Migration Management in an IAB Communication System

Description

1 / 81 “MIGRATION MANAGEMENT IN AN IAB COMMUNICATION SYSTEM” FIELD OF THE INVENTION

[0001] The present invention relates generally to methods for use in a process for migrating nodes between Integrated Access and Backhaul (IAB) topologies of a wireless communication system involving mobile IAB nodes. In particular, the present invention relates to a method for use in managing a migration process to migrate a Distributed Unit (DU) from an IAB node, for example, a mobile IAB node, between IAB topologies. BACKGROUND

[0002] Wireless communication systems are widely deployed to address a wide range of applications, from mobile broadband and massive machine-type communications to ultra-reliable low-latency communications (URLLC). Such systems allow a plurality of user equipment (UE) or mobile terminals to share the wireless medium to exchange various types of data content (e.g., video, voice, message transmission...) over a radio access network (RAN) via one or more base stations. Base stations are conventionally wired (e.g., via fiber) to a core network, forming an intermediate network called backhaul (BH).

[0003] Examples of such wireless multiple access communication systems include systems based on 3rd generation society design standards (3GPP - RTM), such as fourth generation Long Term Evolution (LTE) (4G) or the recent fifth generation New Radio (NR) (5G) systems, or systems based on IEEE 802.11 standards, such as Wi-Fi.

[0004] The demand for network densification increases due to the growing number of users requiring higher transmission capacity.

[0005] Facing the problems of high deployment costs and time of wired backhaul networks with network densification, 3GPP proposed, starting with release 16 for 5G NR, a wireless backhaul, also known as Integrated Access and Backhaul, IAB, where part of the wireless spectrum (i.e., radio) is used. Petition 870250083679, dated 09 / 17 / 2025, page 14 / 130 2 / 81 for backhaul connection of base stations instead of fiber. Wireless backhaul communications (between base stations) can use the same radio / network resources as access communications (between a base station and UEs).

[0006] IAB has become a competitive alternative to filter-based backhauling in dense or hard-to-reach areas, as it allows for quick and scalable installations without the cabling burden of base stations.

[0007] IAB is more likely to operate in the millimeter wave (mmWave) band to achieve the required Gbps (gigabits per second) data rate. However, millimeter waves are known to be subject to strong signal strength attenuation in some weather conditions (rain, fog) and blockage in case of obstacles located in the path between the transmitter and the receiver.

[0008] To manage these potential radio link failures, topological redundancy can be provided in the IAB structure, where multiple data paths are established between the IAB base station directly connected to the core network (also called the “IAB donor”) and the IAB base station serving UEs (also called the “IAB access node” for the UEs). Several intermediate IAB base stations (also called IAB nodes) can be involved in each of the multiple paths between the IAB donor and the IAB access node, thus forming alternative data paths in a multi-hop IAB topology.

[0009] In addition, 3GPP is considering inter-donor redundancy, where an IAB node, called a boundary IAB node, can access two different parent nodes connected to two different IAB donors, with each IAB donor managing a different IAB topology (also called an IAB network). The boundary IAB node, while belonging to a single IAB topology, i.e., belonging to a single IAB donor for configuration and management, is thus able to route packets from a first IAB topology managed by a first IAB donor to a second IAB topology managed by a second IAB donor. The advantage of this inter-donor redundancy lies in the ability of the first IAB donor to perform offloading by routing some of its own packets. Petition 870250083679, dated 09 / 17 / 2025, page 15 / 130 3 / 81 through the second IAB topology, thus mitigating congestion problems or overcoming radio link failure problems that may arise in the first IAB topology.

[0010] There are other situations in which an IAB node becomes a boundary node. For example, in the case of a partial migration of an IAB node, decided by the IAB donor, where the Mobile Termination (MT) of the IAB node becomes connected to a single parent IAB node belonging to another IAB topology controlled by another IAB donor. This situation can also occur in the case of an IAB node that has experienced a radio link failure (RLF) and has recovered through a parent IAB node belonging to another IAB topology. In these cases, the migrated IAB node and its potential descendant IAB node(s) still belong to the initial IAB topology, and such a partial migration can be called MT migration. To ensure that traffic can be routed through another IAB topology, MT migration must be followed by traffic migration where the traffic related to the boundary node and its descendant IAB nodes is routed through the other IAB topology to the boundary node (i.e., the migrated IAB node).

[0011] Stationary IAB nodes should only require a single MT migration. Indeed, a backhaul link (defined between two successive IAB nodes in the wireless backhaul) can experience radio failure due to fluctuations in radio conditions, and for non-moving IAB nodes, this should be a temporary situation with possible link recovery after some time. Thus, such stationary IAB nodes should not be required to perform multiple MT migrations within the same IAB topology or towards another IAB topology, and the transmission and handling of multiple protocol messages can be avoided. For the same reason, the migration of the Distributed Unit (DU) of the IAB node, leaving control of the IAB node to a new IAB Donor, should not be necessary for stationary nodes. Furthermore, it is noted that such a DU migration, which can be called a full migration, also involves the handover of UEs served by the migrating mobile IAB node.

[0012] Urban environments are typically characterized by a high density of users along with the presence of a significant number of vehicles (e.g., private / public passenger transport, delivery of Petition 870250083679, dated 09 / 17 / 2025, page 16 / 130 4 / 81 goods, food trucks...). Some of these vehicles (e.g., buses, trams, trains) may have predictable routes and a significant number of UEs (i.e., passenger devices) deployed. 3GPP is considering that such vehicles could offer an opportunity to increase network coverage and connectivity for UEs within the vehicles, or even for UEs in proximity to the vehicles, by installing onboard base stations (or base station elements) in these vehicles that would act as mobile relays. These mobile relays would rely on 5G wireless backhaul (typically IAB, or Integrated Access & Backhaul) to connect with a fixed donor device.

[0013] Thus, based on the fixed IAB foundations of releases 16 and 17, 3GPP is now considering Mobile IAB systems and architectures as part of the release 18 framework to address scenarios focusing on mobile IAB nodes mounted in vehicles (such as buses, trains, taxis). In such scenarios, mobile IAB nodes may be referred to as Vehicle Mounted Repeaters (VMRs), providing 5G coverage / capacity to UEs on board and / or around them.

[0014] The technical benefits of using VMRs include, among others, the ability of the VMR to offer good radio link conditions to nearby UEs. Additionally, compared to a solution using a UE as a relay (i.e., a sidelink relay solution), a vehicle-mounted IAB node is expected to have better antenna / RF capabilities and less stringent power / battery limitations than a relay UE.

[0015] For a mobile IAB node, it may be worthwhile to perform multiple MT migrations or DU migrations, since the connection to a parent IAB node belonging to a first IAB topology may not occur again for a long period of time as the mobile IAB node moves, or never again in the case where the mobile IAB node moves in the opposite direction to the parent IAB node. Furthermore, with flexible IAB network management, DU migration for an IAB node can be performed towards a different IAB donor than the IAB donor associated with that IAB node's MT.

[0016] In reality, the criteria for DU migration and MT handover Petition 870250083679, dated 09 / 17 / 2025, page 17 / 130 5 / 81 differ: MT handover is triggered by radio conditions, while the DU migration decision may be based, for example, on available connectivity between IAB donors and / or for load balancing purposes. Thus, the source IAB donor can select a suitable target IAB donor for DU migration from an IAB node based on its own criteria. However, the target IAB donor may not be able to handle the migrating IAB node and the served UEs, for example, due to current load on the target IAB donor and / or current network load. Therefore, some new mechanisms are needed to allow for the revocation or rejection of DU migration from an IAB node. SUMMARY

[0017] According to a first aspect of the present invention, a method is provided for use in managing a migration process to migrate a Distributed Unit, DU, of an Integrated Access Backhaul, IAB, node, from a source IAB topology managed by a Central Unit, CU, of source IAB donor, to a target IAB topology managed by a target IAB donor CU, performed in the target IAB donor CU.The method comprises: receiving, from the source IAB donor CU, a request to request DU migration from the IAB node DU from the source IAB donor CU to the target IAB donor CU; determining whether to accept, partially accept, or reject the DU migration from the IAB node; after determining whether to accept, partially accept, or reject the DU migration, sending a response to the source IAB donor CU indicating that the target IAB donor CU has determined to accept, partially accept, or reject the request for DU migration to the target IAB donor CU.

[0018] According to a second aspect of the present invention, a method is provided for use in managing a migration process to migrate a Distributed Unit, DU, of an Integrated Access Backhaul, IAB, node, from a source IAB topology managed by a Central Unit, CU, of a source IAB donor, to a target IAB topology managed by a target IAB donor CU, performed in the target IAB donor CU. The method comprises: determining that the IAB node DU should be migrated to the target IAB donor CU; sending, to the Petition 870250083679, dated 09 / 17 / 2025, p. 18 / 130 6 / 81 The target IAB donor CU submits a request to migrate DUs from the IAB node's DU of the source IAB donor CU to the target IAB donor CU; and receives a response from the target IAB donor CU indicating that the target IAB donor CU has partially accepted or rejected the request to migrate DUs to the target IAB donor CU.

[0019] According to a third aspect of the present invention, a method is provided for use in managing a migration process to migrate a Distributed Unit, DU, of an Integrated Access Backhaul, IAB, node, from a source IAB topology managed by a Central Unit, CU, of source IAB donor, to a target IAB topology managed by a target IAB donor CU, performed in the target IAB donor CU.The method comprises: receiving, from the IAB node, an F1 establishment request to request the establishment of an F1 connection between the target IAB donor CU and the IAB node and to indicate that the F1 connection to be established refers to a request for DU migration from the IAB node's DU to the target IAB donor CU; determining whether to accept, partially accept, or reject the DU migration from the IAB node; sending a response indicating that the target IAB donor CU has determined to accept, partially accept, or reject the request for DU migration to the target IAB donor CU.

[0020] According to a fourth aspect of the present invention, a method is provided for use in managing a migration process to migrate a Distributed Unit, DU, of an Integrated Access Backhaul, IAB, node, from a source IAB topology managed by a source IAB donor Central Unit, CU, to a target IAB topology managed by a target IAB donor CU, performed in the target IAB donor CU. The method comprises: determining that the IAB node DU should be migrated to the target IAB donor CU; sending a request to the IAB node to establish an F1 connection between the target IAB donor CU and the IAB node and informing the target IAB donor CU that the F1 connection to be established refers to a request for DU migration from the IAB node to the target IAB donor CU; receive a response indicating that the target IAB donor CU has accepted, partially accepted, or rejected the request for DU migration to the Petition 870250083679, dated 09 / 17 / 2025, p. 19 / 130 7 / 81 Target IAB donor CU.

[0021] According to a fifth aspect of the present invention, a method is provided for use in managing a migration process to migrate a Distributed Unit, DU, of an Integrated Access Backhaul, IAB, node, from a source IAB topology managed by a Central Unit, CU, of source IAB donor, to a target IAB topology managed by a target IAB donor CU, performed at the IAB node.The method comprises: receiving, from the source IAB donor CU, a request to establish an F1 connection between the target IAB donor CU and the IAB node and to inform the target IAB donor CU that the F1 connection to be established refers to a request for DU migration from the IAB node to the target IAB donor CU; sending, to the target IAB donor CU, an F1 establishment request to request the establishment of the F1 connection and to indicate that the F1 connection to be established refers to a request for DU migration from the IAB node to the target IAB donor CU; receiving an F1 establishment response indicating that the target IAB donor CU accepted, partially accepted, or rejected the F1 establishment request regarding the DU migration request to the target IAB donor CU.

[0022] In one example, a decision to accept (i.e., fully accept) corresponds to a decision to accept all traffic (i.e., all traffic associated with the traffic profile(s) of the IAB node to be migrated) and all UEs served by the IAB node. A decision to partially accept corresponds to a decision to accept some or part of the traffic (i.e., accept some or a subset of the traffic profile(s) associated with the IAB node to be migrated) and / or a limited number or subset or some of the UEs served by the IAB node. In particular, a decision to partially accept may correspond to a decision to accept the F1 establishment connection with the IAB node, but accept some or part of the traffic (i.e., accept some or a subset of the traffic profile(s) associated with the IAB node to be migrated) and / or a limited number or subset or some of the UEs served by the IAB node.

[0023] According to a sixth aspect of the present invention, a Petition 870250083679, dated 09 / 17 / 2025, p. 20 / 130 8 / 81 device for an IAB donor CU as mentioned in claim 57 of the appended claims.

[0024] According to a seventh aspect of the present invention, an apparatus is provided for an IAB node as mentioned in claim 58 of the appended claims.

[0025] The method / device according to one or more embodiments of the present invention enables the target IAB donor CU to accept or partially accept or reject or revoke the DU migration (and thus the subsequent handover of UEs served by the IAB node) and send a response indicating whether the DU migration was accepted or rejected or revoked. The target IAB donor CU can inform the source IAB donor CU of the decision to accept or partially accept or reject or revoke the DU migration by sending a message to the source IAB donor CU or to the IAB node (which can then inform the source IAB donor CU). With the target IAB donor CU sending a response to the source IAB donor CU to indicate that the DU migration was accepted or partially accepted or rejected, the triggering of a second logical DU on the IAB node when the DU migration is rejected can be avoided.With the target IAB donor CU sending a response to the IAB node indicating that the DU migration has been accepted, partially accepted, or rejected, the F1 establishment procedure will already have been completed, saving establishment time when the DU migration is accepted. Thus, the method / device according to one or more embodiments of the present invention enables the target IAB donor CU to reject or revoke the DU migration (and thus the subsequent handover of UEs served by the IAB node) if the target IAB donor CU is unable to accommodate the IAB node DU and the traffic related to the served UEs (due to some lack of processing resources or some lack of radio / network resources) and inform the source IAB donor CU so that appropriate action can be taken.

[0026] Additional example features of the invention are described in other independent and dependent claims.

[0027] Any feature in one aspect of the invention can be applied to other aspects of the invention. Petition 870250083679, dated 09 / 17 / 2025, page 21 / 130 9 / 81 aspects of the invention, in any appropriate combination. In particular, method aspects can be applied to apparatus / device / unit aspects and vice versa.

[0028] Additionally, features implemented in hardware can be implemented in software, and vice versa. Any reference to software and hardware features in the present invention shall be interpreted accordingly. For example, according to other aspects of the invention, a computer program comprising instructions is provided which, when the program is executed by one or more processing units, causes one or more processing units to perform the method of any aspect or example described above, and a computer-readable storage medium containing the computer program. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Different aspects of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0030] Figure 1 is a schematic diagram of a communication system in which the present invention can be implemented according to one or more embodiments;

[0031] Figures 2a and 2b schematically illustrate stacks of some protocol layers involved in IAB operations;

[0032] Figure 3 is a schematic diagram illustrating the shape of a BAP Protocol Data Unit (PDU) or packet;

[0033] Figure 4 is a block diagram of an example wireless communication device according to embodiments of the present invention;

[0034] Figure 5 is a schematic diagram of an example IAB communication system (or IAB network system) in which embodiments and examples of embodiments of the present invention can be implemented;

[0035] Figure 6 is a simplified schematic diagram illustrating an example of an IAB node architecture enabling its DU migration from a source IAB topology to a target IAB topology; Petition 870250083679, dated 09 / 17 / 2025, page 22 / 130 10 / 81

[0036] Figure 7 is a simplified diagram illustrating example message flows for performing DU migration from an IAB node including the handover of UEs served by the migrating IAB node;

[0037] Figure 8 is a simplified diagram illustrating example message flows, according to one or more embodiments of the invention, to enable a target F1 termination donor CU to partially accept or reject DU migration from an IAB node;

[0038] Figure 9a is a simplified diagram illustrating an example message flow, according to one or more embodiments of the invention, of a procedure used by a RAN node CU to report configuration information to another RAN node CU;

[0039] Figure 9b is a simplified diagram illustrating an example message flow, according to one or more embodiments of the invention, of a procedure used by a RAN node CU to manage DU migration from a RAN node in coordination with another RAN node CU, including signaling to partially accept, reject, or revoke DU migration;

[0040] Figure 10a is a simplified diagram illustrating an example message flow, according to one or more embodiments of the invention, of a procedure for performing the activation of a logical DU on a RAN node, including signaling to partially accept, reject or revoke by a RAN node CU the RAN node DU migration;

[0041] Figure 10b is a simplified diagram illustrating an example message flow, according to one or more embodiments of the invention, of a procedure for establishing a logical DU on a RAN node, including signaling to partially accept, reject, or revoke a RAN node DU migration by a RAN node CU;

[0042] Figure 10 is a simplified diagram illustrating an example message flow of a procedure for removing a logical DU in a RAN node;

[0043] Figure 11a is a flowchart of an example method according to embodiments of the present invention, for managing, in the termination donor CU Petition 870250083679, dated 09 / 17 / 2025, page 23 / 130 11 / 81 of F1 from an IAB node source, the DU migration from the IAB node;

[0044] Figure 11b is a flowchart of an example method according to embodiments of the present invention, for managing, in the F1 Target termination donor CU of an IAB node, the DU migration from the IAB node;

[0045] Figure 12a is a flowchart of another example method according to embodiments of the present invention, for managing, in the F1 source termination donor CU of an IAB node, the DU migration from the IAB node;

[0046] Figure 12b is a flowchart of an example method according to embodiments of the present invention, for managing, in an IAB node, its DU migration to a target F1 termination donor CU;

[0047] Figure 12c is a flowchart of another example method according to embodiments of the present invention, for managing, in the target F1 termination donor CU of an IAB node, the DU migration from the IAB node. DETAILED DESCRIPTION

[0048] Figure 1 illustrates an example communication system 100, in particular a mobile radio communication system as a fifth-generation (5G) New Radio (NR) system including an integrated wireless Access and Backhaul network supporting mobile IAB node(s). Although in the following description, embodiments and examples of embodiments of the present invention are described with respect to a 5G NR system, it will be recognized that the present invention is not intended to be limited to 5G NR systems and can be used in any wireless communication systems having a mobile base station. In particular, the following description predominantly uses 5G-specific terminology, but it should be recognized that such terminology also applies to elements or processes that perform an equivalent function in other communication systems.

[0049] System 100 comprises a plurality of UEs (User Equipment) 132, 133, 131 and 134, a remote core network 110, a main Base Station 120 and two Integrated Access and Backhaul (IAB) stations or IAB nodes 121 and 122 (also referred to hereinafter as IAB nodes) and a mobile Access station. Petition 870250083679, dated 09 / 17 / 2025, page 24 / 130 12 / 81 and Integrated Backhaul (IAB) 123 mounted on a vehicle 105 (e.g., a bus, a train, a taxi, a car, etc.).

[0050] The main Base Station 120, also called the IAB 120 donor, is connected to the core network 110 via a wired link 101, preferably an optical fiber or any other wired medium. In embodiments and examples of embodiments of the invention, the IAB 120 donor is a gNB NR 5G with additional functionality to support IAB features, as defined in specification document 3GPP TS 38.300 v17.2.0.

[0051] To extend the network coverage of donor IAB 120 and reach remote UEs 132, 133, and 131, IAB stations 121 and 122, also called IAB nodes 121 and 122, were installed by the operator. By acting as relay nodes between donor IAB 120 and UEs 132 and 133, IAB nodes 121 and 122 overcome the reachability problem resulting from the presence of building 108, which is an obstacle to radio wave propagation and consequently to direct linking and additional communications between the UEs and donor IAB 120. This is particularly true when communications between donor IAB 120 and UEs 132 and 133 are operated at millimeter wave frequencies, which are highly sensitive to shadowing phenomena.

[0052] The IAB 120 donor also serves UE 134, which is directly connected to it.

[0053] Mobile IAB station 123, also called mobile IAB node 123 or mIAB node 123, is an IAB node that is mounted on vehicle 105 and provides network coverage and capacity extension, allowing the IAB donor 120 to reach remote UEs on board, such as remote UE 135, as well as UEs around or near IAB node 123, such as remote UE 136.

[0054] Donor IAB 120 and nodes IAB 121, 122, and 123 are thus forming a backhaul network or IAB network, or IAB topology, which accommodates UEs 132, 133, 131, 134, 135, and 136. The terms IAB network and IAB topology will be used interchangeably hereafter.

[0055] The Integrated Access and Backhaul (IAB) specification is spread Petition 870250083679, dated 09 / 17 / 2025, page 25 / 130 13 / 81 regarding various 3GPP standard documents, including: - TS 38.300 RAN architecture (V17.2.0), - TS 38.321 MAC protocol (V17.2.0), - TS 38.331 Radio Resource Control (RRC) protocol (V17.2.0), - TS 38.340 Backhaul Adaptation Protocol Layer (V17.2.0), - TS 38.401 RAN architecture (V17.2.0), - TS 38.423 Application Protocol (V17.2.0), - TS 38.473 F1 application protocol (V17.2.0).

[0056] An IAB 120 donor and IAB nodes 121, 122, and 123 are respectively connected to UEs 134, 131, 132, 133, 135, and 136; these are considered as IAB access nodes for their respectively connected UEs.

[0057] The IAB 120 donor is a logical node that provides NR-based wireless backhaul and consists of a central unit (CU or gNBCU functionality) and connected distributed donor unit(s) (DU or gNBDU functionality). The IAB donor CU or donor CU (also referred to herein as IAB donor CU or IAB donor CU) hosts upper-layer protocols such as PDCP (Packet Data Convergence Protocol) and RRC (Radio Resource Control) protocols to control the operation of one or more DUs, and each of the one or more IAB donor DUs or donor DUs (also referred to herein as IAB donor DU or donor DU) includes lower-layer protocols such as RLC, MAC, and physical layer protocols. A donor IAB CU or donor CU and donor IAB DU or donor DU can be located far from each other or can be located on the same physical device. The gNB-DU functionality is defined in 3GPP TS 38.401.Its aim is to complete the NR access interface with the UEs and IAB nodes of the next hop, and to complete the F1 protocol for the IAB donor gNB CU functionality as shown in Figures 2a and 2b discussed below.

[0058] The IAB nodes, which can serve multiple radio sectors, are wirelessly backhauled with the IAB 120 donor via one or multiple hops over one or more intermediate IAB nodes. They form an acyclic graph topology. Petition 870250083679, dated 09 / 17 / 2025, page 26 / 130 14 / 81 directed (DAG) with the IAB donor at its root.

[0059] IAB nodes each consist of an IAB DU (IA Distributed Unit) and an IAB-MT (IAB Mobile Termination). The gNB-DU functionality in an IAB node is also called IAB-DU and allows downstream connection (towards the UE) with the next-hop IAB or UE. The IABMT functionality includes, for example, physical layer, layer-2, RRC and Non-Accessible Layer (NAS) functionalities to connect to the gNB-DU of an upstream IAB node (including the donor IAB 120 in which case it connects to the donor IAB gNB CU, consequently to the core network 110, for example, for initialization, registration and configuration).

[0060] In this DAG topology, the neighboring node on the IAB DU interface is called the child node and the neighboring node on the IAB MT interface is called the parent node. The direction to the child node is additionally called downstream while the direction to the parent node is called upstream.

[0061] The IAB 120 donor (e.g., the IAB donor CU) performs centralized resource, topology, and route management for the entire IAB topology. This includes configuring IAB nodes according to the network topology, for example, to perform appropriate data packet routing.

[0062] Figures 2a and 2b schematically illustrate stacks of some protocol layers involved in IAB operations.

[0063] The F1 interface supports the exchange of signaling information (e.g., control traffic) between endpoints, as well as the transmission of data (e.g., user traffic transmission) to the respective endpoints. From a logical point of view, the F1 interface is a point-to-point interface between endpoints.

[0064] In NR 5G, F1-C is the functional interface in the Control Plane (CP) between the donor CU IAB and a node DU IAB (e.g., node IAB 2) and between the donor CUa IAB and a donor DU IAB. F1-U is the functional interface in the User Plane (UP) for the same units. F1-C and F1-U are shown by reference 212 in Figure 2a. In this example, F1-U and F1-C are carried by two hops of Petition 870250083679, dated 09 / 17 / 2025, p. 27 / 130 15 / 81 backhaul (from donor IAB to node IAB and then from node IAB to node2 of IAB).

[0065] In the User Plane, boxes 210 in the IAB donor CU and IAB node DU refer to the GTP-U layer and boxes 211 refer to the UDP layer. GTP-U stands for GPRS Tunneling Protocol User Plane. GTP-U tunnels are used to transport encapsulated PDUs and signaling messages between a given pair of GTP-U Tunnel endpoints (see 3GPP TS 29.281 for more details), here boxes 210 in the IAB donor CU and in the IAB node DU. The well-known User Datagram Protocol (UDP) is a transport layer protocol that provides a best-effort, out-of-the-box datagram service with an IP protocol.

[0066] In the Control Plane, squares 210 indicate the FIAP (F1 Application Protocol) layer and squares 211 indicate the SCTP (Flow Control Transmission Protocol) layer. The F1 Application Protocol (as defined in GPP TS38.473 and TS 38.401) provides signaling services between the IAB donor CU and the IAB node DU or UE-associated services. These services are, for example, initialization, configuration, etc. The well-known SCTP layer provides reliable, sequential message transport with congestion control.

[0067] F1-U and F1-C are based on an IP transport layer between the IAB donor CU and the IAB node DU as defined in 3GPP TS 38.401.

[0068] Transport between the IAB donor DU and the IAB donor CU also uses an IP transport layer over multiple media, such as fiber optic cables when the IAB donor CU is remote from the IAB donor DU, or locally in a virtual instantiation of the IAB donor CU and the IAB donor DU on the same physical machine. The specific IAB transport between IAB donor CU and IAB donor DU is specified in 3GPP TS 38.401.

[0069] L1 and L2 in figure 2a mean, respectively, the transport and physical layers appropriate for the medium in use.

[0070] The IP layer can also be used for non-F1 traffic, such as Petition 870250083679, dated 09 / 17 / 2025, p. 28 / 130 16 / 81 Operations, Administration and Maintenance traffic.

[0071] In wireless backhaul, the IP layer is itself carried in the Backhaul Adaptive Protocol (BAP) sublayer, which enables multi-hop routing. The BAP sublayer is specified in TS 38.340.

[0072] IP traffic from the IAB DU is routed over the wireless backhaul via the BAP sublayer. In a downstream direction, upper-layer packets are encapsulated by the BAP sublayer in the donor IAB DU, thus forming BAP packets or packet data units (PDUs) or data packets. The BAP packets are routed by the BAP entity or layer (and corresponding BAP entities in the IAB DU and IAB MT) of the intermediate IAB nodes, if any. The packets and BAP are finally decapsulated by the BAP sublayer at the destination IAB node (which may be an access IAB node if the upper-layer packets in the BAP packets are destined for a UE).

[0073] In an upstream direction, upper-layer packets are encapsulated by the BAP sublayer at an initiator IAB node (which may be an access IAB node if the upper-layer packets come from a UE), thus forming BAP packets or data units (PDUs) or data packets. The BAP packets are routed by the BAP layer (and corresponding BAP entities in the IAB DU and IAB MT) of intermediate IAB nodes, if any. The BAP packets are finally decapsulated by the BAP sublayer at the donor IAB DU.

[0074] In the BAP sublayer, packets are routed based on the BAP routing ID, which is carried in the BAP header of the BAP packets, and which is defined by the BAP sublayer of the issuing IAB donor DU or initiating IAB node (e.g., a network node in the IAB network generating the BAP packets). Figure 3 illustrates the format of a BAP data packet or Protocol Data Unit (PDU). It is specified in paragraph 6.2 of the standardized version of 3GPP TS38.340 release 17.2.0.

[0075] Payload section 307 is typically an IP packet. Header 30 includes fields 301 through 306. Field 301, called the D / C field, is a Boolean. Petition 870250083679, dated 09 / 17 / 2025, page 29 / 130 17 / 81 indicating whether the corresponding BAP packet is a BAP data packet or a BAP control packet. Fields 302-304 are reserved 1-bit fields, preferably set to 0 (to be ignored by the receiver).

[0076] Fields 305 and 306 together indicate the BAP routing ID for the BAP packet. The BAP address field 305, called the DESTINATION field, is located in the leftmost 10 bits, while the BAP route identity field 306, also called the PATH field, is located in the rightmost 10 bits.

[0077] Field 305 carries the BAP address (i.e., in the BAP sublayer) of the destination IAB node or IAB donor DU for the BAP packet. For routing purposes, each IAB node and IAB donor DU in an IAB network is configured (per IAB donor CU of the IAB network) with a designated and unique BAP address. Field 306 carries a path ID identifying the routing path that the BAP packet should follow to that destination in the IAB topology. For routing purposes, routing paths, including their path ID, are configured (per IAB donor CU of the IAB network) on the IAB nodes of the IAB network.

[0078] The BAP header is added to the packet when it arrives from the upper layers to the BAP layer and is extracted by the BAP layer when it reaches its destination node. The selection of the packet's BAP routing ID is configured by the IAB donor CU.

[0079] For example, when the BAP packet is generated by a node, i.e., by the IAB donor DU for downstream transmission or by an initiator (which may be an access IAB node if the upper-layer packets come from a UE) for upstream transmission, the BAP header with the BAP Routing ID is constructed by that node according to a configuration table defined in 3GPP TS 38.340. This table is called the Downlink Traffic Configuration table for Routing ID Mapping in the IAB donor DU or the Uplink Traffic Configuration table for Uplink Traffic Configuration table for Routing ID Mapping in the initiator IAB node. In intermediate IAB nodes, the fields of Petition 870250083679, dated 09 / 17 / 2025, page 30 / 130 18 / 81 BAP headers are already specified in the BAP package for issuance.

[0080] As mentioned above, these configuration tables that define the BAP paths (consequently the routing strategy and configuration of the IAB nodes given in the IAB network topology) are normally defined by the IAB donor CU and transmitted to the IAB nodes to configure them.

[0081] To transport messages over the 5G NR radio medium, three more sublayers (RLC, MAC, and PHY) are implemented in each IAB node below the BAP sublayer. The RLC (Radio Link Control) sublayer is responsible for packet segmentation or reconstruction. It is also responsible for requesting retransmission of missing packets. The RLC layer is further described in TS38.322. The MAC (Medium Access Channel) protocol sublayer is responsible for selecting available transmission formats for user data and for logical channel mapping to transport channels. The MAC also handles part of the Hybrid Automated Repeat request scheme. The MAC layer is detailed in TS 38.321. On the sender or transmitter side, the NAC encapsulates the data packet emitted from the RLC. It adds a header containing information necessary for the MAC function.On the receiving side, the MAC decapsulates the data packet emitted from the PHY sublayer, deletes its header, and passes the remaining data to the RLC. The PHY sublayer provides an electrical interface to the transmission medium (the air) by converting the information stream into physical modulation signals, modulating a carrier frequency on the transmitting side. On the receiving side, the PHY sublayer converts the physical modulation signals back into an information stream. The PHY layer is described in TS 38.201, TS 38.211, TS 38.212, TS 38.213, and TS 38.214.

[0082] To pass messages towards the control or user plane, two other sublayers are used in the IAB donor UE and CU; the PDCP (Packet Data Convergence Protocol) sublayer and the SDAP (Service Data Adaptation Protocol) sublayer for the User Plane Communications or RRC (Radio Resource Control) sublayer for communications. Petition 870250083679, dated 09 / 17 / 2025, page 31 / 130 19 / 81 of the Control Plan.

[0083] The PDCP sublayer handles IP Header compression / decompression, encryption / decryption, and packet integrity, if necessary. It mandatorily numbers packets on the sender side and reorders packets on the receiver side. The PDCP sublayer is described in 3GPP TS38.323.

[0084] SDAP sublayer 220 for the User Plane handles Quality of Service. It is described in TS38.324. On the UE side, the SDAP sublayer exchanges payload data with the user application (voice, video, etc. - not shown in the figure). On the IAB donor CU side, the SDAP sublayer exchanges data with the Core Network 110 (Internet traffic, Cloud, etc.).

[0085] The RRC 220 sublayer for the Control Plane deals with the configuration of the protocol entities of the User Plane protocol stack. It is described in TS38.331. It is responsible for handling, among other things, broadcasting information necessary for a UE to communicate with a cell; transmitting paging messages; managing connections, including establishing carriers; mobility functions; metering and reporting configuration; and device capabilities.

[0086] The interface (for both CP and UP) between nodes using the PDCP, RLC, MAC, and PHY layers is referred to as NR-Uu. This mainly refers to the interface with the UE.

[0087] The interface (for both CP and UP) between nodes using the BAP, RLC, MAC, and PHY layers is called the Backhaul RLC Channel (BH RLC Channel). This mainly refers to the interface between IAB nodes.

[0088] NR-Uu is the interface between the UE and the radio access network, that is, its access IAB node (for both CP and UP).

[0089] Figure 2b comes from 3GPP TS 38300 v17.2.0 and illustrates the protocol stack for supporting NAS and IAB MT RRC connections. The Non-Accessible Stratum (NAS) protocol handles messages between the core network and a user device or an IAB node. It manages the establishment of communication sessions and maintains communication with the IAB node or user device. Petition 870250083679, dated 09 / 17 / 2025, page 32 / 130 20 / 81 when moving. The 5G NAS is described in 3GPP TS 24.501. The 5G Core Mobility and Access Management (AMF) function in the Core Network receives all connection and session-related information from the UEs connected to the IAB node, as well as similar information for the IAB node. AMF is only responsible for handling connection and mobility management tasks.

[0090] The IAB MT establishes Signaling Radio Carriers (SRBs) (carriers carrying NAS and RRC messages) with the IAB donor CU. These SRBs are transported between the IAB MT and its parent node(s) over NR-Uu interface(s).

[0091] Figure 4 shows a schematic representation of an example communication device (appliance) or station, according to one or more example embodiments of the present disclosure.

[0092] The communication device 400 may be a device such as a microcomputer, a workstation, or a lightweight portable device. The communication device 400 may comprise a communication bus 413 to which the following are preferably connected: - A central processing unit 411, such as a microprocessor, designated CPU. The central processing unit 411 may be a single processing unit or processor or may comprise two or more processing units or processors performing the processing required for the operation of the communication device 400. The number of processors and the allocation of processing functions to the central processing unit 411 is a matter of design choice for a technician in the field; - Memory for storing data and computer programs containing instructions for the operation of the communication device. Computer programs may contain a number of different program elements (modules) or subroutines containing instructions. Petition 870250083679, dated 09 / 17 / 2025, page 33 / 130 21 / 81 for a variety of operations and to implement the methods in accordance with one or more embodiments of the invention; and - at least one 402 communication interface for communicating with other devices or nodes in a communication system, such as the communication system in Figure 1. The at least one 402 communication interface may be connected to the 403 radio communication network, such as a 5G NR wireless communication network (e.g., according to release 17 and / or subsequent releases), over which digital data packets or frames or control frames are transmitted. Frames are written from a FIFO send memory in RAM 412 to the communication interface for transmission or are read from the communication interface for reception and written to a FIFO receive memory in RAM 412 under the control of a software application running on CPU 411.

[0093] Each of a donor CU, a donor DU, an IAB node and a UE can be implemented in such a communication device / appliance 100.

[0094] Memory may include: - a read-only memory 407, indicated as ROM, for storing computer programs to implement methods according to one or more embodiments of the invention; - a random access memory 412, indicated as RAM, for storing the executable code of methods according to one or more embodiments of the invention, as well as registers adapted for recording variables and parameters necessary to implement methods according to one or more embodiments of the invention.

[0095] Optionally, the 400 communication device may also include the following components: - a data storage medium such as a hard disk drive, used to store computer programs for implementing methods of Petition 870250083679, dated 09 / 17 / 2025, page 34 / 130 22 / 81 in accordance with one or more embodiments of the invention; - a 405 disk drive to a 406 disk drive, the disk drive being adapted to read data from the 1106 disk or write data onto said disk; - a screen 409 to display decoded data and / or serve as a graphical user interface, via a keyboard 410 or any other input / output means.

[0096] In an example arrangement, the 413 communication bus provides communication and interoperability between the various elements included in or connected to the 400 communication device. The bus representation is not limiting, and in particular the central processing unit is operable to communicate instructions with any element of the 400 communication device directly or through another element of the 400 communication device.

[0097] The 406 disk can optionally be replaced by any information medium such as, for example, a rewritable or non-rewritable compact disk (CD-ROM), a ZIP disk, a USB key or a memory card; it is, in general terms, by an information storage medium that can be read by a microcomputer or by a microprocessor, integrated or not in the communication device, possibly removable and adapted to store one or more programs whose execution enables a method according to embodiments of the invention to be implemented.

[0098] The executable code may optionally be stored in read-only memory 407, on hard disk 404, or on a removable digital medium such as, for example, a disk 406, as described previously. According to an optional variant, the executable code of the programs may be received via the communication network 403, via interface 402, to be stored on one of the storage media of the communication device 400, such as hard disk 404, before being executed.

[0099] The central processing unit 411 can be adapted to control and guide the execution of instructions or portions of software code of Petition 870250083679, dated 09 / 17 / 2025, page 35 / 130 23 / 81 program or programs according to the invention, whose instructions are stored in one of the aforementioned storage devices. In the connection, the program or programs that are stored in non-volatile memory, for example, in hard disk 404 or read-only memory 407, are transferred to random access memory 412, which then contains the executable code of the program or programs, as well as registers to store the variables and parameters necessary to implement the invention.

[0100] In an example implementation, the communication device (appliance) is a programmable device / appliance that uses software to implement the invention. Instructions may be executed by one or more processors in the appliance, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable logic arrays (FPGAs), or other equivalent discrete or integrated logic circuitry to implement the invention for a network node (e.g., IAB node, IAB donor CU). Therefore, the term “central processing unit,” as used in the present invention, may refer to any of the above structures or any other suitable structure for implementing the techniques described in the present invention.Alternatively, the present invention can be implemented in hardware (for example, in the form of an Application-Specific Integrated Circuit or ASIC or other logic element).

[0101] Figure 5 illustrates an example of an IAB communication system (or IAB network system) in which embodiments and examples of embodiments of the present invention can be implemented. In an example implementation, the radio links between IAB nodes and between IAB nodes and IAB donor DUs (called BH radio links) are operated over the millimeter wave frequency band (i.e., above 30 GHz), which is highly sensitive to radio channel interference. An IAB network will also be referred to as an IAB topology or topology, and thus in this application, the terms IAB network and IAB topology and topology will be used interchangeably. Petition 870250083679, dated 09 / 17 / 2025, page 36 / 130 24 / 81

[0102] The IAB 500 communication system is composed of three IAB networks or IAB topologies 5001, 5002, and 5003, with each IAB topology comprising a set of IAB nodes (for example, the set may comprise a plurality of IAB nodes or at least one IAB node) and an IAB donor CU to control or manage the plurality of IAB nodes. The set of IAB nodes may include one or more IAB nodes, such as initiator IAB nodes that generate BAP packets and also relay or intermediate IAB nodes. Each of the IAB nodes communicates with at least one other IAB node over a wireless backhaul (BH) link. Although Figure 5 shows three IAB topologies 5001, 5002 and 5003, the present invention is not limited to three IAB topologies and can be implemented in an IAB communication system comprising more than two IAB topologies, with each topology comprising a set of IAB nodes and an IAB donor CU as discussed above.

[0103] As discussed above, each IAB node comprises a Mobile Termination (MT) or unit portion, controlled and configured by the IAB donor using RRC message sending as defined in 3GPP TS 38.331, and a Distributed Unit (DU) portion, controlled and configured by the IAB donor using F1-AP message sending as defined in 3GPP TS 38.473. For example, IAB node 510 comprises an MT or unit portion 511 and a DU portion 512.

[0104] The IAB 5001 topology includes donor CU IAB 501 (identified as donor CU in Figure 5) and its associated donor DU IAB 504 (identified as donor DU1 in Figure 5) and a plurality of IAB 510 and 520 nodes, similar to IAB 121 and 122 nodes.

[0105] The IAB 5002 topology includes donor CU IAB 502 (identified as donor CU 2 in Figure 5), its associated donor DUs IAB 505 (identified as donor DU1 2 in Figure 5) and donor DU IAB 506 (identified as donor DU2 2 in Figure 5), and a plurality of IAB nodes 530, 540, 550, similar to IAB nodes 121 and 122, and node IAB 570, which may be similar to mobile IAB node 123. All IAB nodes may be access nodes serving UEs such as UE 580 served by mobile IAB node 570. The IAB 5002 topology is transparent to UE 580 connecting to donor CU 502 via a unit or part of a DU. 572 Petition 870250083679, dated 09 / 17 / 2025, p. 37 / 130 25 / 81 of the mobile IAB node 570. Although Figure 5 shows a UE 580, it will be recognized that there will be a plurality of UEs connected to the network nodes of the IAB 500 communication system.

[0106] The IAB 5003 topology includes donor CU IAB 503 (identified as donor CU in Figure 5) and its associated donor DU IAB 507 (identified as donor DU13 in Figure 5) and an IAB 560 node, similar to IAB 121 and 122 nodes.

[0107] A wired IP backhaul network interconnects the IAB 501, 502, and 503 donor CUs and the IAB 504, 505, 506, and 507 donor DUs via wired backhaul 508. For example, this wired backhaul 508 consists of fiber optic cables.

[0108] The IAB 501 donor CU, IAB 504 donor DU, and IAB 510 and 520 nodes are part of the same IAB network or IAB 5001 topology, which is configured and managed or controlled by IAB 501 donor CU.

[0109] A donor CU IAB 502, donor DUs IAB 505 and 506 and nodes IAB 530, 540 and 550 are part of the same IAB network or IAB 5002 topology, which is configured and managed or controlled by an IAB 502 donor CU.

[0110] The IAB 503 donor CU, IAB 507 donor DU, and IAB 560 node are part of the same IAB network or IAB 5003 topology, which is configured and managed or controlled by IAB 803 donor CU.

[0111] Each IAB DU and IAB donor DU supports wireless communication in a coverage area(s) called a cell(s) (not shown in Figure 5). In other words, each IAB DU and IAB donor DU is associated with a cell(s). Wireless communication devices (such as UEs, or other IAB nodes) located in a cell can establish communication links with the node (i.e., IAB DU or IAB donor DU) serving the cell to communicate with other devices (e.g., other UEs, IAB nodes, servers providing Internet access, etc.) via the node.

[0112] It is assumed that mobile node IAB 570 initially had a single parent node IAB 520 and that node IAB 570 belongs to the IAB 5001 topology controlled by the donor CU IAB 501. The donor CU IAB is thus operating as the CU of Petition 870250083679, dated 09 / 17 / 2025, page 38 / 130 26 / 81 F1 termination donor (which may also be called an F1 termination IAB donor CU or F1 donor CU). During displacement and in view of its proximity to the IAB 5002 topology, in particular to the IAB 530 node when the mobile IAB 570 node is in the position shown by dashed lines in Figure 5, the mobile IAB 570 node may be able to establish a wireless BH link 5030 with the IAB 530 node. Such a BH link is possible for a stationary IAB node and is very likely to occur for a mobile IAB node such as the IAB 570 node moving, for example, in the direction of the IAB 5002 topology (shown by arrow 590 in Figure 5).

[0113] So, donor CU F1 501 may have decided to perform the migration of the MT 571 portion of IAB node 570 towards the IAB topology controlled by donor CU 502, which became the non-terminating donor CU F1 (which may also be called a non-terminating IAB donor CU F1 or non-F1 donor CU, or RRC terminating donor CU) to IAB node 570 (that is, the MT 571 portion of IAB node 570 is migrated towards the parent IAB node 530). For this purpose, donor CU F1 501 may have initiated the inter-CU Topology Adaptation procedure described in TS 38.401 V17.2.0 section 8.17.3.1 or section 8.17.3.2 (when node IAB 570 has descendant IAB nodes). As a result, node IAB 570 still belongs to the IAB 5001 topology with its F1 connection to donor CU 501, but its connection is now to donor CU2 502.Following this procedure, the IAB donor CU 501 can request the migration of backhaul traffic (e.g., user traffic, control traffic) related to the IAB node 570 toward the IAB topology 5002 (i.e., via the donor DU 505). In this case, the donor CU 501 triggers the IAB transport migration management procedure specified in TS 38.423 V17.2.0 section 8.5.2. In the IAB communication system, all traffic communicated over backhaul links uses an F1 interface (F1-C or F1-U) between an IAB donor CU and an IAB DU. Thus, the traffic or backhaul traffic that is offloaded or migrated is F1 traffic and may include control and user traffic.

[0114] Although mobile node IAB 570 is still moving in the direction shown by arrow 590, part MT 571 of node IAB 570 may then have been migrated Petition 870250083679, dated 09 / 17 / 2025, page 39 / 130 27 / 81 via the non-F1 donor CU 502 toward the parent IAB node 550, using the 5050 backhaul link between IAB node 550 and IAB node 570. For this purpose, the non-F1 donor CU 502 may have applied the intra-CU topology adaptation procedure described in TS 38.401 V17.2.0 section 8.2.3.1 (or section 8.17.3.2), resulting in a consecutive MT migration (or another MT migration to another IAB node) from IAB node 570 to a new single parent IAB node 550. Furthermore, IAB node 501 has its F1 connection to donor CU 501 and its RRC connection to donor CU2 502.

[0115] After being instructed to use donor DU 506 instead of donor DU 505 to route F1 traffic related to IAB node 570, donor CU 501 may request the migration of traffic related to IAB node 570 toward topology 5002. In this case, donor CU 501 triggers the IAB transport migration management procedure specified in TS 38.423 V17.2.0 section 8.5.2.

[0116] While still moving, this time in the direction of IAB 5003 topology controlled by donor CU 503, node IAB 570 can be in a position where a 5060 backhaul link with node IAB 560 can have better quality than the 5050 backhaul link with node IAB 550. In this way, donor CU 502 can apply the Inter-CU Topology Adaptation procedure described in TS 38.401 V17.2.0 section 8.17.3.1 or 8.17.3.2. Following this consecutive MT migration, node IAB 501 still belongs to the IAB 5001 topology, with its connection to donor CU 501, but its RRC connection is now with donor CU 503, and thus donor CU 503 becomes non-terminating donor CU F1 (or non-F1 donor CU, or RRC-terminating donor CU).However, donor CU 501 must be informed about the new non-F1 donor CU 503 for IAB node 570 and the new donor DU 507 to redirect unloaded traffic (F1 traffic, user traffic, and control traffic) through donor DU 507 instead of donor DU 506.

[0117] In all MT migration cases described above, UE 580 still connects to donor CU 501 via unit or part of DU 572 of node IAB. Petition 870250083679, dated 09 / 17 / 2025, p. 40 / 130 28 / 81 mobile 570. In the case of IAB node 570 having any child IAB node(s), such child IAB node still belongs to the IAB 5001 topology and is still fully controlled (through the F1 and RRC connections) by the donor CU 501.

[0118] In any migration state of the MT 571 portion of the IAB 570 node, regardless of whether the MT 571 portion of the IAB 570 node has migrated to the IAB 5002 topology or another IAB topology, and regardless of whether the IAB 570 node has a non-terminating F1 donor CU, and if so, whether it is the non-terminating F1 502 donor CU or another donor CU, the F1 501 donor CU may decide to perform the DU portion migration of the IAB 570 node. The reason for performing DU migration may be to reduce the processing load of the F1 501 donor CU, or because the IAB 570 node is geographically distant from the F1 501 donor CU and close to an area where there is no longer Xn connectivity between the F1 501 donor CU and a donor CU. Target donor. After the decision to execute the DU migration from node IAB 570, donor CU F1 501 must also decide towards which donor CU (which is called the target donor CU F1) the DU migration will be executed.This could be a DU migration toward the current F1 non-terminating donor CU (i.e., the default choice) if there is a current F1 non-terminating donor CU, in which case the F1 non-terminating donor CU becomes the target F1 donor CU, or to another target F1 donor CU. It is optimal for an IAB node to have the same donor CU controlling both the MT and the DU of the IAB node, as this avoids configuring transport migration from one IAB topology to another IAB topology for backhaul traffic to / from the IAB node. However, the reason for performing DU migration to a different donor CU from the current F1 non-terminating donor CU 502 might be to anticipate the IAB node's next displacement toward another IAB topology. For example, the IAB 570 node might be positioned so that a 5060 backhaul link with the IAB 560 node could have better quality than a 5050 backhaul link with the IAB 550 node.Since node IAB 560 belongs to the IAB 5003 topology controlled by donor CU 503, donor CU 503 can soon become the non-terminating F1 donor CU for node IAB 570 (after a new consecutive MT migration), and this is natural. Petition 870250083679, dated 09 / 17 / 2025, page 41 / 130 29 / 81 select donor CU 503 as the target F1 termination donor CU for IAB node 570. Additionally, if IAB node 570 is mobile and its trajectory is predictable (e.g., for a bus or train), donor CU F1 501 may be aware of a target F1 donor CU controlling cells through which IAB node 570 will soon connect to the network. For example, although the non-terminating donor CU F1 of IAB node 570 is donor CU 502, donor CU F1 may decide that the DU migration from IAB node 570 should be directly towards donor CU 503, since IAB node 570 can quickly cross over and not remain in the IAB 5002 topology controlled by donor CU 502. To avoid performing the DU migration towards donor CU 502 and instead perform the DU migration towards donor CU 503 will avoid protocol messages for the intermediate DU migration from IAB node 570.When DU migration is performed, handover of UEs served by IAB node 570 must also be performed. Therefore, not performing DU migration towards donor CU 502 will also prevent the intermediate handover of UEs served by IAB node 570 to donor CU 502, before a new DU migration and UE handover towards donor CU 503.

[0119] The procedure for performing a DU migration and UE handover towards a selected target F1 donor CU is described in more detail with reference to the subsequent figures.

[0120] Figure 6 illustrates an example of an IAB 600 node architecture that enables IAB node DU migration (DU migration) from a source IAB topology to a target IAB topology.

[0121] The IAB 601 node, which may be a mobile IAB node similar to the IAB 570 node, is composed of an MT-IAB part or IAB-MT unit 610 (like the MT or MT 571 part of the IAB 570 node in Figure 5), an IAB-DU1 part or unit 611, and an IAB-DU2 part or unit 612. IAB-DU1 and IAB-DU2 are two logical DU entities (also called logical DUs) that share the same hardware for the BAP, RLC, and MAC layers. In one instance, they share the same physical layer (i.e., the same hardware resources), while in another instance they are Petition 870250083679, dated 09 / 17 / 2025, page 42 / 130 30 / 81 are based on separate physical layers. In the DU migration of IAB node 601, both logical DUs are active: one logical DU terminates the F1 interface with a source F1 donor CU (such as donor CU 501 in Figure 5), while the other logical DU terminates the F1 interface with a target F1 donor CU (such as donor CU 502 or 503 in Figure 5). Otherwise (i.e., when DU migration should not be performed), only one logical DU is sufficient for IAB operations. As an example and with reference to the IAB communication system in Figure 5, the terminating F1 donor CU of IAB node 601 (i.e., IAB node 570) can be donor CU 501, which is thus operating as the source F1 donor CU. The donor F1 CU from source 501 can identify the donor IAB 503 CU as a target donor F1 CU.Alternatively, for an IAB node that is connected to the parent IAB node or parent IAB donor DU of the IAB 5001 topology managed by the donor CU 501 as the terminating donor CU F1 and that is stationary but is in proximity to or near one or more IAB nodes in a neighboring IAB topology, such as IAB 5002 topology, the source donor CU F1 501 may determine that the donor CU IAB 502 is a suitable target donor CU F1 when the source donor CU F1 501 determines (for example, based on signal measurements performed at the IAB node on radio signals received at the IAB node from all IAB nodes in proximity to the IAB node and which may include IAB nodes in the neighboring IAB topology 5002) that the IAB node can soon connect to an IAB node in the neighboring IAB topology 5002.

[0122] Before DU migration, a UE 602 (similar to UE 580 in Figure 5) is, for example, connected to the donor CU F1 from source 501 via logical DU IAB-DU1 611 with access link 621 in the cell served by logical DU IAB-DU1 611, and logical DU IAB-DU2 612 is deactivated. During DU migration, the logical DU IABDU2 612 is activated and connects to the target F1 donor CU 502, to which UE 602 can also connect via the logical DU IAB-DU2 612 with link 622 in the cell served by the logical DU IAB-DU2 612. The activation of the logical DU IAB-DU2 612 can be triggered by the source F1 donor CU and executed with the procedures described with reference to Figures 10a and 10b. After the handover of Petition 870250083679, dated 09 / 17 / 2025, page 43 / 130 31 / 81 UE 602 is completed from a cell controlled by the logic DU IAB-DU1 611 to a cell controlled by the logic DU IAB-DU2 612, the logic DU IAB-DU1 611 can be deactivated. Deactivation can be triggered by the donor CU F1 from source 501 with the procedure described with reference to Figure 10c, after detection of the completion of the handover for all UEs serviced by IAB-DU1 611.

[0123] Figure 7 is a simplified schematic diagram 700 illustrating some example message flows, to perform DU migration from an IAB node, with or without (multiple) MT migration(s), and which includes the configuration of data path(s) for packets routing between the target F1 donor CU and the IAB node through an IAB topology controlled by the non-F1 donor CU / RRC terminating donor CU of the IAB node.

[0124] This figure 7 shows a UE 708 as UE 580, a source F1 donor CU 703 as donor CU 501, a target F1 donor CU 707 as donor CU 503, a non-F1 donor CU 709 as donor CU 502, the core network (5GC) 702 as core network 110 of figure 1. This figure 7 also shows an IAB node 701 which may be a mobile IAB node similar to the IAB node 570 composed of an MT part or IAB-MT unit 704, a DU part or IAB-DU1 unit 705 (e.g., source or first logical DU entity or DU) and a DU part or IAB-DU2 unit 706 (e.g., target or second logical DU entity or DU). Each of the first 705 and second 706 logical DU entities serves one or more cells that are identified by identifiers (e.g., Physical Cell Identifier (PCI), New Radio Cell Group Identifier (NCGI)).The IAB-DU1 705 cell(s) are identified by different values ​​(e.g., Physical Cell Identifier (PCI), New Radio Cell Group Identifier (NCGI)) compared to the values ​​for the identifiers for the IAB-DU2 706 cell(s). IAB-DU1 705 and IAB-DU2 706 are two logical DU entities that share the same hardware for the BAP, RLC, and MAC layers. In one instance, they share the same physical layer (i.e., the same hardware resources), while in another instance they rely on separate physical layers. The non-F1 709 donor CU for the IAB 701 node may be the CU itself. Petition 870250083679, dated 09 / 17 / 2025, page 44 / 130 32 / 81 donor F1 source 703 (e.g., donor CU 501) if IAB-MT 704 has not been migrated. The non-F1 donor CU for node IAB 701 can be target donor F1 CU 707 (e.g., donor CU 503) if IAB-MT 704 was previously migrated toward target donor F1 CU 707, or another donor CU (e.g., donor CU 502) if IAB-MT 704 was previously migrated toward that other donor CU (e.g., donor CU 502).

[0125] At the start of the flow, node IAB 701 belongs to the IAB source topology controlled by donor CU F1 of source 703. UE 708 is served by node IAB 701 through an IAB-DU1 cell 705 (for example, the DU of node IAB 701 has an active IAB-DU1 705 having an F1 connection with donor CU IAB F1 of source 703), while the logical IAB-DU2 706 is inactive. User data in the downstream direction is provided by 5GC 702 to the source donor CU F1 703 via carrier 710, then the data is transmitted to the logical DU IAB-DU1 705 of node IAB 701 via backhaul carrier 711 and finally to UE 708 via data radio carrier 712. Backhaul carrier 711 can be established in the source IAB topology controlled by the source donor CU F1 703, or in the IAB topology controlled by the non-F1 donor CU F1 709 of node IAB 701 (if IAB-MT 704 was previously migrated towards that non-F1 donor CU).User data in the upstream direction (not shown in the figure) is transmitted via similar carriers in the opposite direction.

[0126] The IAB-MT 704 can send measurement reports (not shown in Figure 7) to its non-terminating donor CU F1 708 as the result of measurements regularly performed by IAB-MT 704 on signals received from the server cell and one or more target cells, such as the Synchronization Block (SSB) signals transmitted in the server cell and target cells. The non-terminating donor CU F1 will be the terminating donor CU F1 for the IAB node (e.g., source donor CU F1 703) if the MT has not migrated from its terminating donor CU F1. Target cells can be cells neighboring the server or source cell (i.e., the current server cell). After IAB-MT 704 discovers at least one SSB that meets predefined criteria (e.g., a power). Petition 870250083679, dated 09 / 17 / 2025, p. 45 / 130 33 / 81 received that exceeds a predefined threshold), a measurement report can be generated and transmitted to provide radio link quality information to different cells in the vicinity of node IAB 701. The identity of each cell is included in the measurement report to allow the non-F1 donor CU if IABMT 705 has been migrated, or the F1 termination donor CU 703 if IABMT 704 has not migrated, to identify the target donor CU associated with the cell. In effect, the identification of a donor CU can be deduced from the Physical Cell Identity (PCI) broadcasted on each cell managed by that donor CU in a synchronization signal and / or from the New Radio Cell Group Identifier (NCGI) also broadcast on each cell managed by that donor CU in a System Information Block (SIB) message. PCI and / or NCGI can be reported by node IAB 701 in the measurement report.

[0127] Based on the measurement reports received, the non-F1 709 donor CU if IAB-MT 704 has been migrated, or the F1 703 termination donor CU if IAB-MT 704 has not been migrated, may detect that the IAB 701 node receives radio signals in a target cell from a target parent IAB node with better quality than in the source server cell. The non-F1 709 donor CU if IAB-MT 704 has been migrated, or the F1 703 termination donor CU if IAB-MT 704 has not been migrated, you may decide to apply a procedure to perform the migration of IAB-MT 704 towards a target parent IAB node that belongs to the same IAB topology (intra-CU topology adaptation), or to another IAB topology (inter-CU topology adaptation).In either case, the F1 donor CU from source 703 will be informed about this MT migration by the non-F1 donor CU 709 if IAB-MT 704 has been migrated, or the F1 donor CU from source 703 will be informed once it has decided to execute MT migration directly from the measurement reports received from node IAB 701 if IAB-MT 704 has not been migrated, and this information can be used by the F1 donor CU from source 703 to trigger a DU migration from node IAB 701. In another example, the non-F1 donor CU 709 can relay the information in the measurement reports received from node IAB 701 to the F1 donor CU from source 703. In this way, the F1 donor CU from... Petition 870250083679, dated 09 / 17 / 2025, p. 46 / 130 34 / 81 source 703 can base its decision for DU migration from IAB node 701 directly from these measurement reports relayed by non-F1 donor CU 709.

[0128] In this way, the F1 donor CU of source 703 determines that the DU of IAB node should be migrated from the IAB topology (also called the source IAB topology) of the F1 donor CU of source 703 to another IAB topology (also called the target IAB topology) of a target IAB donor CU. The determination can be based on the determination that a migration of an IAB node MT towards a new parent IAB node has been completed.Another example of a trigger event to determine that the IAB node's DU should be migrated might include the decision to migrate the DU being based on the detection of a MT migration from one IAB topology (e.g., first IAB topology) towards another IAB topology (e.g., second IAB topology) and on a known (predefined) IAB node path indicating to the source donor CU F1 that the MT will subsequently be migrated to yet another IAB topology (e.g., third IAB topology). In this case, to avoid signaling DU migration / UE handover messages towards another IAB topology (e.g., second IAB topology), the DU is migrated directly towards yet another IAB topology (e.g., third IAB topology). Another example of a trigger event to determine that the IAB node's DU should be migrated might include the processing load level being detected above a predefined threshold in the source donor CU F1.Then DU migration is triggered and the choice of target F1 donor CU is based on the processing load of other donor CUs connected to the source F1 donor CU.

[0129] After the decision or determination by the source donor CU F1 703 to execute the DU migration from IAB node 701 towards another IAB topology managed by another donor CU that becomes the target donor CU F1 707, the first step 720 corresponds to sending a request to IAB node 701 to establish a new F1 connection between the target donor CU F1 707 and the mobile IAB node 701. This may require activation of the second logical IAB-DU2 706 on the mobile IAB node 701 and thus the first step 720 may include the activation of the second Petition 870250083679, dated 09 / 17 / 2025, page 47 / 130 35 / 81 Logical DU IAB-DU2 706 on mobile IAB node 701. This operation is performed using, for example, the procedures described with reference to Figures 10a and 10b. In particular, the message sent by the source donor CU F1 703 to IAB node 701 for the activation of IAB-DU2 706 (e.g., 1003 in Figure 10a) may include identification information to identify the target donor DU, such as the TNL address (i.e., IP address) of the target donor CU F1 707, so that a new F1 connection or F1 association (e.g., an F1AP interface connection) can be established with target donor CU 707 (between IAB-DU2 706 and target donor CU 707). If the address of the target F1 donor CU is not included in the activation request, then by default, and in the case where IAB-MT 704 has been migrated to a non-F1 donor CU 709, the non-F1 donor CU 709 is considered to be the target F1 donor CU.In this case, node IAB 701 has already been informed of the identity (e.g., TNL address / IP address) of the target F1 donor CU when IAB-MT 704 was migrated to non-F1 donor CU 709. In other words, source F1 donor CU 703 can send identifying information to identify target F1 donor CU 707 if IAB-MT 704 has been migrated to a non-F1 donor CU 709 that is different from (not equal to) target F1 donor CU 707. Alternatively, source F1 donor CU 703 can send identifying information to identify non-F1 donor CU 709 as the target IAB donor CU.

[0130] After determining that the DU of node IAB 701 should be migrated and after IABDU2 706 has been activated, then IAB-DU2 706 can send an F1 Establishment Request message (e.g., 1013 in Figure 10b) to the target F1 donor CU 707 to request the establishment of the F1 connection between node IAB 701 and target F1 donor CU 707. This message can include identifying information to identify the source IAB donor CU, such as the TNL address (i.e., the IP address) and / or the identifier (i.e., Global NG-RAN Node ID as specified in TS 38.423 V17.2.0 section 9.2.2.3) of the source F1 donor CU 703 of node IAB 701. The destination address of the F1 Establishment Request message is the donor CU. F1 target 707, and when that IP packet is Petition 870250083679, dated 09 / 17 / 2025, page 48 / 130 The 36 / 81 signal received by the donor DU on path F1 to node IAB 701 can be routed on the wired backhaul (508 in Figure 5) to the target donor CU F1 707. For example, in an example where node IAB 701 is node IAB 570 in Figure 5, which is connected to node IAB 550 via backhaul link 5050, and where the MT (MT 571, which corresponds to IABMT 704 in Figure 7) of node IAB 570 has been migrated to non-F1 donor CU 502, and donor CU IAB 501 is the source donor CU F1, the path from F1 between donor CU F1 501 to node IAB 570 uses donor DU 506. In the case where donor CU IAB 503 has been identified (by donor CU F1 50) as the target donor CU F1 (e.g., target donor CU F1 707), the F1 establishment request message to the target donor CU F1 (e.g., donor CU 503) is sent through IAB nodes 550, 540 and then to donor DU 506 from where it can be routed on the wired backhaul (508 in figure 5) to target donor CU F1 503.In the F1 establishment response (e.g., 1014 in Figure 10b), the target F1 donor CU 707 (e.g., donor CU 503 in the example described above with reference to Figure 5) can request that IAB-DU2 706 activate new cell(s) with associated identifiers (CPI, NCGI). Typically, the DU activates / deactivates cell(s) under the control of the donor CU that is controlling the DU. See, for example, TS 38.473 section 8.2.3.2.

[0131] After the procedure described with reference to figure 10b, and using for example the procedure described with reference to figure 9a, the target donor CU F1 707 (for example, in configuration update message 903) can inform the source donor CU F1 705 about the activation of new cell(s) from IAB-DU2 706 of node IAB 701.

[0132] The next step 730 consists of handing over UEs (e.g., UE 708 in Figure 7) served by node IAB 701, from the cell(s) of the first logical DU IAB-DU1 705 to the cell(s) of the second logical DU IAB-DU2 706. This procedure can be the standardized procedure described in TS 38.300 section 9.2.3.2 (handover), or the standardized procedure described in TS 38.300 section 9.2.3.4 (conditional handover). In one example, to trigger the handover of UE 708, the donor CU F1 of source 703 sends a REQUEST message. Petition 870250083679, dated 09 / 17 / 2025, page 49 / 130 37 / 81 HANDOVER to the target donor CU F1 707 including the necessary information related to UE 708 for handover (e.g., identification information identifying the UE, UE context information such as security context (e.g., security parameters such as security key, UE security capabilities), metering configuration, radio configuration (e.g., UE radio capability), carrier information, etc.). TS 38.423, section 9.1.1.1 provides details regarding the content of a REQUEST HANDOVER message. After an admission control step in which the target donor CU F1 707 determines whether the donor CU can accept the handover of UE 708, when the target donor CU F1 707 accepts the request, the target donor CU F1 707 sends a handover confirmation message to the source donor CU F1 705, including configuration information for UE 708 for the handover.The configuration may include radio configuration information indicating the radio configuration to be used by UE 708 to connect to the second logical DU IAB-DU2 706 of node IAB 701 in an identified target cell of the second logical DU IAB-DU2 706 (e.g., the radio configuration may include frequency, radio carrier configuration, etc.). The handover confirmation may include an identifier for each of one or more new cells (e.g., the target cell(s)) that were activated in the second logical DU IAB-DU2 706. The donor CU F1 of source 705 then sends this configuration information to UE 708 via node IAB 701 in an RRC Reconfiguration message, including the identifier of the target cell of IAB-DU2 706 to which UE 708 should connect. The RRC reconfiguration message (specified in TS 38.331) is incorporated into an F1 DL RRC MESSAGE TRANSFER message (specified in TS 38.473), sent to IAB-DU1 705 and relayed by IAB-DU1 705 to UE 708. Upon receiving this configuration information, UE 708 executes a random access procedure on the indicated target cell of IAB-DU2 706 to obtain uplink resources, and then to transmit a complete RRC Reconfiguration message to the target donor CU F1 707. The complete RRC Reconfiguration message (specified in TS 38.331) is sent to IAB-DU2 706, and. Petition 870250083679, dated 09 / 17 / 2025, page 50 / 130 38 / 81 is then incorporated into an F1 UL RRC MESSAGE TRANSFER message (specified in TS 38.473), sent to the target F1 donor CU 707. The source F1 donor CU 705 can be informed of the completion of the UE handover 708 via the HANDOUVEL SUCCESS message (specified in TS 38.423) received from the target F1 donor CU 707.

[0133] After the handover of all UEs served by IAB-DU1 705 from node IAB 701 is completed, the donor CU F1 from source 703 can deactivate the logical DU IABDU1 705 from mobile node IAB 701 through the procedure described with reference to figure 10c. This is generally represented by procedure 735 in figure 7.

[0134] Also, the F1 donor CU from source 705 can release traffic (user traffic, control traffic) related to UEs that were served by IAB node 701 through IAB-DU1 705 and the F1 donor CU from source 705. If the traffic was offloaded in an IAB topology controlled by the non-F1 donor CU 709 (for example, when the MT of IAB node 701 is migrated to the non-F1 donor CU 709), the F1 donor CU from source 705 can apply the IAB transport migration management procedure specified in TS 38.423 V17.2.0 section 8.5.2 to request the release of traffic to the non-F1 donor CU 709. This is generally represented by procedure 735 in Figure 7.

[0135] Finally, the target F1 donor CU 707 must establish the data path(s) to / from the migrated IAB node 701, either in its own topology if there is a backhaul path to reach IAB node 701 in the IAB topology controlled by the target F1 donor CU 707 (i.e., the target F1 donor CU 707 is a non-terminating F1 donor CU for IAB node 701 since IAB=MT 704 was previously migrated to the target F1 donor CU 707), or through the IAB topology of the non-F1 donor CU 709 of IAB node 701 if there is no backhaul path to reach IAB node 701 in the IAB topology controlled by the target F1 donor CU 707 (i.e., IAB-MT 704 and IAB-DU2). 706 are connected to different donor CUs). In the last mentioned case, the target F1 donor CU 707 can trigger the transport migration and route change procedure 731, including the traffic migration request to the non-F1 donor CU 709 from the IAB node 701. Petition 870250083679, dated 09 / 17 / 2025, p. 51 / 130 39 / 81 (for example, through the IAB transport migration management procedure specified in TS 38.423 V17.2.0 section 8.5.2), and the path change procedure towards the core network 702. As an example of the last mentioned case with reference to figure 5, node IAB 701 is node IAB 570 from figure 5 connected to node IAB 550 via backhaul link 5050 and where the MT (MT 571 which corresponds to IAB-MT 704 in figure 7) of node IAB 570 was migrated to non-F1 donor CU 502 and donor CU IAB 501 is donor CU F1.When the DU (DU 572 which corresponds to IAB-DU2 706 in Figure 7) of node IAB 570 has been migrated to target donor CU 503, and thus has an F1 connection with donor CU F1 503, but MT 571 remains connected through its RRC connection with non-F1 donor CU 502 (its RRC connection), the data path(s) or backhaul path(s) to / from node IAB 570 is established in the IAB 5002 topology controlled by donor CU IAB 502 (i.e., a backhaul path to node IAB 570 through donor DU IAB 506, nodes IAB 540 and 550) by executing the traffic migration management procedure. Also, the target donor CU 503 can execute a path switching procedure towards the core network 702 to request the distribution of user data related to UE 708 / 580. For example, the target donor CU 503 can execute the path switching handshake procedure described in 3GPP TS 38.413 v17.2.0 section 8.4.4.

[0136] After the UE handover 708 and the establishment of the new data paths has been executed (731), the downstream user data is transmitted by the core network 702 to the target donor CU F1 707 via the carrier 740, then it is transmitted to the logical DU IAB-DU2 706 of node IAB 701 via the backhaul carrier 741 and finally to the UE 708 via the data radio carrier 742. The backhaul carrier 741 can be established in the IAB topology controlled by the target donor CU F1 707, or in the IAB topology controlled by the non-F1 donor CU 709 of node IAB 707 (for example, depending on whether IAB-MT 704 and IAB-DU2 706 of node IAB 701 are connected to different donor CUs). User data in the upstream direction (not shown in the figure) is transmitted via similar carriers. Petition 870250083679, dated 09 / 17 / 2025, p. 52 / 130 40 / 81 in the opposite direction.

[0137] If the target F1 donor CU 707 is unable to accommodate the IAB node DU (IAB-DU2 706) and related traffic from the UEs served as UE 708 (due to some lack of processing resources, or some lack of network / radio resources), the target F1 donor CU 707 should be allowed to reject or revoke the DU migration (and thus the subsequent handover of UEs). The target F1 donor CU may also be allowed to partially accept the DU migration, for example, by accepting a limited amount of traffic or a limited number of UEs served.

[0138] Examples of methods, according to one or more embodiments of the present invention, that enable a target donor CU to partially accept, reject, or revoke a request for DU migration from an IAB node will now be described. Although the following methods / devices are described primarily with respect to a mobile IAB node, it will be recognized that the invention is not intended to be limited to mobile IAB nodes. The methods according to one or more embodiments of the present invention may apply to stationary IAB nodes, for example, that are on the edge of an IAB topology and in the vicinity of or near one or more IAB nodes in a neighboring IAB topology.

[0139] In general terms, methods (and devices configured to execute such methods) for use in managing DU migration from an IAB node DU, from a source IAB topology managed by a source IAB donor CU to a target IAB topology managed by a target IAB donor CU according to one or more embodiments of the invention comprise receiving, in the target IAB donor CU, a message indicating a DU migration from the IAB node DU from the source IAB donor CU to the target IAB donor CU. The message sent to the target IAB donor CU may be sent by the source IAB donor CU (e.g., migration request 811, 913 as discussed below with reference to Figures 8 and 9b) or the message may be sent by the IAB node (e.g., F1 establishment request 814, 1013 as Petition 870250083679, dated 09 / 17 / 2025, p. 53 / 130 41 / 81 discussed below with reference to Figures 8 and 10b). The message is sent after a determination that the IAB node should be migrated to the target IAB donor CU. For example, the source IAB donor CU may determine that there is a need (e.g., a trigger event for migration has occurred) to migrate the IAB node's DU to another IAB donor CU and may then decide to which IAB donor CU the DU migration will be performed. Examples of reasons and trigger events for determining that the IAB node's DU should be migrated were discussed above with respect to Figure 7. The message sent to the target IAB donor CU may include context information regarding the context of the DU migration to help the target IAB donor CU decide whether to accept or reject the request for IAB node DU migration or, in some cases, partially accept the IAB node DU migration.

[0140] In response to the received message (or after receiving the message), the target IAB donor CU determines whether to accept (fully), partially accept, or reject the IAB node's DU migration. The decision may be based, for example, on whether the target IAB donor CU is capable of accommodating the IAB node (e.g., all traffic associated with the IAB node) and the traffic related to all UEs served by the IAB node (e.g., based on the resources available in the target IAB donor CU, such as processing resources and / or network / radio resources). The target IAB donor CU sends a response indicating that the target IAB donor has determined to accept, partially accept, or reject the IAB node's DU migration.As an optimization, the target IAB donor CU may partially accept the DU migration by accepting a subset or some of the traffic related to the UEs served by the IAB node (e.g., by accepting at least one of one or more traffic profiles associated with the IAB node) and / or by accepting a subset or some of the UEs served by the IAB node (e.g., by accepting at least one of the UEs served by the IAB node). The decision to partially accept may be based on a comparison of available resources, such as processing resources and / or network resources, in the target IAB donor (and in the controlled IAB topology (i.e., the topology controlled by the target IAB donor), with the resources, such as network / processing resources, required by the profile(s). Petition 870250083679, dated 09 / 17 / 2025, p. 54 / 130 42 / 81 traffic to be migrated and / or in comparison of the number of additional UEs that can be connected to the target IAB donor CU with the number of UEs served by the IAB node. If the available radio / processing resources are not sufficient to accommodate all the traffic (e.g., including all traffic associated with the traffic profile(s) to be migrated) and / or all served UEs, the target IAB donor CU may select a subset or some of the traffic profile(s) and / or a limited number or a subset or some of the served UEs to support. The selection criterion may be related to QoS parameters indicating some priority between traffic profiles / UEs, and the target IAB donor CU may choose to accept the traffic profiles / UEs with the highest priority.For a served UE, one criterion could be the UE's onboard status relative to the IAB node: that is, whether the UE is physically inside a moving vehicle equipped with the IAB node or otherwise encircling and moving with the IAB node. Indeed, if the handover of an onboard UE towards the target IAB donor CU for DU migration is rejected, then that UE will have been delivered to another cell (controlled by another CU) and will lose the benefit of the mobile cell served by the IAB node. One advantage of partially accepting a DU migration is to give the source donor CU a chance to keep some UEs with the highest priority connected to the IAB node's mobile cell, especially when there is an alternative choice to a target IAB donor CU different from the target IAB donor CU.

[0141] In response to or after determining that it should reject (or partially accept) the DU migration, the target IAB donor CU sends a response (e.g., a message) indicating that the target IAB donor CU has rejected (or partially accepted) the request for DU migration to the target IAB donor CU. The message sent by the target IAB donor CU may be sent to the source IAB donor CU (e.g., migration response 812, 914 as discussed below with reference to Figures 8 and 9b or a configuration update message 903 sent based on F1 establishment as discussed below with reference to Figure 9a) or the message may be sent to the IAB node (e.g., F1 establishment response 815, 1014 as discussed below) Petition 870250083679, dated 09 / 17 / 2025, p. 55 / 130 43 / 81 with reference to figures 8 and 10b). In the event that the DU migration is rejected or revoked by the target IAB donor CU, the migration process is not executed (e.g., the source IAB donor CU does not send a DU activation request 813) or, if it has already been initiated, the execution of the migration process is canceled. In the case of partial acceptance, the response may include the identification of the portion of the traffic that is accepted (e.g., the index(es) of the accepted traffic profile(s) that were accepted, and / or the number of UEs that are accepted.

[0142] In response to or after determining (fully or partially) to accept the DU migration, the target IAB donor CU sends a message indicating that the target IAB donor CU has accepted (fully or partially) the DU migration and in response, the source IAB donor CU may initiate the migration process which is then executed or continues to execute the migration process (e.g., the migration process steps described above with reference to Figure 7 are executed). In the case of partial acceptance, the source IAB donor CU may not execute the migration process and in such a case, the source IAB donor CU may send a new request later or select another target IAB donor CU.The message sent by the target IAB donor CU can be sent to the source IAB donor CU (e.g., migration response 812, 914 as discussed below with reference to figures 8 and 9b or a configuration update message 903 sent based on F1 establishment as discussed below with reference to figure 9a) or the message can be sent to the IAB node (e.g., F1 establishment response 815, 1014 as discussed below with reference to figures 8 and 10b).

[0143] After determining to (fully or partially) accept the DU migration, the target IAB donor CU may determine to revoke the DU migration from the IAB node to the target IAB donor CU and may send a revocation response indicating that the target IAB donor CU has determined to revoke the DU migration from the IAB node to the target IAB donor CU. For example, in the case of acceptance or partial acceptance of the DU migration request, and during the execution of the DU migration process together with the served UEs or even after the Petition 870250083679, dated 09 / 17 / 2025, p. 56 / 130 44 / 81 Once the DU migration process has been completed or terminated, the target IAB donor CU detects that it is no longer able to accommodate the migrated IAB node and the served UEs, so the target IAB donor CU can revoke the DU migration. The revocation response indicating that the target IAB donor CU has determined the revocation of the DU migration can be sent to the source IAB donor CU. For example, the procedure described with reference to Figure 9b can be used to signal the revocation to the source IAB donor CU. The revocation response indicating that the target IAB donor CU has determined the revocation of the DU migration can be sent to the IAB node. For example, the target IAB donor CU can also take the opportunity of the F1 establishment procedure described with reference to Figure 10b to revoke the previously accepted DU migration. Upon receiving the message indicating the revocation, the DU migration process is interrupted.If some UEs have already been delivered to the target IAB donor CU, these UEs are returned to the source IAB donor CU. If the second logical DU of the IAB node has already been activated, it is removed by the target IAB donor CU using the procedure described with reference to Figure 10c.

[0144] The message sent by the target IAB donor CU to reject or revoke a DU migration includes a cause statement to indicate the reason for the rejection or revocation of the DU migration request to the target donor CU. The message sent by the target IAB donor CU to partially accept a DU migration may include a cause statement to indicate the reason for the partial acceptance of the DU migration request to the target donor CU (e.g., overload). It may also include an identification of the portion of the traffic that is accepted (e.g., the index(es) of the accepted traffic profile(s) and / or the number of UEs that are accepted).

[0145] After partial acceptance, rejection or revocation, the source IAB donor CU may decide to postpone the DU migration and make a new attempt later or may decide to select another target donor CU.

[0146] Thus, the method / device according to one or more embodiments of the present invention enables the target IAB donor CU to reject or Petition 870250083679, dated 09 / 17 / 2025, p. 57 / 130 45 / 81 revokes the DU migration (and thus the subsequent handover of UEs served by the IAB node) if the target IAB donor CU is unable to accommodate a portion or all of the traffic related to the served UEs (due to a lack of processing resources or a lack of radio / network resources). In the case of partial acceptance, the source IAB donor CU performs the handover towards the target IAB donor CU (for DU migration) for the UEs for which the traffic was accepted and / or for a number of UEs accepted by the target IAB donor CU. The other UEs are delivered towards a different CU (which can be any base station, not just an IAB donor CU).

[0147] Figure 8 is a simplified diagram illustrating example message flows, according to one or more embodiments of the invention, to enable a target F1 termination donor CU to partially accept or reject DU migration from an IAB node. For example, the message flows shown in Figure 8 enable a target IAB donor CU (e.g., target F1 termination donor CU) to determine whether to (fully or partially) accept or reject DU migration from an IAB node to the target IAB donor CU and, in response to or after determining whether to fully or partially accept or reject the DU migration, inform the source IAB donor CU (e.g., source F1 termination donor CU) that the target IAB donor CU has fully or partially accepted or rejected the request for DU migration.

[0148] Figure 8 shows a source F1 donor CU 803 as donor CU 501, a target F1 donor CU 807 as donor CU 503, and an IAB node 801 which may be a mobile IAB node such as IAB node 570 composed of an MT part or IAB-NT unit 804, a DU part or IAB-DU1 unit 805 (e.g., source or first logical DU entity or DU) and a DU part or IAB-DU2 unit 806 (e.g., target or second logical DU entity or DU). Each of the first 805 and second 806 logical DU entities serves one or more cells. IAB-DU1 805 and IAB-DU2 806 are two logical DU entities that share the same hardware for the BAP, RLC, and MAC layers. In one example, they share the same physical layer (that is, the same resources of Petition 870250083679, dated 09 / 17 / 2025, p. 58 / 130 46 / 81 hardware), while in another example they rely on separate physical layers.

[0149] At the beginning of the flow, node IAB 801 belongs to the source IAB topology controlled by donor CU F1 of source 803. According to one embodiment of the invention, after the decision or determination by donor CU F1 of source 803 to perform the DU migration of node IAB 801 towards the IAB topology managed by donor CU F1 target 807, the first step corresponds to sending a request to request DU migration from node IAB 801 from donor CU F1 of source 803 to donor CU F1 target 807. The request can be sent as a DU migration request message 811 by donor CU F1 of source 803 to donor CU F1 target 807. Message 811 is used to inform donor CU F1 target 807 that it has been selected by the donor CU. F1 from source 803 to be the new F1 termination donor CU for IAB node 801.Message 811 may be followed by a response, such as the DU migration response message 812, sent by the target F1 donor CU 807 to the source F1 donor CU 803 to (fully or partially) accept the DU migration or reject the DU migration. The decision to (fully or partially) accept or reject may be based on the current processing resource load of the target F1 donor CU 807, or on the current network resource load (wired and / or wireless backhaul) in the IAB topology managed by the target F1 donor CU 807. To assist the decision by the target F1 donor CU 807, the request, such as the DU migration request message 811, may include context information relating to or associated with the context of the DU migration to the target F1 donor CU 807. The context information may include some or all of the following information, which may be referred to as the context of the DU migration. - Identification information to identify the IAB node. The identification information may include the IAB node identifier 801 as shown by the F1 donor CU of source 803, with the F1 Termination IAB donor UE XnAP information element identifying the MT 804 of IAB node 801, or with the element of Petition 870250083679, dated 09 / 17 / 2025, p. 59 / 130 47 / 81 gnNB-DU ID information identifying the first logical DU IABDU1 805 of node IAB 801. The identification information may additionally or alternatively include the identifier of node IAB 801 as known by the IAB donor CU serving MT 804 of node IAB 801, if MT 804 has been migrated to a non-F1 donor CU (or RRC termination donor CU) and if that non-F1 donor CU is different from the target Fe donor CU 807, with the non-F1 termination donor IAB UE XnAP information element identifying MT 804 of node IAB 801. - Identification information to identify the IAB donor CU serving MT 804 of IAB node 801, if MT 804 has been migrated to a non-F1 donor CU and if that non-F1 donor CU is different from the target F1 donor CU 807, for example, with the TNL address (i.e., the IP address) and / or the identifier (i.e., Global NG-RAN Node ID as specified in TS 8.423 V17.2.0 section 9.2.2.3) of the non-F1 donor CU of IAB node 801, - An indication related to the priority for considering the DU migration request. For example, priority information to indicate a priority level for the DU migration request. It can be a value within a predefined range (e.g., from 1 to 5), where a low value indicates that DU migration is not critical for the 803 source F1 donor CU, while a high value indicates that DU migration is critical for the 803 source F1 donor CU, for example, due to some load issue associated with processing or network / radio resources in the IAB topology of the source F1 donor CU. - An indication related to the user traffic profile associated with IAB node 801 (e.g., traffic profile information to indicate a user traffic profile associated with the IAB node), including QoS (Quality of Service) parameters, as defined in TS. Petition 870250083679, dated 09 / 17 / 2025, pp. 60 / 130 48 / 81 38.423 V17.2.0 section 9.2.2.81. Each traffic profile can be identified by a traffic index. - An indication related to the transmission capacity of user traffic associated with IAB node 801 (e.g., traffic profile information to indicate a traffic profile of the transmission capacity of user traffic associated with IAB node), both upstream (from IAB node) and downstream (towards IAB node 0). - The number of UEs, such as UE 580, served by IAB node 801 that would be delivered to the target F1 donor CU 807 along with the DU migration from IAB node 801. Additionally, the number of UEs on board can be indicated (i.e., UEs physically inside the vehicle equipped with the IAB node or otherwise surrounding and moving with the IAB node).

[0150] F1-terminated IAB donor EU XnAP ID and F1-terminated IAB donor EU XnAP ID correspond to an NGRAN node EU XnAP ID as specified in TS 38.423 section 9.2.3.16.

[0151] In the case of partial acceptance or rejection of the DU migration request, the target F1 donor CU 807 may include the cause of the partial acceptance or rejection in the DU migration response message 812. The cause may be, for example, a lack of processing resources or a lack of radio / network resources. Each possible cause may be associated with a predefined value, as, for example, specified in TS 38.423 V17.2.0 section 9.2.3.2. In the case of partial acceptance, the response may include the index of the traffic profile that is accepted and / or the number of UEs that are accepted.

[0152] Messages 811 and 812 may correspond to the procedure described with reference to Figure 9b, where message 811 corresponds to message 913 and message 812 corresponds to message 914 in Figure 9b. These are exchanged between the source donor CU F1 803 and the target donor CU F1 807 before the migration process or procedure described with reference to Figure 7 is executed, which is executed only if the target donor CU F1 807 has (fully or partially) accepted the DU migration request. Petition 870250083679, dated 09 / 17 / 2025, pp. 61 / 130 49 / 81

[0153] As another example of a method to allow a target F1 donor CU to partially accept or reject DU migration from an IAB node, the source F1 donor CU 803 can trigger the procedure described with reference 720 in Figure 7. After the decision or determination by the source F1 donor CU 803 to perform DU migration from IAB node 801 towards the IAB topology managed by the target F1 donor CU 807, the first step corresponds to sending a request to establish an F1 connection between the target F1 donor CU 807 and the mobile IAB node 8801 to inform the target F1 donor CU 807 that the F1 connection to be established refers to a request for DU migration from IAB node 801 to the target F1 donor CU 807. The request can be sent as a DU activation request message 813 to The IAB node 801, to establish a new F1 connection between the target donor CU F1 807 and the mobile IAB node 801, through the second logical DU IAB-DU2 804.The activation of the second logical IAB-DU2 806 on mobile IAB node 801 is performed with operation 810. Message 813, sent by the source donor CU F1 803 to IAB node 801 for the activation of IAB-DU2 806, is sent to the first logical DU IAB-DU1 805 when the source donor CU F1 803 has an F1 connection with that first logical DU of IAB node 801. The DU activation request message 813 can be a configuration request message 1003 as shown in Figure 10a. This message 813 includes a request to establish an F1 connection and to inform the target donor CU 807 of the identity of the IAB donor CU serving the MT 804 of IAB node 801.The request may include (explicitly or implicitly) for IAB node 801 that the IAB node must inform the target donor CU F1 807 that the F1 connection to be established refers to a request for DU migration from IAB node 801 to the target donor CU F1 807, and may also inform the target donor CU F1 807 of the DU migration context as described above. For example, the DU activation request message 813 may include the context information as described above with respect to message 811, and message 813 may indicate (explicitly or implicitly) that IAB node 801 must provide at least some of the context information in the message. Petition 870250083679, dated 09 / 17 / 2025, p. 62 / 130 50 / 81 DU activation request message received 813 for donor CU F1 target 807.

[0154] After activation of the second logical DU IAB-DU2 806, the information contained in message 813 can be transmitted from the first logical DU IAB-DU1 805 to the second logical DU IAB-DU2 806.

[0155] In particular, message 813 may include identifying information to identify the target F1 donor DU 807, such as the TNL address (i.e., IP address) of the target F1 donor CU 807, so that a new F1 connection or F1 association (e.g., an F1AP interface connection) can be established with the target donor CU 807 (between IAB-DU2 806 and the target donor CU 807). This message 813 may also include a request to inform the identified target F1 donor CU, 807, of the context of the DU migration as described above. For example,

[0156] After activation, IAB-DU2 806 can send an F1 Establishment Request message 814 to the target F1 donor CU 807 to request the establishment of the F1 connection between IAB node 801 and the target F1 donor CU 807 and to indicate that the F1 connection to be established refers to a request for DU migration from IAB node 801 to target F1 donor CU 807. This message 814, also described with reference 1013 in Figure 10b, can include information that the F1 Establishment Request is related to DU migration from IAB node 801. Thus, message 814 can include identifying information to identify the source F1 donor CU 803, such as the TNL address (i.e., the IP address) and / or the identifier (i.e., Global NG-RAN Node ID as specified in TS). 38.423 V17.2.0 section 9.2.2.3) of the donor CU F1 of source 803 of node IAB 801.This message 814 may also include information related to the DU migration context as described above. For example, message 814 may include the context information described above with reference to message 811. Finally, message 814 may include the gNB-DU ID identifier of the second logical DU IAB-DU2 806 of node IAB 801. As specified in TS 38.473 section 9.3.1.19, the gNB-DU ID identifies... Petition 870250083679, dated 09 / 17 / 2025, page 63 / 130 51 / 81 exclusively to gNB-DU at least in one gNB-CU. Thus, a logical DU of an IAB node is assigned a unique ID by configuration. The unique ID can be provided to the donor IAB CU F1 terminating the F1 connection with the logical DU in the F1 establishment procedure (described in Figure 10b).

[0157] In the F1 establishment response 815 (and also described with reference 1014 in Figure 10b), the target donor CU F1 807 can accept or reject the F1 establishment request. Because the F1 establishment request relates to the DU migration of an IAB node, the F1 establishment request can be accepted by the target donor CU F1 807 if the DU migration from the IAB node is partially or fully accepted, and the F1 establishment request can be rejected by the target donor CU F1 807 if the DU migration from the IAB node is not accepted or rejected. The decision by the target donor CU F1 807 can be based on information related to the context of the DU migration (if context information is included in message 814). In the event of acceptance (full or partial), the donor's CU target F1 807 may request that IAB-DU2 806 activate new cell(s) with associated identifiers (PCI, NCGI).Normally, the DU activates / deactivates cell(s) under the control of the donor CU that is controlling the DU. See, for example, TS 38.473 section 8.2.3.2. In the case of partial rejection or acceptance, the target donor CU F1 807 may indicate (e.g., via cause information included in message 815) the cause of the partial rejection / acceptance as described above with respect to message 812. In the case of partial acceptance, the response may identify the portion of the traffic that is accepted (e.g., the index(es) of the accepted traffic profile(s) and / or the number of UEs that are accepted).

[0158] After receiving the F1 establishment response message 815, IAB-DU2 806 can inform IAB-DU1 805 of the result of the activation procedure (i.e., activation of IAB-DU2 806 and activation of new cell(s)). Then, IAB-DU1 805 can relay this information to the source F1 donor CU 803 via a response, such as the DU activation response message 816, which indicates whether the target F1 donor CU 807 accepted or rejected the request to establish an F1 connection between the target F1 donor CU 807 and Petition 870250083679, dated 09 / 17 / 2025, page 64 / 130 52 / 81 the IAB node 801 and consequently (partially or totally) accepted or rejected the request for DU migration from IAB node 801. In the case of successful activation (i.e., if the target donor CU F1 807 accepts (partially or totally) the DU migration from IAB node 801), this message 816 may include the gNB-DU ID of the second logical DU IAB-DU2 806 from IAB node 801. In the case of partial acceptance, message 816 may indicate the cause of this partial acceptance. Message 816 is further described with reference 1004 in Figure 10a. In the case where the target F1 donor CU 807 rejected the request for DU migration from IAB node 801, response 816 indicates that the target IAB donor CU rejected the request to establish an F1 connection between the target F1 donor CU 807 and IAB node 801, and consequently rejected the request for DU migration from IAB node 801.Response 816 may include cause information to indicate the reason for the rejection of the request to migrate from a DU to the target donor CU, as described in relation to message 812.

[0159] As a variant of the above method, when the target donor CU F1 807 rejected or revoked the DU migration from IAB node 801 and thus rejected the F1 establishment request 814, IAB node 801 may not send message 816 or may send message 816 without the cause of unsuccessful DU activation. In this case, it will be the target donor CU F1 807 that will directly inform the source donor CU F1 803, for example, with the procedure described in figure 9a. For example, in such a case, the target donor CU F1 807 can send a response (as described in message 903 with reference to Figure 9a) to the source donor CU F1 803, whose response indicates that the target donor CU F1 807 rejected / revoked the request to migrate DUs from node IAB 801 to the target donor CU F1 807. This response may also include cause information to indicate the reason for the rejection / revocation of the request to migrate DUs to the target donor CU as described above with respect to message 812.

[0160] Figure 9a is a simplified schematic diagram 900 illustrating an example message flow, of a procedure according to embodiments of the present invention, used by a RAN node CU to report information of Petition 870250083679, dated 09 / 17 / 2025, page 65 / 130 53 / 81 configuration for another RAN node CU as per an example.

[0161] This figure shows two RAN nodes, CUa of RAN node 901 and CUb of RAN node 902, which can be two IAB donor CUs, like two of the IAB donor CUs 501, 502 and 503 from figure 5. With respect to the example shown in figure 8, the CUa of RAN node 901 can be the target F1 donor CU 807 and the CUb of RAN node 902 can be the source F1 donor CU 803. The RAN node can be IAB node 801.

[0162] In particular, message 903 can be sent by RAN node 901's CUa to report the status of an F1 establishment procedure related to RAN node DU migration, for which RAN node 902's CUb is the F1 termination donor CU that previously triggered the F1 establishment procedure after the decision to migrate the RAN node DU to RAN node 901's CUa. The RAN node DU can be the DU of an IAB node similar to IAB node 801.

[0163] In the case of a successful F1 establishment operation, meaning that RAN node 901's CUa has accepted (fully or partially) the RAN node's DU migration, the CONFIGURATION UPDATE message 903 can be sent by RAN node 901's CUa. For the CUb of RAN node 902 to inform the CUb of RAN node 902 about the activation of new cell(s) in a logical DU of a RAN node such as IAB-DU2 806 of node IAB 801.

[0164] For example, the source donor CU F1 803 receives the CONFIGURATION UPDATE 903 message from the target donor CU F1 807 and the CONFIGURATION UPDATE 903 message includes identification information (e.g., PCI NRGI) identifying one or more new cells that have been activated in a second logical DU entity (IAB-DU2 806) of the IAB node 801 DU.

[0165] 903 messages may also include at least one of: - The RAN node identifier migrated as known by the CUa of RAN node 901, with the donor UE-IAB termination information element F1 identifying the Mobile Termination (MT) of the migrated node or with the gNB-DU information element identifying the logical DU. Petition 870250083679, dated 09 / 17 / 2025, p. 66 / 130 54 / 81 of the migrated RAN node having an F1 connection with the CUa of RAN node 901. - The MT identifier of the migrated RAN node as known by the RAN node CU terminating the RRC connection with the migrated RAN node, via the donor IAB non-terminating F1 donor UE XnAP ID information element, - The gNB-DU identifier of a logical DU from the migrated RAN node having an F1 connection to the CUb of RAN node 902, - The information regarding the cause of partial acceptance in the case of partial acceptance of DU migration, - The index of traffic profiles that are accepted, and / or the number of UEs that are accepted in the case of partial acceptance.

[0166] In the case of an unsuccessful F1 establishment operation, meaning that the RAN node 901 CUa rejected or revoked the RAN node's DU migration, the CONFIGURATION UPDATE message 903 can be sent by the RAN node 901 CUa to the RAN node 902 CUb to inform the RAN node 902 CUb about the rejection / revocation of the RAN node's DU migration. In this case, message 903 can include an information element (e.g., cause information) indicating the cause of the rejection / revocation, as described with reference to message 812 in Figure 8.

[0167] RAN node 902 CUb can respond with the CONFIGURATION ACKOWLEDGE message 904 sent to RAN node 901 CUa.

[0168] According to an example, figure 9a corresponds to the NG-RAN node configuration update procedure described in TS 38.423 V17.2.0 section 8.4.2, and message 903 corresponds to the NG-RAN NODE CONFIGURATION UPDATE message described in TS 38.423 V17.2.0 section 9.1.3.4, modified with IEs listed above, while message 904 corresponds to the NGRAN NODE CONFIGURATION UPDATE ACKNOWLEDGE message described in TS 38.423 V17.2.0 section 9.1.3.5.

[0169] Figure 9b is a simplified diagram 910 illustrating a flow of Petition 870250083679, dated 09 / 17 / 2025, p. 67 / 130 55 / 81 Example message, according to one or more embodiments of the invention, of a procedure used by a RAN node CU to manage DU migration from a RAN node in coordination with another RAN node CU, including signaling to partially accept, reject, or revoke DU migration.

[0170] This figure shows two RAN nodes, CUa of RAN node 911 and CUb of RAN node 912, which may be two IAB donor CUs, like two of the IAB donor CUs 501, 502 and 503 in figure 5.

[0171] The MIGRATION REQUEST message 913 is sent by the RAN node CU 911 to the RAN node CU 912 to request the migration of DU from a RAN node, which may be an IAB node such as IAB node 801. For example, with reference to Figure 8, the source donor CU F1 803 may send a MIGRATION REQUEST 913 to the target donor CU F1 807 to request the migration of DU from IAB node 801. In other words, MIGRATION REQUEST 913 may correspond to the message 811 described above with reference to Figure 8.

[0172] Message 913 may also include context information relating to or associated with the context of the DU migration to the target F1 donor CU 807. The context information may include some or all of the following information, which may be referred to as the context of the DU migration. - Identification information to identify the RAN node. The identification information may include the RAN node identifier as known by the RAN node CUa 911, with the F1 Termination IAB Donor UE XnAP information element identifying the RAN node MT, or with the gnNB-DU ID information element identifying a first logical DU of the RAN node. The identification information may additionally or alternatively include the RAN node identifier as known by the RAN node CU serving the RAN node MT, if the MT has been migrated to a non-F1 RAN node CU and if that non-F1 donor CU is different from the RAN node CUb 912, with the F1 Termination IAB Donor UE XnAP information element identifying the RAN node MT. - Identification information to identify the RAN node CU serving the Petition 870250083679, dated 09 / 17 / 2025, p. 68 / 130 56 / 81 RAN node MT, if the MT has been migrated to a non-F1 RAN node CU and if that non-F1 RAN node CU is different from RAN node CUb 912, for example, with the TNL address (i.e., the IP address) and / or the identifier (i.e., Global NG-RAN Node ID as specified in TS 8.423 V17.2.0 section 9.2.2.3) of the non-F1 RAN node CU, - An indication related to the priority for considering the DU migration request. For example, priority information to indicate a priority level for the DU migration request. It can be a value within a predefined range (e.g., from 1 to 5), where a low value indicates that DU migration is not critical for the RAN 911 node CU, while a high value indicates that DU migration is critical for the RAN 911 node CU, for example, due to some load issue associated with processing or network / radio resources in the IAB topology controlled by the RAN 911 node CU. - An indication related to the user traffic profile associated with the RAN node (e.g., traffic profile information to indicate a user traffic profile associated with the RAN node), including QoS (Quality of Service) parameters, as defined in TS 38.423 V17.2.0 section 9.2.2.81. Each traffic profile can be identified by a traffic index. - An indication related to the transmission capacity of user traffic associated with the RAN node (e.g., traffic transmission capacity information to indicate the transmission capacity of user traffic associated with the RAN node), both in the upstream direction (from the RAN node) and the downstream direction (towards the IAB node). - The number of UEs that would be delivered to the CUb of node RAN 912 along with the migration of the DU of node RAN. In addition, the number of UEs on board can be indicated (i.e., UEs physically inside the vehicle equipped with the IAB node or otherwise surrounding and moving with the IAB node). Petition 870250083679, dated 09 / 17 / 2025, p. 69 / 130 57 / 81

[0173] F1-terminated IAB donor EU XnAP ID and F1-terminated IAB donor EU XnAP ID correspond to an NGRAN node EU XnAP ID as specified in TS 38.423 section 9.2.3.16.

[0174] RAN node 912's CUb responds with the MIGRATION RESPONSE message 914, sent to RAN node 911's CUa to (fully or partially) accept or reject the request.

[0175] The procedure described in Figure 9b can be used by the CUb of node RAN 912 to revoke a previously accepted DU migration. For this purpose, the CUb of node RAN 912 sends another MIGRATION RESPONSE 914 message to indicate the revocation to the CUa of node RAN 911.

[0176] In the case of partial acceptance, rejection or revocation, message 914 may include an information element (e.g., cause information) indicating the cause of the partial acceptance, rejection or revocation, as described with reference to message 812 in Figure 8. In the case of partial acceptance, the response may include the index of the traffic profiles that are accepted and / or the number of UEs that are accepted.

[0177] Figure 9b may correspond to the handover preparation procedure specified in TS 38.423 V17.2.0 section 8.2.1, and modified with the information elements and behavior described above. Message 913 may correspond to the HAHDOVER REQUEST message specified in TS 38.423 V17.2.0 section 9.1.1.1. In the case of acceptance (total or partial) of the DU migration, message 914 may correspond to the HANDOVER REQUEST ACKNOWLEDGE message specified in TS 38.423 V17.2.0 section 9.1.1.2, while in the case of rejection or revocation of the DU migration, message 914 may correspond to the HANDOVER PREPARATION FAILURE message specified in TS 38.423 V17.2.0 section 9.1.1.3.

[0178] Figure 10a is a simplified diagram 1000 illustrating an example message flow, according to one or more embodiments of the invention, of Petition 870250083679, dated 09 / 17 / 2025, pp. 70 / 130 58 / 81 a procedure for executing the activation of a logical DU on a RAN node, including signaling to partially accept, reject, or revoke by a RAN node CU the RAN node DU migration.

[0179] This figure shows: - a RAN node 1001 DU, which can be an IAB node DU such as IAB-DU 572 from IAB node 570 in Figure 5 (and IAB-DU1 805 from IAB node 801 in Figure 8), - a RAN 1002 node CU, which may be an IAB donor CU such as IAB donor CU 501 in Figure 5 (and source 803 f1 donor CU in Figure 8).

[0180] The CONFIGURATION REQUEST message 1003 is sent by the RAN node CU 1002 to the RAN node DU 1001 to request the activation of new cell(s) controlled by the RAN node DU 1001, or to request the activation of a logical DU or to request the deactivation of cell(s) in the RAN node DU 1001. In the case of a logical DU activation, the 1003 message may include the TNL address (i.e., IP address) of a target RAN node CU (e.g., target donor CU F1 807 in Figure 8) that will connect to the logical DU after activation.For example, CONFIGURATION REQUEST 1003 can be sent by the source IAB donor CU to the IAB node (e.g., the first logical DU entity 805 having an F1 connection with the source IAB donor CU) to request the establishment of an F1 connection between a target IAB donor CU and the IAB node (e.g., CONFIGURATION REQUEST 1003 may correspond to request 813 described above with reference to Figure 8, which is a request to establish an F1 connection between a target IAB donor CU and the IAB node to inform the target IAB donor CU that the F1 connection to be established refers to a request for DU migration from the IAB node to the target IAB donor CU). Message 1003 can also include an information element (IE) indicating that the request relates to DU migration from the RAN node.This IE can be limited to one bit: one value (i.e., “0” or “1”) of this one-bit IE means that no specific action is requested, and another value (i.e., “1” or “0”) means... Petition 870250083679, dated 09 / 17 / 2025, page 71 / 130 59 / 81 send the DU migration context to the target RAN node CU (e.g., the target donor CU F1 807 in Figure 8) which will connect to the logical DU after activation. This IE can be extended to include context information which may include part or all of the following information which can be called the DU migration context: - Identification information to identify the RAN node. The identification information may include the RAN node identifier as known by the RAN node CUa 1002, with the F1 Termination IAB Donor UE XnAP information element identifying the RAN node MT, or with the gnNB-DU ID information element identifying the logical DU of RAN node 1001. The identification information may additionally or alternatively include the RAN node identifier as known by the RAN node CU serving the RAN node MT, if the MT has been migrated to a non-F1 RAN node CU (or RRC) and if that non-F1 donor CU (or RRC termination donor CU) is different from RAN node CUb 1002, with the non-F1 Termination IAB Donor UE XnAP information element identifying the RAN node MT. - Identification information to identify the RAN node CU serving the RAN node MT, if the MT has been migrated to a non-F1 RAN node CU and if that non-F1 RAN node CU is different from RAN node CUb 1002, for example, with the TNL address (i.e., the IP address) and / or the identifier (i.e., Global NG-RAN Node ID as specified in TS 8.423 V17.2.0 section 9.2.2.3) of the non-F1 RAN node CU, - An indication related to the priority for considering the DU migration request. For example, priority information to indicate a priority level for the DU migration request. It can be a value within a predefined range (e.g., from 1 to 5), where a low value indicates that DU migration is not critical for the RAN 1002 node CU, while a high value indicates that DU migration is critical for the RAN 1002 node CU, for example, due to some... Petition 870250083679, dated 09 / 17 / 2025, p. 72 / 130 60 / 81 load problem associated with network / radio processing or resources in the IAB topology controlled by the RAN 1002 node CU, - An indication related to the user traffic profile associated with the RAN node (e.g., traffic profile information to indicate a user traffic profile associated with the RAN node), including QoS (Quality of Service) parameters, as defined in TS 38.423 V17.2.0 section 9.2.2.81. Each traffic profile can be identified by a traffic index. - An indication related to the transmission capacity of user traffic associated with the RAN node (e.g., traffic transmission capacity information to indicate the transmission capacity of user traffic associated with the RAN node), both in the upstream direction (from the RAN node) and the downstream direction (towards the IAB node). - The number of UEs that would be delivered to the CUb of node RAN 1002 along with the RAN node. In addition, the number of UEs on board can be indicated (i.e., UEs inside the vehicle equipped with the IAB node or otherwise encircling and moving with the IAB node).

[0181] The RAN node 1001 DU can confirm the request with the CONFIGURATION RESPONSE message 1004 sent to the RAN node 1002 CU. The 1004 message can be used to report to the RAN node 1002 CU the status of the F1 connection with the target RAN node F1 CU.

[0182] In the case of successful F1 establishment for RAN node DU migration, it means that the target RAN node F1 CU has accepted (fully or partially) the DU migration. Then, message 1004 may include an Information Element (IE) (e.g., second DU gNB_DU ID) to identify the enabled logical DU on the RAN node. In the case of partial acceptance of DU migration, message 1004 may include the reason for the partial acceptance.

[0183] In the case of an unsuccessful F1 establishment for RAN node DU migration, it means that the target RAN node F1 CU rejected or revoked the DU migration. In this last mentioned case, message 1004 may include a cause. Petition 870250083679, dated 09 / 17 / 2025, page 73 / 130 61 / 81 (e.g., reason information) for rejection or revocation as described with reference to message 812 in Figure 8.

[0184] According to an example, the flow in Figure 10a corresponds to the gNB-CU Configuration Update procedure described in TS 38.473 V17.0.0 section 8.2.5, and modified with the information elements and behavior described above. Message 1003 corresponds to the GNBCU CONFIGURATION UPDATE message described in TS 38.473 V17.2.0 section 9.2.1.10, while message 1004 corresponds to the GNB-CU CONFIGURATION UPDATE ACKNOWLEDGE message described in TS 38.473 V17.2.0 section 9.2.1.11.

[0185] Figure 10b is a simplified diagram illustrating an example message flow, according to one or more embodiments of the invention, of a procedure for establishing a logical DU on a RAN node, including signaling to partially accept, reject, or revoke a RAN node DU migration by a RAN node CU.

[0186] This figure shows: - a RAN node 1011 DU, which may be a DU of an IAB node such as IAB-DU 572 of IAB node 570 in Figure 5 (and IAB-DU2 806 of IAB node 801 in Figure 8), - a RAN 1012 node CU, which may be an IAB donor CU such as IAB donor CU 503 in Figure 5 (and F1 Target donor CU 807 in Figure 8).

[0187] The message SETUP REQUEST (SETUP REQUEST) SETUP REQUEST 1013 is sent by the RAN node's DU 1011 to the RAN node's CU 1012 to request the establishment of an F1 connection for the logical DU. For example, SETUP REQUEST 1013 can be sent by the IAB node (e.g., by the second logical DU entity 806 that was activated on IAB node 801) to the target IAB donor CU 807 to request the establishment of an F1 connection between a target IAB donor CU and the IAB node (e.g., with the second logical DU entity 806 of IAB node 801). SETUP REQUEST 1013 can correspond to request 814 described above with reference to Figure 8, which is an F1 establishment request. Petition 870250083679, dated 09 / 17 / 2025, page 74 / 130 Message 62 / 81 requests the establishment of the F1 connection and indicates that the F1 connection to be established refers to a request for DU migration from node IAB 801 to the target IAB donor CU. The SETUP REQUEST 1013 message can be sent after an activation request as described with reference to Figure 10a. This SETUP REQUEST 1013 message can include the number of cells to be activated along with the activation of the logical DU. This SETUP REQUEST 1013 message can include an indication that it relates to DU migration from the RAN node and can include all or part of the DU migration context (e.g., context information) as described with reference to message 1003 in Figure 10a.

[0188] Message 1013 may also include the TNL address (i.e., the IP address) and / or the identifier (i.e., Global NG-RAN Node ID as specified in TS 38.423 V17.2.0 section 9.2.2.3) of the source RAN node CU that requested the establishment of F1.

[0189] The RAN node 1012 CU responds with the SETUP RESPONSE message 1014 sent to the RAN node 1011 DU. SETUP REQUEST 1014 may correspond to response 815 described above with reference to Figure 8, which is an F1 setup response indicating that the target IAB donor CU has accepted or rejected the F1 setup request regarding the request to migrate the DU to the target IAB donor CU. The RAN node 1012 CU may accept or reject the F1 setup request.If the F1 establishment request relates to the DU migration of an IAB node, the F1 establishment request may be accepted by the RAN 1012 node CU if the IAB node's DU migration is (partially or fully) accepted, or the F1 establishment request may be rejected by the RAN 1012 node CU if the IAB node's DU migration is rejected, or the F1 establishment request may be revoked by the RAN 1012 node CU if the IAB node's DU migration was previously accepted and then revoked. The decision by the RAN 1012 node CU may be based on information related to the DU migration context (if context information is included in message 1013). In the case of acceptance (total)... Petition 870250083679, dated 09 / 17 / 2025, page 75 / 130 63 / 81 or partial), the RAN node 1012 CU may include a list of cell(s) to activate with the logical DU, along with the associated PCI and NCGI values ​​to be used. In the case of partial acceptance, rejection, or revocation, the RAN node 1012 CU may indicate (e.g., via cause information included in message 1014) the cause of the partial acceptance, rejection, or revocation, as described above with respect to message 812. In the case of partial acceptance, the response may include identification of the portion of traffic that is accepted (e.g., the index(es) of the accepted traffic profile(s) and / or the number of UEs that are accepted).

[0190] According to an example, the flow in figure 10b corresponds to the F1 setup procedure described in TS 38.473 V17.2.0 section 8.2.3, modified with the information elements and behavior described above. Message 1013 may correspond to the F1 SETUP REQUEST message described in TS 38.473 V17.2.0 section 9.2.1.4. Message 1014 may correspond to the F1 SETUP RESPONSE message described in TS 38.473 V17.2.0 section 9.2.1.5, if the CU of RAN node 102 accepted the request (for example, when the CU of RAN node 1012 accepted (fully or partially) the DU migration from the RAN node), while message 1014 may correspond to the F1 SETUP FAILURE message described in TS 38.473 V17.2.0 section 9.2.1.6, if the CU of RAN node 1012 rejected the request (for example, when the CU of RAN node 1012 rejected the DU migration from the RAN node).

[0191] Figure 10c is a simplified diagram 1020 illustrating an example message flow of a procedure for removing a logical DU.

[0192] This figure shows: - a RAN node 1021 DU, which may be a DU of an IAB node such as IAB-DU 572 of node IAB 570 in Figure 5 (and IAB-DU1 805 of node IAB 801 in Figure 8), - a RAN 1022 node CU, which may be an IAB donor CU such as IAB donor CU 501 in Figure 5 (and F1 donor CU from source 803 in Figure 8). Petition 870250083679, dated 09 / 17 / 2025, page 76 / 130 64 / 81

[0193] The REMOVAL REQUEST message 1023 is sent by the CU of RAN node 1022 to the DU of RAN node 1021 to request the removal (which is equivalent to deactivation) of the logical DU.

[0194] The DU of node RAN 1021 responds with the message REMOVAL RESPONSE 1014 sent to the CU of node RAN 1022.

[0195] According to an example, the flow in figure 10c corresponds to the F1 removal procedure described in TS 38.473 V17.2.0 section 8.2.8, and message 1023 corresponds to the F1 REMOVAL REQUEST message described in TS 38.473 V17.2.0 section 9.2.1.16, while message 1024 corresponds to the F1 REMOVAL RESPONSE message described in TS 38.473 V17.2.0 section 9.2.1.7.

[0196] Figure 11a is a flowchart of an example method 1100 according to embodiments of the present invention, for managing, in the source F1 termination donor CU of an IAB node, the migration of DU from the IAB node. For example, method 1100 according to embodiments of the present invention is performed in the source IAB donor CU and is for use in managing, or as part of, a migration procedure / process to migrate a DU from an IAB node from the source IAB donor CU to a target IAB donor CU.

[0197] For example, with reference to the IAB 500 communication system shown in and described in relation to Figure 5, the source IAB donor CU executing method 1100 may be the IAB 501 donor CU (for example, an F1 termination donor CU or F1 donor CU of the IAB 570 node with which the IAB 570 node maintains an F1 connection). The IAB node can be the mobile IAB node 570 belonging to the IAB topology 5001 (also called the source IAB topology) controlled by the donor CU IAB 501. The migration process may involve migrating the DU 572 of the IAB node 570 from the IAB topology 5001 to the IAB topology 5003 (also called the target IAB topology) managed by the donor CU IAB 503, which is the target IAB donor CU. With reference to Figures 7 and 8, the IAB node Petition 870250083679, dated 09 / 17 / 2025, page 77 / 130 65 / 81 can be IAB node 701, 801 and the migration process may involve migrating the DU of IAB node 701, 801 from the source termination donor CU F1 703, 803 to the target termination donor CU F1 707, 807. Method 1100 as shown in and described with reference to Figure 11a can be executed by software elements and / or hardware elements. The source IAB donor CU can be implemented in a communication device 400 as shown in and described with reference to Figure 4 with the method as shown in and described with reference to Figure 11a being executed by an appliance for the source IAB donor CU including one or more processing units, such as the central processing unit 411.

[0198] In step 1101, the source F1 termination donor CU, such as donor CU 501 in figure 5 (703, 803), determines that the IAB node DU, such as node IAB 570 in figure 5 (701, 801), must be migrated from source F1 donor CU 501, 703, 803, to a target F1 termination donor CU, such as donor CU 503 in figure 5 (707, 807). For example, the F1 termination donor CU from source 501, 703, 803 decides the DU migration from an IAB node, such as IAB node 570, towards a target F1 donor CU, such as donor CU 503, 707, 807. For example, the F1 donor CU from source 501, 703, 803 might determine that DU 572 from IAB node 570, 701, 801 should be migrated in response to the determination that the migration of MT 571, 704, 804 from IAB node 570, 701, 801 towards a new parent IAB node (which could be a new IAB node or a new IAB donor DU) has been completed. Examples of other triggers for determining that the DU should be migrated are described above.The details of how the source F1 termination donor CU 501, 703, 803 determines the target F1 termination donor CU 503, 707, 807 are also described above.

[0199] In step 1102, the source F1 termination donor CU 501, 703, 803 sends a request to the target F1 termination donor CU 503, 707, 807 to migrate the IAB node DU (e.g., a request to request DU migration from IAB node DU 570, 701, 801 from the source F1 termination donor CU 501, 703, 803 to the target F1 termination donor CU). Petition 870250083679, dated 09 / 17 / 2025, page 78 / 130 66 / 81 503, 77, 807). The message sent in step 1102 may be a migration request message like message 811 in figure 8.

[0200] In step 1103, the source F1 termination donor CU 501, 703, 803 receives a response from the target F1 donor CU 503, 707, 807 indicating whether the target F1 termination donor CU 503, 707, 807 accepts (fully or partially) or rejects the DU migration from the IAB node. The message received in step 1103 may be a migration response message such as message 812 in Figure 8. As discussed above, the response received in step 1103 may include CU cause information to indicate the reason for the partial acceptance or rejection of the DU migration request to the target donor CU. In the case of partial acceptance, the response may include identification of the portion of the traffic that is accepted (e.g., the index(es) of the accepted traffic profile(s) and / or the number of UEs that are accepted).

[0201] When the target F1 termination donor CU 503, 707, 807 determines to partially accept or reject the DU migration from IAB node 570, 701, 801, the response indicates that the target F1 termination donor CU 503, 707, 807 has partially accepted or rejected the request for DU migration. After receiving (or in response to receiving) a rejection response, the migration process is not executed or the execution of the migration process terminates (for example, the source IAB donor CU does not send a DU activation request 813). After partial acceptance or rejection, the source IAB donor CU may decide to postpone the DU migration and retry later or may decide to select another target donor CU.

[0202] If the DU migration is (fully or partially) accepted by the target F1 donor CU 503, 707, 807, the response received in the source F1 termination donor CU 501, 703, 803 indicates that the target F1 donor CU 503, 77, 807 has accepted (fully or partially) the DU migration and in response, the source F1 termination donor CU 501, 703, 803 can start the migration process which is then executed (e.g., the steps described above with reference to figure 7 are executed). Petition 870250083679, dated 09 / 17 / 2025, pp. 79 / 130 67 / 81

[0203] Figure 11b is a flowchart of an example method 1110 according to embodiments of the present invention, for managing, in the target F1 termination donor CU of an IAB node, the migration of DU from the IAB node. For example, method 1110 according to embodiments of the present invention is performed in the target IAB donor CU and is for use in managing, or as part of, a migration procedure / process to migrate a DU from an IAB node from a source IAB donor CU to a target IAB donor CU.

[0204] For example, with reference to the IAB 500 communication system shown in and described in relation to Figure 5, the target IAB donor CU executing method 1110 could be the IAB 5013 donor CU controlling the IAB 5003 topology. The IAB node could be the mobile IAB node 570 belonging to the IAB 5001 topology controlled by the IAB 501 donor CU. The migration process could involve migrating the DU 572 from the IAB 570 node of the IAB 5001 topology to the IAB 5003 topology. With reference to Figures 7 and 8, the IAB node could be IAB 701, 801 and the migration process could involve migrating the DU from IAB 701, 801 from the source F1 termination donor CU 703, 803 to the donor CU. of F1 target 707, 807. The 1110 method as shown in and described with respect to figure 11b can be executed by software elements and / or hardware elements.The target IAB donor CU can be implemented in a communication device 400 as shown in and described with reference to Figure 4, with the method as shown in and described with reference to Figure 11b being performed by an apparatus for the target IAB donor CU including one or more processing units, such as the central processing unit 411.

[0205] In step 1111, the target F1 termination donor CU, such as donor CU 503 in Figure 5 (707, 807), receives a request to request DU migration from the IAB node DU 570, 701, 801 from the source F1 termination donor CU to the target F1 termination donor CU. The request can be sent as a DU migration request from the source F1 termination donor CU, such as IAB donor CU 501 in Figure 5 (703, 803), to request DU migration from IAB node 570, 701, 801 in the IAB topology controlled by the CU of Petition 870250083679, dated 09 / 17 / 2025, pp. 80 / 130 68 / 81 termination donor F1 target 503, 707, 807. The message received in step 1111 may be message 811 in figure 8.

[0206] In step 1112, the target F1 termination donor CU 503, 707, 807 determines whether to accept (fully), partially accept, or reject the DU migration from IAB node 570, 701, 801. The decision may be based on the current processing resource load of the target F1 termination donor CU 503, 707, 807, or on the current network resource load (wired backhaul and / or wireless backhaul) in the IAB topology managed by the target F1 termination donor CU 503, 707, 807. To assist the decision, the target F1 termination donor CU 503, 707, 807 may use the DU migration context information included in the message received in step 1111 (e.g., context information as described above with respect to message 811).

[0207] In step 1113, the target F1 termination donor CU 503, 707, 807 sends a response to the source F1 donor CU 501, 703, 803, indicating whether the target F1 termination donor CU 503, 707, 807 accepts (fully or partially) or rejects the DU migration from IAB node 570, 701, 801. The message sent in step 1113 may be message 812 in Figure 8. After the target F1 termination donor CU 503, 707, 807 determines whether to partially accept or reject the DU migration from IAB node 570, 701, 801, the response indicates that the target F1 termination donor CU 503, 707, 807 partially accepted or rejected the Request for DU migration.

[0208] As discussed above, although not shown in Figures 11a and 11b, after determining whether to accept (fully or partially) the request for DU migration, the target F1 donor CU 503, 707, 807 may determine the revocation of DU migration from the IAB node to the target F1 donor CU 503, 707, 807 (e.g., when the target F1 donor CU 503, 707, 807 cannot support the DU migration (and any served UEs)). In this case, the target F1 donor CU 503, 707, 807 sends a revocation response (e.g., a message such as message 914) to the source F1 donor CU 501, 703, 803 indicating that the target F1 donor CU 503, 707, 807 has determined the revocation of the DU migration from the IAB node to CU Petition 870250083679, dated 09 / 17 / 2025, pp. 81 / 130 69 / 81 of donor F1 target 503, 77, 807.

[0209] Figure 12a is a flowchart of another example method 1200 according to embodiments of the present invention, for managing, in the source F1 termination donor CU of an IAB node, the migration of DU from the IAB node. For example, method 1200 according to embodiments of the present invention is performed in the source IAB donor CU and is for use in managing, or as part of, a migration procedure / process to migrate a DU from an IAB node from the source IAB donor CU to a target IAB donor CU.

[0210] For example, with reference to the IAB 500 communication system shown in and described in relation to Figure 5, the source IAB donor CU executing method 1200 may be the IAB 501 donor CU (for example, an F1 termination donor CU or F1 donor CU of IAB node 570 with which IAB node 570 maintains an F1 connection). The IAB node may be mobile IAB node 570 belonging to IAB topology 5001 (also called the source IAB topology) controlled by IAB donor CU 501. The migration process may involve migrating IAB node 572's DU from IAB topology 5001 to IAB topology 5003 (also called the target IAB topology) managed by IAB donor CU 503, which is the target IAB donor CU. With reference to figures 7 and 8, the IAB node can be IAB node 701, 801 and the migration process can involve migrating the DU from IAB node 701, 801 from the source F1 termination donor CU 703, 803 to the target F1 termination donor CU 707, 807.The method 1200 as shown in and described with reference to Figure 12a can be executed by software elements and / or hardware elements. The source IAB donor CU can be implemented in a communication device 400 as shown in and described with reference to Figure 4, with the method as shown in and described with reference to Figure 12a being executed by an apparatus for the source IAB donor CU including one or more processing units, such as the central processing unit 411.

[0211] In step 1201, the source termination donor CU F1, like the donor CU 501 in figure 5 (703, 803), determines that the node IAB DU, like node IAB Petition 870250083679, dated 09 / 17 / 2025, page 82 / 130 70 / 81 570 of figure 5 (701, 801) must be migrated from the source F1 termination donor CU 501, 703, 803, to a target F1 termination donor CU, such as donor CU 503 of figure 5 (707, 807). For example, the F1 termination donor CU from source 501, 703, 803 decides the DU migration from an IAB node, such as IAB node 570, 701, 801, towards a target F1 termination donor CU, such as donor CU 503, 707, 807. For example, the F1 termination donor CU from source 501, 703, 803 might determine that the DU from IAB node 570, 701, 801 should be migrated in response to the determination that the migration of MT 571, 704, 804 from IAB node 570, 701, 801 towards a new parent IAB node (which could be a new IAB node or a new IAB donor DU) has been completed. Examples of other triggers for determining that the DU should be migrated are described above.The details of how the source F1 termination donor CU 501, 703, 803 determines the target F1 termination donor CU 503, 707, 807 are also described above.

[0212] In step 1202, the source F1 termination donor CU 501, 703, 803 sends a request to IAB node 570, 701, 801 to establish an F1 connection (i.e., a new F1 connection) between the target IAB donor CU 503, 707, 807 and IAB node 570, 701, 801 (e.g., a new F1 association with the target IAB donor CU) and to inform the target IAB donor CU that the F1 connection is related to a DU migration from IAB node 570, 701, 801. The request from the source F1 termination donor CU 501, 703, 803 may indicate (explicitly via an IE or implicitly) to IAB node 570, 701, 801 that the IAB node must inform the target IAB donor CU 503, 707, 807 that the F1 connection is related to the DU migration of the IAB node 570, 701, 801. The request may also inform the target IAB donor CU 503, 707, 807 of the DU migration context as described above. For example, the request may include the context information as described above with reference to message 811.The request can indicate (explicitly via an IE or implicitly) that IAB nodes 570, 701, 801 should transmit the DU migration context (which can also be included in the request) to the target IAB donor CU 503, 707, 807. The message sent in step 1202 can be message 813 in Figure 8. Petition 870250083679, dated 09 / 17 / 2025, page 83 / 130 71 / 81

[0213] Not shown in figure 12a, the F1 termination donor CU of source 501, 703, 803 may have executed the procedure described with figure 9b before step 1202, and may have received DU migration acceptance from the target IAB donor CU 503, 707, 807 (e.g., in a migration response 914).

[0214] In step 1203, the F1 termination donor CU from source 501, 703, 803 receives a response indicating whether the target IAB donor CU 503, 707, 807 has (fully) accepted, partially accepted, or rejected (or revoked if the target IAB donor CU 503, 707, 807 previously accepted the DU migration from IAB node 570, 701, 801) the request to migrate DUs to the target IAB donor CU 503, 707, 807. The response may be a DU activation response from IAB node 570, 701, 801. The message received in step 1203 may be message 816 shown in and described in relation to Figure 8.

[0215] In the case where the target IAB donor CU 503, 707, 807 rejects or revokes the request for DU migration from IAB node 570, 701, 801, response 816 indicates that the target IAB donor CU rejected the request to establish an F1 connection between the target IAB donor CU 503, 707, 807 and IAB node 570, 701, 801 and consequently rejected or revoked the request for DU migration from IAB node 570, 701, 801. Response 816 may include cause information to indicate the reason for the rejection of the DU migration request for the target donor CU as described in relation to message 812. In the case of partial acceptance of DU migration (with acceptance of the F1 establishment request), response 816 may include the reason for the partial acceptance.

[0216] In another example (not shown in Figure 12a), when the target IAB donor CU 503, 707, 807 rejects or revokes the DU migration from IAB node 570, 701, 801 and thus rejects the establishment of an F1 connection between the target IAB donor CU 503, 707, 807 and IAB node 570, 701, 801, the source F1 terminating donor CU 501, 703, 803 may receive a response indicating that the target IAB donor CU 503, 707, 807 rejected or revoked the request for DU migration to the target IAB donor CU 503, 707, 807 from the target F1 donor CU 807 using, for example, the procedure described in Figure 12a. 9a. Tal Petition 870250083679, dated 09 / 17 / 2025, page 84 / 130 Response 72 / 81 may also include cause information to indicate the reason for the rejection or revocation of the request for DU migration to the target donor CU as described above. In the case of partial acceptance of DU migration (with acceptance of the F1 establishment request), the target F1 donor CU 807 may inform the source F1 donor CU 803 of the reason for the partial acceptance.

[0217] After receiving (or in response to receiving) a rejection / revocation response, the migration process is not executed or the execution of the migration process terminates (for example, the source IAB donor CU does not send a DU 813 activation request). After rejection / revocation, the source IAB donor CU may decide to postpone the DU migration and make a new attempt later or may decide to select another target donor CU.

[0218] Figure 12b is a flowchart of an example method 1210 according to embodiments of the present invention, for managing, on an IAB node, its DU migration to a target F1 termination donor CU. For example, method 1210 according to embodiments of the present invention is performed on the IAB node and is for use in, or as part of, managing a migration procedure / process to migrate a DU from an IAB node from a source IAB donor CU to a target IAB donor CU.

[0219] For example, with reference to the IAB 500 communication system shown in and described in relation to Figure 5, the IAB node executing method 1210 may be mobile IAB node 570 belonging to IAB topology 5001 (also called the source IAB topology) controlled by donor CU IAB 501 (for example, a terminating donor CU F1 of mobile IAB node 570 with which mobile IAB node 570 maintains an F1 connection) which is the source IAB donor CU. The migration process may involve migrating DU 572 of IAB node 570 from IAB topology 5001 to IAB topology 5003 (also called the target IAB topology) managed by donor CU IAB 503 which is the target IAB donor CU. With reference to Figures 7 and 8, the IAB node can be mobile IAB node 701, 801, and the migration process may involve migrating the DU of IAB node 701, 801 from the F1 termination donor CU of source 703, 803 to the F1 termination donor CU. Petition 870250083679, dated 09 / 17 / 2025, p. 85 / 130 73 / 81 target 707, 807. The method 1210 as shown in and described with reference to figure 12b can be executed by software elements and / or hardware elements. The IAB node can be implemented in a communication device 400 as shown in and described with reference to figure 4 with the method as shown in and described with reference to figure 12b being executed by an apparatus for the IAB node including one or more processing units, such as the central processing unit 411.

[0220] In step 1211, an IAB node, such as IAB node 570 in Figure 5 (701, 801), receives a request from a source F1 termination donor CU, such as donor CU 501 in Figure 5 (703, 803), to establish an F1 connection or a new F1 connection (e.g., an F1 connection between IAB node 570, 701, 801 and a target F1 donor CU, such as donor CU 503 in Figure 5 (707, 807)) and to inform the target IAB donor CU that the F1 connection is related to the DU migration of IAB node 570, 701, 801. The request from the source F1 termination donor CU 501, 703, 803 may indicate (explicitly or implicitly) For IAB nodes 570, 701, 801, the IAB node must inform the target IAB donor CU 503, 707, 807 that the F1 connection is related to the DU migration of IAB nodes 570, 701, 801. The request may also inform the target F1 donor CU 807 from the context of the DU migration as described above.For example, the request may include context information as described above with reference to message 811. The request may indicate (explicitly or implicitly) that IAB nodes 570, 701, 801 should provide or transmit the DU migration context (which may also be included in the request) to the target IAB donor CU 503, 707, 807. The message received in step 1211 may be message 813 in Figure 8.

[0221] In step 1212, in response to (or after) receiving a request for a new F1 connection, IAB node 570, 701, 801 then sends to the target F1 termination donor CU 503, 707, 807, an F1 establishment request requesting the establishment of the F1 connection and indicating that the F1 connection to be established refers to a DU migration request from IAB node 570, 701, Petition 870250083679, dated 09 / 17 / 2025, page 86 / 130 74 / 81 801 for the target F1 termination donor CU 503, 707, 807. For example, the F1 establishment request message sent by IAB node 570, 701, 801 may include an indication that the F1 connection to establish is related to the DU migration from IAB node 570, 701, 801. It may also include part or all of the DU migration context (such as all or part of the context information described above). The message sent in step 1212 may be message 814 in Figure 8.

[0222] In step 1213, the IAB node 570, 701, 801 receives an F1 establishment response message from the target F1 termination donor CU 503, 701, 801. This message indicates whether the target F1 termination donor CU 503, 707, 807 accepts or rejects the F1 establishment request. The decision to accept or reject the F1 establishment request may be linked to the decision to accept (fully or partially) or reject (or revoke if the target IAB donor CU 503, 77, 807 has previously accepted the DU migration from IAB node 570, 701, 801) the DU migration from IAB node 570, 701, 801. The message received in step 1213 may be message 815 in Figure 8. In the case of rejection or revocation, the F1 establishment response indicates that the target F1 termination donor CU 503, 707, 807 rejected the F1 establishment request regarding the request for DU migration to the target F1 termination donor CU 503, 707, 807.In this case, the F1 establishment response may also indicate (for example, via cause information included in message 815) the reason for the rejection or revocation of the DU migration as described above in relation to message 812. In the case of partial acceptance of DU migration (with acceptance of the F1 establishment request), the F1 establishment response may indicate the reason for the partial acceptance of the DU migration.

[0223] In step 1214, the IAB node 570, 701, 801 sends a DU activation response to the source F1 termination donor CU 501, 703, 803. This message indicates the status of the F1 connection establishment with the target F1 termination donor CU 503, 707, 807. It may relay the decision by the target F1 termination donor CU 503, 707, 807 to accept (fully or Petition 870250083679, dated 09 / 17 / 2025, page 87 / 130 75 / 81 partially) or reject or revoke the DU migration from IAB node 570, 701, 801. The message sent in step 1214 may be message 816 shown in and described in relation to figure 8.

[0224] In the case where the target IAB donor CU 503, 707, 807 rejects or revokes the request for DU migration from IAB node 570, 701, 801, response 816 indicates that the target IAB donor CU rejected the request to establish an F1 connection between the target IAB donor CU 503, 707, 807 and IAB node 570, 701, 801 and consequently rejected or revoked the request for DU migration from IAB node 570, 701, 801. Response 816 may include cause information to indicate the reason for the rejection or revocation of the DU migration request to the target donor CU as described in relation to message 812. In the case of partial acceptance of DU migration (with acceptance of the F1 establishment request), response 816 may indicate the reason for the acceptance. partial migration of DU.

[0225] Figure 12c is a flowchart of another example method 1220 according to embodiments of the present invention, for managing, in a target F1 termination donor CU of an IAB node, the migration of DU from the IAB node. For example, method 1220 according to embodiments of the present invention is performed in the target IAB donor CU and is for use in managing, or as part of, a migration procedure / process to migrate a DU from an IAB node from a source IAB donor CU to a target IAB donor CU.

[0226] For example, with reference to the IAB 500 communication system shown in and described in relation to Figure 5, the target IAB donor CU executing method 1220 could be the IAB 5013 donor CU controlling the IAB 5003 topology. The IAB node could be the mobile IAB node 570 belonging to the IAB 5001 topology controlled by the IAB 501 donor CU. The migration process could involve migrating the DU 572 from IAB node 570 from IAB 5001 topology to IAB 5003 topology. With reference to Figures 7 and 8, the IAB node could be IAB node 701, 801 and the migration process could involve migrating the DU from IAB node 701, 801 from the source F1 termination donor CU 703, 803 to the donor CU. of F1 target 707, 807. The 1220 method as shown in and described with respect to Petition 870250083679, dated 09 / 17 / 2025, pp. 88 / 130 76 / 81 Figure 12c can be executed by software and / or hardware elements. The target IAB donor CU can be implemented in a communication device 400 as shown in and described with reference to Figure 4, with the method as shown in and described with reference to Figure 12c being executed by an apparatus for the target IAB donor CU including one or more processing units, such as the central processing unit 411.

[0227] In step 1221, the target F1 termination donor CU, such as donor CU 503 in Figure 5 (707, 807), receives an F1 Establishment Request from IAB node 570, 701, 801, requesting the establishment of the F1 connection and indicating that the F1 connection to be established relates to a DU migration request from IAB node 570, 701, 801 to the target F1 termination donor CU 503, 707, 807. For example, the F1 Establishment Request message sent by IAB node 570, 701, 801 may include an indication that the F1 connection to be established is related to the DU migration from IAB node 570, 701, 801. It may also include part or all of the DU migration context (such as all or part of the (Context information described above). The message received in step 1221 could be message 814 in Figure 8.

[0228] In step 1222, the target F1 termination donor CU 503, 707, 807 determines whether to accept (fully) or partially accept or reject (or revoke if it has previously accepted the DU migration from IAB node 570, 701, 801) the DU migration from IAB node 570, 701, 801 and thus the F1 establishment request. The decision can be based on the current processing resource load of the target F1 termination donor CU 503, 707, 807, or on the current network resource load (wired and / or wireless backhaul) in the IAB topology managed by the target F1 termination donor CU 503, 707, 807. To assist the decision, the target F1 termination donor CU 503, 707, 807 can use the information related to the DU migration context included in the message received in step 1221.

[0229] After determining whether to accept (fully or partially) or reject / revoke the DU migration, the target F1 termination donor CU 503, 707, 807 sends a response indicating whether the target IAB donor CU 503, 707, 807 Petition 870250083679, dated 09 / 17 / 2025, page 89 / 130 77 / 81 accepted (fully or partially) or rejected / revoked the request for DU migration to the target IAB donor CU 503, 707, 807. For example, in step 1223, the target F1 termination donor CU 503, 707, 807 sends a response to the IAB node 570, 701, 803 indicating whether the target F1 termination donor CU 503, 707, 807 accepts (fully or partially) or rejects or revokes the DU migration from the IAB node 570, 701, 801 and thus accepts or rejects the F1 establishment request from the IAB node 570, 701, 801. The message sent in step 1223 could be message 815 in Figure 8.

[0230] In an alternative example (not shown in Figure 12c), the target F1 termination donor CU 503, 707, 807 sends a response to the source F1 termination donor CU 501, 703, 803 (e.g., with the procedure described in Figure 9a) indicating whether the IAB donor CU 503, 707, 807 accepted (fully or partially) or rejected or revoked the request for DU migration to the target IAB donor CU 503, 707, 807. Such a response may also include cause information to indicate the cause of the partial acceptance / rejection / revocation of the request for DU migration to the target donor CU as described above.

[0231] In the case of rejection or revocation, the response, whether an F1 establishment response sent to IAB node 570, 701, 801 or a response sent to the source F1 termination donor CU 501, 703, 803, indicates that the target F1 termination donor CU 503, 707, 807 rejected the F1 establishment request regarding the DU migration request to the target F1 termination donor CU 503, 707, 807. In this case, the response may also indicate (e.g., via cause information) the cause of the DU migration rejection or revocation as described above with respect to message 812.

[0232] Thus, the method / device according to one or more embodiments of the present invention enables the target IAB donor CU to partially accept, reject, or revoke the DU migration (and thus, the subsequent handover of UEs served by the IAB node) if the target IAB donor CU is unable to accommodate the IAB node DU and the traffic related to the served UEs (due to some lack of processing resources or some lack of Petition 870250083679, dated 09 / 17 / 2025, pp. 90-130 78 / 81 radio / network resources) and inform the source IAB donor CU so that appropriate action can be taken. With the target IAB donor CU sending a response to the source IAB donor CU to indicate whether the DU migration was accepted (fully or partially) or rejected, triggering a second logical DU on the IAB node when the DU migration is rejected can be avoided. With the target IAB donor CU sending a response to the IAB node to indicate whether the DU migration was accepted (fully or partially) or rejected, the F1 establishment procedure will already have been completed, which saves establishment time when the DU migration is accepted.

[0233] In other words, and as a summary of DU migration acceptance / rejection, it can be observed that when the DU of a mobile IAB node is migrated from a source F1 donor CU towards a target F1 donor CU, the UEs served by the mobile IAB node will also be delivered towards that target F1 donor CU. Upon receiving a handover request for a UE served by the mobile IAB node, the target F1 donor CU may reject the handover. If this occurs, the cause of the handover preparation failure should not be related to the radio network layer since the traffic associated with the UE is handled by the non-F1 donor CU (or RRC termination donor CU) serving the co-located mobile IAB-MT. However, the cause may be a control processing overload since a CU can handle a limited number of connected UEs. If only some donor CUs support mobile IAB, those donor CUs would handle many IAB nodes and thus many UEs.

[0234] A situation should be avoided where most UE handovers served by a mobile IAB node are rejected by the target F1 donor CU, since these UEs, and especially onboard UEs, will have to be delivered to another cell and will lose the benefit of the mobile cell. Therefore, it may be useful to obtain the status at the target F1 donor CU before initiating the first UE handover.

[0235] For this purpose, the request to establish F1 within the scope of a DU migration may include information related to the number of UEs served by the mobile IAB node. This information would assist the target donor CU in Petition 870250083679, dated 09 / 17 / 2025, pp. 91 / 130 79 / 81 decision to accept or reject the F1 establishment request (due to control processing overload). In case of rejection, another target donor CU may be selected, or a new attempt may be made later.

[0236] So, it is proposed that in the scope of DU migration from a mobile IAB node, the F1 establishment request sent to the target F1 donor CU may include the number of connected UEs served by the mobile IAB node.

[0237] In addition, the target F1 donor CU may be allowed to partially accept DU migration. For example, the target F1 donor CU may partially accept DU migration in the F1 establishment response by indicating the number of UEs it can accommodate.

[0238] So, it is proposed that the target F1 donor CU can accept DU migration from a mobile IAB node with some conditions, for example, with a maximum number of UEs that can be served.

[0239] Although the present invention has been described with reference to examples and embodiments, it should be understood that the invention is not limited to the examples and embodiments disclosed. It will be recognized by those skilled in the art that various alterations and modifications can be made without departing from the scope of the invention as defined in the appended claims. All features disclosed in this descriptive report (including any appended claims, abstract and drawings), and / or all steps of any method or process so disclosed, may be combined in any combination except combinations where at least some of these features and / or steps are mutually exclusive. Each feature disclosed in this descriptive report (including any appended claims, abstract and drawings) may be substituted for alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.Thus, unless expressly stated otherwise, each disclosed feature is only an example of a generic series of equivalent or similar features.

[0240] In claims, the word “including” does not exclude others Petition 870250083679, dated 09 / 17 / 2025, pp. 92 / 130 80 / 81 elements or steps and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain different features are cited in mutually different dependent claims does not indicate that a combination of these features cannot be used advantageously.

[0241] In the preceding embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored in or transmitted through, as one or more instructions or code in a computer-readable medium and executed by a hardware-based processing unit.

[0242] Computer-readable media may include computer-readable storage media that corresponds to a tangible medium such as data storage media, or communication media including any media that facilitates the transfer of a computer program from one place to another, for example, according to a communication protocol. Thus, computer-readable media may generally correspond to (1) tangible computer-readable storage media that is non-transient or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and / or data structures for implementing the techniques described in this disclosure. A computer program product may include computer-readable media.

[0243] By way of example, and not limitation, such computer-readable storage media may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory, or any other media that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly called a computer-readable medium. For example, if instructions are transmitted from a website, Petition 870250083679, dated 09 / 17 / 2025, pp. 93 / 130 81 / 81 server or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave can be included in the definition of medium. It should be understood, however, that computer-readable storage medium and data storage medium do not include connections, carrier waves, signals, or other transient media, but are instead directed to tangible, non-transient storage media. Disc and disk, as used in the present invention, include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc where discs normally reproduce data magnetically while disks reproduce data optically with lasers. Combinations of the above should also be included in the scope of computer-readable medium. Petition 870250083679, dated 09 / 17 / 2025, pp. 94 / 130

Claims

1 / 9 CLAIMS 1. A method for use in managing a migration process to migrate a Distributed Unit (DU) from an Integrated Access Backhaul Node (IAB) from a source IAB topology managed by a Central Unit (CU) of a source IAB donor, to a target IAB topology managed by a target IAB donor CU, the method in the target IAB donor CU being characterized in that it comprises: Receiving, from the IAB node, an F1 establishment request to request the establishment of an F1 connection between the target IAB donor CU and the IAB node and to indicate that the F1 connection to be established refers to a request for DU migration from the IAB node's DU to the target IAB donor CU; Determining whether to accept, partially accept, or reject the DU migration from the IAB node; Send a response indicating that the target IAB donor CU has determined to accept, partially accept, or reject the request for DU migration to the target IAB donor CU.

2. Method, according to claim 1, characterized in that sending a response includes sending, to the IAB node, an F1 establishment response indicating that the target IAB donor CU has determined to accept or reject the F1 establishment request regarding the request for DU migration to the target IAB donor CU.

3. Method, according to claim 1, characterized in that sending a response includes sending, to the source IAB donor CU, a response indicating that the target IAB donor CU has determined to accept, partially accept, or reject the request for DU migration to the target IAB donor CU.

4. A method, according to any one of claims 1 to 3, characterized in that sending comprises: after determining that it should reject the DU migration, sending a response indicating that the target IAB donor CU rejected the request for DU migration to the target IAB donor CU.

5. Method, according to any of claims 1 to 4, Petition 870250083679, dated 09 / 17 / 2025, pp. 121 / 130 2 / 9 characterized in that if the response indicates that the target IAB donor CU has partially accepted or rejected the request for DU migration to the target IAB donor CU, the response includes cause information to indicate the cause of the partial acceptance or rejection of the request for DU migration to the target IAB donor CU.

6. Method, according to any one of claims 1 to 3, characterized in that sending comprises: after determining that it should accept or partially accept the DU migration, sending a response indicating that the target IAB donor CU has accepted or partially accepted the request for DU migration to the target IAB donor CU.

7. A method according to claim 1 or claim 6, characterized in that the determination comprises: Comparing resources available in the target IAB donor CU with resources required to support the IAB node and the User Equipment (UEs) served by the IAB node; after determining that the available resources are not sufficient to support the resources required by the IAB node and the UEs served by the IAB node, selecting at least one of: some of one or more traffic profiles associated with the IAB node; and some of the UEs served by the IAB node; and deciding to partially accept the request for DU migration to the selected traffic profiles and / or UEs.

8. Method according to claim 7, characterized in that the comparison of resources available in the target IAB donor CU comprises at least one of: Comparing the resources available in the target IAB donor CU with the resources required to support all of one or more traffic profiles associated with the IAB node; Comparing a number of additional UEs that can be connected to the target IAB donor CU with the number of UEs served by the IAB node.

9. Method, according to claim 7 or claim 8, characterized in that the selection comprises selecting based on one or more of: Priority of each traffic profile associated with the IAB node; Onboard status of each UE served by the IAB node.

10. A method, according to any one of claims 6 to 9, characterized in that it further comprises: After determining whether to accept or partially accept the request for DU migration, determining the revocation of the DU migration from the IAB node to the target IAB donor CU; Sending a revocation response indicating that the target IAB donor CU has determined the revocation of the DU migration from the IAB node to the target IAB donor CU.

11. Method, according to claim 10, characterized in that sending a revocation response includes sending, to the IAB node, an F1 establishment response indicating that the target IAB donor CU has determined to revoke the F1 establishment request regarding the request for DU migration to the target IAB donor CU.

12. Method, according to claim 10, characterized in that sending a response includes sending, to the source IAB donor CU, a response indicating that the target IAB donor CU has determined to revoke the request for DU migration to the target IAB donor CU.

13. Method for use in managing a migration process to migrate a Distributed Unit, DU, of an Integrated Access Backhaul, IAB, node, from a source IAB topology managed by a source IAB donor Central Unit, CU, to a target IAB topology managed by a target IAB donor CU, the method in the source IAB donor CU being characterized by comprising: Determining that the IAB node's DU should be migrated to the target IAB donor CU; Sending a request to the IAB node to establish an F1 connection between the target IAB donor CU and the IAB node; Petition 870250083679, dated 09 / 17 / 2025, p. 123 / 130 4 / 9 Receive a response indicating that the target IAB donor CU has accepted, partially accepted, or rejected the request to migrate DU to the target IAB donor CU.

14. Method, according to claim 13, characterized in that the transmission comprises sending, to the IAB node, a request to establish an F1 connection between the target IAB donor CU and the IAB node and informing the target IAB donor CU that the F1 connection to be established refers to a request for DU migration from the IAB node to the target IAB donor CU.

15. Method, according to claim 13 or claim 14, characterized in that receiving a response comprises: receiving, from the IAB node, a response indicating whether the target IAB donor CU has accepted or rejected a request to establish the F1 connection between the target IAB donor CU and the IAB node relating to the request for DU migration to the target IAB donor CU.

16. Method, according to claim 13 or claim 14, characterized in that receiving a response comprises: receiving, from the target IAB donor CU, a response indicating that the target IAB donor CU has accepted, partially accepted, or rejected the request for DU migration from the IAB node to the target IAB donor CU.

17. A method, according to any one of claims 13 to 16, characterized in that the receipt comprises: receiving a response indicating that the target IAB donor CU rejected the request for DU migration to the target IAB donor CU, when the DU migration was rejected by the target IAB donor CU.

18. Method, according to any one of claims 13 to 17, characterized in that if the response indicates that the target IAB donor CU has partially accepted or rejected the request for DU migration to the target IAB donor CU, the response includes cause information to indicate the cause of the partial acceptance or rejection of the request for DU migration to the target IAB donor CU. Petition 870250083679, dated 09 / 17 / 2025, pp. 124 / 130 5 / 9 19. A method according to claim 13 or claim 17, characterized in that it further comprises: after receiving a response indicating that the target IAB donor CU has rejected the request for DU migration, terminating the execution of the migration process to migrate the DU from the IAB node to the target IAB donor CU.

20. A method, according to any one of claims 13 to 16, characterized in that the receipt comprises: receiving a response indicating that the target IAB donor CU has accepted or partially accepted the request for DU migration to the target IAB donor CU, when the request has been accepted or partially accepted by the target IAB donor CU.

21. Method, according to claim 20, characterized in that it further comprises: receiving a revocation response indicating that the target IAB donor CU has determined the revocation of the DU migration from the IAB node to the target IAB donor CU.

22. A method, according to any one of claims 10 to 12 or claim 21, characterized in that the revocation response includes cause information to indicate the cause of the revocation of the DU migration to the target IAB donor CU.

23. Method for use in managing a migration process to migrate a Distributed Unit (DU) from an Integrated Access Backhaul (IAB) node, from a source IAB topology managed by a source IAB donor Central Unit (CU), to a target IAB topology managed by a target IAB donor CU, the method on the IAB node being characterized by comprising: Receiving from the source IAB donor CU a request to establish an F1 connection between the target IAB donor CU and the IAB node; Sending to the target IAB donor CU an F1 establishment request to request the establishment of the F1 connection and indicating that the F1 connection to be established refers to a request for DU migration from the IAB node to the target IAB donor CU; Receive a response from the F1 establishment indicating that the CU of Petition 870250083679, dated 09 / 17 / 2025, page.125 / 130 6 / 9 Target IAB donor accepted or rejected the F1 establishment request regarding the request for DU migration to the target IAB donor's CU.

24. Method, according to claim 23, characterized in that receiving a request to establish an F1 connection comprises receiving, from the source IAB donor CU, a request to establish an F1 connection between the target IAB donor CU and the IAB node and informing the target IAB donor CU that the F1 connection to be established refers to a request for DU migration from the IAB node to the target IAB donor CU.

25. A method according to claim 23 or claim 24, characterized in that it further comprises: sending to the source IAB donor CU a response indicating whether the target IAB donor CU has accepted or rejected a request to establish the F1 connection between the target IAB donor CU and the IAB node related to the request for DU migration to the target IAB donor CU.

26. Method, according to claim 23 or claim 24 or claim 25, characterized in that receiving an F1 establishment response comprises: receiving an F1 establishment response indicating that the target IAB donor CU rejected the F1 establishment request regarding the request for DU migration to the target IAB donor CU, when the DU migration was rejected by the target IAB donor CU.

27. Method, according to claim 26, characterized in that the F1 settlement response includes cause information to indicate the reason for the rejection of the request for DU migration to the target IAB donor CU.

28. Method, according to claim 27, characterized in that the response sent to the source IAB donor CU includes cause information to indicate the reason for the rejection of the request for DU migration to the target IAB donor CU.

29. Method, according to claim 23 or claim 24 or claim 25, characterized in that receiving an F1 establishment response comprises: receiving an F1 establishment response indicating that the target IAB donor CU has accepted the F1 establishment request regarding the request for DU migration to the target IAB donor CU, when the DU migration has been accepted or partially accepted by the target IAB donor CU.

30. Method, according to claim 29, characterized in that in the case where the DU migration was partially accepted, at least one of the F1 establishment response and the response sent to the source IAB donor CU includes cause information to indicate the cause of the partial acceptance of the request for DU migration to the target IAB donor CU.

31. A method according to claim 29 or claim 30, characterized in that it further comprises: receiving, from the target IAB donor CU, a revocation response indicating that the target IAB donor CU has determined the revocation of the DU migration from the IAB node to the target IAB donor CU.

32. Method, according to claim 31, characterized in that the revocation response includes cause information to indicate the cause of the revocation of the DU migration to the target IAB donor CU.

33. A method, according to any one of claims 13 to 32, characterized in that the request to establish an F1 connection is included in a DU activation request message.

34. A method, according to any one of claims 13 to 33, characterized in that the request to establish an F1 connection includes an Information Element, IE, to indicate that the IAB node must inform the target IAB donor CU that the F1 connection to be established refers to a request for DU migration from the IAB node to the target IAB donor CU.

35. A method, according to any one of claims 13 to 34, characterized in that the request to establish an F1 connection includes context information relating to the context of DU migration to the target IAB donor CU.

36. Method, according to claim 35, characterized by the fact that Petition 870250083679, dated 09 / 17 / 2025, pp. 127 / 130 8 / 9, indicates that the application states that the IAB node must provide at least some of the context information to the target IAB donor CU.

37. A method, according to any one of claims 1 to 12 or claims 23 to 36, characterized in that the F1 establishment request to establish an F1 connection includes context information relating to the context of DU migration to the target IAB donor CU.

38. Method, according to claim 35 or claim 36 or claim 37, characterized in that the context information includes at least one of: Identification information to identify the IAB node; Identification information to identify an IAB donor CU serving the Mobile Termination, MT of the IAB node; Priority information to indicate a priority level for the DU migration request; Traffic profile information to indicate a user traffic profile associated with the IAB node; Traffic transmission capacity information to indicate the user traffic transmission capacity associated with the IAB node; User Equipment, UE, information to indicate a number of UEs served by the IAB node; Onboard UE information to indicate a number of onboard UEs served by the IAB node.

39. Method according to claim 38, characterized in that the identification information for identifying the IAB node includes at least one of: identification information known by the IAB donor CU of the source for identifying the IAB node; identification information known by an IAB donor CU serving the IAB node MT for identifying the IAB node.

40. Apparatus for an Integrated Backhaul and Access, IAB, Donor Central Unit, CU, node of an IAB communication system, the apparatus being characterized by comprising: Petition 870250083679, dated 09 / 17 / 2025, pp. 128 / 130 9 / 9 One or more processing units configured to perform the method according to any one of claims 1 to 12 or claims 33 to 39.

41. Apparatus for an Integrated Backhaul and Access, IAB, node of an IAB communication system, the apparatus being characterized in that it comprises: One or more processing units configured to execute the method according to any of claims 23 to 39.

42. Computer-readable storage medium characterized in that it contains a computer program comprising program instructions which, when the computer executes it through one or more processing units in a device, causes the device to perform the method as defined in any one of claims 1 to 39. Petition 870250083679, dated 09 / 17 / 2025, pp. 129 / 130

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