Conditional reconfiguration failure recovery

Abstract

An apparatus comprising means for: receiving conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and includes a reconfiguration failure recovery indication; in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations, in dependence on the reconfiguration failure recovery indication; and executing the second RRC configuration associated with one of the candidate secondary nodes, in dependence on satisfaction of the condition.

Description

[0001] TITLE

[0002] Conditional Reconfiguration Failure Recovery

[0003] TECHNOLOGICAL FIELD

[0004] Examples of the disclosure relate to conditional reconfiguration failure recovery. Some relate to conditional RRC reconfiguration failure recovery.

[0005] BACKGROUND

[0006] Multi-Radio Dual Connectivity (MR-DC) enables a user equipment (UE) with multiple receivers / transmitters to utilise resources provided by different network nodes. During dualconnectivity, the UE stores a configuration.

[0007] An established dual-connectivity connection can be reconfigured by transmitting reconfiguration information. In 3GPP (3rd Generation Partnership Project) systems, the reconfiguration information is referred to as a RRC (Radio Resource Control) reconfiguration message or RRC reconfiguration message.

[0008] In some circumstances, the reconfiguration information is conditional reconfiguration information. For instance, an RRC reconfiguration message transmitted to a UE can include a plurality of configurations for different network cells, and associated execution conditions relating to radio signal strength and / or quality of that cell. The UE monitors the execution conditions, and when one is satisfied the UE executes the configuration associated with the satisfied condition.

[0009] In response to a failure occurring when the UE attempts to apply one of the configurations, the RRC reconfiguration message may need to be reprepared.

[0010] BRIEF SUMMARY

[0011] According to various, but not necessarily all, examples there is provided examples as claimed in the appended claims. According to various, but not necessarily all, examples there is provided an apparatus comprising means for: receiving conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and includes a reconfiguration failure recovery indication; in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations, in dependence on the reconfiguration failure recovery indication; and executing the second RRC configuration associated with one of the candidate secondary nodes, in dependence on satisfaction of the condition.

[0012] In some, but not necessarily all examples, the apparatus is a User Equipment.

[0013] In some, but not necessarily all examples, the reconfiguration failure recovery indication comprises one or more of: an instruction to attempt recovery by evaluating at least the condition associated with the second RRC configuration, in response to reconfiguration failure; a recovery condition based at least in part on radio signal measurement, and wherein performing the evaluation is conditional on satisfaction of the recovery condition; an allowed number of recovery attempts.

[0014] In some, but not necessarily all examples, the apparatus comprises means for at least one of: determining whether a master node communication link is available, wherein performing the evaluation is conditional on the master node communication link being available; rejecting a subset of the plurality of RRC configurations, the subset comprising the first RRC configuration, in dependence on determining the reconfiguration failure; sending failure information in response to the reconfiguration failure; In some, but not necessarily all examples, the sending is initiated by the reconfiguration failure, before the second RRC configuration is executed. In some, but not necessarily all examples, the failure information comprises an indicator that the evaluation of the condition associated with the second RRC configuration is being performed after the sending of the failure information.

[0015] In some, but not necessarily all examples, the apparatus comprises means for aggregating failure information based on one or more reconfiguration failures associated with the plurality of RRC configurations, and sending the aggregated failure information in dependence on at least one of: successful execution of the second RRC configuration; or monitoring of whether an allowed number of recovery attempts has been reached.

[0016] In some, but not necessarily all examples, the apparatus comprises means for performing a compliance check on the second RRC configuration, and wherein selection of a security counter from a list of security counters is dependent on the compliance check being successful.

[0017] In some, but not necessarily all examples, the first RRC configuration is a delta configuration, and wherein the apparatus comprises means for determining which of a delta portion and a reference portion associated with the delta configuration caused the reconfiguration failure. In some, but not necessarily all examples, the apparatus comprises means for at least one of: rejecting the delta configuration in dependence on the delta portion being a determined cause of the reconfiguration failure, and wherein the second RRC configuration is a delta configuration dependent on the reference portion; rejecting the first and second RRC configurations that are dependent on the reference portion, in dependence on the reference portion being a determined cause of the reconfiguration failure.

[0018] According to various, but not necessarily all, examples there is provided an apparatus comprising means for: sending conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and the conditional reconfiguration information further including a reconfiguration failure recovery indication, wherein the reconfiguration failure recovery indication comprises an instruction to attempt recovery in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, wherein attempting the recovery comprises evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations.

[0019] In some, but not necessarily all examples, the apparatus is a Master Node.

[0020] In some, but not necessarily all examples, the apparatus comprises means for receiving a reply indicating which one of the plurality of RRC configurations the user equipment has executed based on the plurality of RRC configurations and the reconfiguration failure recovery indication.

[0021] In some, but not necessarily all examples, the apparatus comprises means for receiving failure information from the user equipment in response to the reconfiguration failure. In some, but not necessarily all examples, the failure information comprises an indicator that the evaluation of the condition associated with the second RRC configuration is being performed after the sending of the failure information. In some, but not necessarily all examples, the apparatus comprises means for inhibiting preparation of further conditional reconfiguration information, based on the indicator.

[0022] In some, but not necessarily all examples, the failure information is aggregated failure information based on one or more reconfiguration failures associated with the plurality of RRC configurations.

[0023] According to various, but not necessarily all, examples there is provided a method comprising: receiving conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and includes a reconfiguration failure recovery indication; in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations, in dependence on the reconfiguration failure recovery indication; and executing the second RRC configuration associated with one of the candidate secondary nodes, in dependence on satisfaction of the condition.

[0024] According to various, but not necessarily all, examples there is provided a method comprising: sending conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and the conditional reconfiguration information further including a reconfiguration failure recovery indication, wherein the reconfiguration failure recovery indication comprises an instruction to attempt recovery in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, wherein attempting the recovery comprises evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations.

[0025] According to various, but not necessarily all, examples there is provided a computer program that when executed by one or more processors causes: receiving conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and includes a reconfiguration failure recovery indication; in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations, in dependence on the reconfiguration failure recovery indication; and executing the second RRC configuration associated with one of the candidate secondary nodes, in dependence on satisfaction of the condition. According to various, but not necessarily all, examples there is provided a computer program that when executed by one or more processors causes: sending conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and the conditional reconfiguration information further including a reconfiguration failure recovery indication, wherein the reconfiguration failure recovery indication comprises an instruction to attempt recovery in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, wherein attempting the recovery comprises evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations.

[0026] BRIEF DESCRIPTION

[0027] Some examples will now be described with reference to the accompanying drawings in which:

[0028] FIG. 1 shows an example wireless communication network system;

[0029] FIG. 2 shows an example node implementing a first radio access technology;

[0030] FIG. 3 shows an example node implementing a second radio access technology;

[0031] FIG. 4 shows an example reconfiguration procedure;

[0032] FIG. 5 shows an example reconfiguration procedure;

[0033] FIG. 6 shows an example reconfiguration procedure;

[0034] FIG. 7 shows a flowchart of an example method;

[0035] FIG. 8 shows a flowchart of an example method;

[0036] FIG. 9 shows an example apparatus; and

[0037] FIG. 10 shows an example delivery mechanism.

[0038] The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Similar reference numerals are used in the figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures. DEFINITIONS

[0039] 3GPP 3rdGeneration Partnership Project

[0040] 5G 5thGeneration Standard for Cellular Networks

[0041] AMF Access and Mobility Management Function

[0042] AS Access Stratum

[0043] CHO Conditional Handover

[0044] CPAC Conditional PSCell Addition or Change

[0045] CPC Conditional PSCell Change

[0046] DC Dual Connectivity

[0047] E-LITRA Evolved Universal Terrestrial Radio Access eNB eNodeB

[0048] EPC Evolved Packet Core gNB gNodeB gNB-CU gNodeB centralized unit gNB-DU gNodeB distributed unit

[0049] MAC Medium Access Control layer

[0050] MCG Master Cell Group

[0051] MME Mobility Management Entity

[0052] MN Master Node

[0053] NAS Non-Access Stratum

[0054] NR New Radio

[0055] NW Network

[0056] PCell Primary Cell

[0057] PCI Physical Cell Identity

[0058] PDCP Packet Data Convergence Protocol

[0059] PHY Physical layer

[0060] PSCell Primary Secondary Cell

[0061] QoS Quality of Service

[0062] RAN Radio Access Network

[0063] RAT Radio Access Technology

[0064] RLC Radio Link Control

[0065] RLF Radio Link Failure

[0066] RRC Radio Resource Control

[0067] RSRP Reference Signal Receive Power RSRQ Reference Signal Received Quality

[0068] S-GW Service Gateway

[0069] SCell Secondary Cell

[0070] SCG Secondary Cell Group

[0071] SCPAC Subsequent CPAC (Selective Activation for SCG)

[0072] SDAP Service Data Adaptation Protocol

[0073] SgNB Secondary gNodeB

[0074] SI NR Signal to Interference and Noise Ratio

[0075] SN Secondary Node

[0076] UE User Equipment

[0077] DETAILED DESCRIPTION

[0078] FIG. 1 is a block diagram schematically illustrating a wireless communication network system 1 configured for dual-connectivity. In at least some examples the system 1 is a 3GPP-defined network system.

[0079] The system 1 of FIG. 1 comprises a UE 100, a RAN comprising at least a first node 102 and a second node 104, and a core NW entity 108. FIG. 1 further illustrates a third node 112 and fourth node 114 of the RAN, enabling the UE 100 to change nodes during mobility.

[0080] The term ‘node’ herein refers to an access node. In a 3GPP-defined system 1 a node is a base station. A base station implementing NR (first RAT) is referred to as a gNB. A base station implementing E-UTRA (second RAT) is referred to as an eNB.

[0081] FIG. 2 illustrates an example of a node 104 / 114 (e.g., gNB) configured to implement a first RAT (e.g., NR). In this example, the node 104 has a disaggregated (split) architecture. The gNB 104 comprises one or more distributed units (gNB-DU) 20 and a centralized unit (gNB- CU) 10. An apparatus 2 is configured to implement the functionality of at least part of a node 104, 114 such as a gNB-CU, and / or one or more gNB-DUs, or the whole gNB.

[0082] The gNB-CU 10 is a logical node configured to host an RRC layer and other layers of the gNB 120. The gNB-CU 10 controls the operation of one or more gNB-DUs 20. The gNB-DU 20 is a logical node configured to host a RLC layer, a MAC layer and PHY layer of the access node (gNB) 120. The gNB-Dll 20 communicates via a dedicated interface (F1) to the RRC layer hosted by the gNB-CU.

[0083] One gNB-Dll 20 can support one or multiple cells (not illustrated in the figure). One cell is supported by one gNB-Dll 20.

[0084] FIG. 3 illustrates an example of a node 102 / 112 (e.g., eNB) configured to implement a second RAT (e.g., E-LITRA). In this example, the node 102 does not have a disaggregated architecture. The eNB 102 is a logical node configured to host a Radio Resource Control layer (RRC) and other layers of the eNB 102. An apparatus 2 is configured to implement the functionality of at least part of a node 102, 112 such as an eNB.

[0085] Referring back to FIG. 1 , the nodes 102, 104, 112, 114 are operably coupled to one another via a network interface 103. In an example implementation the network interface 103 comprises an X2 interface.

[0086] A UE 100 can operably couple to a node 102 via a radio interface 101. In this example, the radio interface 101 is a wireless interface. In an example implementation the radio interface 101 comprises a llu interface. During dual-connectivity, the UE 100 can concurrently couple to another node 104 via a radio interface 105. In some examples, the radio interfaces 101 , 105 comprise the same type of interface.

[0087] One node 102 to which the UE 100 is operably coupled can be configured to act as a Master Node (MN). The other node 104 to which the UE 100 is operably coupled can be configured to act as a Secondary Node (SN).

[0088] In FIG. 1 , the first node 102 is a first Master Node (MN1), the second node 104 is a first Secondary Node (SN1), the third node 112 is a second Master Node (MN2), and the fourth node 114 is a second Secondary Node (SN2). In FIG. 1 , MN1 102 and SN1 104 are serving (source) nodes.

[0089] At least an MN 102, 112 can operably couple to a core network entity 108, via an interface 107. An SN 104, 114 may operably couple to a core network entity 108. In FIG. 1 , MN1 102 and MN2 112 are operably coupled to different core network entities 108 via the interface 107, or can be operably coupled to the same entity. In a first example, the MN 102, 112 is an eNB configured to implement E-LITRA. The core network entity 108 comprises an EPC entity. The entity 108 may comprise an MME and / or an S-GW. The interface 107 comprises an S1 interface.

[0090] In a second example, the MN 102, 112 is a gNB configured to implement NR. The core network entity 108 comprises a 5G Core (5GC) entity. The entity 108 may comprise an AMF. The interface 107 comprises an NG-C interface.

[0091] Examples of dual-connectivity (MR-DC) are described below. In most, but not all of these examples, an SN 104,114 implements a different RAT from the MN 102, 112.

[0092] One example is E-LITRA - NR Dual Connectivity (EN-DC), in which an eNB acts as an MN 102 / 112 and a gNB acts as an SN 104 / 114. This example is referred to throughout this specification. However, aspects of the present disclosure are also applicable to the other examples set out below.

[0093] Another example is next generation RAN (NG-RAN) E-LITRA - NR Dual Connectivity (NGEN-DC), in which an eNB (e.g., next generation eNB: ng-eNB) acts as an MN and a gNB acts as an SN.

[0094] Another example of dual-connectivity is NR - E-LITRA Dual Connectivity (NE-DC), in which a gNB acts as an MN and an ng-eNB acts as an SN.

[0095] Another example of dual-connectivity is NR - NR Dual Connectivity (NR-DC), in which one gNB acts as an MN and another gNB acts as an SN. In another example of NR-DC, a UE 100 is connected to two gNB-DUs, one serving a master cell group (MCG) and the other serving a secondary cell group (SCG), connected to the gNB-Cll, acting as an MN and as an SN.

[0096] In at least some examples of dual-connectivity, a node 102, 104, 112, 114 comprises a cell group of one or more cells. A cell group comprises a primary cell (PCell) and zero or more secondary cells (SCells). A cell relates to a geographical area with radio signal i.e., covered by a base station where a UE can connect and get service. A cell can be identified by a lower layer PCI and higher layer cell identity.

[0097] A PCell of a cell group is the cell, operating on a primary frequency, in which a UE 100 either performs an initial connection establishment procedure or initiates a connection reestablishment procedure, or is the cell indicated as the primary cell in a handover procedure. In at least some examples, a primary cell is a cell configured to provide NAS mobility information during connection establishment, re-establishment or handover. The primary cell may be configured to provide security input during connection re-establishment or handover.

[0098] An SCell of a cell group is the cell, operating on a secondary frequency, which may be configured once an RRC connection is established and which may be used to provide additional radio resources. Secondary Cells (SCells) can be configured to form a set of serving cells together with the PCell.

[0099] In dual-connectivity, a cell group of an MN 102 / 112 is a master cell group (MCG). A cell group of an SN 104 / 114 is a secondary cell group (SCG). An MCG comprises a primary cell (PCell) and zero or more secondary cells (SCells). An SCG comprises a primary secondary cell (PSCell) and zero or more secondary cells (SCells). In at least some examples, MCGs and SCGs comprise at least one SCell in addition to a PCell or a PSCell.

[0100] When dual-connectivity is first established, a UE 100 stores a configuration in memory. The configuration comprises information identifying an MCG including a PCell and zero or more SCells, and an SCG including a PSCell and zero or more SCells, and one or more bearers.

[0101] The configuration may include one or more of: information for measurement configuration; information for mobility control; radio resource configuration information (including radio bearers, MAC main configuration and physical channel configuration); and / or an AS security configuration.

[0102] After applying (executing) a configuration, the UE 100 can be able to receive and transmit data over MCG and SCG bearers using radio links provided by the MN and the SN. A dual-connectivity connection can be reconfigured by transmitting a reconfiguration message, to be executed (applied) by the UE 100. When executed, the stored configuration is updated. 3GPP standard 37.340 for dual-connectivity defines reconfiguration messages as RRC reconfiguration messages.

[0103] An SN-initiated RRC reconfiguration message can be sent from a PSCell or from an SCell, or both in the case of carrier aggregation duplication. An MN-initiated RRC Reconfiguration message can be sent from a PCell or from an SCell, or both.

[0104] Examples of reconfiguration messages in dual-connectivity include, but are not limited to: a) SN Modification (MN / SN-initiated) for modifying, establishing (adding) or releasing (removing) bearer contexts (configurations / properties), to transfer bearers to and from the SN 104, or to modify other properties of the UE context within the SN 104. Examples include the addition, modification or release of SCG bearer(s) and the SCG RLC bearer of split bearer(s), as well as configuration changes for SN-terminated MCG bearers. A bearer is a data tunnel associated with a termination point in the RAN or core network. Modification of a bearer may comprise changing a termination point, e.g., from MN to SN, changing the mapping of QoS flows to radio bearers, changing logical channel identities, changing RLC bearer properties including timers, changing RLC mode e.g., changing SDAP, PDCP, and RLC properties. b) SN Change (MN / SN-initiated) to transfer a UE context from a source SN 104 to a target SN 114 and to change the SCG configuration in the UE 100 from the source SN 104 to that of the target SN 114. c) Inter-MN handover (with / without MN-initiated SN change) to transfer context data from a source MN 102 to a target MN 112 while the context at the SN 104 is kept or moved to another SN 114. During an Inter-MN handover, the target MN 112 may decide whether to keep or change the source SN 104, or release the source SN 104.

[0105] A configuration may be a full configuration or a delta configuration. A delta configuration is dependent on a current, reference configuration (e.g., SCG configuration) stored in the memory of the UE 100 whereas a full configuration is not dependent on a reference configuration for its execution.

[0106] A delta configuration is a delta update that provides the UE 100 with the parameters of the reference configuration that have a different value (the ones to be changed, added, or removed). The delta configuration omits the parameters that have the same values as those in the reference configuration. For the other parameters of the reference configuration, the UE 100 uses the existing values from the reference configuration for the new configuration.

[0107] To execute (apply) a delta configuration during mobility, e.g., from SN1 to SN2, the UE 100 overwrites existing parameter values in the reference configuration (SN1 configuration) with the parameter values from the delta configuration (delta SN2 configuration), to arrive at an SN2 configuration. The UE 100 maintains existing parameter values in the reference configuration which are not changed by the delta configuration, i.e. , which are common to the SN1 configuration and the SN2 configuration.

[0108] Delta configurations are prepared by the NW to minimize the bandwidth and delay related to configuration changes during mobility.

[0109] In contrast to a delta configuration, a full configuration comprises a whole configuration, including those parameter values which are unchanged relative to the current configuration, and those parameters with a different value. If there are issues with modifying existing parameters, the NW may provide full configurations instead of delta configurations.

[0110] In at least some examples, an RRC reconfiguration message can be a conditional RRC reconfiguration message containing a conditional configuration, for the conditional addition or change of a PSCell, i.e., mobility to another SN. Examples of those conditional configurations are CPA, CPC, CPAC and SCPAC.

[0111] A conditional RRC reconfiguration message triggers the UE 100 to apply the RRC configuration (SCG configuration) of one of the SNs 104, 114, for example by changing or adding to an SCG (current / reference SCG configuration), in dependence on a condition (‘execution condition’ herein) being satisfied.

[0112] An execution condition can comprise one or more trigger conditions. Trigger conditions can relate to different trigger quantities, e.g., RSRP, RSRQ, SINR, between the UE 100 and the associated SN 104, 114.

[0113] CPAC execution conditions can be offset-based and / or threshold-based, for example. An offset-based execution condition can be satisfied when Mt > Ms + Offset, wherein Mt is the measurement of the target PSCell (e.g., SN2 114), Ms is the measurement of the serving PSCell (e.g., SN1 104), and the offset is a configured offset.

[0114] A threshold-based execution condition can be satisfied when Ms < thresholdl (Ms becomes less than thresholdl) and Mt > threshold2 (Mt becomes greater than threshold2). Both the offset method and the threshold method can be applied concurrently and if at least one is satisfied, the CPAC execution condition can be satisfied.

[0115] FIG. 4 is a message sequence chart illustrating an example reconfiguration procedure comprising an SN-initiated conditional SN change, with MN involvement. The procedure is used for CPAC configuration and CPAC execution.

[0116] The procedure is initiated while the UE 100 is connected to at least a first MN, MN1 102. If dual-connectivity (e.g., MR-DC) is active, the UE 100 will be concurrently connected to a first SN, SN1 104. Alternatively, the procedure may start from single-connectivity with MN1 102, the first time the UE 100 is attempting to connect to an SN 104.

[0117] In summary, FIG. 4 illustrates: at block 416, receiving conditional reconfiguration information for execution by the UE 100 during connectivity between the UE 100 and MN1 102, wherein the conditional reconfiguration information includes a plurality of RRC configurations associated with candidates SN2 114 and SN3 124, and includes a reconfiguration failure recovery indication; at block 434, in response to a reconfiguration failure (block 426) associated with a first RRC configuration of the plurality of RRC configurations, evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations, in dependence on the reconfiguration failure recovery indication; and at block 438, executing the second RRC configuration associated with one of the candidate secondary nodes, in dependence on satisfaction of the condition.

[0118] Further optional blocks 402, 404, 406, 408, 410, 412, 414, 418, 420, 422, 424, 428, 430, 432, 436, 440, 442, 444 are also illustrated in FIG. 4, and are described below. At block 402, SN1 104 transmits towards MN1 102 a request message (‘SN / SgNB Change Required’) initiating the procedure. The message contains candidate node ID(s) and may include the serving SCG configuration of SN1 104 (to support delta configurations). The candidate node ID(s) can include the identifiers of candidate SNs (target SNs), such as SN2 114 and SN3 124 in FIG. 4. The message requests MN1 102 to prepare CPAC configurations of the candidate SNs 114, 124.

[0119] A CPAC configuration refers to the an RRC configuration of the secondary nodes (SCG configuration).

[0120] An RRC configuration may take the form of a full configuration (full SCG configuration) or a delta configuration (delta SCG configuration).

[0121] In response to receiving the request, MN1 102 prepares CPAC configurations of the candidate SNs, in this case SN2 114 and SN3 124. Blocks 404 to 414 illustrate this process. At block 404, MN1 102 sends a request (‘SN / SgNB Addition Request’) to candidate SN2 114.

[0122] If there are further candidate SNs such as SN3 124, block 406 comprises the MN1 102 sending a further request(s) (‘SN / SgNB Addition Request’) towards the further candidate SN(s).

[0123] At block 408 (‘Decides on target PSCells’), SN2 114 determines (decides) a set of candidate PSCells associated with SN2 114, in response to the request of block 404. Similarly, at block 410 (‘Decides on target PSCells’), SN3 124 determines a set of candidate PSCells associated with SN3 124, in response to the request of block 406.

[0124] If a delta configuration is provided, SN2 114 and SN3 124 will use this RRC configuration (SCG configuration) of SN1 104 as a reference configuration and generate the delta configuration to be applied over the RRC configuration (SCG configuration) at the time of handover execution.

[0125] At block 412 (‘SN / SgNB Addition Request Acknowledge’), SN2 114 sends towards MN1

[0126] 102 a reply (‘SN / SgNB Addition Request Acknowledge’), in the form of an NR RRC reconfiguration message comprising a first RRC configuration (SCG configuration) CPAC_1 , and an associated first execution condition.

[0127] Similarly, at block 414 (‘SN / SgNB Addition Request Acknowledge’), SN3 124 sends towards MN1 102 a reply (‘SN / SgNB Addition Request Acknowledge’) in the form of an NR RRC reconfiguration message comprising a second RRC configuration (SCG configuration) CPAC_N, and an associated second execution condition.

[0128] MN1 102 now has the first and second SCG configurations (RRC configurations) CPAC_1 , CPAC_N, and the first and second execution conditions. MN1 102 also has any further SCG configurations and execution conditions associated with any further SNs.

[0129] At block 416 (‘RRC reconfiguration’), MN1 102 sends towards the UE conditional reconfiguration information which will herein be referred to as an RRC reconfiguration message. This message is for execution by the UE 100 during connectivity between the UE 100 and MN1 102. The RRC reconfiguration message includes a plurality of CPAC configurations CPAC_1 , CPAC_N. Each CPAC configuration comprises an RRC configuration comprising the SCG configuration prepared by one of the candidate SNs. The RRC reconfiguration message further comprises an associated execution condition.

[0130] In other words, the RRC reconfiguration message sent by MN1 102 at block 416 includes the CPAC configurations, i.e., a list of RRC reconfiguration messages of the SNs. The RRC reconfiguration message further includes the associated execution conditions. Each RRC reconfiguration message from this list contains the RRC configuration (SCG configuration) of SNs 114, 124 in block 412 or 414.

[0131] Optionally, the RRC reconfiguration message sent by MN1 102 at block 416 can include an updated MCG configuration, e.g., to configure the execution conditions.

[0132] Optionally, the RRC reconfiguration message sent by MN1 102 at block 416 can include an RRC reconfiguration message generated by the source (currently-serving) SN1 104, containing the RRC configuration (SCG configuration) of SN1 104, e.g., to configure the conditional measurements. The RRC configurations sent at block 416 may comprise full configurations and / or delta configurations.

[0133] In case there is a compliance issue (failure) with the UE 100 applying one of the RRC configurations when its associated execution condition is satisfied, the RRC reconfiguration message sent at block 416 advantageously further includes a reconfiguration failure recovery indication (‘Information for RRC reconfiguration failure recovery’), controlling how the UE 100 is to handle such a failure if it occurs. This is described in more detail later, from block 426 onwards.

[0134] At block 418 (‘RRC reconfiguration complete’), the UE 100 sends an acknowledgement of the message received at block 416. The UE 100 also stores the RRC configurations of the candidate SNs 114, 124.

[0135] At block 420 (‘SN / SgNB change confirm’), MN1 102 sends a message towards SN1 104, to indicate that the CPACs (RRC configurations) have been configured in the UE 100. After receiving the message, SN1 104 continues providing user data towards the UE 100.

[0136] At block 422 (‘UE Evaluates CPAC condition’), the UE 100 starts evaluating the execution conditions associated with the CPAC configurations CPAC_1 , CPAC_N.

[0137] At block 424 (‘CPAC_1 condition is met’), one of the execution conditions holds (is satisfied), for example the CPAC_1 execution condition.

[0138] At block 426 (‘RRC reconfiguration failure (compliance)’), the UE 100 attempts to execute (apply) the RRC configuration associated with CPAC_1 and SN2 114, but there is a compliance issue (reconfiguration failure) associated with the RRC configuration. Block 426 can be regarded as an operation where a compliance check by the UE 100 is performed.

[0139] Some compliance issues may be caused by the RRC configuration itself, and not with the execution condition, meaning that there are some fields or values in the RRC configuration that the UE 100 cannot accept. For example, the NW may have incorrectly requested a feature that the UE 100 does not support, such as dual-connectivity, multi-panel UEs, etc. If the RRC reconfiguration message received by the UE 100 at block 416 did not include a reconfiguration failure recovery indication controlling how the UE 100 is to handle such failures, a first (non-recovery) approach is for the UE 100 to handle the failure by rejecting all of the CPAC configurations (RRC configurations of the candidate SNs 114, 124). The UE 100 informs MN1 102 of the failure, applies the RRC configuration that was in use before block 416, and rejects the CPAC configurations by not evaluating / ignoring them (not by releasing them). As a result, the NW may reprepare the CPAC configurations and execution conditions (blocks 404-414).

[0140] However, impacts of the above non-recovery approach include:

[0141] - The UE 100 experiences interruptions on the SN link with SN1 104 until MN1 102 reconfigures the UE 100 with a new SN link, since the UE 100 goes back to the previous RRC Configuration and reject the rest of the CPACs (RRC configurations).

[0142] - The repreparation of the CPACs (RRC configurations) and execution conditions, and retransmission of the RRC configurations and execution conditions over the air, will cause large overheads.

[0143] - In case of delta configuration, the UE 100 does not distinguish the non-compliance of the delta or the reference configuration. Therefore, the repreparation of the CPACs should include both the reference and delta configurations.

[0144] The above non-recovery approach may be relevant when a compliance issue associated with one RRC configuration is associated with a high probability of compliance issues with the other RRC configurations.

[0145] However, in this disclosure, it is considered that a compliance issue with an RRC configuration may arise for a variety of reasons, not necessarily affecting all of the other RRC configurations. If at least one of the other RRC configurations does not have a compliance issue, then repreparation should not be necessary and the above impacts can be advantageously avoided.

[0146] Therefore, the RRC reconfiguration message received by the UE 100 at block 416 has been configured to include a reconfiguration failure recovery indication. This second (recovery) approach permits the UE 100 to continue evaluating the other CPACs (RRC configurations) received at block 416 in response to a reconfiguration failure associated with one of them at block 426. This process is illustrated as blocks 428-444, and described below. Firstly, the reconfiguration failure recovery indication can comprise a flag (‘Indication of the recovery’) or equivalent instruction for the UE 100 to attempt recovery in response to a reconfiguration failure, by evaluating (continuing to evaluate) the other execution condition(s) of the other RRC config uration(s). For instance, when the UE 100 fails to execute (apply) the CPAC_1 configuration, the UE 100 can continue to evaluate the execution condition of CPAC_N.

[0147] A value of the flag, or presence / absence of the reconfiguration failure recovery indication, may indicate whether to follow the non-recovery approach (if available) or to attempt recovery via the recovery approach. The value of the flag may be predetermined or automatically determined by the NW.

[0148] Alternatively, or in addition, the reconfiguration failure recovery indication can comprise a recovery condition(s) based at least in part of radio signal measurement. A recovery condition is herein referred to as a ‘radio condition’ of the recovery. This recovery condition requires that the UE’s continued evaluation of other execution conditions is conditional on satisfaction of the radio condition.

[0149] The radio condition refers to a radio signal measurement condition, such as any one or more of RSRP, RSRQ, SI NR, etc. The radio condition is a separate condition than the execution conditions for the RRC configurations. For example, a radio condition relating to a same trigger quantity as an execution condition may have a lower threshold and / or offset than the execution condition, and as such is easier to satisfy than the execution condition.

[0150] Therefore, a radio condition advantageously allows the UE 100 to anticipate and avoid future reconfiguration failures at an early stage.

[0151] The threshold or offset of the radio condition may be determined either automatically by the NW, or predetermined.

[0152] The radio condition ensures that radio signal measurements performed by the UE 100 of another other candidate cell SN3 124 reaches a threshold signal strength to be a candidate for recovery. In examples, the reconfiguration failure recovery indication can comprise a plurality of radio conditions. Different ones of the plurality of radio conditions can be conditions for evaluating different ones of the execution conditions. This is advantageous where the different execution conditions have different thresholds / offsets.

[0153] Alternatively, or in addition, the reconfiguration failure recovery indication can comprise an allowed number of recovery attempts (‘maximum trials of the recovery’). The allowed number of recovery attempts may designate an allowed number of times that the UE 100 is allowed to attempt recovery. The allowed number may allow one or more attempts, depending on implementation.

[0154] The allowed number of recovery attempts may be less than the number of RRC configurations (number of candidate SNs 114, 124). In situations where the failure of one RRC configuration suggests a high probability that all the other RRC configurations will fail, the NW vendor may advantageously decide to set the allowed number to be less than the number of RRC configurations. In some situations, the NW may automatically determine the allowed number of recovery attempts.

[0155] A recovery attempt is defined as an attempt to complete (finish the execution) another CPAC configuration, such as the CPAC_N configuration of SN3 124. A recovery attempt is successful if later-described block 438 is executed. A recovery attempt is unsuccessful if a failure (block 426) occurs in relation to the other RRC configuration.

[0156] Blocks 428-444 are now described, which govern the behaviour of the UE 100 in response to a reconfiguration failure, the behaviour being dependent on the reconfiguration failure recovery indication.

[0157] First, the UE 100 may determine whether an MN communication link (e.g., with MCG) is available (e.g., active). Initiating the recovery attempt(s) is conditional on the MN communication link being available.

[0158] Box A) relates to the situation where the MCG is affected (e.g., suspended). Box B) relates to the situation where the MCG is unaffected (active). Within box A), block 428 (‘initialize reestablishment’) comprises the UE 100 initiating a reestablishment process. The UE 100 releases all the preparations (RRC configurations and execution conditions) received at block 416, and re-establishes the MN communication link with a PCell.

[0159] Following reestablishment, the method may return to block 402 or 404, causing repreparation of the RRC reconfiguration message.

[0160] Within box B), the MCG is unaffected so blocks 430-434 are executed (performed), and then either block 436 (option B.1)) or blocks 438-444 (option B.2)) is / are executed.

[0161] At block 430 (‘Apply the previous RRC configuration’), the UE 100 executes (applies) the previous RRC Configuration that was in use before the reconfiguration failure.

[0162] In other words, the reconfiguration failure may result in the UE 100 not having a usable RRC configuration, so the UE 100 returns to its previous RRC configuration.

[0163] At block 432 (‘Release only the non-compliant configurations’), the UE 100 rejects (e.g., releases, ignores, or discards) a subset (e.g., one) of the plurality of CPAC configurations that the reconfiguration failure related to. For example, where the reconfiguration failure related to CPAC_1 , the UE 100 rejects the RRC configuration and execution condition associated with CPAC_1.

[0164] The synchronization of security keys in a dynamic key environment is relevant because this selective activation procedure allows partial failures to occur without forcing repreparation of RRC reconfiguration messages. By way of context, a security key is applied by the UE 100 to connect to a candidate SN 114, 124, the security key being known to the UE 100, MN 102, and relevant SN. A security key is generated from a security counter selected from a list of security counters. The NW may prohibit the re-use of security keys, hence the list of security counters. When executing the procedure in FIG. 4, it is possible that the UE 100 might determine to connect to another SN 114, 124 (block 424), before returning to the serving SN1 104 (block 430). By requiring the compliance check to be successful before the UE 100 selects a security counter, issues with key synchronization or re-use of keys can be avoided. At block 434 (‘If the radio conditions / radio conditions hold, continue evaluating other CPAC configurations’), the UE 100 evaluates the execution condition(s) associated with the other RRC configuration(s), as permitted by the reconfiguration failure recovery indication.

[0165] In other words, blocks 432-434 cause the UE 100 to reject the non-compliant configuration and continue evaluating the rest of the CPAC configurations (RRC configurations).

[0166] This way, the signaling overheads can be advantageously reduced because repreparation of the RRC reconfiguration message may not be required.

[0167] The evaluation of an RRC configuration may be conditional on satisfaction of an associated radio condition, as provided by MN1 102 in block 416.

[0168] Regarding the reporting of information to MN1 102, Box B.1) defines option 1 : ‘Report SCG failure after each failure’.

[0169] Within option 1 , block 436 (‘SCG failure information, indicating the recovery attempt, e.g., flag’) comprises the UE 100 informing MN1 102 about the failed attempt before another of the RRC configurations is executed.

[0170] In other words, the UE 100 sends the failure information (‘SCG failure information’) in response to the reconfiguration failure, wherein the sending is initiated by the reconfiguration failure. The failure information received by MN1 102 can be regarded as a reply from the UE 100, received immediately in response to the configuration failure.

[0171] This approach means that failure information is sent in response to individual reconfiguration failures. If both the CPAC_1 and CPAC_N configurations fail, two such failure information messages are sent.

[0172] If the UE 100 continues to evaluate one of the other RRC configurations after sending the failure information, the failure information may include an indication that the evaluation of another execution condition associated with another RRC configuration is being executed by the UE after the sending of the failure information. This signals to MN1 102 that recovery is ongoing at UE 100. This can help to avoid NW attempts for recovery, so MN1 102 does not perform blocks 404-414 again (repreparation of the PSCells, i.e., RRC configurations). Additionally, or alternatively, the failure information may indicate which one of the RRC configurations the reconfiguration failure was associated with, and / or which one or more of the RRC configurations the UE 100 is evaluating following the reconfiguration failure.

[0173] If the allowed number of recovery attempts is reached, the failure information sent at block 436 may indicate that the UE 100 is no longer evaluating CPAC configurations, and / or may comprise a request for repreparation.

[0174] Box B.2) defines option 2: ‘report multiple SCG failures in a single message’. The failure information is not sent immediately, and is instead triggered / initiated either by successful execution of one of the other RRC configurations, or the allowed number of recovery attempts being reached (if there is a limit), whichever occurs first.

[0175] Within option 2, block 438 (‘if the UE successfully finishes the execution of another CPAC’), refers to the UE 100 successfully executing (applying) one of the RRC configurations following one or more recovery attempts. For example, the UE 100 may successfully execute (apply) the second RRC configuration associated with CPAC_N.

[0176] Block 438 can be regarded as an operation where a compliance check by the UE 100 is performed on the second RRC configuration. If a reconfiguration failure is identified, the process of blocks 428-438 may be repeated to evaluate and attempt execution of a further RRC configuration from the message received at block 416, if one exists.

[0177] In relation to security, the UE’s selection of a security counter from a list of security counters may be dependent on the compliance check being successful, in some examples. After block 432, if the UE 100 encounters a reconfiguration failure due to the compliance check at block 438, the UE 100 does not attempt to use a SN security counter from the list of security counters provided to the UE 100 to generate an SN security key. This can help to maintain synchronization of security keys.

[0178] Block 438 acts as a trigger / initiator for the UE 100 to send MN1 102 a message at block 440 (‘RRC reconfiguration complete message with SCG failure information of the failed CPACs’). The message may be an RRC reconfiguration complete message, received by MN1 102 as a form of reply from the UE 100. The message indicates which one of the plurality of RRC configurations the UE 100 has executed (applied).

[0179] The MN1 102 subsequently executes a mobility procedure in response to the message (block 440). The procedure is outside the scope of this disclosure, and further enables the handover from SN1 104 towards SN3 124.

[0180] In some examples, the message further comprises aggregated (bundled) failure information (‘SCG failure information’) identifying the RRC configuration(s) for which reconfiguration failure(s) occurred.

[0181] In other words, the UE 100 aggregates the failure information based on one or more reconfiguration failures (block 426) associated with the plurality of RRC configurations, and sends the aggregated (bundled) failure information (‘SCG failure information of the failed CPACs’, i.e., failed RRC configurations).

[0182] Unlike option 1 , in option 2 the sending of the failure information is initiated by successful execution of one of the RRC configurations (e.g., by a PSCell change). Further, the failure information may be embedded within an existing RRC Configuration Complete message identifying the RRC configuration that the UE 100 has applied.

[0183] Within option 2, block 442 (‘if the UE reached the maximum number of retrials’) refers to the situation where the allowed number of recovery attempts has been reached without successful execution of an RRC configuration, i.e., the recovery attempts have failed (reconfiguration failure) and no more recovery attempts are permitted.

[0184] Block 442 acts as a trigger / initiator for the UE 100 to send MN1 102 a message at block 444 (‘SCG failure information of all the failed CPACs’). The message may be the type described in relation to block 436, except the message this time comprises aggregated (bundled) failure information.

[0185] Options B.1) and B.2) advantageously reduce signaling overheads compared to option A), because the failure information is aggregated rather than being sent in response to individual reconfiguration failures. MN-initiated conditional SN change is another SN change procedure. Embodiments of the disclosure are also applicable to MN-initiated conditional SN changes. FIG. 5 illustrates the initial stages of an MN-initiated conditional SN change.

[0186] At block 502, MN1 102 transmits to candidate SN2 114 a request message (‘SN addition request’) initiating the procedure. By sending this message, MN1 102 requests the candidate SN2 114 to allocate resources to the UE 100 by means of the SN Addition procedure, indicating that the request is for CPAC. MN1 102 also provides to SN2 114 the candidate cells recommended by MN1 102 via the latest radio measurement results, for SN2 114 to choose and configure the SCG cells. MN1 102 also provides the upper limit for the number of PSCells that can be prepared by the candidate SN2 114.

[0187] Block 504 is the type of message of block 502, but sent to candidate SN3 124.

[0188] Within the list of cells as indicated within the measurement results indicated by the MN 102, the candidates SN2 114 and SN3 124 decide the list of PSCell(s) to prepare (considering the upper limit indicated by MN1 102). For a prepared PSCell, the candidate SN2 114, SN3 124 decides the other SCG SCells to form part of the SCG configuration.

[0189] The candidate SN2 114, SN3 124 can either accept or reject individual candidate cells listed within the measurement results indicated by the MN 102, and may not be permitted to configure any alternative candidates.

[0190] At block 506 (‘SN / SgNB addition request acknowledge’), SN2 114 sends towards MN1 102 the corresponding RRC configuration (SCG configuration) towards MN1 102 in the form of an NR RRC reconfiguration message contained in the SN Addition Request Acknowledge message, with the prepared PSCell identifier(s).

[0191] The message from the candidate SN2 114, SN3 124 includes an indication of whether the configuration is a full configuration or a delta configuration.

[0192] Block 508 is the type of message from block 506, but sent from candidate SN3 124. Block 510 (‘RRC reconfiguration message’) is as described in relation to block 416, and includes the RRC configurations of the candidates SN2 114 and SN3 124 as well as the reconfiguration failure recovery indication.

[0193] Block 512 (‘RRC reconfiguration complete’) is as described in relation to block 418, defining the UE’s acknowledgement.

[0194] At Block 514 (‘Xn-ll Address Indication’), MN1 102 sends a message towards SN1 104 via the Xn-ll address indication procedure, informing SN1 104 that the CPACs (RRC configurations) have been configured in the UE 100. After receiving the message, SN1 104 continues providing user data to the UE 100.

[0195] The subsequent procedure comprises blocks then 422-444 of FIG. 4, which have not been repeated in FIG. 5 for conciseness.

[0196] FIG. 6 is a message sequence chart illustrating an alternative reconfiguration procedure, which can be employed when the RRC configurations are delta configurations.

[0197] In summary, if the RRC configurations that the UE 100 is configured with are delta configurations, at block 632 the UE 100 performs a compliance check on the delta and reference configurations in response to the reconfiguration failure of block 426. If the delta configuration (delta portion) is non-compliant, the delta configuration is rejected. If the reference configuration (reference portion) is non-compliant, the dependent configurations dependent on the non-compliant reference configuration are rejected. Therefore, the UE 100 can advantageously anticipate and avoid future reconfiguration failures at an early stage.

[0198] The initial operations depend on whether the procedure is SN-initiated or MN-initiated. When the procedure is SN-initiated, as shown in FIG. 6, blocks 402 to 430 are performed in the manner of FIG. 4. When the procedure is MN-initiated, FIG. 5 illustrates the different initial operations.

[0199] Following block 430, block 632 is performed: ‘if the radio conditions hold, perform compliance check on delta and reference configurations’. In other words, the UE 100 determines which one or both of the delta portion (delta configuration) and reference portion (reference configuration) caused the reconfiguration failure at block 426. The UE 100 may for example perform separate compliance checks on the delta portion and the reference portion.

[0200] Performing the compliance check may be first conditional on satisfaction of the radio condition described earlier.

[0201] At block 634 (‘if the delta is non-compliant, then release that delta configuration’), the UE 100 rejects the delta portion in dependence on the delta portion being a determined cause of the reconfiguration failure. The UE 100 can continue to evaluate the other RRC configurations including other delta portions dependent on the reference portion.

[0202] At block 636 (‘if the reference is non-compliant, then release all of the dependent configurations’), the UE 100 identifies and rejects the other delta portions (RRC configurations) which are dependent on the reference portion, in dependence on the reference portion being a determined cause of the reconfiguration failure.

[0203] In this example, the subset of RRC configurations that are rejected can comprise a plurality of RRC configurations, where more than one of them are dependent on the reference portion.

[0204] Block 638 (‘SCG failure information’) is as described in relation to block 436, in other words the UE 100 sends MN1 102 the failure information in response to each reconfiguration failure / individual reconfiguration failures. At block 640 (‘continue evaluating other CPAC configurations’), the UE 100 continues evaluating the other RRC configurations other than those that were rejected at blocks 632-636.

[0205] The above approach is in accordance with option 1 (box B.1 )) from FIG. 4, where MN1 102 is informed immediately.

[0206] However, it would be appreciated that option 2 (box B.2)) of FIG. 4 can be followed instead, where failure information is aggregated (bundled), and sent in response to successful execution of one of the other RRC configurations, or the allowed number of recovery attempts being reached, whichever occurs first. FIG. 7 illustrates an example of a computer-implemented method 700, which may be executed by the UE 100. The method comprises: at block 702, receiving conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and includes a reconfiguration failure recovery indication; at block 704, in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations, in dependence on the reconfiguration failure recovery indication; and at block 706, executing the second RRC configuration associated with one of the candidate secondary nodes, in dependence on satisfaction of the condition.

[0207] FIG. 8 illustrates an example of a computer-implemented method 800, which may be executed by the MN 102. The method comprises: at block 802, sending conditional reconfiguration information to be executed by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and the conditional reconfiguration information further including a reconfiguration failure recovery indication, wherein the reconfiguration failure recovery indication comprises an instruction to attempt recovery in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, wherein attempting the recovery comprises evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations.

[0208] FIG. 9 illustrates an example of a controller 900 suitable for use in an apparatus 100, 102, 104. Implementation of a controller 900 may be as controller circuitry. The controller 900 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware).

[0209] As illustrated in FIG. 9 the controller 900 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 906 in a general-purpose or special-purpose processor 902 that may be stored on a computer readable storage medium (disk, memory etc.) to be executed by such a processor 902.

[0210] The processor 902 is configured to read from and write to the memory 904. The processor 902 may also comprise an output interface via which data and / or commands are output by the processor 902 and an input interface via which data and / or commands are input to the processor 902.

[0211] The memory 904 stores a computer program 906 comprising computer program instructions (computer program code) that controls the operation of the apparatus 100, 102, 104 when loaded into the processor 902. The computer program instructions, of the computer program 906, provide the logic and routines that enables the apparatus to perform the methods illustrated in the accompanying Figs. The processor 902 by reading the memory 904 is able to load and execute the computer program 906.

[0212] The apparatus 100 comprises: at least one processor 902; and at least one memory 904 including computer program code the at least one memory 904 and the computer program code configured to, with the at least one processor 902, cause the apparatus 100 at least to perform: at block 702, receiving conditional reconfiguration information to be executed by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and includes a reconfiguration failure recovery indication; at block 704, in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations, in dependence on the reconfiguration failure recovery indication; and at block 706, executing the second RRC configuration associated with one of the candidate secondary nodes, in dependence on satisfaction of the condition.

[0213] The apparatus 102 comprises: at least one processor 902; and at least one memory 904 including computer program code, the at least one memory 904 and the computer program code configured to, with the at least one processor 902, cause the apparatus 102 at least to perform: at block 802, sending conditional reconfiguration information to be executed by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and the conditional reconfiguration information further including a reconfiguration failure recovery indication, wherein the reconfiguration failure recovery indication comprises an instruction to attempt recovery in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, wherein attempting the recovery comprises evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations.

[0214] The apparatus 100 comprises: at least one processor 902; and at least one memory 904 storing instructions that, when executed by the at least one processor 902, cause the apparatus at least to: at block 702, receive conditional reconfiguration information to be executed by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and includes a reconfiguration failure recovery indication; at block 704, in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, evaluate a condition associated with a second RRC configuration of the plurality of RRC configurations, in dependence on the reconfiguration failure recovery indication; and at block 706, execute the second RRC configuration associated with one of the candidate secondary nodes, in dependence on satisfaction of the condition.

[0215] The apparatus 102 comprises: at least one processor 902; and at least one memory 904 storing instructions that, when executed by the at least one processor 902, cause the apparatus at least to: at block 802, send conditional reconfiguration information to be executed by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and the conditional reconfiguration information further including a reconfiguration failure recovery indication, wherein the reconfiguration failure recovery indication comprises an instruction to attempt recovery in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, wherein attempting the recovery comprises evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations.

[0216] As illustrated in FIG. 10, the computer program 906 may arrive at the apparatus 100, 102, 104 via any suitable delivery mechanism 908. The delivery mechanism 908 may be, for example, a machine readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid-state memory, an article of manufacture that comprises or tangibly embodies the computer program 906. The delivery mechanism may be a signal configured to reliably transfer the computer program 906. The apparatus 100, 102, 104 may propagate or transmit the computer program 906 as a computer data signal.

[0217] The computer program 906 can comprise instructions for causing an apparatus 100 to perform at least the following or for performing at least the following: at block 702, receiving conditional reconfiguration information to be executed by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and includes a reconfiguration failure recovery indication; at block 704, in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations, in dependence on the reconfiguration failure recovery indication; and at block 706, executing the second RRC configuration associated with one of the candidate secondary nodes, in dependence on satisfaction of the condition.

[0218] The computer program 906 can comprise instructions for causing an apparatus 102 to perform at least the following or for performing at least the following: at block 802, sending conditional reconfiguration information to be executed by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and the conditional reconfiguration information further including a reconfiguration failure recovery indication, wherein the reconfiguration failure recovery indication comprises an instruction to attempt recovery in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, wherein attempting the recovery comprises evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations.

[0219] The computer program instructions may be comprised in a computer program, a non- transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program.

[0220] Although the memory 904 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable and / or may provide permanent / semi-permanent / dynamic / cached storage.

[0221] Although the processor 902 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable. The processor 902 may be a single core or multi-core processor.

[0222] References to ‘computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’ etc. or a ‘controller’, ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single / multi- processor architectures and sequential (Von Neumann) / parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc.

[0223] As used in this application, the term ‘circuitry’ may refer to one or more or all of the following:

[0224] (a) hardware-only circuitry implementations (such as implementations in only analog and / or digital circuitry) and

[0225] (b) combinations of hardware circuits and software, such as (as applicable):

[0226] (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and

[0227] (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory or memories that work together to cause an apparatus, such as a mobile phone or server, to perform various functions and

[0228] (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (for example, firmware) for operation, but the software may not be present when it is not needed for operation.

[0229] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely 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 for a mobile device or a similar integrated circuit in a server, a cellular network device, or other computing or network device.

[0230] The blocks illustrated in the accompanying Figs may represent steps in a method and / or sections of code in the computer program 906. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

[0231] Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described.

[0232] The apparatus can be provided in an electronic device, for example, a mobile terminal, according to an example of the present disclosure. It should be understood, however, that a mobile terminal is merely illustrative of an electronic device that would benefit from examples of implementations of the present disclosure and, therefore, should not be taken to limit the scope of the present disclosure to the same. While in certain implementation examples, the apparatus can be provided in a mobile terminal, other types of electronic devices, such as, but not limited to: mobile communication devices, hand portable electronic devices, wearable computing devices, portable digital assistants (PDAs), pagers, mobile computers, desktop computers, televisions, gaming devices, laptop computers, cameras, video recorders, GPS devices and other types of electronic systems, can readily employ examples of the present disclosure. Furthermore, devices can readily employ examples of the present disclosure regardless of their intent to provide mobility.

[0233] The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one...” or by using “consisting”.

[0234] In this description, the wording ‘connect’, ‘couple’ and ‘communication’ and their derivatives mean operationally connected / coupled / in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e., so as to provide direct or indirect connection / coupling / communication. Any such intervening components can include hardware and / or software components.

[0235] As used herein, the term "determine / determining" (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, measuring, investigating, identifying, looking up (for example, looking up in a table, a database or another data structure), ascertaining and the like. Also, "determining" can include receiving (for example, receiving information), accessing (for example, accessing data in a memory), obtaining and the like. Also, " determine / determining" can include resolving, selecting, choosing, establishing, and the like.

[0236] In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example.

[0237] Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

[0238] Features described in the preceding description may be used in combinations other than the combinations explicitly described above.

[0239] Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0240] Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

[0241] The term ‘a’, ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / an / the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

[0242] The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

[0243] In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described.

[0244] The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure.

[0245] Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon. l / we claim:

Claims

CLAIMS1 . An apparatus comprising means for: receiving conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and includes a reconfiguration failure recovery indication; in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations, in dependence on the reconfiguration failure recovery indication; and executing the second RRC configuration associated with one of the candidate secondary nodes, in dependence on satisfaction of the condition.

2. An apparatus as claimed in claim 1 , wherein the reconfiguration failure recovery indication comprises an instruction to attempt recovery by evaluating at least the condition associated with the second RRC configuration, in response to reconfiguration failure.

3. An apparatus as claimed in claim 1 or 2, wherein the reconfiguration failure recovery indication comprises a recovery condition based at least in part on radio signal measurement, and wherein performing the evaluation is conditional on satisfaction of the recovery condition.

4. An apparatus as claimed in any preceding claim, wherein the reconfiguration failure recovery indication comprises an allowed number of recovery attempts.

5. An apparatus as claimed in any preceding claim, comprising means for determining whether a master node communication link is available, wherein performing the evaluation is conditional on the master node communication link being available.

6. An apparatus as claimed in any preceding claim, comprising means for rejecting a subset of the plurality of RRC configurations, the subset comprising the first RRC configuration, in dependence on determining the reconfiguration failure.

7. An apparatus as claimed in any preceding claim, comprising means for sending failure information in response to the reconfiguration failure.

8. An apparatus as claimed in claim 7, wherein the sending is initiated by the reconfiguration failure, before the second RRC configuration is executed.

9. An apparatus as claimed in claim 7 or 8, wherein the failure information comprises an indicator that the evaluation of the condition associated with the second RRC configuration is being performed after the sending of the failure information.

10. An apparatus as claimed in claim 7, comprising means for aggregating failure information based on one or more reconfiguration failures associated with the plurality of RRC configurations, and sending the aggregated failure information in dependence on at least one of: successful execution of the second RRC configuration; or monitoring of whether an allowed number of recovery attempts has been reached.

11. An apparatus as claimed in any preceding claim, comprising means for performing a compliance check on the second RRC configuration, and wherein selection of a security counter from a list of security counters is dependent on the compliance check being successful.

12. An apparatus as claimed in any preceding claim, wherein the first RRC configuration is a delta configuration, and wherein the apparatus comprises means for determining which of a delta portion and a reference portion associated with the delta configuration caused the reconfiguration failure.

13. An apparatus as claimed in claim 12, comprising means for rejecting the delta configuration in dependence on the delta portion being a determined cause of the reconfiguration failure, and wherein the second RRC configuration is a delta configuration dependent on the reference portion.

14. An apparatus as claimed in claim 12 or 13, comprising means for rejecting the first and second RRC configurations that are dependent on the reference portion, independence on the reference portion being a determined cause of the reconfiguration failure.

15. An apparatus as claimed in any preceding claim, wherein the apparatus is a User Equipment.

16. An apparatus comprising means for: sending conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and the conditional reconfiguration information further including a reconfiguration failure recovery indication, wherein the reconfiguration failure recovery indication comprises an instruction to attempt recovery in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, wherein attempting the recovery comprises evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations.

17. An apparatus as claimed in claim 16, comprising means for receiving a reply indicating which one of the plurality of RRC configurations the user equipment has executed based on the plurality of RRC configurations and the reconfiguration failure recovery indication.

18. An apparatus as claimed in claim 16 or 17, wherein the reconfiguration failure recovery indication comprises an instruction to attempt recovery by evaluating at least the condition associated with the second RRC configuration, in response to reconfiguration failure.

19. An apparatus as claimed in any one of claims 16 to 18, wherein the reconfiguration failure recovery indication comprises a recovery condition based at least in part on radio signal measurement, and wherein performing the evaluation is conditional on satisfaction of the recovery condition.

20. An apparatus as claimed in any one of claims 16 to 19, wherein the reconfiguration failure recovery indication comprises an allowed number of recovery attempts.

21. An apparatus as claimed in any one of claims 16 to 20, comprising means for receiving failure information from the user equipment in response to the reconfiguration failure.

22. An apparatus as claimed in claim 21 , wherein the failure information comprises an indicator that the evaluation of the condition associated with the second RRC configuration is being performed after the sending of the failure information.

23. An apparatus as claimed in claim 22, comprising means for inhibiting preparation of further conditional reconfiguration information, based on the indicator.

24. An apparatus as claimed in claim 21 , wherein the failure information is aggregated failure information based on one or more reconfiguration failures associated with the plurality of RRC configurations.

25. An apparatus as claimed in any one of claims 16 to 24, wherein the apparatus is a Master Node.

26. A method comprising: receiving conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and includes a reconfiguration failure recovery indication; in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations, in dependence on the reconfiguration failure recovery indication; and executing the second RRC configuration associated with one of the candidate secondary nodes, in dependence on satisfaction of the condition.

27. A method as claimed in claim 26, wherein the reconfiguration failure recovery indication comprises one or more of:an instruction to attempt recovery by evaluating at least the condition associated with the second RRC configuration, in response to reconfiguration failure; a recovery condition based at least in part on radio signal measurement, and wherein performing the evaluation is conditional on satisfaction of the recovery condition; or an allowed number of recovery attempts.

28. A method as claimed in any one of claims 26 to 27, comprising determining whether a master node communication link is available, wherein performing the evaluation is conditional on the master node communication link being available.

29. A method as claimed in any one of claims 26 to 28, comprising rejecting a subset of the plurality of RRC configurations, the subset comprising the first RRC configuration, in dependence on determining the reconfiguration failure.

30. A method as claimed in any one of claims 26 to 29, comprising sending failure information in response to the reconfiguration failure.

31. A method as claimed in claim 30, wherein the sending is initiated by the reconfiguration failure, before the second RRC configuration is executed.

32. A method as claimed in claim 30 or 31 , wherein the failure information comprises an indicator that the evaluation of the condition associated with the second RRC configuration is being performed after the sending of the failure information.

33. A method as claimed in claim 30, comprising aggregating failure information based on one or more reconfiguration failures associated with the plurality of RRC configurations, and sending the aggregated failure information in dependence on at least one of: successful execution of the second RRC configuration; or monitoring of whether an allowed number of recovery attempts has been reached.

34. A method as claimed in any one of claims 26 to 33, comprising performing a compliance check on the second RRC configuration, and wherein selection of a security counter from a list of security counters is dependent on the compliance check being successful.

35. A method as claimed in any one of claims 26 to 34, wherein the first RRC configuration is a delta configuration, and wherein the method comprises determining which of a delta portion and a reference portion associated with the delta configuration caused the reconfiguration failure.

36. A method as claimed in claim 35, comprising rejecting the delta configuration in dependence on the delta portion being a determined cause of the reconfiguration failure, and wherein the second RRC configuration is a delta configuration dependent on the reference portion, and / or rejecting the first and second RRC configurations that are dependent on the reference portion, in dependence on the reference portion being a determined cause of the reconfiguration failure.

37. A method comprising: sending conditional reconfiguration information for execution by user equipment during connectivity between the user equipment and a master node, wherein the conditional reconfiguration information includes a plurality of radio resource control (RRC) configurations associated with candidate secondary nodes, and the conditional reconfiguration information further including a reconfiguration failure recovery indication, wherein the reconfiguration failure recovery indication comprises an instruction to attempt recovery in response to a reconfiguration failure associated with a first RRC configuration of the plurality of RRC configurations, wherein attempting the recovery comprises evaluating a condition associated with a second RRC configuration of the plurality of RRC configurations.

38. A method as claimed in claim 37, comprising receiving a reply indicating which one of the plurality of RRC configurations the user equipment has executed based on the plurality of RRC configurations and the reconfiguration failure recovery indication.

39. A method as claimed in claim 37 or 38, wherein the reconfiguration failure recovery indication comprises one or more of: an instruction to attempt recovery by evaluating at least the condition associated with the second RRC configuration, in response to reconfiguration failure;a recovery condition based at least in part on radio signal measurement, and wherein performing the evaluation is conditional on satisfaction of the recovery condition; or an allowed number of recovery attempts.

40. A method as claimed in any one of claims 37 to 39, comprising receiving failure information from the user equipment in response to the reconfiguration failure.

41. A method as claimed in claim 40, wherein the failure information comprises an indicator that the evaluation of the condition associated with the second RRC configuration is being performed after the sending of the failure information.

42. A method as claimed in claim 41 , comprising inhibiting preparation of further conditional reconfiguration information, based on the indicator.

43. A method as claimed in claim 40, wherein the failure information is aggregated failure information based on one or more reconfiguration failures associated with the plurality of RRC configurations.

44. A computer program that when executed by one or more processors causes a method as claimed in any one or more of claims 26 to 43 to be performed.

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