Methods and apparatus for a wireless communication system

Abstract

Methods and apparatus for managing a PDU session established for a wireless access backhaul, WAB, node are disclosed. The WAB node includes a gNB component WAB-gNB and a MT component, WAB-MT and the g

Description

FIELD OF THE INVENTION The present invention generally relates to methods and apparatus for a wireless communication system. In particular, the disclosure relates to methods for use in managing a PDU session established for a Wireless Access Backhaul, WAB node in a wireless communication system. BACKGROUND Wireless communication systems are largely deployed to address a wide range of applications, from mobile broadband, 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 several types of data content (e.g. video, voice, messaging ...) over a radio access network (RAN) through one or more base stations (gNBs). The base stations are conventionally wired-connected (e.g. through fiber) to a core network, forming an intermediate network, named backhaul (BH). Examples of such wireless multiple-access communication systems include systems based on 3rd generation partnership project (3GPP - RTM) standards, such as fourth-generation (4G) Long Term Evolution (LTE) or recent fifth-generation (5G) New Radio (NR) systems, or systems-based IEEE 802.11 standards, such as WiFi. The demand for network densification increases due to the rising number of users and higher throughput requirement. Facing the issues of high deployment costs and time of the wired backhaul networks with network densification, 3GPP has proposed, from release 16 for 5G NR, a wireless backhaul, also known as Integrated Access and Backhaul, IAB, where part of the wireless (i.e. radio) spectrum is used for the backhaul connection of base stations instead of fiber. The wireless backhaul communications (between base stations) may use the same radio resources as access communications (between a base station and UEs). IAB turns out to be a competitive alternative to the fiber-based backhauling in dense areas or areas difficult to cover, as it allows scalable and rapid installations without the burden of cabling the base stations. IAB is most likely to operate in the millimeter wave (mmWave) band to achieve the required Gbps (gigabits per second) data rate. Urban environments are usually characterised by a high density of users along with the presence of a significant number of vehicles (e.g. public / private passengers transportation, goods delivery, food trucks ...). The speed of some of the vehicles may be pretty low or at least similar to pedestrian speed and some of these vehicles may even be temporarily stationary. Some of these vehicles (e.g. buses, trains or trams), may have predictable routes and / or limited mobility areas (e.g. some vehicles, such as food trucks or promotional vehicles, may be located outside stadiums or show venues) while others may have predictable stationary locations (e.g. taxis). 3GPP is considering that such vehicles could offer an opportunity to increase network coverage and connectivity to the UEs inside the vehicles, or even to UEs in proximity to the vehicles, by installing on these vehicles on-board base stations (or base station elements) that would act as relays. These relays would rely on 5G wireless backhaul (typically IAB, or Integrated Access &Backhaul) for connecting to a fixed donor device. Thus, based upon the fixed IAB foundations set out in Releases 16 and 17, 3GPP is now considering mobile IAB systems and architecture, as a part of the Release 18 framework, in order to address scenarios focusing on mobile lAB-nodes mounted on vehicles (for example, a bus, a train, a taxi). In such scenarios, mobile lAB-nodes can also be referred to as Vehicle Mounted Relays (VMR), providing 5G coverage / capacity to on-board and / or surrounding UEs. The technical benefits of using vehicle relays include, among others, the ability of the relay vehicle to get better coverage than the nearby UE, thanks to better RF / antenna capabilities, thus providing the UE with a better link to the macro network. Additionally, a vehicle relay is expected to have less stringent power / battery constraints than the UEs. Some enhancements further considered by 3GPP for Release 19, consider the need for 5G access for UEs onboard aircrafts, cruise ships, helicopters and vehicles in remote areas with limited sky visibility (e.g. where terrestrial cellular coverage or Wi-Fi coverage is not available), support for onboard / on-site mobile edge computing (MEC), local services, and direct local inter-UE communications, or local gNB deployment in public safety or disaster recovery scenarios. The backhauling links for the base stations providing the 5G access in such scenarios would then be operated over either a terrestrial network (TN), or a non-terrestrial network (NTN), with a possibility to handover communications from a terrestrial network to a non-terrestrial network and vice-versa. Such base stations can be referred to as Wireless Access Backhaul (WAB) nodes, or mobile WAB nodes, or WAB nodes. As part of these wireless backhauling enhancements, 3GPP is also considering some evolution to the former LTE-based Femto framework, including a new 5G Femto or 5G Femtocell that would offer 5G indoor coverage improvement while allowing high bandwidth and throughput at home for new immersive applications such as AR / VR / MR gaming, e-sports, UHD 8K video, telepresence, etc. It can be noted that a WAB node may deploy 5G Femto cells to serve UEs inside vehicles. WAB nodes serving UEs use backhaul links to exchange data (in the user plane and the control plane) and these backhaul links are wireless in the context of WAB networks. It means that the NG protocol messages exchanged between the base station of a WAB node and the core network, and the Xn protocol messages exchanged between the base station of a WAB node and other base stations of the Radio Access Network, are transmitted through a wireless link. Actually, NG and Xn protocols are designed for wired networks, meaning that these protocols assumed that the medium used for the transmission of messages is reliable. When applied to communication through wireless links, these protocols are not resilient to degradation of the wireless link quality. As a consequence, some NG and Xn procedures may fail in the context of WAB networks because of poor radio conditions and / or high load (congestion) on the wireless backhaul link. This situation may lead to system failure and interruption of service at the UEs served by a WAB node. There is therefore a need to manage communications over wireless links in a network including a WAB node. SUMMARY In accordance with an aspect of the present invention there is provided a method for managing a PDU session established for a wireless access backhaul, WAB, node. The WAB node includes a gNB component and a MT component, and the gNB component is configured to serve a User Equipment, UE. The method at the WAB node includes requesting modification of the WAB node PDU session based on at least one of: configuration of one or more radio bearers established for one or more radio interfaces at the WAB node; link quality of each of one or more radio interfaces at the WAB node. The requesting modification may include adding a new QoS flow to the WAB node PDU session or modifying an existing QoS flow of the WAB node PDU session. The configuration may include one of an AM, UM, TM configuration. In accordance with another aspect of the present invention there is provided an apparatus for a WAB node as recited in claim 47 of the accompanying claims. The invention provides a mechanism for modifying a PDU session established for a WAB node based on configuration of one or more radio bearers for one or more radio interfaces of the WAB node and / or link quality of each of one or more radio interfaces. QoS flows of the PDU session at a radio interface of the WAB node (e.g. a backhaul PDU session at a Uu_MT radio interface connecting the WAB-MT to the backhaul or UE PDU session at a Uu_UE radio interface connecting the WAB-gNB to a UE) can therefore be modified so as to match or substantially match one or more QoS or signalling flows at another radio interface of the WAB node (e.g. a Uu_UE radio interface connecting the UE to the WAB-gNB or Uu_MT radio interface), with a result that the configuration of the two radio interfaces (Uu interfaces of the WAB node) can be aligned. In the case where the backhaul part (Uu_MT up to core network) becomes less reliable because of disturbances on Uu_MT, the alignment on Uu_UE allows securing the communications while legacy systems always consider the communications between the base station and core network to be reliable because it is implemented on wired technologies. In the case where a WAB node serves one or more UEs which involves communication (data and signalling) between a UE and the network over at least two wireless radio interfaces (Uu_UE interface and Uu_MT), aligning the radio interfaces (e.g. the QoS / signalling flows and the radio bearers (DRB / SRB) helps to optimise use of resources, minimise latency where possible, whilst maintaining reliability as required. In addition, modifying the configuration so as to align the two Uu interfaces helps to avoid any differences in behaviour between base stations provided by different manufacturers. When the PDU session is modified based on both the configuration of radio bearers and link quality (for example, see the discussions with respect to figure 12), the accuracy of the reliability assessment is improved which helps to ensure the ‘best’ or ‘optimum’ modification of the radio interfaces is followed. Further example features of the invention are described in other independent and dependent claims. Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus / device / unit aspects, and vice versa. Furthermore, features implemented in hardware may be implemented in software, and vice versa. Any reference to software and hardware features herein should be construed accordingly. For example, in accordance with other aspects of the invention, there are provided a computer program comprising instructions which, when the program is executed by one or more processing units, cause the one or more processing units to carry out the method of any aspect or example described above and a computer readable storage medium carrying the computer program. BRIEF DESCRIPTION OF THE DRAWINGS Different aspects of the invention will now be described, by way of example only, and with reference to the following drawings in which: Figure 1 is a schematic diagram of a communication system in which the present invention may be implemented according to one or more example embodiments; Figure 2 is a simplified schematic diagram of a 5G system in which the present invention may be implemented according to one or more example embodiments; Figure 3 is a simplified schematic diagram of a 5G system involving a Wireless Access Backhaul (WAB) node, and in which the present invention may be implemented according to one or more example embodiments. Figure 4 is a block schematic diagram of an example network node or base station in accordance with one or more embodiments of the invention; Figure 5 is a simplified schematic diagram showing an example of a wireless communication system, including a WAB network or WAB network system, in which embodiments and examples of embodiments of the present invention may be implemented; Figure 6 is a schematic diagram illustrating the protocol stack associated to the NG interface in the control plane (NG-C); Figure 7 is a schematic diagram illustrating the protocol stack associated to the NG interface in the user plane (NG-U); Figure 8 is a schematic diagram showing example message flows for establishing a PDU session for a UE in accordance with one or more embodiments of the invention; Figure 9 is a schematic diagram showing example message flows for establishing a control interface in accordance with one or more embodiments of the invention; Figure 10 is a schematic diagram showing an example message flows for monitoring a backhaul PDU Session in accordance with one or more embodiments of the invention; Figure 11 is a table showing an example comparing different bearer configurations on Uu_UE and Uu_MT in accordance with one or more embodiments of the invention; Figure 12 is a table showing an example comparing both the different bearer configurations and the link qualities on Uu_UE and Uu_MT in accordance with one or more embodiments of the invention; Figure 13 is a flowchart of an example method 1300 for managing backhaul sessions at a WAB-MT of a WAB-node in accordance with one or more embodiments of the present invention. DETAILED DESCRIPTION Figure 1 illustrates an example communication system 100 in which the present invention may be implemented according to one or more embodiments. As depicted, the example system 100 is a wireless communication system, in particular a mobile radio communication system such as a fifth-generation (5G) New Radio (NR) system including a Wireless Access Backhaul (WAB) communication system or network. Although in the following description, embodiments and examples of embodiments of the present invention will be described with respect to a 5G NR system, it will be appreciated that it is not intended that the present invention is limited to 5G NR systems and may be used in any wireless communication systems having an integrated access and backhaul communication system which shares radio resources for wireless access links and wireless backhaul links. The system 100 comprises a plurality ofUEs (User Equipment) 111, 112, 113, 121, 122, 123, 131, 132, 133, 134, 141, 142, 143, 151, 152, 153 and 154, a communication satellite 160, a satellite dish 101, a remote core network 170, three fixed Base Stations 102, 103 and 104, a plurality of Wireless Access Backhaul (WAB) nodes 110 (mounted on plane 161), 120a and 120b (mounted on train 162), 140 (mounted on Unmanned Aerial Vehicle (UAV) UAV 164) and 150 (mounted on backpack 165 or other carrier that can be carried by a user (e.g. in a disaster zone)), and a Wireless Access Backhaul node 130 (or Home gNB, mounted in house 163) which is fixed but based on the same architecture as a WAB node. In more general terms, the WAB node may be mounted on or in a vehicle (such as a train, bus, taxi, tram, etc.) and / or an aircraft or flying vehicle (such as a plane, UAV, helicopter, etc. ) and / or a building (such as a house, enterprise / company / office building, hotel building, airport building, sports / event buildings, shopping centre building, etc..) and / or a portable carrier that can be carried by a user (such as a backpack, bag, etc), for example, in a disaster zone or for public safety or for emergency services, and / or public infrastructure elements or units (such as lamp posts, traffic lights, etc.). In an example where the WAB node is implemented in a Femto network, the WAB node functions as a 5G Femto node and may be mounted at a building (such as a house, enterprise / company / office building, hotel building, airport building, sports / event buildings, shopping centre building, etc..) and / or public infrastructure elements or units (such as lamp posts, traffic lights, etc.). When it is a mobile base station, a WAB node is also referred to as a Mobile WAB (MWAB) node. Some examples ofUEs include smartphones / tablets (such as UEs 111, 123, 134, 142, 152), XR headsets (such as UEs 112, 122, 132), cameras (such as UEs 141 and 151), fixed video cameras (such as UEs 113, 121, 133, 153) or mobile / wearable video cameras (such as UEs 143 and 154). In general, the UE may be any portable or handheld or mobile telephone, a smartphone, a tablet, a portable or fixed computer, fixed or mobile camera, portable television or other similar wireless communication device. In the following description, the term UE will be used and it is not intended to limit the description to any particular type of wireless communication device. Base stations 102, 103 and 104 are interconnected through a wired link infrastructure 180, preferably based on optical fiber or any other wired means. Base stations 102, 103 and 104 are also connected to the core network 170 through a wired link infrastructure 190, preferably based on optical fiber or any other wired means. In embodiments and examples of embodiments of the invention, base stations 102, 103 and 104 are 5G NR base stations (referred to as a gNB), as defined in 3GPP TS 38.300 vl8.0.0 specification document. Satellite dish 101 (e.g. satellite gateway) is also connected to wired link infrastructure 180 or 190, or to both infrastructures. Besides infrastructures 180 and 190 may be the same infrastructure. In one example, a part of a base station is embedded in the satellite 160 while the other part is embedded in the gateway 101, meaning that the base station is split between the satellite 160 and the gateway 101. In another example, a full base station is embedded in the satellite 160 and the gateway 101 connects the base station 160 with the infrastructure 180 or 190. In case of non-geostationary satellite, the satellite 160 may connect to different gateways, like the gateway 101, while the satellite 160 is moving around the earth. In order to extend the network coverage of base stations 102,103 and 104 and reach the remote UEs 111, 112, 113, 121, 122, 123, 131, 132, 133, 134, 141, 142, 143, 151, 152, 153 and 154, mobile WAB nodes or WAB nodes, or WAB-nodes, 110, 120a, 120b, 130, 140 and 150, have been installed on vehicles / mobile equipment 161, 162, 163, 164 and 165. By acting as relaying nodes between the base stations 102, 103 and 104 and the UEs 111, 112, 113, 121, 122, 123, 131, 132, 133, 134, 141, 142, 143, 151, 152, 153 and 154, WAB-nodes 110, 120a, 120b, 130, 140 and 150 allow overcoming the reachability issue resulting from limited sky visibility while ensuring support for onboard / on-site mobile edge computing (MEC), local services, and direct local inter-UE communications. This allows further communication between base stations 102, 103 and 104 and the UEs 111, 112, 113, 121, 122, 123, 131, 132, 133, 134, 141, 142, 143, 151, 152, 153 and 154 and / or communications between the UEs served by a same WAB-node (e.g., UEs 151, 152, 153 and 154 connected to WAB node 150). The base stations 102, 103 and 104, the WAB nodes 110, 120a, 120b, 130, 140 and 150, the satellite 160, the satellite dish 101 are thus forming a backhaul network or WAB network (also referred to as WAB topology), or WAB network (also referred to as WAB topology), which accommodates UEs 111, 112, 113, 121, 122, 123, 131, 132, 133, 134, 141, 142, 143, 151, 152, 153 and 154. The terms WAB network, WAB network, WAB topology and WAB topology will be used interchangeably in the following. The WAB network is part of the Radio Access Network (RAN) or as referred to with respect to 5G, the Next Generation (NG) RAN. The base stations 102, 103 and 104, the WAB nodes 110, 120a, 120b, 130, 140 and 150, the satellite 160, the satellite dish 101, and the core network 170 are thus forming a WAB system, or WAB system, which accommodates UEs 111, 112, 113, 121, 122, 123, 131, 132, 133, 134, 141, 142, 143, 151, 152, 153 and 154. The terms WAB system and WAB system will be used interchangeably in the following. A base station, or gNB, such as base station 102, 103 or 104, is a logical node that provides the NR-connectivity, hosting both higher layer protocols, such as PDCP (Packet Data Convergence Protocol) and RRC (Radio Resource Control) protocols, and lower layer protocols, such as the RLC (Radio Link Control), MAC (Medium Access Control) and physical layer protocols. The WAB nodes 110, 120a, 120b, 130, 140 and 150, which may serve multiple radio sectors, are wireless backhauled to the base station 102, 103 or 104, via a single logical hop associated to a single radio link (i.e., radio links D1041a, D1041b, D1031, D1022, D1021), or split into two radio links in the case of satellite relaying (radio links DI60la and DI60lb). Although a single logical hop is shown in figure 1, it will be appreciated that the WAB nodes could be wirelessly backhauled to the base station over multiple logical hops (for example, similar to the multiple hops provided in an IAB network). Each WAB node consists of or includes a gNB or RAN node or base station component or entity which is referred to as a WAB-gNB, or WAB base station, and Mobile Termination (MT) component or entity which is referred to as an IAB-MT, or WAB-Mobile Termination. The WAB-gNB functionality on an WAB-node allows or enables the WAB-node to serve UEs. The WAB-MT functionality includes, e.g., physical layer, layer-2, RRC and Non-Access Stratum (NAS) functionalities and allows or enables the WAB-MT to connect to a fixed base station, or gNB, such as base station 102, 103 or 104 and to support backhauling of traffic related to the WAB-gNB of the WAB node. The WAB-gNB may also be referred to as a NG-RAN node (of a WAB node) and the WAB-MT may also be referred to as a UE (of a WAB node). WAB nodes 110, 120a, 120b, 140 and 150 are intended to be mobile devices that will move along with the vehicle they are mounted on. However, these WAB nodes may remain at a fixed location for a significant duration when their associated vehicle is remaining still (e.g., a train may stop at a railway station, a plane may be parked at an airport for a while, a car / truck / fire engine or any other emergency vehicle may be parked nearby a disaster area). WAB node 130 is likely to remain at fixed location and may be a 5G Femto node, which provides NR access at home or at enterprise premises. In such case, the 5G Femto node 130 may have a direct connection DI700 to the Core Network 170 through the wired link infrastructure 190, which is preferably based on optical fiber or any other wired means. Figure 2 is a simplified schematic diagram of a 5G system 200 in which the present invention may be implemented according to one or more example embodiments. This figure illustrates the possible standardized interfaces between the various elements composing the system. First, it represents a User Equipment (UE) 201 having a Uu interface with the New Generation (NG) Radio Access Network (RAN or NG-RAN) 202, and a N1 interface with an Access and Mobility management Function (AMF) entity or AMF 212 in a 5G core network (5GC) 210. Each base station composing the RAN 202 has a N2 interface with one or more Access and Mobility management Function (AMF) entity or AMF, like AMF 212, and a N3 interface with one or more User Plane Function (UPF) entity or UPF, like UPF 211. The N1 interface is used to convey Non-Access Stratum (NAS) protocol messages between a UE 201 and an AMF 212. NAS messages are used for the signaling between the UE and the core network for various procedures such as registration, session establishment, security, and mobility management. Actually, NAS messages are conveyed through the Uu interface between the UE 201 and the RAN 202, and the N2 interface between the RAN 202 and the AMF 212. An AMF 212 is responsible for handling registration, authentication, connection and mobility management tasks for a UE. For a WAB node, the AMF may apply the procedures defined in NAS protocol specifications (TS 24.502 section 5), considering the WAB node is a Mobile Base Station Relay (MBSR) introduced in Release 18. There may be several AMFs in a 5G core network, a standardized interface N14 enables the communications between AMFs. When a UE registers to the network through a serving base station, the serving base station will connect to an AMF suitable to handle the UE. When the UE 201 is registered, one or more Protocol Data Unit (PDU) session(s) can be set up to transfer data flows between the UE 201 and the Data Network (DN) 220 providing internet access. A PDU session is established between a UE 201 and a User Plane Function (UPF) 211 in the 5G core network 210. In the user plane, the UPF 211 connects to the Data Network (DN) 220 through the interface N6, and it is responsible for data packets routing with the required Quality of Service (QoS). There may be several UPFs on the data path with a N9 interface between UPFs. The user data between a UE 201 and the Data Network 220 are thus conveyed through interfaces Uu, N3, N6 and potentially N9. In the control plane, the setup of PDU sessions is handled through NAS messages involving the Session Management Function (SMF) entity or SMF 213 in the 5G core network 210. The NAS messages are still exchanged between the UE 201 and the AMF 212 through the N1 interface, but an additional interface N11 between an AMF 212 and the SMF 213 is used to reach the SMF 213. In a 5G core network, the SMF is responsible for the setup, modification, and release of PDU sessions for a UE, as well as the Internet Protocol (IP) address allocation for the UE. To manage a PDU session, the SMF 213 controls the UPF 211 (configuration) based on QoS policy defined for the PDU session. For this purpose, a N4 interface exists between the SMF 213 and the UPF 211. A base station in RAN 202 operating in a first Public Land Mobile Network (PLMN) may serve a UE having a subscription for a second PLMN (called home PLMN) different from the first PLMN (called visited PLMN). In such a roaming case, there are two options to provide the UE 201 with an access to the Data Network 220. In a first option called home routed, the UPF and its controlling SMF to access the Data Network 220 are located in the 5G core network for the home PLMN. However, the SMF of the visited PLMN controls the intermediate UPF(s) of the visited PLMN, and interacts with the SMF of the home PLMN. In a second option called local breakout, the UPF and its controlling SMF to access the Data Network 220 are located in the 5G core network for the visited PLMN. However, the SMF interacts with the home 5G core network to get QoS policies associated with the UE’s PDU session(s). Nl, N2, N3, N4, N6, N9, Nil, N14 may also be called reference points as defined in TS 23.501. Figure 3 is a simplified schematic diagram of a 5G system 300 involving a Wireless Access Backhaul (WAB) node (or a MW AB node), and in which the present invention may be implemented according to one or more example embodiments. This figure first represents a User Equipment (UE) 301 served by a WAB node 310 through the Uu interface (which may be referred to as a Uu_UE interface or link). The WAB node 310 is composed of or includes a MT or WAB-MT or MWAB-MT unit / component / entity 311 (also called WAB-UE), and a gNB or WAB-gNB, or MWAB-gNB unit / component / entity 312. Through the WAB-gNB 312, a WAB node acts as a gNB for UEs providing access to the 5G network, i.e. providing a NR access link to the UEs that can be located inside or outside the entity, such as a vehicle, equipped with the WAB node 310 (e.g. on entering / leaving the vehicle). In other words, the WAB-gNB 312 includes full base station or gNB function (including both Central Unit (CU) and distributed unit (DU)) and MT function, where the gNB function is used to communicate with UEs for access service and the MT function is used to communicate with another gNB for backhauling purpose. The WAB node 310 wirelessly connects to the 5G Core Network (using NR Uu interface) through an IP connectivity provided by PDU session(s) established by the WAB-MT 311 via a gNB 320, which can be called a backhaul RAN node, BH RAN node, backhaul base station, backhaul gNB or BH gNB. The Uu interface between the WAB-MT 311 and the BH gNB 320 may be referred to as a Uu_MT interface or link. Acting as a legacy UE, the WAB-MT 311 connects via a NG-RAN cell of the BH gNB 320, through a backhaul link (e.g. a wireless backhaul link) that may be a direct link or via a satellite (e.g. when the WAB node 310 is embedded in an airplane). Thus, a PDU session is provided either by a Terrestrial Network (TN) or by a Non-Terrestrial Network (NTN). In addition, the WAB node 310 may embed some core network functions, like a UPF 313, to enable local services to the served UEs. The traffic associated to these local services does not need to use the links to / from the core network via the BH gNB 320, which has the advantages to reduce the load on these links and to run applications having very low latency requirements. For example, where the WAB node 310 includes a UPF 313, the WAB node can connect to one or more local servers (e.g. mounted at the same entity as the WAB 310) enabling a UE served by the WAB access to local services provided by the local servers with no traffic required outside of the WAB node / server environment. The BH gNB 320 provides N3 and N2 interfaces so that the WAB-MT 311 can access the functions of its 5G core network 330 (or backhaul 5GC or BH 5GC). Indeed, a WAB-MT 311 may have access to some or several PLMNs through the appropriate subscriptions, and it may connect in a non-roaming manner to one PLMN, e.g. PLMN1 supported by the BH gNB 320, and may then have access to the corresponding 5G core network 330. In particular the WAB-MT 311 interacts with the AMF 332, which can be called the WAB AMF or backhaul AMF or BH AMF, and establishes PDU session(s) with the UPF 331, which can be called the WAB UPF or backhaul UPF or BH UPF. The WAB UPF 331 is controlled by the SMF 333 (through N4 interface), which can be called the WAB SMF or backhaul SMF of BH SMF, and which also interacts with the WAB AMF 332 (through N11 interface). There may be one or several intermediate UPFs between the BH gNB 320 and the WAB UPF 331 as mentioned in the Figure 2. An interface internal to the WAB node 310 exists between the WAB-gNB 312 and the WAB-MT 311, which may be implemented on different or the same hardware resources. For instance, these two functions are implemented on the same processing unit 402 of Figure 4, and interactions exist between the two functions. Once the WAB-MT 311 has established a PDU session with the WAB UPF 331, the WAB node is ready to serve UEs and the WAB-gNB 312 can start operating as a legacy gNB. The WAB-gNB may support various PLMNs and the UE 301 connects to one PLMN, e.g. PLMN2, which may be different from the PLMN 1 the WAB-MT 311 connects to. In the case where PLMN 1 and PLMN2 are different, the UE 301 connects to the 5G core network 340 (or UE 5GC), including a UPF 341, which can be called the UE UPF, an AMF 342, which can be called the UE AMF, and a SMF 343, which can be called the UE SMF. The UE SMF 343 interacts with the UE AMF 342 (through N11 interface) and the UE UPF 341 (through N4 interface). In the case where the PLMN1 and the PLMN2 are the same, the UE UPF 341, the UE AMF 342, the UE SMF 343, the WAB UPF 331, the WAB AMF 332, and the WAB SMF 333 belong to the same 5G core network 350. In addition, the UE UPF 341 and the WAB UPF 331 may be the same UPF, the UE AMF 342 and the WAB AMF 332 may be the same AMF, the UE SMF 343 and the WAB SMF 333 may be the same SMF. The connections between the UE 301 to the UE UPF 341 and to the UE AMF 342 are possible thanks to the N6 interface between the UE UPF 341 and the WAB UPF 331, and thanks to the N6 interface between the WAB UPF 331 and the UE AMF 342. These N6 interfaces enable the establishment of N2 interface between the WAB-gNB 312 and the UE AMF 342, and the establishment of N3 interface between the WAB-gNB 312 and the UE UPF 341, which allows the UE 301 to access the Data Network 360. In case the WAB-MT 311 connects to the 5G network in a roaming manner corresponding to the home routed option, then the PLMN1 is the visited PLMN and the WAB UPF 331 connects to another UPF not represented in the Figure 3 in the home PLMN through a N9 interface. It is this other UPF that provides the connection to the UE UPF 341 and the UE AMF 342 through N6 interfaces. In case the WAB-MT 311 connects to the 5G network in a roaming manner corresponding to the local breakout option, then the PLMN1 is the visited PLMN and the WAB UPF 331 directly connects to the UE UPF 341 and the UE AMF 342 through N6 interfaces as shown in the Figure 3. Figure 4 is a block schematic diagram of an example network node or RAN node or base station 400, such as base stations or gNBs or WAB nodes shown in Figure 1, in accordance with one or more embodiments of the invention. Each of a WAB node 110, 120a, 120b, 130, 140, or 150 of figure 1 may comprise the elements of the base station of figure 4. Also, the satellite 160 of figure 1 may comprise the elements of the base station of figure 4. In the following description, the network node 400 will be referred to generally as a base station. As will be apparent to a skilled person, Figure 4 is a simplified schematic diagram and shows only some of the functional components of an example base station 400 for use in describing the one or more embodiments of the invention. The base station 400 includes components for transmitting and receiving communications. As shown in Figure 4, the base station 400 includes a processing unit 402, a wireless interface 404, one or more antennas 410, a network interface 432, and memory 418. The network interface 432 manages communications of the base station 400 with the core network, other base stations, local network functions (like UPF), or local servers. It may provide a standardized interface, wired (e.g. fiber) or wireless, to support these communications. Through this network interface 432, the base station 400 may implement the standardized interfaces N2 (based on NGAP protocol) and N3 (based on GPRS tunneling protocol) with the core network, and the standardized interface Xn (based on XnAP protocol) with other base station of the Radio Access Network (RAN), all defined by the 3GPP standard. The network interface 432 may not be present or active in case the base station 400 is a WAB node that does not support local services, that is not used as a legacy base station like base station 102, 104 in Figure 1, and that is not used as a home base station providing Femto cells like base station 130 in Figure 1. The wireless interface 404 is configured to provide wireless communication via communication links (414) with other wireless devices, such as one or more UEs, e.g. link D1041b between base station 104 and the MT / UE unit of WAB node 120b, or link D1202 between the gNB unit of WAB node 120b and the UE 122. In case of WAB node, the wireless interface 404 may then be used both for the wireless backhaul link(s) with backhaul base station(s) and for the wireless link(s) with the UE(s) served by the WAB node. The wireless interface 404 may be compliant with a fifth-generation (5G) New Radio (NR) system and thus implementing the Uu interface defined by 3GPP standard, or with other wireless communication system. The wireless interface 404 is coupled to the processing unit 402 and to one or more antennas (such as the antenna 410). The wireless interface 404 typically includes a receiving unit 406 and a transmitting unit 408. The configuration of the wireless interface 404 may be limited to connect to one antenna, but preferably several antennas are used, in order to provide beamforming capability. Although not shown in Figure 4, the receiving unit 406 typically includes elements such as a receiver, demodulator, decoder, and the transmitting unit 408 typically includes elements such as a transmitter, modulator, coder. The receiving unit 406 and transmitting unit 408 may together be referred to as a transceiver. The processing unit 402 is configured to carrying out processing for operation of the base station 400. The processing unit 402 may be a single processor (e.g. Central Processing Unit) or may comprise two or more processors. The number of processors and the allocation of processing functions to the processors is a matter of design choice for a skilled person. The base station 400 includes memory 418 for storing data and computer programs containing instructions for the operation of the base station 400. Memory 418 includes RAM (Random Access Memory), ROM (Read Only Memory), or combination of both or as a non-limiting example a mass storage device such as a disk or a Solid-State Drive. Memory 418 includes a program memory in which are stored programs containing processor instructions for operation of the base station 400 and for implementing the methods in accordance with one or more embodiments of the invention. The programs may contain a number of different program elements or sub-routines (represented by element 420 in memory 418) containing processor instructions for a variety of different tasks, for example, an element for requesting modification of a WAB node PDU session established for a WAB node, an element for determining the status or link quality of a communication link or radio interface (radio conditions, congestion...). Memory 418 may further include memory (e.g. RAM) for storing information such as, communication link status (e.g. information indicating link status or link quality of a wireless link), information for indicating a configuration or type of each radio bearer (SRB, DRB) configured for radio interfaces of the WAB node, information (e.g. 5 Qi value(s)) indicating a Quality of Service (QoS) associated with each of the configured radio bearers, list of supported acknowledged mode(s), list of connected device(s), list of acknowledged mode(s) activated for each connected device. The operation of the program elements or sub-routines 420 will be described in more detail below. In an example arrangement, a communication bus 424 provides communication and interoperability between the various elements included in the base station 400 or connected to it. The representation of the bus is not limiting and in particular, the processing unit 402 is operable to communicate instructions to any element of the base station 400 directly or by means of another element of the base station 400. In an example implementation, the base station 400 may be or may include an apparatus comprising one or more processing units or processors for performing or implementing the methods in accordance with one or more embodiments of the invention. In other words, the apparatus is capable of performing one or more functions of the base station including performing the methods in accordance with one or more embodiments of the invention by means of the one or more processing units. For example, the one or more processing units uses software to implement the one or more embodiments of the invention as described above with reference to the processing unit 402 of Figure 4. Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, a CPU of a microcontroller Unit (MCU), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated (e.g. on an Integrated Circuit) or discrete logic circuitry. However, alternatively, the one or more processing units for performing or implementing the methods may be implemented in hardware: for example, in the form of an Application Specific Integrated Circuit or ASIC or other hardware comprising logic element (s). Accordingly, the term “processing unit” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In a 5G core network, an AMF (Access and Mobility management Function) like the WAB AMF 332 or the UE AMF 342, may be implemented with the apparatus described in the Figure 4 where the Wireless Interface 404 and the antenna 410 is not present. Figure 5 illustrates an example of a wireless communication system 500, including a WAB network or WAB network system, in which embodiments and examples of embodiments of the present invention may be implemented. A WAB network will also be referred to as a WAB network system, WAB topology, WAB system, topology or system and so in this application, the terms WAB network system, WAB network, WAB topology, WAB system, topology or system will be used interchangeably. The WAB network system of Figure 5, is composed of three base stations 501, 502 and 503, also referred to as Backhaul base stations, or backhaul RAN nodes (also referred to as BH RAN nodes), or backhaul gNBs (also referred to as BH-gNB), two core networks 510 and 520, with the respective AMF entities 511a and 511b (for Core Network 510) and 521a and 521b (for Core Network 520) and the respective UPF entities 512a and 512b (for Core Network 510) and 522a and 522b (for Core Network 520), and two WAB nodes 530 and 540. A wired backhaul IP network 590 interconnects the base stations 501, 502 and 503 and the Core Networks 510 and 520. For instance, this wired link consists of optical fiber cable(s). As discussed above, each WAB node comprises a Mobile Termination (MT) component or part or unit (WAB-MT 531 for WAB node 530 and WAB-MT 541 for WAB node 540) and a RAN node or base station or gNB component or part or unit (WAB-gNB 532 for WAB node 530 and WAB-gNB 542 for WAB node 540). WAB node 530 and WAB node 540 may also embed a UPF entity, respectively UPF entity 533 and UPF 543, as previously discussed in figure 3, allowing WAB-node 530 to provide UEs 551, 552 and 561 with some local services, such as for instance inter-UE communication where the user data exchanged between the two UEs would be routed through UPF entity 533 / 543 instead of being routed through a UPF entity belonging to Core Network 510 or 520. WAB node 530 is connected to the serving backhaul base station referred to as BH-gNBl, 501 through the wireless backhaul (BH) link 5011. WAB node 540 may be connected to the serving backhaul base station referred to as BH-gNB2, 502 through the wireless backhaul (BH) link 5021 or to the serving backhaul base station referred to as BH-gNB3, 503 through wireless backhaul (BH) link 5031 or, in case of dual connectivity, to both the serving backhaul base station BH-gNB2, 502 through BH link 5021 and the serving backhaul base station BH-gNB3, 503 through BH link 5031. WAB-gNB 532 of WAB node 530 is also connected to UE 551 through communication link or radio link or wireless link 5301 and to UE 552 through communication link or radio link or wireless link 5302. Similarly, WAB-gNB 542 of WAB node 540 is also connected to UE 561 through communication link or radio link 5401. Although Figure 5 shows only UE 561 connected to WAB node 540, it will be appreciated that there will be a plurality of UEs connected to WAB nodes of the wireless communication system via wireless or communication links. WAB-gNB 532 and WAB-MT 531 may be connected to a same AMF function or entity (e.g., AMF 511a) or to different AMF functions or entities belonging to the same Core Network (e.g., AMF 511a and AMF 51 lb) or to different Core Network (e.g., AMF 511a and AMF 521a). Some AMF functions may be implementing WAB-specific features for managing a WAB node (e.g., advanced mobility features). Some AMF functions may not implement such features but may still be capable of serving a WAB node with a limited set of basic features. Some AMF functions may not be capable of serving a WAB node. Several scenarios are possible according to the mobility of WAB nodes 530 and 540. As a first scenario, and taking the example of WAB node 540, a dual-connectivity configuration may be applied to the WAB-MT 541, initially connected to BH-gNB2 502 only through the link 5021. Indeed, the WAB-MT 541 periodically performs a cell search procedure, as defined in 3GPP TS 38.300, trying to detect PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal). The WAB-node may report to BH-gNB2 502 the presence of a new cell, for instance one cell managed by the BH-gNB3 503, through a measurement report. Based on the analysis of the measurement report, the BH-gNB2 502 may request to the BH-gNB3 503 the establishment of a dual connectivity for the WAB-MT 541 with an additional connection through the link 5031. The BH-gNB3 503 may accept the request and proceed to the connection of the WAB-MT 541 according to the procedure described in TS 37.340 section 10.2.2. As a result, the WAB-MT 541, and thus the WAB node 540 is dual-connected. The BH-gNB2 502 may take benefit of the dual connectivity of WAB node 540 to balance the traffic load by offloading some traffic (data / user traffic or control traffic) initially planned to be transmitted through the link 5021. Some or all the traffic associated to the WAB node 540 (i.e. control data related to the WAB node, and control and user data related to the UEs served by the WAB node 540) may be transmitted through the link 5031 and through the IP connectivity between BH-gNB2 502 and BH-gNB3 503. Dual-connectivity configuration is however transparent for the WAB-gNB 542 and for the UEs served by the WAB-gNB 542. As a second scenario, the radio link 5021 may experience radio link deficiency due to some unexpected interference or shadowing phenomena. For such reasons, the WAB-MT 541 may lose the connection with the BH-gNB2 502 and declare a Radio Link Failure (RLF). Then, the WAB-MT 541 will try to reestablish the connection in the same or a different cell controlled by BH gNB2 502 or by another gNB. Thus, the WAB-MT 541 may try to connect to a cell controlled by BH-gNB3 503 by requesting the establishment of the link 5031. In this case, the reestablishment procedure described in TS 38.300 section 9.2.3.3 may be applied, which enables a UE to maintain the RRC connection. With such procedure, the BH gNB3 503 sends to the BH gNB2 502 a request to retrieve the context of the WAB-MT 541. Based on the response from the BH gNB2 502, the BH gNB3 503 may accept the connection of the WAB-MT 541. Then, all the traffic related to the WAB node 540 (and the served UEs) will now transit through the BH gNB 503. The reestablishment procedure does not involve the WAB-gNB 542 and its served UEs. If the reestablishment is rapidly performed after RLF, the service interruption at the UE 561 may be avoided or limited. As a third scenario, the WAB-MT 541 may be handed over from the current serving cell to a new cell. Indeed, based on the measurement reports provided by the WAB-MT 541, the BH-gNB2 502 may detect that the WAB-MT 541 would have a better connection through a cell managed by the BH gNB3 503. Then, the BH-gNB2 502 may trigger a handover procedure described in TS 38.300 section 9.2.3.2. In this procedure, the BH-gNB2 502 sends a handover request to the BH gNB3 503 along with information related to the WAB-MT 541. Based on this information, the BH gNB3 503 may accept the handover request and proceed to the admission of the WAB-MT 541. Then, all the traffic related to the WAB node 540 (and the served UEs) will now transit through the BH gNB 503. The handover procedure does not involve the WAB-gNB 542 and its served UEs, and it may be transparent for the WAB-gNB and the served UEs (no interruption of service). The three situations described above may happen because the backhaul link 5021 between the WAB-MT 541 and the BH gNB2 502 is wireless and subject to degradation, not only because the WAB-node 540 may be mobile, but also because the radio conditions may be changing leading to poor link budget. Moreover, in case of high throughput demand from applications running in UEs served by a WAB node (e.g. UEs 551 and 552 served by the WAB-gNB 532), the wireless backhaul link between the WAB node and the serving backhaul RAN node (e.g. link 5011 between WAB-MT 531 and BH-gNB 501) may be congested even if the radio quality is very good. When the quality of a wireless link is degraded, there may be no solution of handover at that time. Taking the example of the WAB node 530, if the quality of the wireless backhaul link 5011 decreases (because of congestion or bad radio conditions), it may not be possible to handover the WAB-MT 531 to another cell, as the WAB-MT 531 may not be located in a place covered by another cell. Thus, there is a need to manage communications over the wireless links (e.g. at the Uu_MT interface between the WAB-MT 541 and the BH gNB2 502 and at the Uu_UE interface between the WAB-gNB 542 and the UE 561) and to take appropriate action (e.g. modify a backhaul PDU session) as described with the help of figures 8 to 13 which relate to one or more embodiments of the present invention. Figure 6 is a schematic diagram illustrating the protocol stack associated to the NG interface in the control plane, referred to as NG-C. The NG-C interface and the associated Transport Network Layer (TNL) protocol stack are described in the following 3GPP specifications: TS 38.410, TS 38.411, TS 38.412, TS 38.413. The protocol stack associated with the Xn interface in the control plane, referred to as Xn-C, is not shown in figure 6 but is substantially the same as that for the NG-C of figure 6. The Xn-C interface and the associated TNL protocol stack are described in the following 3GPP specifications: TS 38.420, TS 38.421, TS 38.422, TS 38.423. The NG control plane interface (NG-C) is defined between a NG-RAN node and an AMF. The NG control plane interface may also be called or provides the N2 interface discussed above. The Xn control plane interface (Xn-C) is defined between two NG-RAN nodes. Both interfaces are built on IP (Internet Protocol) transport. NGAP (Next Generation Application Protocol) 611 is used on top of SCTP (Stream Control Transmission Protocol) 612 and IP 613 to carry the control plane data between the NG-RAN node and the AMF (for NG-C). Although not shown in figure 6, XnAP (Xn Application Protocol) is used on top of SCTP (Stream Control Transmission Protocol) and IP to carry the control plane data between two NG-RAN nodes (for Xn-C). NGAP 611 is defined in TS 38.413, XnAP is defined in TS 38.423, while SCTP 612 is defined in IETF RFC 4960, IP 613 is defined in IETF RFC 8200 (for IPv6) and IETF RFC 791 (for IPv4). Any data link and physical layer 614 that fulfil the requirements toward the upper layers 611, 612, 613 may be used. For instance, they can be implemented with Ethernet protocol over fiber cables. Details of example NGAP procedures are set out in section 8 of TS 38.413, V.18.3.0. NGAP procedures may also be referred to as NG protocol procedures or signalling procedures of NG application protocol. Several NGAP elementary procedures to manage a NG-C interface are specified in TS 38.413. Details of example XnAP procedures are set out in section 8 of TS 38.423, V.18.3.0. XnAP procedures may also be referred to as Xn protocol procedures or signalling procedures of Xn application protocol. UE control plane layer NAS 615 (Network Access Stratum) is implemented between the UE (e.g. 551, 552, 562) and an AMF entity associated with the UE (such as AMF 521a). The NAS protocol is defined in TS 24.501. From UE side, NAS protocol runs on top of the UuUE 616 signalling radio bearer stack (RRC TS 38.331, PDCP TS 38.323, RLC TS 38.322, MAC TS 38.321, PHY TS 38.211) (e.g. over or through the Uu UE interface or Uu UE link 716 between the UE and the WAB-gNB). Then starting from WAB-gNB up to the AMF, the NAS protocol runs on top of the NGAP protocol 611 over or through the Uu_MT interface or link 617. Similarly, for the Xn-C interface, from the UE, the NAS protocol runs on top of the signalling radio bearer stack (RRC, PDCP, RLC, MAC, PHY layers) over or through the Uu_UE interface or link and then starting from the WAB-gNB up to another NG RAN node (e.g. a BH gNB connected to the WAB-MT), the NAS protocol runs on top of the XnAP protocol over or through the Uu_MT interface or link. The NG setup procedure (described in TS 38.413 section 8.7.1 and some parts of which are illustrated in figure 9) enables the establishment of a NG interface between a NG-RAN node (like WAB-gNB 542) and an AMF (like AMF 521a). This procedure may be the first NGAP procedure triggered after the TNL association (TNLA) has become operational. For this purpose, the NG-RAN node and the AMF need to determine their IP addresses, through for instance, DNS (Domain Name System) resolution. This first TNL association may be reserved for the NGAP elementary procedures that utilize non-UE associated signalling (i.e for generic procedures not associated to a UE). The Xn setup procedure (described in TS 38.423 section 8.4.1) enables the establishment of a Xn-C interface between two NG-RAN nodes (like WAB-gNB 542) and an BH-gNB2 502. The message flow of figure 9 may similarly be applied for the Xn setup procedure. Figure 7 is a schematic diagram illustrating the protocol stack associated to the NG interface in the user plane, referred to as NG-U. The NG-U interface and the associated Transport Network Layer (TNL) protocol stack are described in the following 3GPP specifications: TS 38.410, TS 38.411, TS 38.414. The protocol stack associated with the Xn interface in the user plane, referred to as Xn-U, is not shown in figure 7 but is substantially the same as that for the NG-U of figure 7. The Xn-U interface and the associated TNL protocol stack are described in the following 3GPP specifications: TS 38.420, TS 38.421, TS 38.424 The NG user plane interface (NG-U) is defined between a NG-RAN node and a UPF. The Xn user plane interface (Xn-U) is defined between two NG-RAN nodes. Both interfaces are built on IP (Internet Protocol) transport. GTP-U (GPRS (General Packet Radio Service) Tunnelling Protocol for User Plane) 701 is used on top of UDP (User Datagram Protocol) 702 and IP 703 to carry the user plane PDUs between the NG-RAN node and the UPF (for NG-U). Although not shown in figure 7, GTP-U is used on top of UDP (User Datagram Protocol) and IP to carry the user plane PDUs between two NG-RAN nodes (for Xn-U). GTP-U 701 is defined in TS 29.281, while UDP 702 is defined in IETF RFC 768, and IP 703 is defined in IETF RFC 8200 (for IPv6) and IETF RFC 791 (for IPv4). Any data link and physical layer 704 that fulfil the requirements toward the upper layers 701, 702, 703 may be used. For instance, they can be implemented with Ethernet protocol over fiber cables. UE data plane layer IP 715 (IP PDU layer) is implemented between the UE (e.g. 551, 552, 562), and a UPF entity associated with the UE (such as UPF 522a). From UE side, IP protocol runs on top of the Uu_UE 716 data radio bearer stack (SDAP TS 38.324, PDCP TS 38.323, RLC TS 38.322, MAC TS 38.321, PHY TS 38.211) (e.g. over or through the Uu_UE interface or Uu_UE link 716 between the UE and the WAB-gNB, such as WAB-gNB 542). Then starting from WAB-gNB up to the UPF, the IP protocol runs on top of the GTP-U ((General Packet Radio Service) Tunnelling Protocol for User Plane) 701 over or through the Uu_MT interface or link 717. Similarly, for the Xn-U interface, from the UE, the IP protocol runs on top of the data radio bearer stack (SDAP, PDCP, RLC, MAC, PHY layers) over or through the Uu_UE interface or link and then starting from the WAB-gNB up to another NG RAN node (e.g. a BH gNB, such as BH gNB 502) connected to the WAB-MT (such as WAB-MT 541), the IP protocol runs on top of the GTP-U over or through the Uu_MT interface or link. It is noted that the PDU session for the control plane may be different to the PDU session for the user plane. Thus, different reference numerals are used for the PDU sessions in figures 6 and 7 (e.g. BH PDU sessions 618 and 718). It will however be appreciated that the same PDU session (e.g. the same backhaul PDU session) may be used for both the control and data plane. Figure 8 is a schematic diagram showing example message flows for establishing a PDU session for a UE in accordance with one or more embodiments of the invention. In other words, figure 8 shows example message flows for managing a PDU session established for a WAB node, such as when establishing a PDU session for a UE, in accordance with one or more embodiments of the present invention. For example, a NG-U associated with the UE can be setup via the message flows of figure 8. PDU session establishment follows initially the procedures defined in TS 23.502 (section 4.3.2). A PDU session contains from one to multiple QoS flows. For the simplicity of the description, in the following it will be assumed there is one QoS flow in the PDU session. Each processing described below can be easily duplicated for each QoS flow in the PDU session. For the following description, it is assumed that a PDU session has been established already (e.g. following the procedures defines in TS 23.502 (section 4.3.2)) through the Uu_MT interface between the WAB node (e.g. MT component of the WAB node, WAB-MT) and a core network entity (e.g. UPF associated with the WAB node (e.g. a WAB UPF or BH UPF)) via a backhaul NG RAN node or BH RAN node (and BH-TNL 719). Figure 8 shows a UE 822, like UE 561 of figure 5, a WAB node, such as WAB node 540, including a WAB-gNB 824 (such as WAB-gNB 542) and a WAB-MT 826 (such as WAB-MT 541), a BH gNB 828 (such as, BH-gNB2 502), BH-UPF 830 (such as BH-UPF 522a), UE-AMF 820 (such as AMF 521a) and MT-AMF 821 (such as AMF 521b). First a PDU session establishment request 801 (TS 24.501 8.3.1) is sent from UE 822 to an AMF entity associated with the UE, UE-AMF 820. The purpose of the request is for the UE to establish a communication path to an UPF for a given application (to be executed by the UE). Upon or after the reception of the PDU session establishment request 801, the UE-AMF 820 proceeds with the procedure defined in TS 23.502 (clause 4.3.2, not shown on figure 8 for clarity). When the procedure is successful, the UE-AMF 820 sends a PDU session resources setup request 802 (TS 38.413, clause 8.2.1) to the WAB-gNB 824 managing or serving the UE 822. The PDU session resources setup request 802 includes information indicating the Quality of Service (QoS) required or requested for the PDU session. For example, the information is PDU session QoS flow information, such as a 5G QoS identifier (5Qi), for the flow in the PDU session. When there are more than one flows in the PDU session, the request 802 will include a 5Qi for each flow. The configuration of a radio bearer (e.g. Uu radio bearer (e.g. DRB) such as the radio bearer for the Uu_UE link or interface and / or the radio bearer for the Uu_MT link or interface 717) for the flow in the PDU session is based on or dependent on the PDU session QoS flow information. The 5Qi can be set to one of multiple values, where each value represents a set of QoS characteristics or parameters, such as priority level, packet delay or packet error rate, etc.. Upon or after the reception of the PDU session resources setup request 802 including a 5Qi having a value 5Qi_l, if resources are available for the requested configuration or QoS flow (5Qi_l) for the PDU session (e.g. the WAB-gNB 824 can support the requested QoS flow), the WAB-gNB 824 executes the requested configuration and allocates associated resources over NG and over Uu_UE (e.g. over NG interface and Uu_UE interface 716) for the PDU session for the UE. In this case, the NG interface (e.g. interface between the WAB-gNB and the UPF) includes the Uu_MT interface 717 and the BH-TNL 719. For the Uu_UE part or interface, the WAB-gNB 824 performs AN (access network) resources setup 803. If resources are available for the requested configuration or QoS flow (5Qi_l), the WAB-gNB 824 establishes one Data Radio Bearer, DRB, (e.g. DRB1) based on the QoS flow 5Qi_l and associates the accepted QoS flow (5Qi_l) of the PDU session to the DRB, DRB l. DRB1 corresponds to a DRB (data radio bearer) configuration which is used to communicate user data over or through the Uu_UE link or interface for the UE PDU session. For the NG part or interface, the resources are managed through the backhaul PDU session 718 established from the WAB-MT 826 to a UPF (e.g. BH-UPF 830): for example, over Uu_MT link or interface 717 and BH-TNL 719. So, the WAB-gNB 824 sends flow information (in 804) to the WAB-MT 826 for resource allocation. The flow information (e.g. flow information for the UE PDU session associated with the Uu_UE link or interface 716) may include (but is not limited to) at least one of: DRB1 configuration (e.g. configuration information for the DRB established or to be established as DRB1 for the UE PDU session based on QoS flow 5Qi_l received in the request 802), Linkl (Uu_UE link quality indication or information indicating the quality of the UuUE link) and the PDU session requested information (5Qi_l), that is the QoS flow information included in the PDU session resources setup request 802. DRB configuration information includes information for one or more of SDAP, PDCP and RLC configurations. As discussed below with reference to the tables of figures 11 and 12, in one example, the configuration information includes information on the RLC mode (AM, UM, TM) supported by the DRB. The configuration information may also include information on PDCP DRB vs SRB modes. The WAB-gNB 824 may determine the link quality (Link l) of the UuUE link based on radio link measurements on signals communicated over the UuUE link and / or on the load on the UuUE link. For example, the WAB-gNB 824 may determine link quality as part of a Radio Resources Management (RRM) measurement procedure (e.g. as used for handover decision making by the gNB) in which the WAB-gNB 824 configures the UE to report periodically radio link measurements. The backhaul PDU session includes one to many QoS flows for data transport from WAB-MT to UE-UPF. UuUE QoS flow are encapsulated in one of the backhaul PDU session QoS flow in order to reach the UE-UPF. The encapsulation is performed at WAB-MT Uu_MT interface. As the Uu UE QoS flow is encapsulated or interconnected in one of the backhaul PDU session QoS flows, matching or substantially matching the backhaul QoS flow of the backhaul PDU session and the UE QoS flow of the UE PDU session helps to ensure the reliability of the Uu-UE interface and Uu_MT interface are the same or substantially the same. Then, during step 805, the WAB-MT 826 compares the receivedinformation (DRB1, 5Qi_l, Link l) for the UE PDU session to backhaul PDU session characteristics or parameters. In other words, the WAB-MT 826 compares the flow information associated with the Uu UE interface (e.g. UE PDU session flow information) to the flow information associated with the Uu_MT interface (e.g. backhaul PDU session flow information for the one or more backhaul QoS flows). The backhaul PDU session includes one to multiple QoS flows corresponding to different requested configurations or QoS flows (5Qi). The one or more backhaul QoS flows may have been received previously at the WAB-MT 826, such as when the backhaul PDU session between the WAB-MT 826 and the BH-UPF 830 was established. For example, the WAB-MT 826 may have established a DRB (DRB 2) based on a requested QoS flow (5Qi_2) for the backhaul PDU session. The WAB-MT 826 may compare the DRB configurations (DRB1, DRB 2) and / or the link qualities (Linkl, Link_2) to try and find a matching backhaul QoS flow in the backhaul PDU session relative to the UE QoS flow of the UE PDU session as indicated by the received information. The comparison may be based on the example tables shown in and described with respect to figures 11 and 12. The WAB-MT 826 may determine the link quality (Link_2) of the Uu_MT link by performing measurements on signals communicated over the Uu_MT link and / or by monitoring the load on the Uu_MT link. For example, the WAB-MT 826 is configured by the BH-gNB 828 to perform and report periodically to the BH-gNB 828 radio measurements (i.e. the WAB-MT 826 behaves as a UE). The information obtained as part of this reporting procedure may be used to determine the link quality (Link_2). If the WAB-MT 826 finds a matching QoS flow in the backhaul PDU session relative to the UE PDU session QoS flow received (in 804) from the WAB-gNB 824, then the UE QoS flow and the matching backhaul QoS flow are interconnected or encapsulated at the WAB-node and the NG resources allocation (e.g. for NG-U) is finished. The WAB-MT 826 may send a confirmation or a status message back to the WAB-gNB 824 (not shown on the diagram). If the UE PDU session QoS flow has no matching backhaul PDU session QoS flow, then the WAB-MT 826 may send a PDU session modification request 806 (TS 24.501 8.3.7) to the AMF entity associated with the WAB-MT (e.g. MT-AMF 821) in order to add a new QoS flow with the requested configuration 5Qi_l to the one or more QoS flows of the backhaul PDU session. For example, the PDU session modification request 806 includes the UE PDU session QoS flow information (e.g. 5Qi_l) for the new QoS flow to be added with the aim of providing matching UE and backhaul QoS flows at the WAB-node. Upon or after the reception of the PDU session modification request in 806, the MT-AMF 821 proceeds with the procedure defined in TS 23.502 (clause 4.3.3, not shown on figure 8 for clarity). When the procedure is successful, the MT-AMF 821 sends a PDU session resources modify message 807 (TS 38.413, clause 8.2.3) to the BH-gNB 828 managing the WAB-MT 826. The PDU session resource setup message 807 includes the requested configuration or QoS flow 5Qi_l to setup a new QoS flow with the configuration 5Qi_l. Upon or after the reception of the PDU session resources modify message 807 including a 5Qi having a value 5Qi_l, if resources are available for the requested configuration 5Qi_l (e.g. the BH-gNB 828 can support the requested QoS flow with QoS value 5Qi_l), the BH-gNB 828 executes the requested configuration and allocates associated resources over NG and over Uu_MT (e.g. over NG interface and Uu_MT interface 717) so as to modify the backhaul PDU session through the Uu_MT interface. For the Uu_MT part, the BH-gNB 828 performs AN (access network) resources setup 808. If resources are available for the requested configuration or QoS flow (5Qi_l), the BH-gNB 828 node establishes at least one DRB (DRB 3) and associates the accepted QoS flow (5Qi_l) of the PDU session to the DRB, DRB 3. For the NG part, the resources are managed directly by the BH-gNB 828 through the wired interface BH-TNL 719. Then, during step 809, the WAB-MT 826 compares the Uu_UE QoS flow information (DRB1, Linkl) of the UE PDU session to the new Uu_MT QoS flow information (DRB 3, Link_2) which includes flow information for a new QoS flow (e.g. configuration information for the new DRB (DRB 3) setup by the BH-gNB 828 in 808 for the backhaul PDU session associated with the Uu_MT interface. The comparison may be based on the example tables shown in and described with respect to figures 11 and 12. If the QoS flow of the UE PDU session matches the new QoS flow in the backhaul PDU session, then the UE QoS flow and the backhaul QoS flow are interconnected or encapsulated at the WAB-node and the NG resources allocation is finished. The WAB-MT 826 may send a confirmation or a status message back to the WAB-gNB 824 (not shown on the diagram). If the UE PDU session QoS flow is not matching the new backhaul QoS flow, then it means that for the same 5Qi requirements the BH-gNB 828 and the WAB-gNB 824 did not allocate the same resources. This is possible since the resource allocation is left to the implementation choice. In other words, base stations of different manufacturers may allocate resources differently for the same 5Qi requirements. In that case, the WAB-MT 826 may send a PDU session modification request 810 (TS 24.501 8.3.7) to the MT-AMF 821 in order to modify the newly added QoS flows with a different requested configuration 5Qi_2 that has a better chance to result in a matching Uu_MT DRB configuration (DRB 4) that matches the Uu_UE DRB configuration (DRB1). 5Qi_2 may be determined based on 5Qi_l, DRB1, Link l, DRB 3, Link_2. 5Qi_2 determination may be based on the following: • Knowing that 5Qi_l has been translated to DRB 3 by BH-gNB 828; • Determine 5Qi_2 so that BH-gNB 828 will translate to DRB 4; • Where (DRB1, Link l) matches (DRB 4, Link_2). Upon or after the reception of the PDU session resources modify message 811 including a 5Qi having a value 5Qi_2, if resources are available for the requested configuration or QoS flow (5Qi_2) (e.g. the BH-gNB 828 can support the requested QoS flow with QoS value 5Qi_2), the BH-gNB 828 executes the requested configuration and allocates associated resources over NG and over Uu_MT. In other words, the BH-gNB 828 modifies the newly added QoS flow with 5Qi_l to a QoS flow with 5Qi_2. For the Uu_MT part, the BH-gNB 828 performs AN (access network) resources setup 812. If resources are available for the requested configuration or QoS flow (5Qi_2), the BH-gNB 828 node reconfigures at least one DRB as DRB_4 and associates the modified QoS flow of the PDU session to DRB_4. For the NG part, the resources are managed directly by the BH-gNB 828 through the wired interface BH-TNL 719. At this stage (DRB1, Link l) and (DRB_4, Link_2) have the closet matching characteristics or parameters (e.g. in view of the determination of DRB4 as set out above). The established UE PDU session has a consistent performance across both wireless interfaces (e.g. Uu_UE interface 716 and Uu_MT interface 717). The UE and the backhaul QoS flows are interconnected at the WAB-node and the NG resources allocation is finished. The WAB-MT 826 may send a confirmation or a status message back to the WAB-gNB 824 (not shown on the diagram). Alternatively, the steps 809 to 812 are repeated until reaching a satisfactory result: that is, the steps are repeated until the characteristics of the UE QoS flow (for Uu_UE) and backhaul QoS flow (for Uu_MT) match or substantially match. Figure 9 is a schematic diagram showing example message flows for establishing a control interface in accordance with one or more embodiments of the invention. In other words, figure 9 shows example message flows for managing a PDU session established for a WAB node, such as when establishing a control interface, in accordance with one or more embodiments of the present invention. PDU session establishment follows initially the procedures defined in TS 23.502 (section 4.3.2). Figure 9 shows example message flows for establishing a NG control interface (e.g NG-C). However, it will be appreciated that the message flows of figure 9 may be applied for establishing a Xn control interface (e.g. Xn-C) and Xn user interface (Xn-U). For the following description, it is assumed that a PDU session has been established already (e.g. following the procedures defines in TS 23.502 (section 4.3.2)) through the Uu_MT interface between the WAB node (e.g. MT component of the WAB node, WAB-MT) and core network entity (e.g. UPF associated with the WAB node (e.g. a WAB UPF or BH UPF) via a backhaul NG RAN node or BH RAN node. This figure shows a UE 922, like UE 561 of figure 5, a WAB node, such as WAB node 540, including a WAB-gNB 924 (such as WAB-gNB 542) and a WAB-MT 926 (such as WAB-MT 541), a BH gNB 928 (such as, BH-gNB2 502), BH-UPF 930 (such as BH-UPF 522a), MT-AMF 920 (such as AMF 521a) and WAB-AMF 921 (such as AMF 521b). First a NG Setup request 901 (TS 38.401 9.2.6.1) is sent from WAB-gNB 924 to an AMF entity associated with the WAB-gNB, WAB-AMF 821. The purpose of the request is for the WAB-gNB 924 to establish a communication path to the WAB-AMF 821. Upon or after the reception of the NG Setup request, the WAB-AMF 921 proceeds with the procedure defined in TS 38.401 (clause 8.7.1). When the procedure is successful, the WAB-AMF 921 sends a NG setup response 902 (TS 38.413, clause 9.2.6.2) to the WAB-gNB 924. In other words, the NG setup response 902 confirms that the WAB-AMF 921 has accepted the NG setup request. Upon or after the reception of the NG setup response, the WAB-gNB 924 sends NG setup notification (903) to the WAB-MT 926. The NG setup notification may include flow information (e.g. signalling flow information for NG interface set up associated with the UuUE link or interface 616) which includes (but is not limited to) at least one of: SRB1 configuration, Linkl (Uu UE link quality indication or information indicating the link quality of the Uu UE link 616). SRB1 corresponds to a SRB (signalling radio bearer) configuration used or to be used on Uu UE link or interface to handle the control protocols (e.g. for communicating signalling (e.g. control protocol messages) over or through the Uu UE link or interface). SRB1 is setup as part of a RRC procedure in which the UE establishes a RRC connection to the WAB-gNB (e.g. either by handover, or by cell selection or cell reselection). The WAB-gNB 824 may determine the link quality of the Uu UE link based on measurements on signals communicated over the Uu UE link and / or on the load on the Uu UE link as described above with respect to figure 8. Then, during step 904, the WAB-MT 926 compares the received information (SRB1, Link l) for the signalling flow (also referred to as UE signalling flow) to the backhaul PDU session characteristics or parameters. In other words, the WAB-MT 926 compares the flow information associated with the Uu UE interface (e.g. signalling flow information or UE signalling flow information) to the flow information associated with the Uu_MT interface (e.g. backhaul PDU session flow information for the one or more backhaul QoS flows). The backhaul PDU session includes one to multiple QoS flows corresponding to different requested configurations or QoS flows (5Qi). The one or more backhaul QoS flows may have been received previously at the WAB-MT 926, such as when the backhaul PDU session from the WAB-MT 926 to the BH-UPF 930 was established. For example, the WAB-MT 926 may have established a DRB (DRB1) based on a requested QoS flow (5Qi_l) for the backhaul PDU session. The WAB-MT 926 may compare the bearer configurations (SRB1, DRB1) and / or link qualities (Link l, Link_2) to try and find a matching backhaul QoS flow relative to the signalling flow as indicated by the received information. The comparison may be based on the example tables shown in and described with respect to figures 11 and 12. The WAB-MT 926 may determine the link quality (Link_2) of the Uu_MT link by performing measurements on signals communicated over the Uu_MT link and / or by monitoring the load on the Uu_MT link as described above with respect to figure 8. If the WAB-MT 926 finds a matching QoS flow in the backhaul PDU session relative to the UE signalling flow received (in 903) from the WAB-gNB 924, then the UE signalling flow and the matching backhaul QoS flow are interconnected or encapsulated at the WAB-node and the NG setup (for NG-C) is finished. The WAB-MT 926 may send a confirmation or a status message back to the WAB-gNB 924 (not shown on the diagram). If the UE signalling flow has no matching backhaul PDU session QoS flow, then the WAB-MT 926 may send a PDU session modification request 905 (TS 24.501 8.3.7) to the AMF entity associated with the WAB-MT 926, MT-AMF 920 in order to add a new QoS flow with the requested configuration 5Qi_l to the one or more QoS flows of the backhaul PDU session. The 5Qi_l configuration is deduced by the WAB-MT 926 from the SRB1 configuration and from the Linkl link quality information. For example, the PDU session modification request 905 includes the QoS flow information (e.g. 5Qi_l) for the new QoS flow to be added with the aim of providing matching UE signalling and backhaul QoS flows at the WAB-node. Upon or after the reception of the PDU session modification request, the MT-AMF 920 proceeds with the procedure defined in TS 23.502 (clause 4.3.3, not shown on figure 9 for clarity). When the procedure is successful, the MT-AMF 920 sends a PDU session resource setup request 906 (TS 38.413, clause 8.2.1) to the BH-gNB 928 managing or serving the WAB-MT 926. Upon or after the reception of the PDU session resource setup request 906 including a 5Qi having a value 5Qi_l, if resources are available for the requested configuration 5Qi_l (e.g. the BH-gNB 928 can support the requested QoS flow with QoS value 5Qi_l), the BH-gNB 928 executes the requested configuration and allocates associated resources over NG and over Uu_MT (e.g. over NG interface and Uu_MT interface 617). In other words, the BH-gNB 928 adds a new QoS flow with 5Qi_l to the backhaul PDU session 718. For the Uu_MT part, the BH-gNB 928 performs AN (access network) resources setup 907. If resources are available for the requested configuration (5Qi_l), the BH-gNB 928 node establishes at least one DRB (DRB 2) and associates the accepted QoS flow (5Qi_l) of the PDU session to the DRB, DRB 2. For the NG part, the resources are managed directly by the BH-gNB 928 through the wired interface BH-TNL 619. Then, during step 908, the WAB-MT 926 compares the Uu_UE signalling flow information (SRB1, Link l) to the new Uu_MT QoS flow information (DRB 2, Link_2) as setup by the BH- gNB 928 in 907. The comparison may be based on the example tables shown in and described with respect to figures 11 and 12. If the signalling flow of the UE matches the new QoS flow in the backhaul PDU session, then the UE signalling flow and the backhaul QoS flow are interconnected or encapsulated at the WAB-node and the NG resources allocation (for NG-C) is finished. The WAB-MT 926 may send a confirmation or a status message back to the WAB-gNB 924 (not shown on the diagram). If the UE signalling flow is not matching the new backhaul QoS flow, then it means that for the same 5Qi requirements BH-gNB 928 and WAB-gNB 924 did not allocate the same resources. This is possible since the resource allocation is left to the implementation choice as discussed above. In that case, the WAB-MT 926 may send a PDU session modification request 909 (TS 24.501 8.3.7) to the MT-AMF 920 in order to modify the newly added QoS flows with a different requested configuration 5Qi_2 that has a better chance to result in a matching Uu_MT DRB configuration (DRB 3) that matches the Uu_UE SRB configuration (SRB1). 5Qi_2 may be determined based on SRB1, Linkl, DRB 2, Link_2. 5Qi_2 determination may be based on the following: • Knowing that 5Qi_l has been translated to DRB 2 by BH-gNB 928; • Determine 5Qi_2 so that BH-gNB 928 will translate to DRB 3; • Where (SRB1, Link l) matches (DRB 3, Link_2). Upon or after the reception of the PDU session resources modify message 910 including a 5Qi having a value 5Qi_2, if resources are available for the requested configuration (5Qi_2) (e.g. the BH-gNB 928 can support the requested QoS flow with QoS value 5Qi_2), the BH-gNB 928 executes the requested configuration and allocates associated resources over NG and over Uu_MT. In other words, the BH-gNB 928 modifies the QoS flow with 5Qi_l to a QoS flow with 5Qi_2. For the Uu_MT part, the BH-gNB 928 performs AN (access network) resources setup 911. If resources are available for the requested configuration (5Qi_2), the BH-gNB 928 node reconfigures at least one DRB as DRB 3 and associates the modified QoS flow of the PDU session to DRB 3. For the NG part, the resources are managed directly by the BH-gNB 928 through the wired interface BH-TNL 619. At this stage (SRB1, Link l) and (DRB 3, Link_2) have the closet matching characteristics or parameters (e.g. in view of the determination of DRB 3 as set out above). The UE signalling flow has a consistent performance across both wireless interfaces (e.g. Uu_UE interface 616 and Uu_MT interface 617). The UE signalling and the backhaul QoS flows are interconnected at the WAB-node and the NG setup is finished. The WAB-MT 926 may send a confirmation or a status message back to the WAB-gNB 824 (not shown on the diagram). Alternatively, the steps 908 to 911 are repeated until reaching a satisfactory result: that is, the steps are repeated until the characteristics of the UE signalling flow (for UuUE) and backhaul QoS flow (for Uu_MT) match or substantially match. Figure 10 is a schematic diagram showing example message flow for monitoring a backhaul PDU Session for a QoS or signalling flow (e.g for UE data plane and UE control plane respectively over the backhaul PDU session) in accordance with one or more embodiments of the present invention. In other words, figure 10 shows an example message flow for managing a PDU session established for a WAB node for one or more flows, such as a QoS flow (e.g. for a UE PDU session established as discussed above with reference to figure 8) or a signalling flow (e.g. for a NG or Xn control interface established as discussed above with reference to figure 9), in accordance with one or more embodiments of the present invention. For each managed QoS flow or signalling flow, the WAB-gNB 1024 periodically sends link quality information Linkl to the WAB-MT 1026 in messages, such as message 1001. The link quality information Link l indicates the link quality of the UuUE link. The WAB-gNB 1024 may determine the link quality of the UuUE link based on measurements on signals communicated over the UuUE link and / or the load on the UuUE link as described above with respect to figure 8. Then, during step 1002, the WAB-MT 1026 compares the UuUE flow information (DRB1 / SRB1, Link l) to the associated Uu_MT QoS flow information (DRB 2, Link_2). In other words, the WAB-MT 1026 compares the flow information associated with the UuUE interface (e.g. UE PDU session flow information or signalling flow information) to the flow information associated with the Uu_MT interface (e.g. backhaul PDU session flow information for the one or more backhaul QoS flows). The association between the Uu_MT QoS flow information (DRB 2, Link_2) and the Uu UE flow information (DRB1 / SRB1, Link l) having been made earlier as part of the PDU session establishment (figure 8) or as part of the NG setup procedure (figure 9). The comparison may be based on the example tables shown in and described with respect to figures 11 and 12. If, despite of the changing link quality information (Link l and Link_2), the flow of the UE matches a QoS flow in the backhaul PDU session, then the WAB-MT 1026 just keeps monitoring the link qualities with no further changes or modifications required to the flows. If, for example, because the link qualities Link l (for Uu UE link) and Link_2 (for Uu_MT link) become very different, the UE flow no longer matches the backhaul QoS flow, then the WAB-MT 1026 may send a PDU session modification request 1003 (TS 24.501 8.3.7) to the AMF entity associated with the WAB-MT, MT-AMF 1021 in order to modify the QoS flows with a different requested configuration 5Qi_2 (i.e. different to that requested in 802, 807, 811, 903, 906, 910). Alternatively, the WAB-MT 1026 may decide to request the addition of a new QoS flow (for example if a difference between 5Qi_l and 5Qi_2 is too large). 5Qi_2 (e.g. for both modification of an existing QoS or setup of a new QoS flow) may be determined based on 5Qi_l, DRB1 / SRB1, Linkl, DRB 2, Link_2. 5Qi_2 determination may be based as follows: • Knowing that 5Qi_l has been translated to DRB 2 by BH-gNB 1028 (part of earlier process of figure 8 or figure 9); • Determine 5Qi_2 so that BH-gNB 1028 will translate to DRB 3; • Where (DRB1 / SRB1, Link l) matches (DRB3, Link_2). Upon or after the reception of the PDU session resource modify message 1004 when modifying an existing QoS flow (or a PDU session resource setup message 1004 to setup a new QoS flow), if resources are available for the requested configuration (5Qi_2) (e.g. the BH-gNB 1028 can support the requested QoS flow with QoS value 5Qi_2), the BH-gNB 1028 executes the requested configuration and allocates associated resources over NG and over Uu_MT. In other words, the BH-gNB 1028 modifies an existing QoS flow with 5Qi_l to a QoS flow with 5Qi_2 in the case of a PDU session resource modify message 1004 or the BH-gNB 1028 sets up a new QoS flow with the configuration 5Qi_2 in the case of a PDU session resource setup message 1004. For the Uu_MT part, the BH-gNB 1028 performs AN (access network) resources setup 1005. If resources are available for the requested configuration (5Qi_2), the BH-gNB 1028 reconfigures at least one DRB as DRB 3 and associates the modified / new QoS flow of the PDU session to DRB3. For the NG part, the resources are managed directly by the BH-gNB 1028 through the wired interface BH-TNL 619. At this stage (DRB1 / SRB1, Link l) and (DRB 3, Link_2) are the closet matching characteristics. The UE flow has a consistent performance across both wireless interfaces (UuUE and Uu_MT). Steps 1001 to 1005 are repeated as part of the backhaul PDU session monitoring process. It will be appreciated that the method shown and described with reference to figure 10 enables fluctuations in time of the Uu_MT interface (and the Uu UE interface) which fluctuations can impact the user plane and / or control plane flows through the Uu_MT interface (for the backhaul PDU session) such that the Uu_MT interface (e.g. backhaul PDU session) can be adapted to match the fluctuation of data plane Uu UE (DRB, QoS flow) or control plane Uu UE (SRB, signalling flow). Figure 11 is a table showing an example comparison between different bearer configurations on Uu UE and Uu_MT interfaces. Line 1101 represents some examples of different possible bearer configurations of the Uu_MT interface (e.g. 617, 717). The Uu_MT is a data radio bearer (DRB) so it can be configured either as a DRB AM, a DRB UM or a DRB TM. For example, as a backhaul PDU session is established through the Uu_MT interface, DRBs are configured for the Uu_MT interface. Furthermore, as an example, the possible bearer configurations for the DRBs include the DRBs supporting one of several different acknowledged modes, which may include an Acknowledged Mode (AM), an Unacknowledged mode (UM), and a Transparent Mode (TM). The DRB definitions are specified in TS 38.322. The DRB AM is the acknowledged mode. AM is the most reliable mode possible for a DRB. The DRB UM is the un-acknowledged mode. UM performs data segmentation but no retransmission and is one of the least reliable mode for DRB. The DRB TM is the transparent mode. TM does not implement any protocol and is the least reliable mode for DRB. Although the table of figure 11 shows AM, UM and TM as different bearer configurations, other different bearer configurations may also be considered such as latency, data duplication, split bearer, discard timer, etc.. It is not intended that the invention is limited to only considering AM, UM, TM as the bearer configurations to be used when determining whether and how to modify the PDU session for the WAB node. Column 1102 represents the different possible bearer configuration of the UuUE interface (e.g. 616, 716). The Uu UE can handle either data radio bearers (DRB), or signalling radio bearers SRBs. The radio bearers (SRBs / DRBs) for the Uu UE interface can be configured either as an SRB, a DRB AM, a DRB UM or a DRB TM. The DRB / SRB definitions are specified in TS 38.322. The SRB is the most reliable mode for a bearer. DRB AM can be considered as being almost as reliable as the SRB. Each cell of the table reads as: • Cells 1105, 1106, 1110: indicates that the Uu_MT wireless interface has a more reliable bearer configuration than the Uu UE bearer configuration. For example, in the case of cell 1105 where Uu_MT is configured as DRB AM and Uu UE is configured as DRB UM, the DRB AM of the Uu_MT interface is a much more reliable configuration than the DRB UM of the UuUE interface. In the case of cell 1110 where Uu_MT is configured as DRB UM and Uu UE is configured as DRB TM, the DRB UM of the Uu_MT interface is more reliable configuration than the DRB TM of the Uu UE interface (as TM is the least reliable mode). • Cells 1103, 1104, 1109, 1114: indicates that the Uu_MT wireless interface and Uu_UE interface have the same or almost the same bearer configuration (assuming SRB and DRB AM are almost the same configuration) and so have the same reliability. • Cells 1107, 1108, 1111, 1112: indicates that the Uu_MT wireless interface bearer has a less reliable configuration than the Uu_UE bearer configuration. For example, in the case of cell 1108 where Uu_MT is configured as DRB UM and UuUE is configured as DRB AM, the DRB UM of the Uu_MT interface is a less reliable configuration than the DRB AM of the UuUE interface. In one example, the configuration matching assessment (e.g. the reliability matching assessment), performed during steps 1002, 908, 904, 809 and 805 (during which a configuration comparison is performed), follows or uses the result of table 1100. For example: • If the WAB-MT finds that Uu_MT interface has a better bearer configuration compared to Uu UE interface (as is the case with cells 1105, 1106, 1110) then WAB-MT may send a PDU session modification request (806, 810, 905, 909, 1003) to an AMF with parameters requesting a backhaul QoS flow with less stringent QoS (or less reliable) to the AMF. For example, in such a case the WAB-MT may send a PDU session modification request (806, 810, 905, 909, 1003) to an AMF associated with the WAB-MT including information indicating the WAB-MT requests a backhaul QoS flow with less stringent or reduced QoS requirements compared to the QoS of the current bearer configuration for the Uu_MT interface with the aim of matching the backhaul QoS flow for the Uu_MT interface to the flow for the Uu UE interface. When the Uu_MT interface is over achieving (such as in this example where the Uu_MT has a better bearer configuration compared to Uu UE), having such an over achieving Uu_MT interface is not critical for data reliability but it may mean that some radio resources are over spent in achieving reliability (e.g. additional radio resources are used but are not required). It may mean also that data latency can be improved (e.g. when the Uu_MT interface is overachieving, data latency may be higher than needed). So, relaxing the QoS on the backhaul part may be beneficial to save some radio resources and improve latency. In some cases, for example, if the Uu UE bearer configuration is a signalling radio bearer (SRB) it may be best to not relax the backhaul QoS. Indeed the signalling traffic is critical and low in data quantity, so it is not worth relaxing the QoS. • If the WAB-MT finds that Uu_MT interface configuration is the same (or almost the same) as Uu_UE interface (as is the case with cells 1103, 1104, 1109, 1114) then WAB-MT may decide to not make any changes, and so to not send a PDU session modification request (806, 810, 905, 909, 1003) to an AMF. • If the WAB-MT finds that Uu_MT interface has a less reliable bearer configuration compared to Uu_UE interface (as is the case with cells 1107, 1108, 1111, 1112) then WAB-MT may send a PDU session modification request (806, 810, 905, 909, 1003) to an AMF with parameters requesting more stringent QoS (or better reliability) to the AMF. For example, in such a case the WAB-MT may send a PDU session modification request (806, 810, 905, 909, 1003) to an AMF associated with the WAB-MT including information indicating the WAB-MT requests a backhaul QoS flow with more stringent or increased QoS requirements compared to the QoS of the current bearer configuration for the Uu_MT interface with the aim of matching the backhaul QoS flow for the Uu_MT interface to the flow for the UuUE interface. Since the Uu_MT is replacing part of the wired part of the NG interface, allowing the WAB-gNB to be mobile, it is important that the reliability achieved on the Uu_MT interface can at least match the reliability achieved on UuUE interface. Figure 12 is a table showing an example comparison of both the different bearer configurations on UuUE and Uu_MT interfaces and link quality difference between link quality of the UuUE interface and link quality of the Uu_MT interface. Table 1200 offers better or improved accuracy when performing a reliability assessment (e.g. the configuration matching assessment performed during steps 1002, 908, 904, 809 and 805) compared to the reliability assessment performed using table 1100. By taking into account both the bearer configuration and the link quality, the assessment performed using table 1200 is more accurate than an assessment that is only relying on one parameter, such as the assessment performed using table 1100. As above, although the table of figure 12 shows AM, UM and TM as different bearer configurations, other different bearer configurations may also be considered such as latency, data duplication, split bearer, discard timer, etc.. It is not intended that the invention is limited to only considering AM, UM, TM as the bearer configurations to be used when determining whether and how to modify the PDU session for the WAB node. As discussed above, the link quality (e.g. Link 1) of the UuUE interface may be determined by the WAB-gNB and the link quality (e.g. Link 2) of the Uu_MT interface may be determined by the WAB-MT. Line 1201 represents some examples of different cases of link quality difference, which include: • First column: Uu_MT link quality is better than Uu UE link quality (Link_2 better than Link l); • Second column: Uu_MT link quality is the same as Uu_UE link quality (Link_2 same as linkl); • Third column: Uu_MT link quality is worse than Uu_UE link quality (Link_2 worse than link l). Column 1202 represents some examples of different cases of radio bearer mode (or configuration) difference between Uu_UE and Uu_MT as described in table 1100: • First line or row: Uu_MT bearer mode is more reliable than Uu_UE bearer mode (for example, corresponding to cells 1105, 1106, 1110 of table 1100); • Second line or row: Uu_MT bearer mode is as reliable as Uu_UE bearer mode (for example, corresponding to cells 1103, 1104, 1109, 1114 of table 1100); • Third line or row: Uu_MT bearer mode is less reliable than Uu_UE bearer mode (for example, corresponding to cells 1107, 1108, 1111, 1112, 1113 of table 1100). The cells of figure 12 indicate a match if both bearer modes and link qualities are the same or almost same. A match is also indicated when one side or interface has a more reliable bearer mode and worst link condition while the other side has a less reliable bearer configuration and good or better link condition. For example: • Cells 1203, 1206, 1204 each indicates that the Uu_MT wireless interface is more reliable than the Uu_UE interface (over achieve). For example as shown in cell 1204, both interfaces have the same bearer type or configuration and Link_2 quality is better than Link l quality. • Cells 1209, 1205, 1207 each indicates that the Uu_MT wireless interface is as reliable as the Uu_UE interface (same / match). For example as shown in cell 1209, Uu_MT bearer configuration is more reliable than Uu_UE bearer configuration and Link l quality is better than Link_2 quality. • Cells 1208, 1210, 1211 each indicates that the Uu_MT wireless interface is less reliable than the Uu_UE interface (under achieve). For example as shown in cell 1210, both interfaces have the same bearer type and Link l quality is better than Link_2 quality. In one example, the configuration matching assessment (e.g. the reliability matching assessment), performed during steps 1002, 908, 904, 809 and 805 (during which a configuration comparison is performed), follows or uses the result of table 1200. For example: • If the WAB-MT finds that Uu_MT interface is over achieving compared to Uu_UE interface (as is the case with cells 1203, 1204, 1206) then WAB-MT may send a PDU session modification request (806, 810, 905, 909, 1003) to an AMF with parameters requesting a backhaul QoS flow with less stringent QoS (or less reliable) to the AMF. For example, in such a case the WAB-MT may send a PDU session modification request (806, 810, 905, 909, 1003) to an AMF associated with the WAB-MT including information indicating the WAB-MT requests a backhaul QoS flow with less stringent or reduced QoS requirements compared to the QoS of the current bearer configuration for the Uu_MT interface with the aim of matching the backhaul QoS flow for the Uu_MT interface to the flow for the UuUE interface. When the Uu_MT interface is over achieving compared to the UuUE interface, it is not critical for data reliability but it may mean that some radio resources are over spent in achieving reliability (e.g. additional radio resources are used but are not required). It may mean also that data latency can be improved (e.g. when the Uu_MT interface is overachieving, data latency may be higher than needed). So, relaxing the QoS on the backhaul part may be beneficial to save some radio resources and improve latency. In some cases, for example, if the UuUE bearer configuration is a signalling radio bearer (SRB) it may be best to not relax the backhaul QoS. Indeed the signalling traffic is critical and low in data quantity, so it is not worth relaxing the QoS. • If the WAB-MT finds that Uu_MT is as reliable as Uu_UE (1205, 1207, 1209) then WAB-MT may decide to not make any changes, and not send a PDU session modification request (806, 810, 905, 909, 1003) to an AMF. • If the WAB-MT finds that Uu_MT interface is under achieving compared to UuUE interface (as is the case with cells 1210, 1208, 1211) then WAB-MT may send a PDU session modification request (806, 810, 905, 909, 1003) to an AMF with parameters requesting more stringent QoS (or better reliability) to the AMF. For example, in such a case the WAB-MT may send a PDU session modification request (806, 810, 905, 909, 1003) to an AMF associated with the WAB-MT including information indicating the WAB-MT requests a backhaul QoS flow with more stringent or increased QoS requirements compared to the QoS of the current bearer configuration for the Uu_MT interface with the aim of matching the backhaul QoS flow for the Uu_MT interface to the flow for the Uu UE interface. Since the Uu_MT is replacing part of the wired part of the NG interface, allowing the WAB-gNB to be mobile, it is important that reliability achieved on the Uu_MT interface at least matches the reliability achieved on Uu_UE interface. A method for managing a PDU session established for a WAB node of a wireless communication system in accordance with the present invention will now be described with reference to the figures. The method may be used to modify the PDU session based on configuration of one or more radio bearers for one or more radio interfaces (e.g. Uu_UE and Uu_MT interfaces) of the WAB node and / or link quality of each of one or more radio interfaces so as to ensure the interfaces are aligned (e.g. Uu_UE and Uu_MT interfaces) so that the reliability of the Uu-UE interface and Uu_MT interface are the same or substantially the same. The WAB node includes a gNB component (e.g. WAB-gNB) and a MT component (e.g. WAB-MT or WAB-UE). The method may be performed by a WAB node. Some steps of the method are performed at the MT component of the WAB node and some are performed at the gNB component of the WAB node. Figure 13 shows an example method 1300 for managing a PDU session established for a WAB node in accordance with one or more embodiments of the invention, which method 1300 is performed at the MT component (e.g. WAB-MT) of the WAB node. For example, with reference to the communication system 500 shown in and described with respect to figure 5, the WAB node may be WAB node 540 including a WAB-gNB 542 and a WAB-MT 541. The method may be performed by software elements and / or hardware elements. The WAB node may be implemented in a network node 400 as shown in and described with reference to figure 4 with the method being performed by an apparatus for the WAB node including one or more processing units, such as the processing unit 402. Briefly, the method includes requesting, by the WAB node, modification of the WAB node PDU session based on at least one of: configuration of one or more radio bearers established / setup / operating for one or more radio interfaces (or interface, e.g. Uu_UE, or Uu_MT, or NG, or Xn) at the WAB node; link quality of each of one or more radio interfaces (or interface, e.g. Uu_UE, or Uu_MT, or NG, or Xn) at the WAB node. When there is more than one flow and so more than one radio bearer through a radio interface, each radio bearer will have a particular configuration. The one or more radio interfaces may include at least two radio interfaces, such as a first interface (e.g. Uu_UE interface, such as that between the WAB-gNB 542 and UE 161) and a second interface (e.g. Uu_MT interface, such as that between the WAB-MT 541 and the backhaul e.g. backhaul RAN node 502) where the PDU session is established through the second interface. Requesting modification may include sending, by the WAB node 540, a request for modifying the PDU session for the WAB node (e.g. the WAB node PDU session or WAB PDU session, such as the BH PDU session 618 or 718) or may include initiating, by the WAB node 540, modification of the PDU session for the WAB node (e.g. the WAB node PDU session or WAB PDU session, such as the BH PDU session 618 or 718). The modification may include adding a new QoS flow for the PDU session or modifying an existing QoS flow of the PDU session. In the case a request is sent, the request may be included in a message such as any one of messages 806, 810 of figure 8, 905, 909 of figure 9, 1003 of figure 10. Whether the message is a PDU session modification message or PDU session setup message depends on whether modification includes modifying an existing QoS flow of the PDU session or adding / setting up a new QoS flow for the PDU session. The request may be sent by the WAB-MT 541 (826, 926, 1026 in figures 8-10 and as described in step 1303 of figure 13). The request may be sent to the AMF entity associated with the WAB-MT, such as AMF 521a (820, 920, 1020 in figures 8-10). The modification may be based on the configuration of one or more radio bearers (e.g. DRB, SRB) and / or the link quality. The configuration of one or more radio bearers may include one or more of SDAP, PDCP and RLC configurations and / or PDCP DRB vs SRB modes. As discussed with reference to figures 11 and 12, AM, UM and TM as different bearer configurations may be considered. Other different bearer configurations may also be considered such as latency, data duplication, split bearer, discard timer, etc.. The link quality may relate to load on the radio interface and / or radio conditions over the radio interface. In an example, the WAB node 540 requests modification of the WAB node PDU session when the first radio interface (Uu_UE) is not aligned or does not match the second radio interface (Uu_MT). The two radio interfaces do not match, for example, in the case where the backhaul QoS flow of the backhaul PDU session through the Uu_MT and the UE QoS flow of the UE PDU session through the Uu UE do not match. Thus, the WAB node 540 may request modification of the WAB node PDU session when first flow information for the first radio interface does not match second flow information for the second radio interface. For example, the WAB node 540 may determine whether the first flow information matches the second flow information by performing the comparisons of steps 805, 809, 904, 908, 1002 as described above with reference to figures 8 to 10. The flow information may be QoS flow information for control and user plane for the backhaul PDU session 618, 718 or QoS flow information for the user plane for the UE PDU session or signalling flow information for the control plane for the control plane for the UE PDU session. The flow information may include information indicating a configuration of a radio bearer associated with the respective radio interface (when there is more than one flow and so more than one radio bearer through the radio interface, the information indicates the configurations for each of the radio bearers) and information indicating a link quality of the respective radio interface. Different configurations for the radio bearers are discussed above. The link quality information may indicate the load on the radio interface and / or radio conditions over the radio interface. The flow information may further include information (e.g. 5Qi value) indicating a QoS for a flow through the respective interface. The link quality information may be determined by the WAB node 540 (e.g. by the WAB-gNB 542 and WAB-MT 541) as discussed above. The WAB-MT 541 may receive first flow information associated with the first radio interface (e.g. Uu_UE) from the WAB-gNB 542: for example, in message 804 as part of a UE PDU session establishment procedure (for NG-U) described above with reference to figure 8, where the first flow information is for the UE PDU session established for the UE, or in message 903 as part of a control plane setup procedure (for NG-C, Xn-U, Xn-C) described above with reference to figure 9, where the first flow information is for a NG interface setup or a Xn interface setup. In the case of figure 10, the WAB-MT 541 receives from the WAB-gNB 542 information indicating link quality of the first radio interface in message 1001. In this case, the first flow information is updated to account for changes in link quality over the link between the WAB-gNB 541 and UE 561. The WAB-MT 541 uses the updated first information to determine whether modification of the WAB PDU session (e.g. backhaul PDU session 618, 718) is required (at step 1002), so as to update or modify the WAB PDU session on an ongoing basis (or run time) to account for changes in link quality over the link between the WAB-gNB 541 and UE 561. As discussed above with reference to figure 10, when the link quality of the first radio interface (Uu_UE) has changed significantly compared to the link quality of the second radio interface (Uu_MT), such as when the difference between the two link qualities Link l and Link_2 is greater than a certain threshold, a modification of the WAB PDU session is required and message 1003 is sent. The WAB-MT 541 may receive information indicating one or more configurations of one or more radio bearers established for the WAB PDU session through the second radio interface (e.g. for one or more flows for the backhaul PDU session 618, 718) as part of the establishment of the WAB PDU session. The second flow information provided by the WAB-MT 541 includes the received configuration information and information indicating the link quality of the second radio interface (e.g. the Uu_MT). In an example, the WAB node 540 may send a first request for requesting modification of the WAB PDU session (e.g. backhaul PDU session 618, 718) to add a new QoS flow or to modify an existing QoS flow, such as request 806, 905, 1003, and after modifying the WAB PDU session (e.g. adding a new QoS flow or modifying an existing QoS flow), if the radio interfaces still do not match (e.g. when the flow information associated with the radio interfaces do not match as determined by step 809, 908), the WAB node 540 may send a second request for requesting modification of the WAB PDU session (e.g. backhaul PDU session 618, 718) to add a new QoS flow or to modify an existing QoS flow, such as request 810, 909. Requests may be sent until there is a match e.g. the radio interfaces (Uu_UE and Uu_MT) are matched or aligned or substantially matched or aligned as discussed above with reference to figures 8 to 10. The backhaul PDU session includes one to many QoS flows for data transport from WAB-MT 541 to the UPF entity associated with the UE 561, such as UE-UPF 522a. Uu_UE QoS flow are encapsulated in one of the QoS flows of the backhaul PDU session 618, 718 in order to reach the UE-UPF 522a. The encapsulation is performed at WAB-MT Uu_MT interface (e.g. interface between the WAB-MT 541 and the backhaul. As the Uu_UE QoS flow is encapsulated or interconnected in one of the backhaul PDU session QoS flows, matching or substantially matching the backhaul QoS flow of the backhaul PDU session and the UE QoS flow of the UE PDU session by modifying one of the PDU sessions for the WAB node (e.g. modifying the PDU session so that the QoS flows match or substantially match) helps to ensure the reliability of the Uu-UE interface and Uu_MT interface are the same or substantially the same. By basing the modification on the link quality of the two Uu interfaces, the radio conditions and load level can also be taken into account and thus, reliability of the wireless Uu interfaces can also be managed. Referring now also to figure 13 which is a flowchart of a method for managing a PDU session established for a WAB node in accordance with one or more embodiments of the invention. The method is performed at the WAB node. Some steps of the method are performed at the MT component of the WAB node and some are performed at the gNB component of the WAB node. For example, figure 13 shows a method 1300 for managing backhaul sessions at a WAB-MT of a WAB-node in accordance with one or more embodiments of the invention. For example, method 1300 is an example of a method for use in adjusting a backhaul PDU session QoS requirements. With reference to the communication system 500 shown in and described with respect to figure 5, the WAB node may be WAB node 540 which includes a MT component or WAB-MT 541 and a gNB component or WAB-gNB 542. Method 1300 may be performed by WAB-MT 541. The method 1300 as shown in and described with respect to figure 13 may be performed by software elements and / or hardware elements. The WAB node may be implemented in a network node 400 as shown in and described with reference to figure 4 with the method as shown in and described with respect to figure 13 being performed by an apparatus for the WAB node or WAB-MT including one or more processing units, such as the processing unit 402. First, at step 1301, the WAB-MT 541 receives information from the WAB-gNB 542. The information includes at least: radio bearer information linked to a PDU session used by a UE that is connected to or served by the WAB-gNB, link quality information between the UE and the WAB- gNB (e.g. for the Uu_UE interface), a NG setup information, a Xn setup information. See for example, the discussions above with respect to messages 804, 903, 1001. Then, during step 1302, the WAB-MT 541 compares the reliability characteristics or parameters of both radio interfaces (Uu_MT and Uu_UE). See for example, the discussions above with respect to steps 805, 809, 904, 908, 1002. The comparison is based on at least one of radio link quality (e.g. link quality for the Uu_UE interface and link quality for the Uu_MT interface), and bearer configuration (e.g. bearer configuration types). Then during step 1303, the WAB-MT 541 sends a PDU session modification request to the AMF in the case where the reliability characteristics of the two interfaces needs adjustment. See for example, the discussions above with respect to messages 806, 810, 905, 909, 1003. For example, the WAB-MT 541 sends a request for requesting modification of the WAB PDU session (e.g. backhaul PDU session) in the case where characteristics or parameters associated with reliability of at least one of the two radio interfaces (Uu UE, Uu_MT) needs to be modified or updated, when following the comparison in step 1302, the two radio interfaces are determined to not match (e.g. the QoS flows and / or the link quality of the two radio interfaces do not match). The adjustment can be performed to QoS flows of the backhaul PDU session when establishing a PDU session for the UE (as described with reference to figure 8), or when establishing a control interface (as described with reference to figure 9), or during use or operation of the backhaul PDU session. While the present invention has been described with reference to examples and embodiments, it is to be understood that the invention is not limited to the disclosed examples and embodiments. It will be appreciated by those skilled in the art that various changes and modification might be made without departing from the scope of the invention, as defined in the appended claims. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used. 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 on or transmitted over, as one or more instructions or code, a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory 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 implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium. By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium 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 termed a computer-readable medium. For example, if instructions are transmitted from a website, 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 may be included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transient media, but are instead directed to nontransient, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Claims

1. A method for managing a PDU session established for a wireless access backhaul, WAB, node including a gNB component and a MT component, the gNB component for serving a User Equipment, UE, the method at the WAB node including:requesting modification of the WAB node PDU session based on at least one of:configuration of one or more radio bearers established for one or more radio interfaces at the WAB node;link quality of each of one or more radio interfaces at the WAB node.

2. The method of claim 1, wherein the one or more radio interfaces include a first radio interface and a second radio interface, wherein the WAB node PDU session is established through the second radio interface,wherein requesting modification includes: after determining the first radio interface does not match the second radio interface, requesting modification of the WAB node PDU session.

3. The method of claim 2, wherein requesting modification includes: after determining first flow information for the first radio interface does not match second flow information for the second radio interface, requesting modification of the WAB node PDU session.

4. The method of claim 3, wherein the flow information for each of the first and second radio interfaces includes at least one of:information indicating a configuration of a radio bearer associated with the respective radio interface;information indicating a link quality of the respective radio interface.

5. The method of claim 4, wherein the flow information further includes:information indicating a Quality of Service, QoS, for a flow through the respective radio interface.

6. The method of any one of claims 3 to 5, further including receiving, at the MT component of the WAB node from the gNB component of the WAB node, the first flow information.

7. The method of any one of claims 3 to 6, further including receiving, at the MT component of the WAB node, information indicating one or more configurations of one or more radio bearers established for the WAB PDU session through the second radio interface.

8. The method of any one of the preceding claims, wherein requesting modification includes, sending, by the WAB node, a request for requesting modification of the WAB PDU session.

9. The method of claim 8, wherein the request for requesting modification of the WAB PDU session is one of: a request to add a new QoS flow for the WAB PDU session associated with the second radio interface; a request to modify an existing QoS flow for the WAB PDU session associated with the second radio interface.

10. The method of any one of the claims 1 to 8, wherein requesting modification includes, sending, by the WAB node, a first request for requesting modification of the WAB PDU session to add a first new QoS flow for the WAB PDU session associated with the second radio interface.

11. The method of any one of claims 3 to 5 and claim 10, wherein requesting a modification includes after determining the first flow information does not match new flow information associated with the first new QoS flow, sending, by the WAB node, a second request for requesting modification of the WAB PDU session to add a second new QoS flow for the WAB PDU session associated with the second radio interface or to modify the first new QoS flow.

12. The method of any one of claims 3 to 11, further including after determining the first flow information associated with the first radio interface matches flow information associated with the second radio interface, configuring a radio bearer for the WAB PDU session for the second radio interface based on the matched flow information associated with the second radio interface.

13. The method of any one of claims 2 to 12, wherein the first radio interface is a radio interface through which the WAB node serves the UE and the second radio interface is a radio interface supporting the WAB node PDU session via a backhaul RAN node.

14. The method of claim 1, wherein the one or more radio interfaces include a first radio interface and a second radio interface, wherein the WAB node PDU session is established through the second radio interface, the method further including:receiving, at the MT component of the WAB node from the gNB component of the WAB node, first flow information for a UE PDU session established for the UE associated with the first radio interface.

15. The method of claim 14, the method further including:receiving, at the gNB component of the WAB node as part of establishing the UE PDU session for the UE, information indicating a Quality of Service, QoS, for the UE PDU session;establishing a radio bearer for the UE PDU session for the first radio interface based on the indicated QoS.

16. The method of claim 14 or claim 15, further including receiving, at the MT component of the WAB node, information indicating one or more configurations of one or more radio bearers established for the WAB PDU session through the second radio interface.

17. The method of claim 16, wherein requesting modification includes: after determining the first flow information does not match the second flow information, requesting modification of the WAB node PDU session.

18. The method of claim 17, wherein requesting modification includes: after determining the first flow information does not match second flow information associated with flows through the second radio interface, sending, by the MT component of the WAB node, a first request for requesting modification of the WAB PDU session, the request including the information indicating the QoS for the UE PDU session.

19. The method of claim 18, wherein the first flow information includes at least one of: information indicating a configuration of a radio bearer for the UE PDU session associated with the first radio interface;information indicating a link quality of the first radio interface;information indicating the QoS for the UE PDU session,wherein the second flow information includes at least one of:the information indicating one or more configurations of one or more radio bearers established for the WAB PDU session associated with the second radio interface;information indicating a link quality of the second radio interface;information indicating the QoS for the WAB PDU session.

20. The method of claim 18 or claim 19, wherein the first request for requesting modification of the WAB PDU session is a request for adding a new QoS flow for the WAB PDU session associated with the second radio interface, the new QoS flow having a first QoS corresponding to the QoS for the UE PDU session.

21. The method of claim 20, further including: after sending the first request for requesting modification to add a new QoS flow for the WAB PDU session and after determining the first flow information for the UE PDU session associated with the first radio interface does not match new flow information associated with the new QoS flow for the WAB PDU session associated with the second radio interface and having the first QoS, sending, by the MT component of the WAB node, a second request for requesting modification of the WAB PDU session to add another new QoS flow for the WAB PDU session associated with the second radio interface or to modify the new QoS flow, the second request including information indicating a second QoS.

22. The method of claim 18 or claim 19, wherein the first request for requesting modification of the WAB PDU session is a request for modifying an existing QoS flow for the WAB PDU session associated with the second radio interface such that the modified existing QoS flow has a first QoS corresponding to the QoS for the UE PDU session.

23. The method of claim 22, further including: after sending the first request for requesting modification to modify an existing QoS flow for the WAB PDU session and after determining the first flow information for the UE PDU session associated with the first radio interface does not match new flow information associated with the modified existing QoS flow for the WAB PDU session associated with the second radio interface and having the first QoS, sending, by the MT component of the WAB node, a second request for requesting modification of the WAB PDU session to add another new QoS flow for the WAB PDU session associated with the second radio interface or to further modify the modified existing QoS flow, the second request including information indicating a second QoS.

24. The method of claim 21 or claim 23, wherein the new flow information includes at least one: information indicating a configuration of a radio bearer established for the new QoS flow or modified existing QoS flow for the WAB PDU session associated with the second radio interface;information indicating a link quality of the second radio interface.

25. The method of claim 21 or claim 23 or claim 24, wherein the second QoS is determined based on one or more of:QoS for the UE PDU session;information indicating a configuration of the radio bearer established for the UE PDU session associated with the first radio interface;information indicating link quality of the first radio interface;information indicating link quality of the second radio interface;information indicating a configuration of a radio bearer established for the new QoS flow or modified existing QoS flow for the WAB PDU session associated with the second radio interface.

26. The method of any one of claims 14 to 25, further including after determining the first flow information associated with the first radio interface matches flow information associated with the second radio interface, configuring a radio bearer for the WAB PDU session for the second radio interface based on the matched flow information associated with the second radio interface.

27. The method of claim 1, wherein the one or more radio interfaces include a first radio interface and a second radio interface, wherein the WAB node PDU session is established through the second radio interface, the method further including:receiving, at the MT component of the WAB node from the gNB component of the WAB node, first flow information for NG interface setup or Xn interface setup associated with the first radio interface.

28. The method of claim 27, further including receiving, at the MT component of the WAB node, information indicating one or more configurations of one or more radio bearers established for the WAB PDU session associated with the second radio interface.

29. The method of claim 28, wherein requesting modification includes: after determining the first flow information does not match the second flow information, requesting modification of the WAB node PDU session.

30. The method of claim 29, wherein the first flow information includes at least one of: information indicating a configuration of a radio bearer for NG interface or Xn interface associated with the first radio interface;information indicating a link quality of the first radio interface;wherein the second flow information includes at least one of:the information indicating one or more configurations of one or more radio bearers established for the WAB PDU session associated with the second radio interface;information indicating a link quality of the second radio interface.

31. The method of claim 29 or claim 30, wherein requesting modification includes: after determining the first flow information does not match second flow information associated with flows through the second radio interface, sending, by the MT component of the WAB node, a first request for requesting modification of the WAB PDU session to add a new QoS flow for the WAB PDU session associated with the second radio interface, the first request including information indicating a first QoS for the new QoS flow to be added.

32. The method of claim 31, further including after sending the first request for requesting modification to add a new QoS flow for the WAB PDU session and after determining the first flow information does not match new flow information associated with the new QoS flow for the WAB PDU session associated with the second radio interface, sending, by the MT component of the WAB node, a second request for requesting modification of the WAB PDU session to add another new QoS flow for the WAB PDU session associated with the second radio interface or to modify the new QoS flow, the second request including information indicating a second QoS.

33. The method of claim 29 or claim 30, wherein requesting modification includes: after determining the first flow information does not match second flow information associated with flows through the second radio interface, sending, by the MT component of the WAB node, a first request for requesting modification of the WAB PDU session to modify an existing QoS flow for the WAB PDU session associated with the second radio interface, the first request including information indicating a first QoS for use in modifying the existing QoS flow.

34. The method of claim 33, further including after sending the first request for requesting modification to modify an existing QoS flow for the WAB PDU session and after determining the first flow information does not match new flow information associated with the modified existing QoS flow for the WAB PDU session associated with the second radio interface, sending, by the MT component of the WAB node, a second request for requesting modification of the WAB PDU session to add a new QoS flow for the WAB PDU session associated with the second radio interfaceor to further modify the existing QoS flow, the second request including information indicating a second QoS.

35. The method of claim 32 or claim 34, wherein the new flow information includes at least one: information indicating a configuration of a radio bearer established for the new QoS flow or modified existing QoS flow for the WAB PDU session associated with the second radio interface;information indicating a link quality of the second radio interface.

36. The method of claim 32 or claim 34 or claim 35, wherein the second QoS is determined based on one or more of:information indicating a configuration of the radio bearer for NG interface or Xn interface associated with the first radio interface;information indicating link quality of the first radio interface;information indicating link quality of the second radio interface;information indicating a configuration of a radio bearer established for the new QoS flow or modified existing QoS flow for the WAB PDU session associated with the second radio interface.

37. The method of any one of claims 27 to 36, further including after determining the first flow information associated with the first radio interface matches flow information associated with the second radio interface, configuring a radio bearer for the WAB PDU session for the second radio interface based on the matched flow information associated with the second radio interface.

38. The method of claim 1, wherein the one or more radio interfaces include a first radio interface and a second radio interface, wherein the WAB node PDU session is established through the second radio interface, the method further including:receiving, at the MT component of the WAB node from the gNB component of the WAB node, information indicating link quality of the first radio interface.

39. The method of claim 38, wherein requesting modification includes, sending, by the WAB node, a request for requesting modification of the WAB PDU session, wherein the request for requesting modification of the WAB PDU session is based on the received information indicating the link quality of the first radio interface and is one of: a request to add a new QoS flow for the WAB PDU session associated with the second radio interface; a request to modify an existing QoS flow for the WAB PDU session associated with the second radio interface.

40. The method of claim 38, further including:updating first flow information associated with the first radio interface based on the received information indicating link quality of the first radio interface,wherein requesting modification includes: after determining the updated first flow information associated with the first radio interface does not match second flow information associated with the second radio interface, sending, by the MT component of the WAB node, a first request for requesting modification of the WAB PDU session to add a new QoS flow for the WAB PDU session associated with the second radio interface, the request including information indicating a QoS for the new QoS flow to be added.

41. The method of claim 38, further including:updating first flow information associated with the first radio interface based on the received information indicating link quality of the first radio interface,wherein requesting modification includes: after determining the updated first flow information associated with the first radio interface does not match second flow information associated with the second radio interface, sending, by the MT component of the WAB node, a first request for requesting modification of the WAB PDU session to modify an existing QoS flow for the WAB PDU session associated with the second radio interface, the request including information indicating a QoS for use in modifying the existing QoS flow.

42. The method of claim 40 or claim 41, wherein the first flow information has been previously matched to the second flow information.

43. The method of claim 40 or claim 41 or claim 42, wherein the updated first flow informationincludes at least one of:information indicating a configuration of a radio bearer associated with the first radio interface;the received information indicating a link quality of the first radio interface;wherein the second flow information includes at least one of:information indicating one or more configurations of one or more radio bearers established for the WAB PDU session associated with the second radio interface;information indicating a link quality of the second radio interface.

44. The method of any one of claims 40 to 43, wherein the QoS is determined based on one or more of:QoS associated with the first radio interface;information indicating a configuration of the radio bearer associated with the first radio interface;information indicating link quality of the first radio interface;information indicating link quality of the second radio interface;information indicating a configuration of a radio bearer established for the new QoS flow for the WAB PDU session associated with the second radio interface.

45. A computer program comprising instructions which, when the program is executed by at least one processor unit, cause the at least one processing unit to carry out the method according to any one of claims 1 to 44.

46. A computer-readable medium carrying a computer program according to claim 45.

47. An apparatus for a wireless access backhaul, WAB, node for a wireless communication system, the apparatus comprising:one or more processing units configured to perform the method as recited in any one of claims 1 to 44.

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