Patent Publication Number: US-2023143694-A1

Title: Preventing reestablishment at descendant nodes with no alternative paths in integrated access backhaul

Description:
FIELD 
     The present disclosure relates to wireless communications, and in particular, to arrangements for preventing reestablishment at descendant nodes with no alternative paths in Integrated Access Backhaul (IAB) networks. 
     BACKGROUND 
     Integrated Access Backhaul Networks 
     The Third Generation Partnership Project (3GPP) is currently standardizing integrated access and wireless access backhaul (IAB) in 3GPP New Radio (NR, also called 5 th  Generation or 5G) in 3GPP Release 16 (Rel-16) (RP-RP-182882). 
     The usage of short range millimeter wave (mmWave) spectrum in NR may result in a densified deployment with multi-hop backhauling. However, optical fiber to every base station may be too costly and sometimes not even possible (e.g., historical sites). One main IAB principle is the use of wireless links for the backhaul (instead of fiber) to enable flexible and very dense deployment of cells without the need for densifying the transport network. Use case scenarios for IAB can include e.g., coverage extension, deployment of massive number of small cells and fixed wireless access (FWA) (e.g., to residential/office buildings). The larger bandwidth available for NR in mmWave spectrum may provide an opportunity for self-backhauling, without limiting the spectrum to be used for the access links. On top of that, the inherent multi-beam and multiple-input multiple-output (MIMO) support in NR may reduce cross-link interference between backhaul and access links allowing higher densification. 
     During the study item phase of the IAB work (summary of the study item can be found in the technical report (TR) 38.874), it was considered to adopt a solution that leverages the Central Unit (CU)/Distributed Unit (DU) split architecture of NR, where the IAB node will be hosting a DU part that is controlled by a central unit. The IAB nodes also have a Mobile Termination (MT) part that they use to communicate with their parent nodes. 
     The specifications for IAB may strive to reuse existing functions and interfaces defined in NR. In particular, MT, gNB-DU, gNB-CU, user plane function (UPF), Access and Mobility Function (AMF) and Session Management Function (SMF), as well as, the corresponding interfaces NR Uu (between MT and gNB), F1, NG, X2 and N4 are used as a baseline for the IAB architectures. Modifications or enhancements to these functions and interfaces for the support of IAB will be explained in the context of the architecture discussion. Additional functionality such as multi-hop forwarding is included in the architecture discussion as it may be used for the understanding of IAB operation and since certain aspects may be standardized. 
     The Mobile-Termination (MT) function may be considered as a component of the IAB node. In the context of this disclosure, MT is referred to as a function residing on an IAB-node that terminates the radio interface layers of the backhaul Uu interface toward the IAB-donor or other IAB-nodes. 
       FIGS.  1 - 3    provide example reference diagrams for IAB in standalone mode (SA), which includes one IAB-donor and multiple IAB-nodes. The IAB-donor may be treated as a single logical node that includes a set of functions such as gNB-DU, gNB-CU-CP, gNB-CU-UP and potentially other functions. In a deployment, the IAB-donor can be split according to these functions, which can all be either collocated or non-collocated as allowed by 3GPP Next Generation Radio Access Network (NG-RAN) architecture. IAB-related aspects may arise when such split is exercised. Also, some of the functions presently associated with the IAB-donor may eventually be moved outside of the donor in case it becomes evident that they do not perform IAB-specific tasks.  FIG.  1    shows a high-level architectural view of an example IAB network. Examples of baseline user plane (UP) and control plane (CP) protocol stacks for IAB are shown in  FIGS.  2  and  3   .  FIG.  2    is an example baseline UP protocol stack for IAB in Rel-16.  FIG.  3    is an example baseline CP protocol stack for IAB in Rel-16. 
     As can be seen from  FIGS.  1 - 3   , the chosen protocol stacks reuse the current CU-DU split specification in 3GPP Release 15 (Rel-15), where the full user plane F1-U (GTP-U/UDP/IP) is terminated at the IAB node (like a normal DU) and the full control plane F1-C (F1-AP/SCTP/IP) is also terminated at the IAB node (like a normal DU). In the above cases, Network Domain Security (NDS) has been employed to protect both UP and CP traffic (Internet Protocol Security (IPsec) in the case of UP, and Datagram Transport Layer Security (DTLS) in the case of CP). IPsec may also be used for the CP protection instead of DTLS (in this case no DTLS layer would be used). 
     Backhaul Adaptation Protocol (BAP) 
     A new protocol layer called Backhaul Adaptation Protocol (BAP) has been introduced in the IAB nodes and the IAB-donor, which is used for routing of packets to the appropriate downstream/upstream node and also mapping the user equipment (UE)/wireless device (WD) bearer data to the proper backhaul radio link control (RLC) channel (and also between ingress and egress backhaul RLC channels in intermediate IAB nodes) to satisfy the end to end Quality of Service (QoS) requirements of bearers. 
     The UE establishes RLC channels to the DU on the UE&#39;s access IAB-node in compliance with 3GPP Technical Specification (TS) 38.300. Each of these RLC-channels is extended via F1-U between the UE&#39;s access DU and the IAB-donor. The information embedded in F1-U may be carried over backhaul RLC-channels across the backhaul links. Transport of F1-U over the wireless backhaul may be performed by the BAP. Since BAP is a newly defined layer for IAB networks, hence, 3GPP has made only the following considerations related to the BAP layer functionality:
         RAN2 (e.g., Radio Layer 2 and Radio Layer 3 Radio Resource) confirms that routing and bearer mapping (e.g., mapping of BH RLC channels) are BAP layer functions.   RAN2 assumes that the transmit (TX) part of the BAP layer performs routing and “bearer mapping”, and the receive (RX) part of the BAP layer performs “bearer de-mapping”.   RAN2 assumes that service data units (SDUs) are forwarded from the RX part of the BAP layer to the TX part of the BAP layer (for the next hop) for packets that are relayed by the IAB node.   For both UL and DL, the BAP header for Data protocol data unit (PDU) has a length of 3B, which hold 1 D/C bit, 3 R bits, 10 bits for the BAP address, and 10 bits for BAP path identification (ID) (this may override earlier considerations).   For BAP routing Next Hop ID, The BAP address of the next hop node to be used as the next hop identifier for the downstream.   For BAP routing Next Hop ID, the BAP address of the next hop node is also to be used as the next hop identifier for the upstream.   Confirm that the BAP address for an IAB node (e.g., to differentiate the data delivered to higher layer in BAP) is configured via Radio Resource Control (RRC).   To configure the association between child IAB-node and Next Hop ID, RAN2 may assume that the CU includes the BAP address of the child IAB-node in a F1AP configuration (e.g., F1AP UE CONTEXT SETUP/MODIFICATION REQUEST message) for the child IAB-node MT. Details may be determined by R3.   To configure the association between parent IAB-node and Next Hop ID (i.e., BAP address of next hop), the CU includes the BAP address of the parent IAB-node together with the cell group identification (ID) of the parent node in the RRC Reconfiguration message (details for further study (FFS)).   Observation: Upstream and downstream bearer mapping tables can use either the backhaul (BH) RLC channel (CH) ID or the Logical Channel ID (LCID) (they are mapped 1-to-1) for BAP ingress and egress RLC channel IDs.   The BH RLC CH ID is used for ingress/egress RLC channel ID in the BAP bearer mapping configuration.       

     Backhaul-Link-Failure 
     Backhaul Link Failure Recovery Scenarios 
     For various reasons, different scenarios of backhaul-link failure may occur in IAB networks. In the following, some example scenarios are illustrated for backhaul-link failure. Each scenario is depicted with an illustrative figure ( FIGS.  4  to  6   ) aiming at establishing a route between IAB-donor and IAB-node D after BH-link failure, where:
         Nodes A1 and A2 are IAB-donor nodes; nodes B to H are IAB-nodes;   The dashed line represents the established connection between two nodes;   The arrow represents the established route after BH-link failure, and the bolded dashed line represents the new established connection.       

     Scenario 1 
     In this scenario (depicted in  FIG.  4   ), the backhaul-link failure occurs between on upstream IAB-node (e.g., IAB-node C) and one of its parent IAB-nodes (e.g., IAB-node B), where the upstream IAB-node (IAB-node C) has an additional link established to another parent node (IAB-node E). 
     Scenario 2 
     In this scenario (depicted in  FIG.  5   ), the backhaul-link failure occurs between an upstream IAB-node (e.g., IAB-node C) and all its parent IAB-nodes (e.g., IAB-nodes B and E). The upstream IAB-node (IAB-node C) has to reconnect to a new parent node (e.g., IAB-node F), and the connection between IAB-node F and IAB-node C is newly established). 
     Scenario 3 
     In this scenario (depicted in  FIG.  6   ), the backhaul-link failure occurs between IAB-node C and IAB-node D. IAB-node D has to reconnect to the new IAB-donor (e.g., IAB-donor A2) via a new route. 
     So far 3GPP has considered the followed related to radio link failure (RLF), which may be performed by one or more network nodes and/or a UE:
         R2 (e.g., Radio Layer 2) confirms that when the IAB-node is not configured with dual connectivity (DC), R2 applies for BH RLF handling the same mechanisms and procedures as UE&#39;s RLF handling currently specified in TS 38.331 (including e.g., detection and recovery). FFS on additional enhancements.   When NR DC is configured for the IAB-node, 2.1 RLF is detected separately for the master cell group (MCG)-link and for the secondary cell group (SCG)-link, and 2.2 existing UE procedures are used for MCG-link and SCG-link failure handling.   The following may be considered as a working assumption: BH RLF recovery for DC case reuses UE&#39;s MCG and SCG failure recovery procedures specified in Rel-16.   For an IAB-node not configured with DC, R2 initiates RRC reestablishment when it receives downstream notification “Recovery Failure”.   For DC case, the IAB-node considers the radio link is failed and uses RRC existing or Rel-16 Mechanism (e.g., MCG or SCG failure report, RRC reestablishment) if “Recovery Failure” notification is received from parent nodes on MCG-link or/and SCG-link.   R2 assumes that RLF notification “recovery failure” would be triggered when RRC reestablishment has failed. FFS whether this need to be specified.   BAP layer is used to transmit BH RLF notification(s).   R2 assumes that Upstream BH RLF notification to Donor CU via current F1-AP signalling is supported.       

     To summarize/clarify the impact of these considerations, when RLF occurs at the IAB BH link, the same mechanisms and procedures are applied as for the access link. This includes BH RLF detection and RLF recovery using RRC reestablishment procedure. 
     For IAB-nodes operating in SA-mode, the IAB-node may transmit an RLF notification message to its child nodes in case the RRC reestablishment procedure to recover the BH link fails. The child node considers the BH link, on which it has received the RLF notification as failed (i.e., as if it has detected RLF on that BH link). The RLF notification message is transmitted on BAP layer. 
     Backhaul Link RLF Notification Types to Downstream/Descendant Nodes 
     3GPP RAN2 considered the following possible notification types to downstream node(s):
         Type 1—“Plain” notification: Indication that BH link RLF is detected by the child IAB-node.   Type 2—“Trying to recover”: Indication that BH link RLF is detected, and the child IAB-node is attempting to recover from it.   Type 3—“BH link recovered”: Indication that the BH link successfully recovers from RLF.   Type 4—“Recovery failure”: Indication that the BH link RLF recovery failure occurs.   Type 4x—“Indicating child nodes to perform RLF procedure”: it may be implementation when the parent node sending this indication, and the child node should perform RLF related procedure when receiving this indication.       

     SUMMARY 
     Some embodiments advantageously provide methods, systems, and apparatuses for preventing reestablishment at descendant nodes with no alternative paths in Integrated Access Backhaul (IAB) networks. 
     According to an aspect of the present disclosure, a method implemented in a network node configured to communicate with at least one descendant node over a backhaul network is provided. The method comprises transmitting an indication to the at least one descendant network node, the indication associated with a radio link failure; and receiving at least one message in response to the indication. The at least one message is associated with an alternative path availability of the at least one descendant network node toward a third network node. 
     In some embodiments, the at least one message indicates at least one of: at least one path that is not available as an alternative path; and at least one path that is available as the alternative path. In some embodiments of this aspect, the at least one message comprises an alternative path availability flag indicating whether the at least one descendant network node has an alternative path toward the third network node. In some embodiments of this aspect, the at least one message comprises an indication of at least one cell that a distributed unit, DU, in the at least one descendant network node is hosting. In some embodiments of this aspect, the method further includes considering at least one first cell in the at least one cell as a candidate for re-establishment. In some embodiments of this aspect, considering the at least one first cell as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level as compared to any other cells the network node measures. 
     In some embodiments of this aspect, considering the at least one first cell as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level among cells in the at least one cell indicated in the at least one message. In some embodiments of this aspect, the method further includes considering none of the cells in the at least one cell as a candidate for re-establishment. In some embodiments of this aspect, the at least one cell indicated in the at least one message comprises a first set of cells and a second set of cells; and the method further comprises: considering none of the first set of cells as a candidate for re-establishment; and considering the second set of cells in the at least one cell as the candidate for re-establishment. 
     In some embodiments of this aspect, the at least one message comprises a dedicated preamble; and the method further comprises using the dedicated preamble to attempt a random access, RA, for a radio resource control, RRC, re-establishment procedure via the at least one descendant network node. In some embodiments of this aspect, the network node is a parent Integrated Access Backhaul, IAB, node and the third network node is a donor IAB node. In some embodiments of this aspect, the method further includes receiving a dual-connectivity indication when the at least one descendent network node is connected via dual-connectivity. 
     According to another aspect of the present disclosure, a method implemented in a first network node that is configured to communicate with a second network node over a backhaul network is provided. The method includes receiving, from the second network node, an indication associated with a radio link failure; and transmitting at least one message to the second network node in response to the indication, the at least one message associated with an alternative path availability of the first network node toward a third network node. 
     In some embodiments, the at least one message indicates at least one of: at least one path that is not available as an alternative path; and at least one path that is available as the alternative path. In some embodiments of this aspect, the method further includes determining whether the first network node has an alternative path toward a third network node, the at least one message being based at least in part on the determination. In some embodiments of this aspect, the at least one message comprises an alternative path availability flag indicating whether the first network node has an alternative path toward the third network node. In some embodiments of this aspect, the at least one message comprises an indication of at least one cell that a distributed unit, DU, in the first network node is hosting. In some embodiments of this aspect, the at least one cell indicated in the at least one message transmitted to the second network node comprises: at least one first cell to be considered by the second network node as a candidate for re-establishment. 
     In some embodiments of this aspect, the at least one first cell is to be considered as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level as compared to any other cells the second network node measures. In some embodiments of this aspect, the at least one first cell is to be considered as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level among cells in the at least one cell indicated in the at least one message. In some embodiments of this aspect, none of the cells in the at least one cell indicated in the at least one message is to be considered as a candidate for re-establishment. 
     In some embodiments of this aspect, the at least one cell indicated in the at least one message comprises a first set of cells and a second set of cells, none of the first set of cells are to be considered by the second network node as a candidate for re-establishment and the second set of cells are to be considered by the second network node as the candidate for re-establishment. In some embodiments of this aspect, the at least one message comprises a dedicated preamble for the second network node to perform a random access, RA, for a radio resource control, RRC, re-establishment procedure via the first network node. In some embodiments of this aspect, the second network node is a parent Integrated Access Backhaul, IAB, node and the third network node is a donor IAB node. 
     According to yet another aspect of the present disclosure, a network node configured to communicate with at least one descendant node over a backhaul network is provided. The network node comprises processing circuitry. The processing circuitry is configured to cause the network node to transmit an indication to the at least one descendant network node, the indication associated with a radio link failure; and receive at least one message in response to the indication, the at least one message associated with an alternative path availability of the at least one descendant network node toward a third network node. 
     In some embodiments, the at least one message indicates at least one of: at least one path that is not available as an alternative path; and at least one path that is available as the alternative path. In some embodiments of this aspect, the at least one message comprises an alternative path availability flag indicating whether the at least one descendant network node has an alternative path toward the third network node. In some embodiments of this aspect, the at least one message comprises an indication of at least one cell that a distributed unit, DU, in the at least one descendant network node is hosting. In some embodiments of this aspect, the processing circuitry is configured to cause the network node to consider at least one first cell in the at least one cell as a candidate for re-establishment. 
     In some embodiments of this aspect, the processing circuitry is configured to cause the network node to consider the at least one first cell as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level as compared to any other cells the network node measures. In some embodiments of this aspect, the processing circuitry is configured to cause the network node to consider the at least one first cell as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level among cells in the at least one cell indicated in the at least one message. 
     In some embodiments of this aspect, the processing circuitry is further configured to cause the network node to consider none of the cells in the at least one cell as a candidate for re-establishment. In some embodiments of this aspect, the at least one cell indicated in the at least one message comprises a first set of cells and a second set of cells; and the processing circuitry is configured to cause the network node to: consider none of the first set of cells as a candidate for re-establishment; and consider the second set of cells in the at least one cell as the candidate for re-establishment. 
     In some embodiments of this aspect, the at least one message comprises a dedicated preamble; and the processing circuitry is configured to cause the network node to use the dedicated preamble to attempt a random access, RA, for a radio resource control, RRC, re-establishment procedure via the at least one descendant network node. In some embodiments of this aspect, the network node is a parent Integrated Access Backhaul, IAB, node and the third network node is a donor IAB node. In some embodiments of this aspect, the processing circuitry is configured to cause the network node to receive a dual-connectivity indication when the at least one descendent network node is connected via dual-connectivity. 
     According to another aspect of the present disclosure, a first network node that is configured to communicate with a second network node over a backhaul network is provided. The first network node comprises processing circuitry. The processing circuitry is configured to cause the first network node to: receive, from the second network node, an indication associated with a radio link failure; and transmit at least one message to the second network node in response to the indication, the at least one message associated with an alternative path availability of the first network node toward a third network node. 
     In some embodiments, the at least one message indicates at least one of: at least one path that is not available as an alternative path; and at least one path that is available as the alternative path. In some embodiments of this aspect, the processing circuitry is further configured to cause the first network node to: determine whether the first network node has an alternative path toward a third network node, the at least one message being based at least in part on the determination. In some embodiments of this aspect, the at least one message comprises an alternative path availability flag indicating whether the first network node has an alternative path toward the third network node. In some embodiments of this aspect, the at least one message comprises an indication of at least one cell that a distributed unit, DU, in the first network node is hosting. In some embodiments of this aspect, the at least cell indicated in the at least one message transmitted to the second network node comprises: at least one first cell to be considered by the second network node as a candidate for re-establishment. 
     In some embodiments of this aspect, the at least one first cell is to be considered as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level as compared to any other cells the second network node measures. In some embodiments of this aspect, the at least one first cell is to be considered as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level among cells in the at least one cell indicated in the at least one message. In some embodiments of this aspect, none of the cells in the at least one cell indicated in the at least one message is to be considered as a candidate for re-establishment. 
     In some embodiments of this aspect, the at least one cell indicated in the at least one message comprises a first set of cells and a second set of cell, none of the first set of cells are to be considered by the second network node as a candidate for re-establishment and the second set of cells are to be considered by the second network node as the candidate for re-establishment. In some embodiments of this aspect, the at least one message comprises a dedicated preamble for the second network node to perform a random access, RA, for a radio resource control, RRC, re-establishment procedure via the first network node. In some embodiments of this aspect, the second network node is a parent Integrated Access Backhaul, IAB, node and the third network node is a donor IAB node. 
     According to another aspect of the present disclosure, a method implemented in a first network node configured to communicate with at least one descendant network node over a backhaul network is provided. The method comprises transmitting a first message type to the at least one descendant network node, the first message type indicating a backhaul link radio link failure and the first message type triggering at the at least one descendant network node at least one of: a reduction of scheduling resource requests; stopping scheduling resource requests; and using an alternative route to a donor Integrated Access Backhaul, IAB, network node. In some embodiments of this aspect, the method further includes transmitting a second message type to the at least one descendant network node, the second message type indicating the backhaul link is recovered and the second message type triggering resumption of the scheduling resource requests. In some embodiments of this aspect, the scheduling resource requests comprise at least one of a scheduling request, SR, and a buffer status report, BSR. 
     According to yet another aspect of the present disclosure, a method implemented in a first network node configured to communicate with a second network node over a backhaul network is provided. The method comprises receiving a first message type from the second network node, the first message type indicating a backhaul link radio link failure and the first message type triggering at least one of: a reduction of scheduling resource requests to the second network node; stopping scheduling resource requests to the second network node; and using an alternative route to a donor Integrated Access Backhaul, IAB, network node. 
     In some embodiments of this aspect, the method further includes receiving a second message type from the second network node, the second message type indicating the backhaul link is recovered and the second message type triggering resumption of the scheduling resource requests. In some embodiments of this aspect, the scheduling resource requests comprise at least one of a scheduling request, SR, and a buffer status report, BSR. 
     According to another aspect, a first network node configured to communicate with at least one descendant network node over a backhaul network is provided. The first network node comprises processing circuitry. The processing circuitry is configured to cause the first network node to: transmit a first message type to the at least one descendant network node, the first message type indicating a backhaul link radio link failure and the first message type triggering at the at least one descendant network node at least one of: a reduction of scheduling resource requests; stopping scheduling resource requests; and using an alternative route to a donor Integrated Access Backhaul, IAB, network node. 
     In some embodiments of this aspect, the processing circuitry is further configured to cause the first network node to: transmit a second message type to the at least one descendant network node, the second message type indicating the backhaul link is recovered and the second message type triggering resumption of the scheduling resource requests. In some embodiments of this aspect, the scheduling resource requests comprise at least one of a scheduling request, SR, and a buffer status report, BSR. 
     According to another aspect, a first network node configured to communicate with a second network node over a backhaul network is provided. The first network node comprises processing circuitry. The processing circuitry is configured to cause the first network node to: receive a first message type from the second network node, the first message type indicating a backhaul link radio link failure and the first message type triggering at least one of: a reduction of scheduling resource requests to the second network node; stopping scheduling resource requests to the second network node; and using an alternative route to a donor Integrated Access Backhaul, IAB, network node. 
     In some embodiments of this aspect, the processing circuitry is further configured to cause the first network node to: receive a second message type from the second network node, the second message type indicating the backhaul link is recovered and the second message type triggering resumption of the scheduling resource requests. In some embodiments of this aspect, the scheduling resource requests comprise at least one of a scheduling request, SR, and a buffer status report, BSR. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present embodiments, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG.  1    illustrates an example reference diagram for IAB-architectures (TR 38.874 v0.7.0); 
         FIG.  2    illustrates an example of Baseline User Plane (UP) Protocol stack for IAB in rel-16 
         FIG.  3    illustrates an example Baseline control plane (CP) Protocol stack for IAB in rel-16; 
         FIG.  4    illustrates an example of backhaul-link failure scenario 1; 
         FIG.  5    illustrates an example backhaul-link failure scenario 2; 
         FIG.  6    illustrates an example backhaul-link failure scenario 3; 
         FIG.  7    is a schematic diagram of an exemplary network architecture illustrating a communication system connected via an intermediate network to a host computer according to the principles in the present disclosure; 
         FIG.  8    is a block diagram of a host computer communicating via a network node with a user equipment over an at least partially wireless connection according to some embodiments of the present disclosure; 
         FIG.  9    is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a user equipment for executing a client application at a user equipment according to some embodiments of the present disclosure; 
         FIG.  10    is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a user equipment for receiving user data at a user equipment according to some embodiments of the present disclosure; 
         FIG.  11    is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a user equipment for receiving user data from the user equipment at a host computer according to some embodiments of the present disclosure; 
         FIG.  12    is a flowchart illustrating exemplary methods implemented in a communication system including a host computer, a network node and a user equipment for receiving user data at a host computer according to some embodiments of the present disclosure; 
         FIG.  13    is a flowchart of an exemplary process in a network node (e.g., a parent IAB node) according to some embodiments of the present disclosure; 
         FIG.  14    is a flowchart of an exemplary process in a network node (e.g., a descendant IAB node) according to some embodiments of the present disclosure; 
         FIG.  15    is a flowchart of an exemplary process in a network node (e.g., a parent IAB node) according to some embodiments of the present disclosure; 
         FIG.  16    is a flowchart of an exemplary process in a network node (e.g., a descendant IAB node) according to some embodiments of the present disclosure; 
         FIG.  17    is a flowchart of an exemplary process in a network node (e.g., a parent IAB node) according to some embodiments of the present disclosure; 
         FIG.  18    is a flowchart of an exemplary process in a network node (e.g., a descendant IAB node) according to some embodiments of the present disclosure; 
         FIG.  19    illustrates an example of parent IAB node 3 with BH RLF on link with IAB1 where descendent node IAB 5 has an alternative path according to some embodiments of the present disclosure; and 
         FIG.  20    illustrates an example of parent IAB node 3 with BH RLF on link with IAB1 where descendant node IAB 5 does not have an alternate path according to some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     With regard to the Type 1-4 messages described above, RAN2 assumes that an IAB node would trigger Type 4 notification, which is an indication from a parent IAB node to child IAB node(s) about RRC re-establishment failure and losing connection with the Donor CU. Thus, this notification message aims at triggering an RRC re-establishment in the child node(s) receiving the message. The other notification types are under discussion in RAN2. It has been considered that Type 2 and Type 3 could be beneficial for the overall network performance. For example, before Type 4 notification is received by child node(s), the child node(s) is likely to transmit a scheduling request (SR) request to its parent node as well as receiving and buffering data from its child node(s) and other UEs. This might lead to buffer overflows in the network. Any lost data due to the buffer overflow may have to be recovered via higher layers e.g., transmission control protocol (TCP) or application. 
     To prevent child nodes from transmitting uplink (UL) data and even request network resources via buffer status report (BSR) or SR, Type 2 and Type 3 could be useful. In some embodiments, when Type 2 is received by a child IAB node, the child IAB node may reduce or stop requesting scheduling resources. In some embodiments, Type 2 may also trigger the child IAB node to use alternative routes, when available. When the situation is solved, Type 3 indication may allow resuming the request of scheduling resources. 
     If an IAB node that has detected BH RLF tries to perform re-establishment attempts towards a cell that is hosted by one of its child nodes, and if the child node has no other alternative path/parent, the re-establishment request may never reach the donor CU (as the child IAB node may try to forward this message via the parent node that already has lost BH connectivity). So far RAN2 has considered to send only Type 4 BH RLF notification, which is an indication from a parent IAB node to child IAB node(s) about the failure to recover the BH connection. Though this BH RLF notification is useful in that it will trigger the child node to re-establish to another parent, it will not help in ensuring the parent node recovers from the BH RLF that has experienced. 
     Additional BH RLF related notification message such as Type 2 message (indicating that parent node has detected BH RLF and is trying to recover the connection) may be used as a guidance to the descendant nodes that they may consider that the upstream node is not operational, at least temporarily. Still, these additional notification messages may not help the parent node to recover from the BH RLF, because it could still end up trying to reestablishing to one of the child nodes that it has sent the Type 2 BH RLF notification messages (as the IAB-MT of the parent node is not aware of the identity of the cells that are hosted by those of the child node&#39;s IAB-DU, and also whether the child node has alternative paths to the donor or not). 
     Accordingly, some embodiments of the present disclosure may prevent the IAB node experiencing BH RLF to avoid re-establishment at its descendant node unless the descendant node has an alternative path/parent towards the donor DU/CU. For this purpose, some embodiments provide a procedure where a descendant node will respond to a Type 2 BH RLF indication (i.e., parent node has detected BH RLF and is trying to recover the link) received from its parent node by sending information about the cells that it (i.e., its DU) is hosting and whether the child node has an alternate path to the donor node. The parent node may then use this information to determine whether or not to perform RRC re-establishment via one of the cells indicated in the response message. 
     Some embodiments of the present disclosure may advantageously ensure that a parent IAB node will not perform RRC re-establishment attempts at its own descendant nodes unless the descendant nodes have an alternative path towards the IAB Donor node. This may prevent a deadlock situation where the parent node is trying to recover the connection through the child node, which is waiting for the parent node to recover the connection. 
     Before describing in detail exemplary embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to arrangements for preventing reestablishment at descendant nodes with no alternative paths in Integrated Access Backhaul (IAB) networks. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Like numbers refer to like elements throughout the description. 
     As used herein, relational terms, such as “first” and “second,” “top” and “bottom,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     In embodiments described herein, the joining term, “in communication with” and the like, may be used to indicate electrical or data communication, which may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example. One having ordinary skill in the art will appreciate that multiple components may interoperate and modifications and variations are possible of achieving the electrical and data communication. 
     In some embodiments described herein, the term “coupled,” “connected,” and the like, may be used herein to indicate a connection, although not necessarily directly, and may include wired and/or wireless connections. 
     The term “network node” used herein can be any kind of network node comprised in a radio network which may further comprise any of an integrated access and backhaul (IAB) donor node, a parent IAB node, a descendent IAB node, a base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi-standard radio (MSR) radio node such as MSR BS, multi-cell/multicast coordination entity (MCE), integrated access and backhaul (IAB) node, relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), self-organizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rd party node, a node external to the current network), nodes in distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network node may also comprise test equipment. The term “radio node” used herein may be used to also denote a user equipment (UE) or a radio network node. 
     In some embodiments, the non-limiting terms wireless device (WD) or a user equipment (UE) are used interchangeably. The UE herein can be any type of wireless device capable of communicating with a network node or another UE over radio signals, such as wireless device (WD). The UE may also be a radio communication device, target device, device to device (D2D) UE, machine type UE or UE capable of machine to machine communication (M2M), low-cost and/or low-complexity UE, a sensor equipped with UE, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (IoT) device, or a Narrowband IoT (NB-IOT) device, etc. 
     Also, in some embodiments the generic term “radio network node” is used. It can be any kind of a radio network node which may comprise any of base station, radio base station, base transceiver station, base station controller, network controller, RNC, evolved Node B (eNB), Node B, gNB, Multi-cell/multicast Coordination Entity (MCE), IAB node, relay node, access point, radio access point, Remote Radio Unit (RRU) Remote Radio Head (RRH). 
     The term “node” is used herein and may indicate an IAB node. In some embodiments, the terms “child” and “descendent” are used interchangeably. The shortened terms “parent”, “child” and “donor” may be used to indicate a parent IAB node, a child IAB node and an IAB donor node, respectively. 
     Note that although terminology from one particular wireless system, such as, for example, 3GPP LTE and/or New Radio (NR), may be used in this disclosure, this should not be seen as limiting the scope of the disclosure to only the aforementioned system. Other wireless systems, including without limitation Wide Band Code Division Multiple Access (WCDMA), Worldwide Interoperability for Microwave Access (WiMax), Ultra Mobile Broadband (UMB) and Global System for Mobile Communications (GSM), may also benefit from exploiting the ideas covered within this disclosure. 
     Note further, that functions described herein as being performed by a user equipment or a network node may be distributed over a plurality of user equipments and/or network nodes. In other words, it is contemplated that the functions of the network node and user equipment described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Some embodiments provide arrangements for preventing reestablishment at descendant nodes with no alternative paths in Integrated Access Backhaul (IAB) networks. 
     Referring again to the drawing figures, in which like elements are referred to by like reference numerals, there is shown in  FIG.  7    a schematic diagram of a communication system  10 , according to an embodiment, such as a 3GPP-type cellular network that may support standards such as LTE and/or NR (5G), which comprises an access network  12 , such as a radio access network, and a core network  14 . The access network  12  comprises a plurality of network nodes  16   a ,  16   b ,  16   c  (referred to collectively as network nodes  16 ), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area  18   a ,  18   b ,  18   c  (referred to collectively as coverage areas  18 ). Each network node  16   a ,  16   b ,  16   c  is connectable to the core network  14  over a wired or wireless connection  20 . Network nodes  16  may be in communication with each other via one or more backhaul links and/or backhaul network. A first user equipment (UE)  22   a  located in coverage area  18   a  is configured to wirelessly connect to, or be paged by, the corresponding network node  16   a . A second UE  22   b  in coverage area  18   b  is wirelessly connectable to the corresponding network node  16   b . While a plurality of UEs  22   a ,  22   b  (collectively referred to as user equipments  22 ) are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding network node  16 . Note that although only two UEs  22  and three network nodes  16  are shown for convenience, the communication system may include many more UEs  22  and network nodes  16 . 
     Also, it is contemplated that a UE  22  can be in simultaneous communication and/or configured to separately communicate with more than one network node  16  and more than one type of network node  16 . For example, a UE  22  can have dual connectivity with a network node  16  that supports LTE and the same or a different network node  16  that supports NR. As an example, UE  22  can be in communication with an eNB for LTE/E-UTRAN and a gNB for NR/NG-RAN. 
     The communication system  10  may itself be connected to a host computer  24 , which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. The host computer  24  may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. The connections  26 ,  28  between the communication system  10  and the host computer  24  may extend directly from the core network  14  to the host computer  24  or may extend via an optional intermediate network  30 . The intermediate network  30  may be one of, or a combination of more than one of, a public, private or hosted network. The intermediate network  30 , if any, may be a backbone network or the Internet. In some embodiments, the intermediate network  30  may comprise two or more sub-networks (not shown). 
     The communication system of  FIG.  7    as a whole enables connectivity between one of the connected UEs  22   a ,  22   b  and the host computer  24 . The connectivity may be described as an over-the-top (OTT) connection. The host computer  24  and the connected UEs  22   a ,  22   b  are configured to communicate data and/or signaling via the OTT connection, using the access network  12 , the core network  14 , any intermediate network  30  and possible further infrastructure (not shown) as intermediaries. The OTT connection may be transparent in the sense that at least some of the participating communication devices through which the OTT connection passes are unaware of routing of uplink and downlink communications. For example, a network node  16  may not or need not be informed about the past routing of an incoming downlink communication with data originating from a host computer  24  to be forwarded (e.g., handed over) to a connected UE  22   a . Similarly, the network node  16  need not be aware of the future routing of an outgoing uplink communication originating from the UE  22   a  towards the host computer  24 . 
     A network node  16  (e.g., parent IAB node) configured to communicate with at least one descendant node over a backhaul network is configured to include an indication unit  32  which is configured to one or more of: transmit an indication to the at least one descendant network node, the indication associated with a radio link failure; receive at least one message in response to the indication, the at least one message associated with an alternative path availability of the at least one descendant network node toward a third node; and optionally, receive a dual-connectivity indication when the at least one descendent network node is connected via dual-connectivity. 
     A network node  16  (e.g., child/descendent IAB node) configured to communicate with a second node over a backhaul network is configured to include a report unit  34  which is configured to one or more of: receive, from the second node, an indication associated with a radio link failure; determine whether the first network node has an alternate path toward a third node; transmit at least one message to the second node in response to the indication, the at least one message based at least in part on the determination; and optionally, transmit a dual-connectivity indication to the second node when the first network node is connected via dual-connectivity. 
     Example implementations, in accordance with an embodiment, of the UE  22 , network node  16  and host computer  24  discussed in the preceding paragraphs will now be described with reference to  FIG.  8   . In a communication system  10 , a host computer  24  comprises hardware (HW)  38  including a communication interface  40  configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system  10 . The host computer  24  further comprises processing circuitry  42 , which may have storage and/or processing capabilities. The processing circuitry  42  may include a processor  44  and memory  46 . In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry  42  may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor  44  may be configured to access (e.g., write to and/or read from) memory  46 , which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). 
     Processing circuitry  42  may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by host computer  24 . Processor  44  corresponds to one or more processors  44  for performing host computer  24  functions described herein. The host computer  24  includes memory  46  that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software  48  and/or the host application  50  may include instructions that, when executed by the processor  44  and/or processing circuitry  42 , causes the processor  44  and/or processing circuitry  42  to perform the processes described herein with respect to host computer  24 . The instructions may be software associated with the host computer  24 . 
     The software  48  may be executable by the processing circuitry  42 . The software  48  includes a host application  50 . The host application  50  may be operable to provide a service to a remote user, such as a UE  22  connecting via an OTT connection  52  terminating at the UE  22  and the host computer  24 . In providing the service to the remote user, the host application  50  may provide user data which is transmitted using the OTT connection  52 . The “user data” may be data and information described herein as implementing the described functionality. In one embodiment, the host computer  24  may be configured for providing control and functionality to a service provider and may be operated by the service provider or on behalf of the service provider. The processing circuitry  42  of the host computer  24  may enable the host computer  24  to observe, monitor, control, transmit to and/or receive from the network node  16  and/or the user equipment  22 . The processing circuitry  42  of the host computer  24  may include a monitor unit  54  configured to enable the service provider to observe, monitor, control, transmit to and/or receive from the network node  16  and/or the user equipment  22 . 
     The communication system  10  further includes a network node  16  provided in a communication system  10  and including hardware  58  enabling it to communicate with the host computer  24  and with the UE  22 . The hardware  58  may include a communication interface  60  for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system  10 , as well as a radio interface  62  for setting up and maintaining at least a wireless connection  64  with a UE  22  located in a coverage area  18  served by the network node  16 . The radio interface  62  may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers. The communication interface  60  may be configured to facilitate a connection  66  to the host computer  24 . The connection  66  may be direct or it may pass through a core network  14  of the communication system  10  and/or through one or more intermediate networks  30  outside the communication system  10 . 
     In the embodiment shown, the hardware  58  of the network node  16  further includes processing circuitry  68 . The processing circuitry  68  may include a processor  70  and a memory  72 . In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry  68  may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor  70  may be configured to access (e.g., write to and/or read from) the memory  72 , which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). 
     Thus, the network node  16  further has software  74  stored internally in, for example, memory  72 , or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node  16  via an external connection. The software  74  may be executable by the processing circuitry  68 . The processing circuitry  68  may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by network node  16 . Processor  70  corresponds to one or more processors  70  for performing network node  16  functions described herein. The memory  72  is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software  74  may include instructions that, when executed by the processor  70  and/or processing circuitry  68 , causes the processor  70  and/or processing circuitry  68  to perform the processes described herein with respect to network node  16 . For example, processing circuitry  68  of the network node  16  may include indication unit  32  and/or report unit  34  configured to perform network node methods discussed herein, such as the methods discussed with reference to  FIGS.  13  and  14   , as well as other figures. 
     The communication system  10  further includes the UE  22  already referred to. The UE  22  may have hardware  80  that may include a radio interface  82  configured to set up and maintain a wireless connection  64  with a network node  16  serving a coverage area  18  in which the UE  22  is currently located. The radio interface  82  may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers. 
     The hardware  80  of the UE  22  further includes processing circuitry  84 . The processing circuitry  84  may include a processor  86  and memory  88 . In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry  84  may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor  86  may be configured to access (e.g., write to and/or read from) memory  88 , which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). 
     Thus, the UE  22  may further comprise software  90 , which is stored in, for example, memory  88  at the UE  22 , or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the UE  22 . The software  90  may be executable by the processing circuitry  84 . The software  90  may include a client application  92 . The client application  92  may be operable to provide a service to a human or non-human user via the UE  22 , with the support of the host computer  24 . In the host computer  24 , an executing host application  50  may communicate with the executing client application  92  via the OTT connection  52  terminating at the UE  22  and the host computer  24 . In providing the service to the user, the client application  92  may receive request data from the host application  50  and provide user data in response to the request data. The OTT connection  52  may transfer both the request data and the user data. The client application  92  may interact with the user to generate the user data that it provides. 
     The processing circuitry  84  may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by UE  22 . The processor  86  corresponds to one or more processors  86  for performing UE  22  functions described herein. The UE  22  includes memory  88  that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software  90  and/or the client application  92  may include instructions that, when executed by the processor  86  and/or processing circuitry  84 , causes the processor  86  and/or processing circuitry  84  to perform the processes described herein with respect to UE  22 . 
     In some embodiments, the inner workings of the network node  16 , UE  22 , and host computer  24  may be as shown in  FIG.  8    and independently, the surrounding network topology may be that of  FIG.  7   . 
     In  FIG.  8   , the OTT connection  52  has been drawn abstractly to illustrate the communication between the host computer  24  and the user equipment  22  via the network node  16 , without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from the UE  22  or from the service provider operating the host computer  24 , or both. While the OTT connection  52  is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network). 
     The wireless connection  64  between the UE  22  and the network node  16  is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the UE  22  using the OTT connection  52 , in which the wireless connection  64  may form the last segment. More precisely, the teachings of some of these embodiments may improve the data rate, latency, and/or power consumption and thereby provide benefits such as reduced user waiting time, relaxed restriction on file size, better responsiveness, extended battery lifetime, etc. 
     In some embodiments, a measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection  52  between the host computer  24  and UE  22 , in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection  52  may be implemented in the software  48  of the host computer  24  or in the software  90  of the UE  22 , or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection  52  passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software  48 ,  90  may compute or estimate the monitored quantities. The reconfiguring of the OTT connection  52  may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect the network node  16 , and it may be unknown or imperceptible to the network node  16 . Some such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating the host computer&#39;s 24 measurements of throughput, propagation times, latency and the like. In some embodiments, the measurements may be implemented in that the software  48 ,  90  causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection  52  while it monitors propagation times, errors etc. 
     Thus, in some embodiments, the host computer  24  includes processing circuitry  42  configured to provide user data and a communication interface  40  that is configured to forward the user data to a cellular network for transmission to the UE  22 . In some embodiments, the cellular network also includes the network node  16  with a radio interface  62 . In some embodiments, the network node  16  is configured to, and/or the network node&#39;s  16  processing circuitry  68  is configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the UE  22 , and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the UE  22 . 
     In some embodiments, the host computer  24  includes processing circuitry  42  and a communication interface  40  that is configured to a communication interface  40  configured to receive user data originating from a transmission from a UE  22  to a network node  16 . In some embodiments, the UE  22  is configured to, and/or comprises a radio interface  82  and/or processing circuitry  84  configured to perform the functions and/or methods described herein for preparing/initiating/maintaining/supporting/ending a transmission to the network node  16 , and/or preparing/terminating/maintaining/supporting/ending in receipt of a transmission from the network node  16 . 
     Although  FIGS.  7  and  8    show various “units” such as indication unit  32 , and report unit  34  as being within a respective processor, it is contemplated that these units may be implemented such that a portion of the unit is stored in a corresponding memory within the processing circuitry. In other words, the units may be implemented in hardware or in a combination of hardware and software within the processing circuitry. 
       FIG.  9    is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of  FIGS.  7  and  8   , in accordance with one embodiment. The communication system may include a host computer  24 , a network node  16  and a UE  22 , which may be those described with reference to  FIG.  8   . In a first step of the method, the host computer  24  provides user data (Block S 100 ). In an optional substep of the first step, the host computer  24  provides the user data by executing a host application, such as, for example, the host application  50  (Block S 102 ). In a second step, the host computer  24  initiates a transmission carrying the user data to the UE  22  (Block S 104 ). In an optional third step, the network node  16  transmits to the UE  22  the user data which was carried in the transmission that the host computer  24  initiated, in accordance with the teachings of the embodiments described throughout this disclosure (Block S 106 ). In an optional fourth step, the UE  22  executes a client application, such as, for example, the client application  92 , associated with the host application  50  executed by the host computer  24  (Block S 108 ). 
       FIG.  10    is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of  FIG.  7   , in accordance with one embodiment. The communication system may include a host computer  24 , a network node  16  and a UE  22 , which may be those described with reference to  FIGS.  7  and  8   . In a first step of the method, the host computer  24  provides user data (Block S 110 ). In an optional substep (not shown) the host computer  24  provides the user data by executing a host application, such as, for example, the host application  50 . In a second step, the host computer  24  initiates a transmission carrying the user data to the UE  22  (Block S 112 ). The transmission may pass via the network node  16 , in accordance with the teachings of the embodiments described throughout this disclosure. In an optional third step, the UE  22  receives the user data carried in the transmission (Block S 114 ). 
       FIG.  11    is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of  FIG.  7   , in accordance with one embodiment. The communication system may include a host computer  24 , a network node  16  and a UE  22 , which may be those described with reference to  FIGS.  7  and  8   . In an optional first step of the method, the UE  22  receives input data provided by the host computer  24  (Block S 116 ). In an optional substep of the first step, the UE  22  executes the client application  92 , which provides the user data in reaction to the received input data provided by the host computer  24  (Block S 118 ). Additionally or alternatively, in an optional second step, the UE  22  provides user data (Block S 120 ). In an optional substep of the second step, the UE provides the user data by executing a client application, such as, for example, client application  92  (Block S 122 ). In providing the user data, the executed client application  92  may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the UE  22  may initiate, in an optional third substep, transmission of the user data to the host computer  24  (Block S 124 ). In a fourth step of the method, the host computer  24  receives the user data transmitted from the UE  22 , in accordance with the teachings of the embodiments described throughout this disclosure (Block S 126 ). 
       FIG.  12    is a flowchart illustrating an exemplary method implemented in a communication system, such as, for example, the communication system of  FIG.  7   , in accordance with one embodiment. The communication system may include a host computer  24 , a network node  16  and a UE  22 , which may be those described with reference to  FIGS.  7  and  8   . In an optional first step of the method, in accordance with the teachings of the embodiments described throughout this disclosure, the network node  16  receives user data from the UE  22  (Block S 128 ). In an optional second step, the network node  16  initiates transmission of the received user data to the host computer  24  (Block S 130 ). In a third step, the host computer  24  receives the user data carried in the transmission initiated by the network node  16  (Block S 132 ). 
       FIG.  13    is a flowchart of an exemplary process in a network node  16  (e.g., parent IAB node) for preventing reestablishment at descendant nodes with no alternative paths in Integrated Access Backhaul (IAB) networks according to some embodiments of the present disclosure. One or more Blocks and/or functions and/or methods performed by the network node  16  may be performed by one or more elements of network node  16  such as by indication unit  32  in processing circuitry  68 , processor  70 , radio interface  62 , etc. according to the example method. The example method includes network node  16  configured to communicate with at least one descendant node over a backhaul network, transmitting (Block S 134 ), such as via indication unit  32 , processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , an indication to the at least one descendant network node, the indication associated with a radio link failure. The method includes network node  16  receiving (Block S 136 ), such as via indication unit  32 , processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , at least one message in response to the indication, the at least one message associated with an alternative path availability of the at least one descendant network node toward a third node (e.g., donor node). The method includes optionally, receiving (Block S 138 ), such as via indication unit  32 , processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , a dual-connectivity indication (e.g., from donor node or descendent node) when the at least one descendent network node is connected via dual-connectivity. 
     In some embodiments, the at least one message comprises at least one of: an alternative path availability flag indicating whether the at least one descendant network node has an alternative path toward the third node; an indication of at least one cell that the at least one descendant network node&#39;s distributed unit (DU) is hosting; and a dedicated preamble that the network node&#39;s mobile termination (MT) is allowed to use to attempt a random access (RA) for radio resource control (RRC) re-establishment procedure via the at least one descendant network node. In some embodiments, the network node  16  is a parent IAB node and the third node is a donor IAB node. 
       FIG.  14    is a flowchart of an exemplary process in a network node  16  for preventing reestablishment at descendant nodes with no alternative paths in Integrated Access Backhaul (IAB) networks according to some embodiments of the present disclosure. One or more Blocks and/or functions and/or methods performed by the network node  16  may be performed by one or more elements of network node  16  such as by report unit  34  in processing circuitry  68 , processor  70 , radio interface  62 , etc. according to the example method. The example method includes network node  16  configured to communicate with a second node over a backhaul network, receiving (Block S 140 ), such as via report unit  34 , processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , from the second node, an indication associated with a radio link failure. The method includes determining (Block S 142 ), such as via report unit  34 , processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , whether the first network node has an alternate path toward a third node. The method includes transmitting (Block S 144 ), such as via report unit  34 , processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , at least one message to the second node in response to the indication, the at least one message based at least in part on the determination. The method includes optionally, transmitting (Block S 146 ), such as via report unit  34 , processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , a dual-connectivity indication to the second node when the first network node is connected via dual-connectivity. 
     In some embodiments, the at least one message comprises at least one of: an alternative path availability flag indicating whether the first network node has an alternative path toward the third node; an indication of at least one cell that the first network node&#39;s distributed unit (DU) is hosting; and a dedicated preamble that the second node&#39;s mobile termination (MT) is allowed to use to attempt a random access (RA) for radio resource control (RRC) re-establishment procedure via the first network node. In some embodiments, the network node  16  is a descendant IAB node, the second node is a parent IAB node and the third node is a donor IAB node. 
       FIG.  15    is a flowchart of an exemplary process in a network node  16  (e.g., parent IAB node) for preventing reestablishment at descendant nodes with no alternative paths in Integrated Access Backhaul (IAB) networks according to some embodiments of the present disclosure. One or more Blocks and/or functions and/or methods performed by the network node  16  may be performed by one or more elements of network node  16  such as by indication unit  32  in processing circuitry  68 , processor  70 , communication interface  60 , radio interface  62 , etc. according to the example method. The example method includes transmitting (Block S 148 ), such as by indication unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , an indication to the at least one descendant network node, the indication associated with a radio link failure. The method includes receiving (Block S 150 ), such as by indication unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , an indication to the at least one descendant network node, at least one message in response to the indication, the at least one message associated with an alternative path availability of the at least one descendant network node toward a third network node. 
     In some embodiments, the at least one message indicates at least one of: at least one path that is not available as an alternative path; and at least one path that is available as the alternative path. In some embodiments, the at least one message comprises an alternative path availability flag indicating whether the at least one descendant network node has the alternative path toward the third network node. In some embodiments, the at least one message comprises an indication of at least one cell that a distributed unit, DU, in the at least one descendant network node is hosting. In some embodiments, the method further includes considering, such as by indication unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , an indication to the at least one descendant network node, at least one first cell in the at least one cell as a candidate for re-establishment. 
     In some embodiments, considering the at least one first cell as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level as compared to any other cells the network node measures. In some embodiments, considering the at least one first cell as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level among cells in the at least one cell indicated in the at least one message. In some embodiments, the method further includes considering, such as by indication unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , an indication to the at least one descendant network node, none of the cells in the at least one cell as a candidate for re-establishment. 
     In some embodiments, the at least one cell indicated in the at least one message comprises a first set of cells and a second set of cells; and the method further comprises: considering, such as by indication unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , an indication to the at least one descendant network node, none of the first set of cells as a candidate for re-establishment; and considering, such as by indication unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , an indication to the at least one descendant network node, the second set of cells in the at least one cell as the candidate for re-establishment. In some embodiments, the at least one message comprises a dedicated preamble; and the method further comprises using, such as by indication unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , an indication to the at least one descendant network node, the dedicated preamble to attempt a random access, RA, for a radio resource control, RRC, re-establishment procedure via the at least one descendant network node. 
     In some embodiments, the network node is a parent Integrated Access Backhaul, IAB, node and the third network node is a donor IAB node. In some embodiments, the method further includes receiving, such as by indication unit  32  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , an indication to the at least one descendant network node, a dual-connectivity indication when the at least one descendent network node is connected via dual-connectivity. 
       FIG.  16    is a flowchart of an exemplary process in a network node  16  for preventing reestablishment at descendant nodes with no alternative paths in Integrated Access Backhaul (IAB) networks according to some embodiments of the present disclosure. One or more Blocks and/or functions and/or methods performed by the network node  16  may be performed by one or more elements of network node  16  such as by report unit  34  in processing circuitry  68 , processor  70 , radio interface  62 , etc. according to the example method. The example method includes receiving (Block S 152 ), such as by report unit  34  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , from the second network node, an indication associated with a radio link failure. The method includes transmitting (Block S 154 ), such as by report unit  34  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , at least one message to the second network node in response to the indication, the at least one message associated with an alternative path availability of the first network node toward a third network node. 
     In some embodiments, the at least one message indicates at least one of: at least one path that is not available as an alternative path; and at least one path that is available as the alternative path. In some embodiments, the method further includes determining, such as by report unit  34  in processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , whether the first network node has the alternative path toward the third network node, the at least one message being based at least in part on the determination. In some embodiments, the at least one message comprises an alternative path availability flag indicating whether the first network node has the alternative path toward the third network node. In some embodiments, the at least one message comprises an indication of at least one cell that a distributed unit, DU, in the first network node is hosting. In some embodiments, the at least one cell indicated in the at least one message transmitted to the second network node comprises: at least one first cell to be considered by the second network node as a candidate for re-establishment. 
     In some embodiments, the at least one first cell is to be considered as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level as compared to any other cells the second network node measures. In some embodiments, the at least one first cell is to be considered as the candidate for re-establishment when the at least one first cell comprises a strongest cell, the strongest cell having a strongest signal level among cells in the at least one cell indicated in the at least one message. In some embodiments, none of the cells in the at least one cell indicated in the at least one message is to be considered as a candidate for re-establishment. In some embodiments, the at least one cell indicated in the at least one message comprises a first set of cells and a second set of cells, none of the first set of cells are to be considered by the second network node as a candidate for re-establishment and the second set of cells are to be considered by the second network node as the candidate for re-establishment. 
     In some embodiments, the at least one message comprises a dedicated preamble for the second network node to perform a random access, RA, for a radio resource control, RRC, re-establishment procedure via the first network node. In some embodiments, the second network node is a parent Integrated Access Backhaul, IAB, node and the third network node is a donor IAB node. 
       FIG.  17    is a flowchart of an exemplary process in a network node  16 . One or more Blocks and/or functions and/or methods performed by the network node  16  may be performed by one or more elements of network node  16  such as by processing circuitry  68 , processor  70 , communication interface  60 , radio interface  62 , etc. according to the example method. The example method includes transmitting (Block S 156 ), such as by processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , a first message type to the at least one descendant network node, the first message type indicating a backhaul link radio link failure and the first message type triggering at the at least one descendant network node at least one of: a reduction of scheduling resource requests; stopping scheduling resource requests; and using an alternative route to a donor Integrated Access Backhaul, IAB, network node. 
     In some embodiments, the method further includes transmitting, such as by processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , a second message type to the at least one descendant network node, the second message type indicating the backhaul link is recovered and the second message type triggering resumption of the scheduling resource requests. In some embodiments, the scheduling resource requests comprise at least one of a scheduling request, SR, and a buffer status report, BSR. 
       FIG.  18    is a flowchart of an exemplary process in a network node  16 . One or more Blocks and/or functions and/or methods performed by the network node  16  may be performed by one or more elements of network node  16  such as by processing circuitry  68 , processor  70 , communication interface  60 , radio interface  62 , etc. according to the example method. The example method includes receiving (Block S 158 ), such as by processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , a first message type from the second network node, the first message type indicating a backhaul link radio link failure and the first message type triggering at least one of: a reduction of scheduling resource requests to the second network node, such as by processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 ; stopping scheduling resource requests to the second network node, such as by processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 ; and using, such as by processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , an alternative route to a donor Integrated Access Backhaul, IAB, network node. 
     In some embodiments, the method further includes receiving, such as by processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 , a second message type from the second network node, the second message type indicating the backhaul link is recovered and the second message type triggering resumption of the scheduling resource requests, such as by processing circuitry  68 , processor  70 , communication interface  60  and/or radio interface  62 . In some embodiments, the scheduling resource requests comprise at least one of a scheduling request, SR, and a buffer status report, BSR. 
     Having described the general process flow of arrangements of the disclosure and having provided examples of hardware and software arrangements for implementing the processes and functions of the disclosure, the sections below provide details and examples of arrangements for preventing reestablishment at descendant nodes with no alternative paths in Integrated Access Backhaul (IAB) networks, which may be implemented by the network node  16 , UE  22  and/or host computer  24 . 
     Example network scenarios shown in  FIG.  19    and  FIG.  20    are used to illustrate some embodiments of the procedure proposed. When IAB3 (in  FIG.  19   ) (e.g., parent network node  16   b ) detects some type of link failure towards its parent node IAB1 e.g., radio link failure, IAB3 (e.g., parent network node  16   b ) sends a first indication (i.e., Type 2—“BH RLF detected, trying to recover”) to descendant node IAB5 (e.g., descendent network node  16   c ). Since the child/descendent IAB node (i.e., IAB5 in  FIG.  19   ) has an alternative path toward the IAB donor (e.g., donor network node  16   a ), IAB5 (e.g., descendent network node  16   c ) may respond with a message that includes one or more of:
         1: (optional) An alternate path availability indicator flag indicating the child node (e.g., IAB5, descendent network node  16   c ) has alternative path;   2. List of cells that the child IAB node&#39;s DU (i.e., IAB5-DU) (e.g., descendent network node  16   c ) is hosting; and/or   3: (optional) a dedicated preamble that the parent node&#39;s MT (i.e., IAB3-MT)) (e.g., parent network node  16   b ) could use to try Random Access for es-establishment procedure via the child IAB node (i.e., IAB5, descendent network node  16   c ).       

     In one realization the absence of the alternate path availability flag can be an implicit indication that the IAB node (e.g., descendent network node  16   c ) has (or does not have) an alternate path. In another realization, the child node (e.g., descendent network node  16   c ) must explicitly indicate that it has an alternate path by including the flag (e.g., setting the value to TRUE). 
     In one realization (a), the parent node (e.g., parent network node  16   b ) will consider one of the cells indicated as the candidate for re-establishment, only if that cell has the strongest signal level (e.g., reference signal received power (RSRP), reference signal received quality (RSRQ), etc.) as compared to any other cell that the parent node&#39;s MT can measure at that time. In another realization (b), the parent node (e.g., parent network node  16   b ) will consider the strongest cell (in terms of measured signal level) among the cells indicated as the candidate for RRC re-establishment, even if the parent node could measure cells other than the indicated cells that have stronger signal levels. Whether the parent node (e.g., parent network node  16   b ) applies behavior a or b can be based on e.g., IAB implementation, can be configurable, or it can be pre-configured and/or specified in 3GPP specifications (e.g., RRC specifications). 
     In another scenario shown in  FIG.  20   , the child IAB node (i.e., IAB5, descendent network node  16   c ) has no alternative path toward the IAB Donor node (e.g., donor network node  16   a ) and has only one parent IAB node (i.e., IAB3, parent network node  16   b ). In this situation, when the child IAB node (i.e., IAB5, descendent network node  16   c ) receives a first indication (i.e., Type 2—“BH RLF detected, trying to recover”) from its parent node (i.e., IAB3, parent network node  16   b ), the child node (i.e., IAB5, descendent network node  16   c ) may respond with a message that includes one or more of:
         1: (optional) An indicator indicating that no alternate paths are available; and/or   2: A list of cell hosting by the child node&#39;s DU (indicating that the parent node&#39;s MT should not try to re-establish to one of these cells).       

     In one embodiment, the absence of the alternate path availability flag can be an implicit indication that the IAB node has no (or has an) alternate path. In another embodiment, the child node (i.e., IAB5, descendent network node  16   c ) must explicitly indicate that it has no alternate path by including the flag (e.g., setting the value to FALSE). 
     In some embodiments, the parent node (i.e., IAB3, parent network node  16   b ) may consider none of the cells indicated as the candidate for re-establishment, even if some of the cells have stronger signal levels (e.g., RSRP, RSRQ, etc.) as compared to any other cell that the parent node&#39;s MT can measure at that time. 
     In some embodiments, an approach can be envisioned where the child IAB node (e.g., descendent network node  16   c ) responds with two sets of cells, where cells indicated in one of the lists are not to be considered as candidate cells for RRC re-establishment by the parent node (e.g., parent network node  16   b ), while the cells indicated in the other list can be considered as candidate cells. For example, one such structure could be: {List1: {cell a, cell b, cell c}, List2: {cell x, cell y, cell z}}, where the List1 includes those cells that can be candidates for re-establishment, while list2 is includes those cells that are not. 
     In some embodiments, if a child IAB node (e.g., descendent network node  16   c ) is connected to the parent node (e.g., parent network node  16   b ) via dual connectivity, (e.g., NR-DC) then the parent IAB node is the Master or Secondary DU. The donor CU (e.g., donor network node  16   a ) (or CUs in case the two DUs are controlled by different donor CUs) is/are aware of this fact, but not necessarily the DU of the parent IAB node. In one embodiment, the IAB-DU (e.g., parent network node  16   b ) is informed whenever a descendant node (e.g., descendent network node  16   c ) gets connected via dual connectivity (e.g., an F1-AP message from the donor CU). Thus, only the indication of the list of cells is enough from the child IAB node in this case, because the parent IAB node could implicitly infer whether the child node has an alternate path or not. 
     Some embodiments provide a mechanism for preventing the IAB node experiencing BH RLF to avoid reestablishing at its descendant nodes that have no alternative paths towards the Donor node. 
     Some embodiments may include one or more of the following: 
     It is noted that the “nodes” referred to below may be IAB nodes. 
     Embodiment A1. A network node configured to communicate with at least one descendant node over a backhaul network, the network node configured to, and/or comprising a radio interface and/or comprising processing circuitry configured to one or more of: 
     transmit an indication to the at least one descendant network node, the indication associated with a radio link failure; 
     receive at least one message in response to the indication, the at least one message associated with an alternative path availability of the at least one descendant network node toward a third node; and 
     optionally, receive a dual-connectivity indication when the at least one descendent network node is connected via dual-connectivity. 
     Embodiment A2. The network node of Embodiment A1, wherein the at least one message comprises at least one of: 
     an alternative path availability flag indicating whether the at least one descendant network node has an alternative path toward the third node; 
     an indication of at least one cell that the at least one descendant network node&#39;s distributed unit (DU) is hosting; and 
     a dedicated preamble that the network node&#39;s mobile termination (MT) is allowed to use to attempt a random access (RA) for radio resource control (RRC) re-establishment procedure via the at least one descendant network node. 
     Embodiment A3. The network node of Embodiment A1, wherein the network node is a parent IAB node and the third node is a donor IAB node. 
     Embodiment B1. A method implemented in a network node configured to communicate with at least one descendant node over a backhaul network, the method comprising one or more of: 
     transmitting an indication to the at least one descendant network node, the indication associated with a radio link failure; 
     receiving at least one message in response to the indication, the at least one message associated with an alternative path availability of the at least one descendant network node toward a third node; and 
     optionally, receiving a dual-connectivity indication when the at least one descendent network node is connected via dual-connectivity. 
     Embodiment B2. The method of Embodiment B  1 , wherein the at least one message comprises at least one of: 
     an alternative path availability flag indicating whether the at least one descendant network node has an alternative path toward the third node; 
     an indication of at least one cell that the at least one descendant network node&#39;s distributed unit (DU) is hosting; and 
     a dedicated preamble that the network node&#39;s mobile termination (MT) is allowed to use to attempt a random access (RA) for radio resource control (RRC) re-establishment procedure via the at least one descendant network node. 
     Embodiment B3. The method of Embodiment B1, wherein the network node is a parent IAB node and the third node is a donor IAB node. 
     Embodiment C1. A first network node configured to communicate with a second node over a backhaul network, the first network node configured to, and/or comprising a radio interface and/or comprising processing circuitry configured to one or more of: 
     receive, from the second node, an indication associated with a radio link failure; 
     determine whether the first network node has an alternate path toward a third node; 
     transmit at least one message to the second node in response to the indication, the at least one message based at least in part on the determination; and 
     optionally, transmit a dual-connectivity indication to the second node when the first network node is connected via dual-connectivity. 
     Embodiment C2. The first network node of Embodiment C1, wherein the at least one message comprises at least one of: 
     an alternative path availability flag indicating whether the first network node has an alternative path toward the third node; 
     an indication of at least one cell that the first network node&#39;s distributed unit (DU) is hosting; and 
     a dedicated preamble that the second node&#39;s mobile termination (MT) is allowed to use to attempt a random access (RA) for radio resource control (RRC) re-establishment procedure via the first network node. 
     Embodiment C3. The first network node of any one of Embodiments C1 and C2, wherein the network node is a descendant IAB node, the second node is a parent IAB node and the third node is a donor IAB node. 
     Embodiment D1. A method implemented in a first network node that is configured to communicate with a second node over a backhaul network, the method comprising one or more of: 
     receiving, from the second node, an indication associated with a radio link failure; 
     determining whether the first network node has an alternate path toward a third node; 
     transmitting at least one message to the second node in response to the indication, the at least one message based at least in part on the determination; and 
     optionally, transmit a dual-connectivity indication to the second node when the first network node is connected via dual-connectivity. 
     Embodiment D2. The method of Embodiment D1, wherein the at least one message comprises at least one of: 
     an alternative path availability flag indicating whether the first network node has an alternative path toward the third node; 
     an indication of at least one cell that the first network node&#39;s distributed unit (DU) is hosting; and 
     a dedicated preamble that the second node&#39;s mobile termination (MT) is allowed to use to attempt a random access (RA) for radio resource control (RRC) re-establishment procedure via the first network node. 
     Embodiment D3. The method of any one of Embodiments D1 and D2, wherein the network node is a descendant IAB node, the second node is a parent IAB node and the third node is a donor IAB node. 
     As will be appreciated by one of skill in the art, the concepts described herein may be embodied as a method, data processing system, computer program product and/or computer storage media storing an executable computer program. Accordingly, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit” or “module.” Any process, step, action and/or functionality described herein may be performed by, and/or associated to, a corresponding module, which may be implemented in software and/or firmware and/or hardware. Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that can be executed by a computer. Any suitable tangible computer readable medium may be utilized including hard disks, CD-ROMs, electronic storage devices, optical storage devices, or magnetic storage devices. 
     Some embodiments are described herein with reference to flowchart illustrations and/or block diagrams of methods, systems and computer program products. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer (to thereby create a special purpose computer), special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer readable memory or storage medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows. 
     Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Java® or C++. However, the computer program code for carrying out operations of the disclosure may also be written in conventional procedural programming languages, such as the “C” programming language. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user&#39;s computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     Many different embodiments have been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and subcombination of these embodiments. Accordingly, all embodiments can be combined in any way and/or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination. 
     Abbreviations that may be used in the preceding description include: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Abbreviation 
                 Explanation 
               
               
                   
                   
               
             
            
               
                   
                 3GPP 
                 3rd Generation Partnership Project 
               
               
                   
                 ACK 
                 Acknowledgement 
               
               
                   
                 BSR 
                 Buffer Status Report 
               
               
                   
                 CN 
                 Core Network 
               
               
                   
                 CP 
                 Control Plane 
               
               
                   
                 CU 
                 Central Unit 
               
               
                   
                 DL 
                 Downlink 
               
               
                   
                 DU 
                 Distributed Unit 
               
               
                   
                 IAB 
                 Integrated Access Backhaul 
               
               
                   
                 MAC 
                 Medium Access Control 
               
               
                   
                 NACK 
                 Negative ACK 
               
               
                   
                 PDCP 
                 Packet Data Convergence Protocol 
               
               
                   
                 PDU 
                 Protocol Data Unit 
               
               
                   
                 RLC 
                 Radio Link Control 
               
               
                   
                 RRC 
                 Radio Resource Control 
               
               
                   
                 SDU 
                 Service Data Unit 
               
               
                   
                 SIB 
                 System Information Block 
               
               
                   
                 SR 
                 Scheduling Request 
               
               
                   
                 UE 
                 User Equipment 
               
               
                   
                 UL 
                 Uplink 
               
               
                   
                 UP 
                 User Plane 
               
               
                   
                   
               
            
           
         
       
     
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims