Method, apparatus and computer program for handling reconfiguration failure

Abstract

An apparatus, e.g. User Equipment, acting as a relay UE between a base station (gNB) and a remote UE, receives a reconfiguration request from the base station S602; means for determining a reconfigura

Description

TECHNICAL FIELD Various example embodiments of this disclosure relate to a method, apparatus, system and computer program. In particular, but not exclusively, various example embodiments relate to handling reconfiguration failure of a relay user equipment BACKGROUND A communication network can be seen as a facility that enables communications between two or more communication devices, or provides communication devices access to a data network. A mobile or wireless communication network is one example of a communication network. A communication device may be provided with a service by an application server. Such communication networks operate in according with standards such as those provided by 3GPP (Third Generation Partnership Project) or ETSI (European Telecommunications Standards Institute). Examples of standards are the so-called 5G (5th Generation) standards provided by 3GPP. SUMMARY Some example embodiments of this disclosure will be described with respect to certain aspects. These aspects are not intended to indicate key or essential features of the embodiments of this disclosure, nor are they intended to be used to limit the scope of thereof. Other features, aspects, and elements will be readily apparent to a person skilled in the art in view of this disclosure. According to a first aspect there is provided an apparatus comprising: means for, whilst the apparatus is acting as a relay between a base station and a remote user equipment, receiving a reconfiguration request from the base station; means for determining a reconfiguration failure at the apparatus in association with the reconfiguration request; means for generating a notification for the remote user equipment, in response to the determining a reconfiguration failure at the apparatus; and means for sending the notification to the remote user equipment. According to some examples the apparatus comprises means for performing a connection re-establishment procedure with the base station or another base station. According to some examples the means for sending the notification to the remote user equipment is configured to send the notification to the remote user equipment before performing the connection re-establishment procedure or before an outcome is known of the connection re-establishment procedure with the base station or another base station. According to some examples the means for sending the notification to the remote user equipment is configured to do so immediately or substantially immediately after the determining a reconfiguration failure. According to some examples the means for generating the notification is configured to generate a notification that is arranged to cause the remote user equipment not to use the apparatus to perform a connection re-establishment procedure with the base station or another base station. According to some examples the means for sending the notification to the remote user equipment is configured to send the notification to the remote user equipment after an outcome is known of the connection re-establishment procedure with the base station or another base station. According to some examples the means for generating the notification is configured to generate the notification in a manner that is dependent on the outcome of the connection re-establishment procedure. According to some examples, when the outcome of the connection re-establishment procedure is failure of the connection re-establishment procedure, the means for generating a notification is configured to generate a notification that is arranged to cause the remote user equipment not to use the apparatus to perform a connection re-establishment procedure for the remote user equipment with the base station or with another base station. According to some examples, when the outcome of the connection re-establishment procedure is success of the connection re-establishment procedure, the means for generating a notification is configured to generate a notification that is further dependent on one or more of: whether there has been a cell change of the apparatus as a result of the connection re-establishment procedure; whether there has been a configuration change of the remote user equipment as a result of the connection re-establishment procedure. According to some examples, when the outcome of the connection re-establishment procedure is success of the connection re-establishment procedure, the means for generating a notification is arranged to generate a notification that is configured to cause the remote user equipment to perform a connection re-establishment procedure for the remote user equipment with the base station or with another base station via the apparatus. According to some examples, the means for generating the notification is configured to generate a notification which indicates one of: reconfiguration failure; or connection reestablishment failure. According to some examples, the means for generating the notification is configured to generate a notification which indicates one of: connection re-establishment success; or handover. According to some examples, the apparatus comprises means for behaving autonomously; and / or the apparatus comprises means for receiving instructions from the base station instructing the apparatus how to behave. According to some examples, the apparatus comprises means for controlling behaviour of the apparatus based on conditions comprising one or more of: a reason or purpose of the reconfiguration of the apparatus; radio channel conditions; mobility state of the apparatus; hardware status of the apparatus. According to some examples the apparatus comprises a relay user equipment. According to some examples the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the apparatus. According to a second aspect there is provided an apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: whilst the apparatus is acting as a relay between a base station and a remote user equipment, receive a reconfiguration request from the base station; determine a reconfiguration failure at the apparatus in association with the reconfiguration request; generate a notification for the remote user equipment, in response to the determining a reconfiguration failure at the apparatus; and send the notification to the remote user equipment. According to a third aspect there is provided and apparatus comprising: circuitry for, whilst the apparatus is acting as a relay between a base station and a remote user equipment, receiving a reconfiguration request from the base station; circuitry for determining a reconfiguration failure at the apparatus in association with the reconfiguration request; circuitry for generating a notification for the remote user equipment, in response to the determining a reconfiguration failure at the apparatus; and circuitry for sending the notification to the remote user equipment. According to a fourth aspect there is provided a method performed by an apparatus, the method comprising: whilst the apparatus is acting as a relay between a base station and a remote user equipment, receiving a reconfiguration request from the base station; determining a reconfiguration failure at the apparatus in association with the reconfiguration request; generating a notification for the remote user equipment, in response to the determining a reconfiguration failure at the apparatus; and sending the notification to the remote user equipment. According to some examples the method comprises performing a connection reestablishment procedure with the base station or another base station. According to some examples the method comprises sending the notification to the remote user equipment before performing the connection re-establishment procedure or before an outcome is known of the connection re-establishment procedure with the base station or another base station. According to some examples the method comprises sending the notification to the remote user equipment immediately or substantially immediately after the determining a reconfiguration failure. According to some examples the method comprises generating a notification that is arranged to cause the remote user equipment not to use the apparatus to perform a connection re-establishment procedure with the base station or another base station. According to some examples the method comprises sending the notification to the remote user equipment after an outcome is known of the connection re-establishment procedure with the base station or another base station. According to some examples the method comprises generating the notification in a manner that is dependent on the outcome of the connection re-establishment procedure. According to some examples, when the outcome of the connection re-establishment procedure is failure of the connection re-establishment procedure, the method comprises generating a notification that is arranged to cause the remote user equipment not to use the apparatus to perform a connection re-establishment procedure for the remote user equipment with the base station or with another base station. According to some examples, when the outcome of the connection reestablishment procedure is success of the connection re-establishment procedure, the method comprises generating a notification is further dependent on one or more of: whether there has been a cell change of the apparatus as a result of the connection re-establishment procedure; whether there has been a configuration change of the remote user equipment as a result of the connection re-establishment procedure. According to some examples, when the outcome of the connection re-establishment procedure is success of the connection re-establishment procedure, the method comprises generating a notification configured to cause the remote user equipment to perform a connection re-establishment procedure for the remote user equipment with the base station or with another base station via the apparatus. According to some examples, the method comprises generating a notification which indicates one of: reconfiguration failure; or connection re-establishment failure. According to some examples, the method comprises generating a notification which indicates one of: connection re-establishment success; or handover. According to some examples, the method comprises behaving autonomously; and / or receiving instructions from the base station instructing the apparatus how to behave. According to some examples, the method comprises controlling behaviour of the apparatus based on conditions comprising one or more of: a reason or purpose of the reconfiguration of the apparatus; radio channel conditions; mobility state of the apparatus; hardware status of the apparatus. According to some examples the apparatus comprises a relay user equipment. According to a fifth aspect there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: whilst the apparatus is acting as a relay between a base station and a remote user equipment, receiving a reconfiguration request from the base station; determining a reconfiguration failure at the apparatus in association with the reconfiguration request; generating a notification for the remote user equipment, in response to the determining a reconfiguration failure at the apparatus; and sending the notification to the remote user equipment. According to a sixth aspect there is provided a non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least the following: whilst the apparatus is acting as a relay between a base station and a remote user equipment, receiving a reconfiguration request from the base station; determining a reconfiguration failure at the apparatus in association with the reconfiguration request; generating a notification for the remote user equipment, in response to the determining a reconfiguration failure at the apparatus; and sending the notification to the remote user equipment. According to a seventh aspect there is provided an apparatus comprising: means for receiving a notification from a relay user equipment that is acting as a relay between the apparatus and a base station, wherein the notification is associated with a reconfiguration failure of the relay user equipment; and means for, in response to receiving the notification, performing a connection re-establishment procedure between the apparatus and the base station or another base station. According to some examples the means for performing the connection reestablishment procedure is configured to perform the connection re-establishment procedure between the apparatus and the base station or the another base station while not using the relay user equipment when the notification indicates one of: the reconfiguration failure of the relay user equipment; connection re-establishment failure of the relay user equipment. According to some examples the means for performing the connection reestablishment procedure is configured to perform the connection re-establishment procedure between the apparatus and the base station or another base station via the relay user equipment when the notification indicates one of: connection re-establishment success of the relay user equipment; handover of the relay user equipment According to some examples the apparatus comprises means for performing the connection re-establishment procedure between the apparatus and the base station or the another base station in a manner that is dependent upon at least one of: a radio resource control state of the apparatus; a multi-path configuration of the apparatus. According to some examples the apparatus comprises a remote user equipment. According to some examples the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the apparatus. According to an eighth aspect there is provided an apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving a notification from a relay user equipment that is acting as a relay between the apparatus and a base station, wherein the notification is associated with a reconfiguration failure of the relay user equipment; and in response to receiving the notification, performing a connection reestablishment procedure between the apparatus and the base station or another base station. According to a ninth aspect there is provided an apparatus comprising: circuitry for receiving a notification from a relay user equipment that is acting as a relay between the apparatus and a base station, wherein the notification is associated with a reconfiguration failure of the relay user equipment; and circuitry for, in response to receiving the notification, performing a connection re-establishment procedure between the apparatus and the base station or another base station. According to a tenth aspect there is provided a method performed by an apparatus, the method comprising: receiving a notification from a relay user equipment that is acting as a relay between the apparatus and a base station, wherein the notification is associated with a reconfiguration failure of the relay user equipment; and in response to receiving the notification, performing a connection re-establishment procedure between the apparatus and the base station or another base station. According to some examples the method comprises performing the connection reestablishment procedure between the apparatus and the base station or the another base station while not using the relay user equipment when the notification indicates one of: the reconfiguration failure of the relay user equipment; connection re-establishment failure of the relay user equipment. According to some examples the method comprises performing the connection reestablishment procedure between the apparatus and the base station or another base station via the relay user equipment when the notification indicates one of: connection reestablishment success of the relay user equipment; handover of the relay user equipment. According to some examples the method comprises performing the connection reestablishment procedure between the apparatus and the base station or the another base station in a manner that is dependent upon at least one of: a radio resource control state of the apparatus; a multi-path configuration of the apparatus. According to some examples the apparatus comprises a remote user equipment. According to an eleventh aspect there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving a notification from a relay user equipment that is acting as a relay between the apparatus and a base station, wherein the notification is associated with a reconfiguration failure of the relay user equipment; and in response to receiving the notification, performing a connection re-establishment procedure between the apparatus and the base station or another base station. According to a twelfth aspect there is provided a non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least the following: receiving a notification from a relay user equipment that is acting as a relay between the apparatus and a base station, wherein the notification is associated with a reconfiguration failure of the relay user equipment; and in response to receiving the notification, performing a connection re-establishment procedure between the apparatus and the base station or another base station. DESCRIPTION OF FIGURES Some example embodiments will now be described, by way of non-limiting and illustrative example only, with reference to the accompanying FIGs in which: FIG. 1 shows a representation of a 5th generation communication system; FIGs 2 to 6 are signalling diagrams according to some example embodiments; FIG. 7 schematically shows a representation of a control apparatus according to some example embodiments; FIG. 8 schematically shows a representation of a user equipment according to some example embodiments; FIG. 9 is a flow-chart of a method according to an example embodiment; FIG. 10 is a flow-chart of a method according to an example embodiment; FIG. 11 shows a representation of an apparatus according to some example embodiments. DETAILED DESCRIPTION In the following, various example embodiments are explained with reference to communication devices capable of communication with a communication system. Before explaining in detail the embodiments of the methods and apparatuses of the present disclosure, a 5th generation communication system (5GS) is briefly explained, by way of example, with reference to FIG. 1. FIG. 1 shows a schematic representation of a 5G communication system (5GS). The 5GS may comprise a user equipment (UE) 100, an access network such as a 5G radio access network (5G-RAN) 102 or next generation radio access network (NG-RAN), a 5G core network (5GC) 104, and one or more application functions 106. An application function may be deployed in the 5GS or may be deployed or hosted on one or more application servers of the data network. The 5GS connects the UE to a data network, the access network and the 5GC (e.g., a UPF of the 5GC). The 5G-RAN may comprise one or more radio access nodes, such as gNodeB (gNB). A gNB may include one or more gNB distributed units connected to one or more gNB centralized units. The 5GC 104 may comprise the following network functions: Network Slice Selection Function (NSSF); Network Exposure Function 108; Network Repository Function (NRF); Policy Control Function (PCF); Unified Data Management (UDM) 110; Application Function (AF) 106; Authentication Server Function (AUSF) 112; an Access and Mobility Management Function (AMF) 114; and Session Management Function (SMF) 116, and a user plane function (UPF) 118, and data network (DN) 120. FIG. 1 also shows the various interfaces (N1, N2 etc.) that may be implemented between the various elements of the system. It is to be noted that Figure 1 is provided as an example of a communication system in which the disclosure may take place; however the disclosure is not limited to a 5G communication system. For example, the disclosure could also apply to other systems such as 4G, 6G etc. The present disclosure relates to NR sidelink (SL) based layer 2 (L2) UE-to-NW(U2N). More particularly, the disclosure relates toaddressing handling of a Relay UE’s failure, or more particularly a Relay UE’s RRCReconfiguration failure. NR L2 U2N relay was first specified in release 17 with support of service continuity in intra-gNB direct-to-indirect (d2i) and indirect-to-direct (i2d) path switching in Layer-2 U2N relay. In some examples, a relay UE may be used to extend coverage to a “remote UE”. For example, a “remote UE” may be a UE that is outside of coverage area of network infrastructure. Clause 5.3.5.8 in 3GPP TS38.331 captures UE behaviour upon Reconfiguration failure in case of a UE’s “inability to comply with RRCReconfiguration”, which will trigger the UE to initiate an RRC connection re-establishment procedure. The present disclosure has identified that, currently, a remote UE may be unaware when a relay UE to which it is connected experiences a reconfiguration failure. In particular, the remote UE may not be notified when there is a Reconfiguration failure in a Relay UE. It is known that a gNB may initiate RRC reconfiguration procedure to a UE (including Relay UE), for example due to adding a new service / QoS flow for Relay UE’s own Uu (UE-RAN) traffic; adding / releasing the SN (secondary node); and / or adding / releasing a Remote UE connected to Relay UE. A gNB may also initiate RRC reconfiguration procedure due to changing network conditions such as change of the cell load, etc. In some situations, an RRC reconfiguration cannot be accepted or decoded by the Relay UE. By way of example this may be due to ASN.1 decoding error at the relay UE side, or use of incorrect parameters by the gNB. In such situations, the Relay UE identifies the RRC reconfiguration failure, which triggers the Relay UE to initiate RRC connection re-establishment procedure. When the Relay UE initiates the RRC connection re-establishment procedure, the configuration related to the PC5 interface towards the Remote UE is released. The re-establishment may even occur in a different cell or even a different gNB that does not have the Remote UE’s context. Thus, when the Relay UE initiates the RRC connection re-establishment procedure, it impacts the service continuity of a Remote UE which is being served by the Relay UE that has the reconfiguration failure. For example, the Remote UE’s pending data will be lost or dropped while the Remote UE is not aware of this as the Remote UE is not notified when there is reconfiguration failure in the Relay UE. In current 3GPP specification the Remote UE does not know whether the Relay UE initiates re-establishment or not following the relay UE’s reconfiguration failure. This is because the relay UE’s re-establishment initiated due to the reconfiguration failure does not trigger a notification (e.g. NotificationMessageSidelink) to be sent to the Remote UE. Thus, the Remote UE may incorrectly assume that the Relay UE is functioning properly for serving the Remote UE. This could result in one or more problems such as loss of data; decreased throughput; or violating latency requirements in data transmission. Thus, in some examples, the present disclosure proposes behaviour for a relay UE. The behaviour may include triggering sending of a notification message towards a remote UE. The notification message may be sent on a sidelink connection between the relay UE and the remote UE. For example, the sidelink notification message may be sent towards the remote UE upon RRC reconfiguration failure of the relay UE. In examples, it is assumed that a relay connection is established for remote UE to the network (e.g. a gNB) via relay UE. For example, the connection may be an L2 U2N connection. In some examples the relay UE may receive RRC Reconfiguration message from a gNB on the relay UE’s configuration. When the relay UE is unable to comply with the reconfiguration, then reconfiguration failure occurs, which triggers the relay UE to initiate RRC connection re-establishment. The RRC connection reestablishment may result in selection of either the same or a different cell in the same gNB or a new cell in a different gNB. According to the present disclosure, there are two main options (Option 1 and Option 2) for the proposed relay UE behaviour. Each of these options is discussed in-turn below. OPTION 1 In the first option, when a specified relay UE behaviour is to initiate RRC connection re-establishment upon reconfiguration failure, the relay UE is configured to maintain a relay related configuration, at least for a period of time. For example, the relay UE may wait for an RRC re-establishment procedure outcome without releasing relay related configuration / entity. For example, the Relay UE may delay releasing, or may maintain information of one or more of: sl-L2RelayUE-Config-, sl-L2RemoteUE-config-, and SRAP entity (where SRAP is sidelink relay adaptation protocol). Subsequently, the relay UE may then send a notification message to the remote UE. For example, the manner of sending (or not sending) the notification message to the Remote UE may depend on the outcome of RRC re-establishment procedure. For example: (i) if RRC re-establishment is successful to the same cell and the configuration related to the connected Remote UE is kept the same, no notification message will be triggered; else (ii) similar to option (i) where RRC re-establishment is successful, but a notification to remote UE is triggered (e.g. a relayUE-HO notification); else (iii) if RRC re-establishment is successful to a different cell or to the same cell but the configuration in the re-established connection doesn’t include / keep the same configuration related to Remote UE, the notification message is transmitted to remote UE using an existing indication type (e.g. relayUE-HO) or a new type of indication. Using an existing message type in this situation (such as relayUE-HO) may minimise changes required to implement the embodiments of the disclosure. The Relay UE releases sl-L2RelayUE-Config, sl-L2RemoteUE-Config, and SRAP entity, else (iv) if RRC re-establishment fails, the notification message is transmitted to remote UE using an existing indication type (e.g. relayUE-Uu-RRC-Failure) or a new type. Then, the Relay UE releases one or more of sl-L2RelayUE-Config-, sl-L2RemoteUE-Config-, and SRAP entity. Upon reception of the notification from the relay UE, the remote UE then takes appropriate action depending on the notification type with or without successful reestablishment. In some examples the action taken by the remote UE may also depend upon an RRC state of the remote UE, e.g. whether the remote UE is in RRC_IDLE / RRC_INACTIVE or RRC_CONNECTED state. When the remote UE is in RRC_CONNECTED state, the action taken by the remote UE may also depend upon whether the remote UE has multi-path configuration. Cases (i) to (iv) set-out above are shown in more detail in Figures 2 to 5, respectively, which show communication between a remote UE 250, a relay UE 200 and a gNB 202. In each of cases (i) to (iv) it is assumed that the remote UE 250 is in an RRC-CONNECTED state with gNB 202 via relay UE 200. This is shown at S201, S301, S401 and S501 in Figures 2 to 5 respectively. Then, there is an RRC reconfiguration request from the gNB 202. This is schematically shown at S202, S302, S402 and S502 in Figures 2 to 5 respectively. For example, the reconfiguration may be related to Uu connection of relay UE 200 or PC5 connection to remote UE 250. The present disclosure deals with a case where there is a reconfiguration failure associated with the RRC configuration request of S202, S302, S402, S502. Thus, the relay UE 200 determines a reconfiguration failure. The determining reconfiguration failure is shown at S203, S303, S403, S503 in Figures 2 to 5 respectively. In response to this reconfiguration failure, an RRC connection reestablishment procedure takes place between the relay UE 200 and the gNB 202. This is schematically shown at S204, S304, S404, and S504 in Figures 2 to 5 respectively. According to examples, the relay UE 200 is capable of generating a notification to be sent to the remote user equipment 250, in response to the determining a reconfiguration failure at the relay UE. In some examples (explained in more detail below) a notification is not sent to the remote UE 250. Thus, in some examples it may be considered that the relay UE may selectively generate and send a notification to the remote UE 250 depending on circumstance, and in response to determining reconfiguration failure. In case (i) to case (iv), the relay UE 200 waits for the outcome of the RRC reestablishment procedure before determining (a) whether a notification should be sent to the remote UE 250, and (b) what the content of that notification should be. Case (i) In case (i), as shown in Figure 2, the RRC connection re-establishment procedure of S204 is completed successfully. There is no cell change for the relay UE 200 and nor is there any configuration change related to the remote UE 250, as part of the RRC connection reestablishment procedure of S204. Thus, in this example, no notification is sent to remote UE 250. This is because no change is required at the remote UE 250 and the relayed connection between the remote UE 250 and the gNB 202 can be continued. Therefore there is no need for remote UE 250 to receive a notification regarding the reconfiguration failure or of the reestablishment procedure. This is schematically shown at S205. In some examples of case (i), the relay UE 200 is configured to maintain one or more pieces of stored information. For example, the relay UE 200 may maintain configuration information relating to one or more of: Sidelink Layer 2 Relay UE Configuration information; Sidelink Layer 2 Remote User Equipment information; Sidelink Relay Adaptation Protocol (SRAP) information. Case (ii) In case (ii), as shown in Figure 3 at S305, the RRC connection re-establishment procedure is completed successfully, without checking whether there is a cell change for the relay UE or a configuration change for the remote UE, associated with the re-established RRC connection. In this example, the relay UE 200 may either release configuration information relating to one or more of: Sidelink Layer 2 Relay UE Configuration information; Sidelink Layer 2 Remote User Equipment information; Sidelink Relay Adaptation Protocol (SRAP) information. Or the relay UE 200 may have released the configuration information already, before the relay UE 200 initiates the RRC connection re-establishment procedure. At S306, the relay UE 200 sends a sidelink notification message to the remote UE 250. In some examples, it may be considered that the notification of S306 is configured to cause the remote UE 250 to perform an RRC reestablishment procedure with gNB 202 (or another gNB). For example, the notification at S306 may be a relayUE-HO notification. Performance of the RRC connection reestablishment procedure is shown at S307. In some examples, for example where relayUE-HO notification is used at S306, then RRC connection reestablishment may be performed with the gNB 202 (or another gNB) via the relay UE 200 (or via another relay UE). Case (iii) In case (iii), as shown in Figure 4 at S405, the RRC connection reestablishment procedure is completed successfully. In some examples, there may be a cell change for the relay UE 200. In other examples, there may not be a cell change for the relay UE 200. In this example, there is a change to the configuration of the remote UE 250. The relay UE 200 releases configuration information relating to one or more of: Sidelink Layer 2 Relay UE Configuration information; Sidelink Layer 2 Remote User Equipment information; Sidelink Relay Adaptation Protocol (SRAP) information. At S406, the relay UE 200 sends a sidelink notification message to the remote UE 250. In some examples, it may be considered that the notification of S406 is configured to cause the remote UE 250 to perform an RRC reestablishment procedure with gNB 202 (or another gNB). For example, the notification at S406 may be a relayUE-HO notification. Performance of the RRC connection reestablishment procedure is shown at S407. In some examples, for example where relayUE-HO notification is used at S406, then RRC connection reestablishment may be performed with the gNB 202 (or another gNB) via the relay UE 200 (or via another relay UE). Case (iv) In case (iv), as shown in Figure 5 at S505, the RRC connection reestablishment procedure fails. The relay UE 200 releases configuration information relating to one or more of: Sidelink Layer 2 Relay UE Configuration information; Sidelink Layer 2 Remote User Equipment information; Sidelink Relay Adaptation Protocol (SRAP) information. At S506. the relay UE 200 sends a sidelink notification message to the remote UE 250. In some examples, it may be considered that the notification of S506 is configured to cause the remote UE 250 to perform an RRC reestablishment procedure with gNB 202 (or another gNB). For example, the notification at S506 may be a relayUE-Uu-RRC-Failure notification (i.e. a notification indicative of failure of the RRC connection reestablishment procedure at S504). Performance of the RRC connection reestablishment procedure is shown at S507. In some examples, for example where relayUE-Uu-RRC-Failure is used at S506, then RRC connection reestablishment may be performed with the gNB 202 (or another gNB) directly (i.e. not via the relay UE 200 or another relay UE) or via another relay UE. In other words, reestablishment of the remote UE 250 is not via the relay UE 200 because relay UE 200 has failed re-establihsment. Therefore, remote UE can be either re-established to the gNB directly or via another relay UE. In some examples, the behaviour of the remote UE 250 is dependent upon one or both of (a) RRC state of the remote UE; (b) multi-path configuration of the remote UE. For example, remote UE behaviour may comprise one or more of: • The Remote UE considers that a cell re-selection occurs if Remote UE is in RRC_ldle / lnactive state and the relayUE-HO notification is received; • The Remote UE initiates RRC connection re-establishment if Remote UE is in RRC_Connected and T301 timer is not running; and / or • The Remote UE indicates to upper layers to trigger PC5 unicast link release if the Remote UE determines to release the PC5-RRC connection with a “current” Relay UE if the relayUE-Uu-RRC-Failure notification is received; or • The Remote UE, if configured with multi-path operation using indirect path and direct path, suspends the transmission over the indirect path. Option 2 In the second option, the Relay UE does not wait for the RRC re-establishment procedure outcome before transmitting a notification message to Remote UE. In some examples the notification message, for example NotificationMessageSidelink message, is transmitted to remote UE 250 when the relay UE 200 initiates RRC connection reestablishment, for example as a result of reconfiguration failure using the existing indication type (e.g. relayUE-Uu-RRC-Failure) or a new type (e.g. relayUE-Uu-RRCReconfiguration-Failure). In some examples, the transmitting of the notification message is in response to when the relay UE 200 initiates RRC connection re-establishment. In some examples, the sending of the notification message occurs immediately or substantially immediately after the relay UE initiates RRC connection re-establishment. Thus, in some examples it may be considered that the notification from relay UE 200 to remote UE 250, in response to determining reconfiguration failure at the remote UE 250, is sent before initiation or completion of the RRC connection reestablishment procedure between the gNB 202 and the relay UE 200. In examples, upon reception of the notification from relay UE, the remote UE takes appropriate action. In some examples, the action that is taken by the remote UE is dependent on the RRC state of the Remote UE e.g. whether the remote UE is in RRCJDLE / RRCJNACTIVE or RRC_CONNECTED state. In the latter case (i.e. RRC_CONNECTED) this may depend on having multi-path configuration (explained in more detail below). Figure 6 is a signalling diagram showing one example implementation of Option 2. Steps S601 to S603 are analogous to the first three steps of Figures 2 to 5, and for conciseness are not discussed in any further detail. At S604, in response to the determining reconfiguration failure at S603, a sidelink notification message is sent from relay UE 200 to remote UE 250. It may be considered that this notification message is configured to cause the remote UE 250 to perform an RRC connection reestablishment procedure with the gNB 202 (or another gNB). For example, the form of the sidelink notification may be relayUE-Uu-RRC-Failure (i.e. indicative of reconfiguration failure at relay UE 200). It is noted that the notification message at S604 is sent before initiation of the RRC connection re-establishment procedure, atS605. In some examples, the notification message at S604 is sent immediately or substantially immediately after the determination at S603. The RRC connection reestablishment procedure between the remote UE 250 and the gNB 202 is shown at S606. In some examples, for example where the notification at S604 indicates the reconfiguration failure of the relay UE 200, then the remote UE 250 performs the RRC connection reestablishment procedure at S606 directly with the gNB 202 (or directly with another gNB) or via another relay UE. Some other features, which may be common to Option 1 and Option 2, will now be discussed. In some examples, the connection re-establishment between the relay UE 200 and the base station may be between the base station originally serving the relay UE or another base station. In some examples, known indication types (e.g. relayUE-Uu-RRC-Failure or relayUE-HO) are used when relay UE 200 sends the notification message to remote UE 250 upon reconfiguration failure triggered connection re-establishment. Reusing existing indication types in the notification message does not require any implementation change in remote UE 250. The remote UE 250 will be triggered to initiate its own connection re-establishment upon receiving the notification message. In some examples, one or more new indication types for the notification message from relay UE 200 to remote UE 250 in response to reconfiguration failure at relay UE 200, may be introduced. For instance, a new indication type e.g. relayUE-Uu-Reestablishment or relayUE-UU-RRCReconfiguration-Failure may be introduced. For example, relayUE-Uu-Reestablishment or relayUE-UU-RRCReconfiguration-Failure may be used in Option 2 or in Option 1 in case of Relay UE re-establishment failure or success but to different cell or without configuration related to remote UE 250 or with the different configuration related to remote UE 250. In another implementation example, a different indication type e.g. relayUE-Uu-ReetablishmentSuccess and relayUE-Uu-ReetablishmentFailure may be introduced for different re-establishment procedure outcomes. In examples where relayUE-Uu-ReetablishmentSuccess indication is used, the remote UE 250 may be triggered to initiate its own connection re-establishment via the relay UE 200, for example if PC5 connection with the Relay UE is kept. In some examples, the gNB 202 may configure the behaviour of relay UE 200. For example the gNB 202 may configure the behaviour of relay UE 200 on ‘notification upon reconfiguration failure’ (e.g. whether sending notification message immediately as proposed in Option 2, or waiting for the re-establishment outcome to send the notification message as proposed in Option 1). In some examples the behaviour of the relay UE 200 is based on configured conditions. Such conditions may depend on the reconfiguration purpose (e.g. addition / change of a service / QoS flow, adding releasing SCG (secondary cell group), change in PC5 configuration, etc.) and / or Relay UE’s Uu or PC5 radio channel conditions. In one example, if ‘notification upon reconfiguration failure’ is enabled (i.e. the sending of the sidelink notification message from the relay UE 200 to the remote UE 250 is enabled), the relay UE 200 may determine which option (i.e. Option 1 or Option 2) to apply by UE implementation. In some examples the relay UE determination may be based on the reconfiguration purpose, Uu and / or PC5 radio channel conditions and mobility state, or its own hardware (HW) status (battery, processing load, etc). In one example, the relay UE 200 may consider service continuity for the remote UE when triggering re-establishment. For example, the relay UE 200 may delay re-establishment up to a maximum time if the remote UE 250 is executing path switch. FIG. 7 illustrates an example of a control apparatus 700 for controlling a function of the access network (e.g., a 5G-RAN or the NG-RAN illustrated in FIG. 1) illustrated on FIG. 1. The control apparatus 700 may comprise at least one random access memory (RAM) 711a, at least on read only memory (ROM) 711b, at least one processor 712, 713 and a network interface 714. The at least one processor 712, 713 may be coupled to the RAM 711a and the ROM 711b. The at least one processor712, 713 may be configured to execute an appropriate software code 715. Execution of the software code 715 may for example cause the apparatus to perform operations for controlling a function of the access network. The software code 715 may be stored in the ROM 711b. The control apparatus 700 may be interconnected with another control apparatus 700 for controlling another function of the 5G-RAN or the NG-RAN. In some embodiments, each function of the 5G-RAN or the NG-RAN is deployed or hosted on a control apparatus 700. In alternative embodiments, two or more functions of the 5G-RAN or the NG-RAN may share a control apparatus. For example, gNB 202 may be in the form of a control apparatus 700. FIG. 8 illustrates an example of a communication device 800, such as the UE or terminal illustrated on FIG. 1. The communication device 800 may be provided by any device capable of sending and receiving radio signals. Non-limiting examples of a communication device 800 comprise a user equipment, a mobile station (MS) or mobile device such as a mobile phone or what is known as a ’smart phone’, a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), a personal data assistant (PDA) or a tablet provided with wireless communication capabilities, a machine-type communications (MTC) device, an Internet of things (loT) type communication device or any combinations of these or the like. The communication device 800 may comprise a transceiver for transmitting and / or receiving, for example, wireless signals carrying communications, for example radio signals. The communications may be one or more of voice, electronic mail (email), text messages, multimedia data, machine data and so on. The communication device 800 may receive wireless signals (e.g., radio signals) over an air or radio interface 807 via appropriate apparatus for receiving and may transmit wireless signals via appropriate apparatus for transmitting radio signals. In FIG. 8 transceiver is designated schematically by block 806. The transceiver 806 may comprise, for example, a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device and may comprise one or more antenna elements. The antenna arrangement may be a multi-input multi output (MIMO) antenna. The communication device 800 may be provided with at least one processor 801, at least one memory ROM 802a, at least one RAM 802b and other possible components 803 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access networks (e.g., the 5G-RAN or NG-RAN illustrated in FIG. 1) and other communication devices. The at least one processor 801 is coupled to the RAM 802b and the ROM 802a. The at least one processor 801 may be configured to execute an appropriate software code 808. The software code 808 may for example allow to perform one or more operations of the communication device 800. The software code 808 may be stored in the ROM 802a. For example, the relay UE 200 or the remote UE 250 may in the form of UE 800. The processor, the ROM, and the RAM, the transceiver and other circuitry of the communication device (e.g., a modem) can be provided on a circuit board, in chipsets, or in a system on chip. This circuit board, chipsets or system on chip is denoted by reference 804. The communication devices may optionally have a user interface such as key pad 805, touch sensitive screen or pad, combinations thereof or the like. Optionally one or more of a display, a speaker and a microphone may be provided depending on the type of the communication device. For example, the relay UE 200 or the remote UE 250 may be in the form of UE 800. Figure 9 is a flow chart of a method viewed from the perspective of an apparatus. For example, the apparatus may be relay UE 200. As shown at S901, the method comprises, whilst the apparatus is acting as a relay between a base station and a remote user equipment, receiving a reconfiguration request from the base station. As shown at S902, the method comprises determining a reconfiguration failure at the apparatus in association with the reconfiguration request. As shown at S903, the method comprises generating a notification for the remote user equipment, in response to the determining a reconfiguration failure at the apparatus. As shown at S904, the method comprises sending the notification to the remote user equipment. Figure 10 is a flow chart of a method viewed from the perspective of an apparatus. For example, the apparatus may be remote UE 250. As shown at S1001 the method comprises receiving a notification from a relay user equipment that is acting as a relay between the apparatus and a base station, wherein the notification is associated with a reconfiguration failure of the relay user equipment. As shown at S1002, the method comprises, in response to receiving the notification, performing a connection re-establishment procedure between the apparatus and the base station or another base station. FIG. 11 shows a schematic representation of non-volatile memory media 1100a (e.g. computer disc (CD) or digital versatile disc (DVD)) and 1100b (e.g. universal serial bus (USB) memory stick) storing instructions and / or parameters 1102 which when executed by a processor allow the processor to perform one or more of the steps of the method of FIGs 9 or 10. It is understood that references in the above to various network functions (e.g., to an AMF, an SMF, TNF etc.) may comprise apparatus that perform at least some of the functionality associated with those network functions. Further, an apparatus comprising a network function may comprise a virtual network function instance of that network function. It should be understood that the apparatuses may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and / or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities. It is noted that whilst some embodiments have been described in relation to 5G networks, similar principles can be applied in relation to other networks and communication systems. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein. It is also noted herein that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention. As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements. In general, the various embodiments may be implemented in hardware or special purpose circuitry, software, logic or any combination thereof. Some aspects of the disclosure may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While various aspects of the disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof. As used herein, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and (b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.” This definition of circuitry applies to all uses of this term herein, including in any claims. As a further example, as used herein, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device. The embodiments of this disclosure may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and / or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computerexecutable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it. Further in this regard it should be noted that any blocks of the logic flow as in the FIGs may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non-transitory media. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM). The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples. Various example embodiments of the disclosure may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate. The scope of protection sought for various example embodiments of the disclosure is set out by the independent claims. The example embodiments and features thereof, if any, described in this disclosure that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various example embodiments of the disclosure. The foregoing description has provided, by way of non-limiting and illustrative examples, a full and informative description of the various example embodiments of this disclosure. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with 5 the accompanying drawings and the claims. However, all such and similar modifications of the teachings will still fall within the various example embodiments of the disclosure as set forth in the claims. By way of non-limiting and illustrative example, there is a further example embodiment comprising a combination of one or more example embodiments with any of the other example embodiments previously discussed.

Claims

1. An apparatus comprising:means for, whilst the apparatus is acting as a relay between a base station and a remote user equipment, receiving a reconfiguration request from the base station;means for determining a reconfiguration failure at the apparatus in association with the reconfiguration request;means for generating a notification for the remote user equipment, in response to the determining a reconfiguration failure at the apparatus; andmeans for sending the notification to the remote user equipment.

2. An apparatus according to claim 1, comprising means for performing a connection re-establishment procedure with the base station or another base station.

3. An apparatus according to claim 2, wherein the means for sending thenotification to the remote user equipment is configured to send the notification to the remote user equipment before performing the connection re-establishment procedure or before an outcome is known of the connection re-establishment procedure with the base station or another base station.

4. An apparatus according to any of claims 1 to 3, wherein the means for sending the notification to the remote user equipment is configured to do so immediately or substantially immediately after the determining a reconfiguration failure.

5. An apparatus according to any of claims 1 to 4, wherein the means for generating the notification is configured to generate a notification that is arranged to cause the remote user equipment not to use the apparatus to perform a connection re-establishment procedure with the base station or another base station.

6. An apparatus according to claim 2, wherein the means for sending thenotification to the remote user equipment is configured to send the notification to the remote user equipment after an outcome is known of the connection re-establishment procedure with the base station or another base station.

7. An apparatus according to claim 6, wherein the means for generating the notification is configured to generate the notification in a manner that is dependent on the outcome of the connection re-establishment procedure.

8. An apparatus according to claim 7, wherein when the outcome of the connection re-establishment procedure is failure of the connection re-establishment procedure, the means for generating a notification is configured to generate a notification that is arranged to cause the remote user equipment not to use the apparatus to perform a connection re-establishment procedure for the remote user equipment with the base station or with another base station.

9. An apparatus according to claim 7, wherein when the outcome of the connection re-establishment procedure is success of the connection re-establishment procedure, the means for generating a notification is configured to generate a notification that is further dependent on one or more of: whether there has been a cell change of the apparatus as a result of the connection re-establishment procedure; whether there has been a configuration change of the remote user equipment as a result of the connection reestablishment procedure.

10. An apparatus according to claim 7 or claim 9, wherein when the outcome of the connection re-establishment procedure is success of the connection re-establishment procedure, the means for generating a notification is arranged to generate a notification that is configured to cause the remote user equipment to perform a connection re-establishment procedure for the remote user equipment with the base station or with another base station via the apparatus.

11. An apparatus according to claim 5 or claim 8, wherein the means for generating the notification is configured to generate a notification which indicates one of: reconfiguration failure; or connection re-establishment failure.

12. An apparatus according to claim 10, wherein the means for generating the notification is configured to generate a notification which indicates one of: connection reestablishment success; or handover.

13. An apparatus according to any of claims 1 to 12, wherein the apparatuscomprises means for behaving autonomously; and / or the apparatus comprises means for receiving instructions from the base station instructing the apparatus how to behave.

14. An apparatus according to any of claims 1 to 13, comprising means for controlling behaviour of the apparatus based on conditions comprising one or more of: a reason or purpose of the reconfiguration of the apparatus; radio channel conditions; mobility state of the apparatus; hardware status of the apparatus.

15. An apparatus comprising:means for receiving a notification from a relay user equipment that is acting as a relay between the apparatus and a base station, wherein the notification is associated with a reconfiguration failure of the relay user equipment; andmeans for, in response to receiving the notification, performing a connection re-establishment procedure between the apparatus and the base station or another base station.

16. An apparatus according to claim 15, wherein the means for performing the connection re-establishment procedure is configured to perform the connection reestablishment procedure between the apparatus and the base station or the another base station while not using the relay user equipment when the notification indicates one of: the reconfiguration failure of the relay user equipment; connection re-establishment failure of the relay user equipment.

17. An apparatus according to claim 15, wherein the means for performing the connection re-establishment procedure is configured to perform the connection reestablishment procedure between the apparatus and the base station or another base station via the relay user equipment when the notification indicates one of: connection reestablishment success of the relay user equipment; handover of the relay user equipment18. An apparatus according to any of claims 15 to 17, wherein the apparatus comprises means for performing the connection re-establishment procedure between the apparatus and the base station or the another base station in a manner that is dependent upon at least one of: a radio resource control state of the apparatus; a multi-path configuration of the apparatus.

19. A method performed by an apparatus, the method comprising:whilst the apparatus is acting as a relay between a base station and a remote user equipment, receiving a reconfiguration request from the base station;determining a reconfiguration failure at the apparatus in association with the reconfiguration request;generating a notification for the remote user equipment, in response to the determining a reconfiguration failure at the apparatus; andsending the notification to the remote user equipment.

20. A method performed by an apparatus, the method comprising:receiving a notification from a relay user equipment that is acting as a relay between the apparatus and a base station, wherein the notification is associated with a reconfiguration failure of the relay user equipment; andmeans for, in response to receiving the notification, performing a connection reestablishment procedure between the apparatus and the base station or another base station.

21. A computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following:whilst the apparatus is acting as a relay between a base station and a remote user equipment, receiving a reconfiguration request from the base station;determining a reconfiguration failure at the apparatus in association with the reconfiguration request;generating a notification for the remote user equipment, in response to the determining a reconfiguration failure at the apparatus; andsending the notification to the remote user equipment.

22. A computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following:whilst the apparatus is acting as a relay between a base station and a remote user equipment, receiving a reconfiguration request from the base station;determining a reconfiguration failure at the apparatus in association with the reconfiguration request;generating a notification for the remote user equipment, in response to the determining a reconfiguration failure at the apparatus; andsending the notification to the remote user equipment.

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