

2. The method of claim 1, further comprising: receiving a request from the distributed unit (DU) to release the temporary Fl-U tunnel when data delivery over the point-to-point (PtP) leg has caught up with data delivery over a point-to-multipoint (PtM) leg; and releasing the temporary Fl-U tunnel.

3. The method of any of claims 1 or 2, wherein the buffering of the incoming data comprises buffering incoming data from a user plane function (UPF) starting from sequence number NO (SN NO) or packet convergence protocol count NO (COUNT NO).

4. The method of claim 3, further comprising: indicating the sequence number NO (SN NO) or the packet convergence protocol count NO (COUNT NO) in a handover request acknowledgement to the source network node.

5. A method, comprising: receiving, at a distributed unit (DU) of a target network node, data forwarded from a source network node and new incoming data over a temporary Fl-U tunnel setup from a central unit (CU) user plane (UP) of the target network node to the distributed unit (DU) of the target network node; and forwarding the forwarded data and the incoming data to at least one user equipment over a point-to-point (PtP) leg.

6. The method of claim 5, further comprising: detecting that delivery of data over the point-to-point (PtP) leg has caught up with the delivery of data over a point-to-multipoint (PtM) leg.

7. The method of claim 6, further comprising: based on the detecting, requesting a central unit (CU) control plane (CP) to release the temporary Fl-U tunnel from the central unit (CU) user plane (UP) of the target network node.

8. A method, comprising: setting up, by a central unit (CU) control plane (CP) of a target network node, a forwarding tunnel from a source network node to a central unit (CU) user plane (UP) of the target network node and a temporary Fl-U tunnel from the central unit (CU) user plane (UP) of the target network node to a distributed unit (DU) of the target network node; processing data received from the source network node over the forwarding tunnel; and transmitting the processed forwarded data to the distributed unit (DU) of the target network node over the temporary Fl-U tunnel releasing the temporary Fl-U tunnel after all PDCP processed forwarded data have been sent to DU.

9. The method of claim 8, further comprising: receiving, at the central unit (CU) control plane (CP), a request from the DU to release the temporary Fl-U tunnel after all PDCP processed forwarded data have been sent over the temporary Fl-U tunnel; and releasing the temporary Fl-U tunnel.

10. The method of claim 9, wherein the release request from the DU is received when an end of the forwarded data is detected and the detection happens when the forwarded data reaches sequence number NO (SN NO) or packet convergence protocol count NO (COUNT NO).

11. The method of claim 10, wherein the sequence number NO (SN NO) or packet convergence protocol count NO (COUNT NO) is received from the DU when the temporary Fl-U tunnel is created.

12. The method of any of claims 10 or 11, wherein the sequence number NO (SN NO) or packet convergence protocol count NO (COUNT NO) is sent to the source network node in a handover request acknowledgement message.

13. The method of any of claims 8-12, wherein the processing comprises packet data convergence protocol (PDCP) processing data received from the source network node over the forwarding tunnel.

14. A method, comprising: receiving, at a distributed unit (DU) of a target network node, data forwarded from a source network node over a first temporary Fl-U tunnel from a central unit (CU) user plane (UP) of the target network node and buffering incoming data received from the central unit (CU) user plane (UP) over a different second shared Fl-U tunnel; and transmitting, to at least one user equipment, over a point-to-point (PtP) leg the forwarded data received over the first temporary Fl-U tunnel and the buffered incoming data received over the second shared Fl-U tunnel until it is detected that delivery of data over the point-to-point (PtP) leg has caught up with the delivery of data over a point-to-multipoint (PtM) leg.

15. The method of claim 14, further comprising: requesting release of the first temporary Fl-U tunnel after all forwarded data has been received over the first temporary Fl-U tunnel.

16. The method of claim 15, wherein the end of the forwarded data is detected when the forwarded data reaches sequence number NO (SN NO) or packet convergence protocol count NO (COUNT NO).

17. The method of any of claims 14-16, wherein the transmitting of the buffered incoming data comprises transmitting the buffered incoming data after the transmitting of the forwarded data to the at least one user equipment.

18. The method of any of cl ims 14-17, wherein the buffering of the incoming data comprises buffering incoming data starting from sequence number NO (SN NO) or packet convergence protocol count NO (COUNT NO).

19. The method of claim 18, further comprising: indicating the sequence number NO (SN NO) or the packet convergence protocol count NO (COUNT NO) to the central unit (CU) control plane (CP) when the first temporary Fl-U tunnel is created in an F1AP message, such as UE context setup response message, or when the distributed unit (DU) starts to buffer incoming data.

20. The method of any of claims 18-19, further comprising: indicating the sequence number NO (SN NO) or the packet convergence protocol count NO (COUNT NO) sent by the central unit (CU) control plane (CP) in a handover request acknowledgement to the source network node.

21. A method, comprising: setting up, by a central unit (CU) control plane (CP) of a target network node, a temporary Fl-U forwarding tunnel directly from a source network node to a distributed unit (DU) of the target network node; receiving a request to release the temporary Fl-U forwarding tunnel after all data have been forwarded; and releasing the temporary Fl-U forwarding tunnel.

22. The method of claim 21, wherein the receiving comprises receiving the request to release from the distributed unit (DU).

23. The method of claim 21, wherein the receiving comprises receiving the request to release from the source network node.

24. The method of any of claims 21-23, wherein it is determined that all of the data has been forwarded when the forwarded data reaches sequence number NO (SN NO) or packet convergence protocol count NO (COUNT NO).

25. The method of any of claims 21-24, wherein the sequence number NO (SN NO) is received by the central unit (CU) control plane (CP) from the distributed unit (DU) when the Fl-U tunnel is created or when the distributed unit (DU) starts to buffer incoming data.

26. The method of any of claims 21-25, further comprising: indicating at least one of the sequence number NO (SN NO) or the packet convergence protocol count NO (COUNT NO) or a tunnel endpoint identifier (TEID) of the temporary Fl-U forwarding tunnel in a handover request acknowledgement to the source network node.

27. The method of claim 26, wherein the tunnel endpoint identifier (TEID) of the temporary Fl-U forwarding tunnel is a downlink tunnel endpoint identifier of the distributed unit (DU) which is received by the central unit (CU) control plane (CP) from the distributed unit (DU) when the Fl-U tunnel is created.

28. A method, comprising: receiving, at a distributed unit (DU) of a target network node, data that is directly forwarded from a source network node over a first Fl-U forwarding tunnel and buffering incoming data from a central unit (CU) user plane (UP) of the target network node received over a second shared Fl-U tunnel; transmitting the forwarded data to at least one user equipment over a point-to-point (PtP) leg until an end of the forwarded data is detected; and transmitting the buffered incoming data and the forwarded data to at least one user equipment over the point-to-point (PtP) leg until it is detected that delivery of data over the point-to-point (PtP) leg has caught up with the delivery of data over a point-to-multipoint (PtM) leg.

29. The method of claim 28, further comprising: requesting the release of the first Fl-U forwarding tunnel after all the forwarded data has been sent over the PtP leg.

30. The method of any of claims 28 or 29, wherein the buffering of the incoming data comprises buffering incoming data starting from sequence number NO (SN NO) or packet convergence protocol count NO (COUNT NO).

31. The method of any of claims 28-30, wherein the end of the forwarded data is detected when the forwarded data reaches sequence number NO (SN NO) or packet convergence protocol count NO (COUNT NO).

32. The method of any of claims 28-31, wherein the sequence number NO (SN NO) is sent to a central unit (CU) control plane (CP) of the target network node, and subsequently to the source network node via the central unit (CU) control plane (CP), when the first Fl-U forwarding tunnel is created or when the distributed unit (DU) starts to buffer incoming data.

33. The method of any of claims 28-32, wherein the transmitting of the buffered incoming data comprises transmitting the buffered incoming data after the transmitting of the forwarded data to the at least one user equipment.

34. An apparatus, comprising: at least one processor; and at least one memory comprising computer program code, the at least one memory and computer program code configured, with the at least one processor, to cause the apparatus at least to perform a method according to any of claims 1-33.

35. An apparatus, comprising: means for performing the method according to any of claims 1-33.

36. An apparatus, comprising: circuitry configured to perform the method according to any of claims

1-33.

37. A computer readable medium comprising program instructions stored thereon for performing at least the method according to any of claims 1-33.