Network node, network unit, further control plane unit and method - Patents.com

Abstract

A communication system is disclosed that includes a distributed base station device with a control plane unit, a user plane unit and a distributed unit. Respective interfaces are set up between the control plane unit and the user plane unit, between the control plane unit and the distributed unit and between the control plane unit and a core network node. The control plane unit acts as a master control plane unit. The user plane unit or the distributed unit obtains information identifying a further control plane unit that acts as a redundant unit in case of failure of the master control plane unit. Corresponding interfaces are set up between the further control plane unit and the user plane unit, between the further control plane unit and the distributed unit and between the further control plane unit and the core network node for restoration.

Description

[Technical field]

[0001] The present invention relates to communication systems. [Background technology]

[0002] The present invention relates particularly, but not exclusively, to wireless communication systems and devices thereof operating in accordance with 3rd Generation Partnership Project (3GPP®) standards or equivalents or derivatives thereof. The present invention relates particularly, but not necessarily exclusively, to restoration of distributed equipment, such as distributed base stations in so-called "5G" (or "New Wireless") systems.

[0003] The latest evolution of the 3GPP standards is called "5G" or "New Radio" (NR). These terms refer to evolving communications technologies that support various applications and services. Various details of 5G networks are described, for example, in the "NGMN 5G White Paper" V1.0 by the Next Generation Mobile Networks (NGMN) Alliance, available from non-patent document 1. 3GPP intends to support 5G by the so-called 3GPP NextGen Radio Access Network (RAN) and 3GPP NextGen core network (NGC).

[0004] Under 3GPP standards, a base station (e.g., an "eNB" for 4G or a "gNB" for 5G) is a node through which communication devices (user equipment or "UE") connect to a core network and communicate with other communication devices or remote servers.

[0005] In the 5G architecture, the gNB internal structure may be split into at least two parts known as the Central Unit (CU) and the Distributed Unit (DU), connected by an F1 interface (or F1 Application Protocol (F1AP)). In this "split" architecture, the typically "higher" CU layer (e.g., PDCP, though not necessarily or exclusively) and the typically "lower" DU layer (e.g., RLC / MAC / PHY, though not necessarily or exclusively) may be run separately. Thus, for example, in each of the gNBs, the higher layer CU functions of some gNBs may be run centrally (e.g., by a single processing unit or in a cloud-based or virtualized system), while keeping the lower layer DU functions local.

[0006] Specifically, a gNB (referred to herein as a “distributed” gNB) may include the following functional units: gNB Central Unit (gNB-CU): A logical node that hosts the Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) layers of a gNB (or the RRC and PDCP layers of an en-gNB) that controls the operation of one or more gNB-DUs. The gNB-CU terminates the F1 interface connected to the gNB-DU. gNB Distributed Unit (gNB-DU): A logical node that hosts the Radio Link Control (RLC), Medium Access Control (MAC) and Physical (PHY) layers of a gNB or en-gNB, and its operation is partially controlled by the gNB-CU. One gNB-DU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected to the gNB-CU. gNB-CU-Control Plane (gNB-CU-CP): A logical node that hosts the control plane part of the RRC and PDCP protocols of the en-gNB or the gNB-CU for a gNB. The gNB-CU-CP terminates the so-called E1 interface (or E1 Application Protocol (E1AP)) connected to the gNB-CU-UP and the F1-C (F1 Control Plane) interface connected to the gNB-DU. gNB-CU-User Plane (gNB-CU-UP): A logical node that hosts the user plane part of the PDCP protocol of the gNB-CU for the en-gNB and the user plane part of the PDCP and SDAP protocols of the gNB-CU for the gNB. The gNB-CU-UP terminates the E1 interface connected to the gNB-CU-CP and the F1-U (F1 user plane) interface connected to the gNB-DU.

[0007] For simplicity, this application uses the term base station to refer to any such base station / gNB, and the term mobile device, user device, or UE to refer to any communication device that can connect to a core network via one or more base stations.

[0008] When using the distributed architecture described above, the division between gNB-CU and gNB-DU allows the deployment of highly centralized gNB-CUs with a large coverage area per gNB-CU, especially in terms of the control plane (gNB-CU-CP). However, in this case there is a risk that the centralized unit can become a single point of failure affecting many users. Therefore, 3GPP considers the recovery of the gNB-CU(-CP) to be of high importance and there is ongoing research into possible recovery enhancements with the following objectives: - A solution for gNB-CU-CP failure recovery should minimize the signaling load to the UE and the signaling load to the network. - The solution for gNB-CU-CP failure recovery should minimize user plane interruption, i.e., minimize service downtime from the end user's perspective. - Solutions should also be targeted to minimize control plane disruptions. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] “NGMN 5G White Paper” V1.0, Next Generation Mobile Networks (NGMN) Alliance,<https: / / www.ngmn.org / 5g-white-paper.html> Summary of the Invention [Problem to be solved by the invention]

[0010] The inventors have identified several issues that need to be addressed to provide improved recovery for distributed base stations. For example, the redundant interface (E1 / F1 / NG) of the secondary CU-CP should be pre-established even before the first UE is connected to the network via the distributed base station device. Also, in case of failure of the main unit, the UE context needs to be backed up / moved from the main unit to the secondary unit in a timely and efficient manner to avoid having to reconfigure all affected UE contexts. Furthermore, when one of the network entities detects the failure of the main (master) CU-CP, it will activate CU-CP recovery. In this case, the secondary CU-CP takes over the control of the UE and the involved entities must be notified and apply appropriate configurations to use the new (secondary) CU-CP. However, it is not yet known how such recovery activation / notification and reconfiguration is realized. [Means for solving the problem]

[0011] Accordingly, preferred embodiments of the present invention aim to provide a method and apparatus that addresses, or at least partially addresses, one or more of the problems set forth above whilst satisfying the above objectives.

[0012] For the sake of efficiency of understanding for those skilled in the art, the present invention will be described in detail in the context of a 3GPP system (NR), but the principles of the present invention can be applied to other systems employing similar distributed equipment.

[0013] In one aspect, the present invention provides a method performed by a control plane unit of a communications device including at least a control plane unit, a user plane unit, and a distributed unit, the method comprising transmitting to at least one of the user plane unit and the distributed unit information identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit.

[0014] In one aspect, the present invention provides a method performed by a communications device including a control plane unit, a user plane unit, and a distributed unit, the method including receiving information from at least one of the control plane unit and an operation and maintenance node identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit.

[0015] In one aspect, the present invention provides a method performed by a communications device including at least a control plane unit, a user plane unit and a distributed unit, the method comprising initiating a procedure for configuring the further control plane unit to act as a restoration node for the control plane unit by sending at least one signaling message to the further control plane unit, and backing up, at the restoration node, user equipment (UE) context associated with UEs served by the control plane unit.

[0016] In one aspect, the invention provides a method performed by a communications device including at least a control plane unit configured as a control plane unit, a user plane unit, and a distributed unit connecting to a further control plane unit configured as a restoration node for the control plane unit, the method comprising determining a failure of the control plane unit and sending a message to the further control plane unit for initiating a procedure to activate the further control plane unit as a restoration node.

[0017] In one aspect, the present invention provides a method performed by a control plane unit configured as a restoration node for a control plane unit of a communications device including a user plane unit and a distributed unit, the method comprising receiving, in case of a failure of the control plane unit of the communications device, a message from the user plane unit or the distributed unit for initiating a procedure for activating the restoration node, and communicating with at least one user equipment (UE) using the user plane unit or the distributed unit.

[0018] In one aspect, the present invention provides a method performed by an operation and maintenance node, comprising transmitting to a node of a communications apparatus including a control plane unit, a user plane unit and a distributed unit information identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit.

[0019] In one aspect, the present invention provides a control plane unit for a communications device including at least a control plane unit, a user plane unit, and a distributed unit, the control plane unit comprising means (e.g. a memory, a controller, and a transceiver) for transmitting information to at least one of the user plane unit and the distributed unit identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit.

[0020] In one aspect, the present invention provides a communications device including a control plane unit, a user plane unit, and a distributed unit, the communications device comprising means (e.g., a memory, a controller, and a transceiver) for receiving information from at least one of the control plane unit and an operation and maintenance node identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit.

[0021] In one aspect, the present invention provides a communications device including at least a control plane unit, a user plane unit, and a distribution unit, the communications device comprising: means (e.g., a memory, a controller, and a transceiver) for initiating a procedure to configure the further control plane unit to act as a restoration node for the control plane unit by sending at least one signaling message to the further control plane unit; and means for backing up user equipment (UE) context associated with UEs served by the control plane unit at the restoration node.

[0022] In one aspect, the present invention provides a communications device including at least a control plane unit configured as a control plane unit, a user plane unit, and a distributed unit connecting to a further control plane unit configured as a restoration node for the control plane unit, the communications device comprising means (e.g., a memory, a controller, and a transceiver) for determining a failure of the control plane unit, and means for sending a message to the further control plane unit to initiate a procedure for activating the further control plane unit as a restoration node.

[0023] In one aspect, the present invention provides a control plane unit to be configured as a restoration node for a control plane unit of a communications device including a user plane unit and a distributed unit, the control plane unit comprising: means (e.g., a memory, a controller, and a transceiver) for receiving a message from the user plane unit or the distributed unit in the event of a failure of the control plane unit of the communications device for initiating a procedure for activating the restoration node; and means for communicating with at least one user equipment (UE) using the user plane unit or the distributed unit.

[0024] In one aspect, the present invention provides an operation and maintenance node comprising means (e.g., a memory, a controller, and a transceiver) for transmitting information to a node of a communication apparatus including a control plane unit, a user plane unit, and a distributed unit, identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit.

[0025] Aspects of the present invention extend to corresponding systems, and to computer program products, such as computer readable storage media having instructions stored thereon, which are operable to program a programmable processor to perform the methods described above or in the claimed aspects and possibilities, and / or to program a suitably adapted computer to provide an apparatus as described in any of the claims.

[0026] Each feature disclosed in this specification (which term includes the claims) and / or shown in the drawings may be incorporated in the present invention independently (or in combination with) any other disclosed and / or shown feature. In particular, but not limited to, any feature of a claim dependent on a particular independent claim may be introduced into that independent claim in any combination or individually.

[0027] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0028] [Figure 1] 1 illustrates generally a mobile (cellular or wireless) telecommunications system in which embodiments of the present invention may be applied; [Diagram 2] 2 illustrates generally an exemplary method by which restoration may be provided in the system illustrated in FIG. 1 . [Diagram 3] FIG. 2 is a block diagram of a user equipment (UE) forming part of the system shown in FIG. 1. [Figure 4] 2 is a block diagram of a base station forming part of the system shown in FIG. 1; [Diagram 5] FIG. 2 is a block diagram of a core network node (or function) forming part of the system shown in FIG. [Figure 6] 2 is a schematic signaling (timing) diagram illustrating an exemplary manner in which an embodiment of the present invention may be implemented in the system of FIG. 1. [Figure 7]2 is a schematic signaling (timing) diagram illustrating an exemplary manner in which an embodiment of the present invention may be implemented in the system of FIG. 1. [Figure 8] 2 is a schematic signaling (timing) diagram illustrating an exemplary manner in which an embodiment of the present invention may be implemented in the system of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] overview FIG. 1 illustrates diagrammatically a mobile (cellular or wireless) telecommunications system 1 in which embodiments of the present invention are applicable.

[0030] In this network, users of mobile devices 3 (UE) can communicate with each other and other users via respective base stations 5 and a core network 7 using an appropriate 3GPP Radio Access Technology (RAT), e.g., 5G RAT. It will be appreciated that several base stations 5 form a (Radio) Access Network or (R)AN. As will be appreciated by those skilled in the art, for illustrative purposes, while one mobile device 3 and one base station 5 are shown in FIG. 1, the system, when implemented, will typically include other base stations and mobile devices (UE).

[0031] Each base station 5 controls (directly or via other nodes such as home base stations, repeaters, remote radio heads, and / or distributed units) one or more associated cells. Base stations 5 supporting next generation / 5G protocols may be referred to as "gNBs". It will be appreciated that some base stations 5 may be configured to support both 4G and 5G, and / or any other 3GPP or non-3GPP communication protocols.

[0032] As shown in Figure 1, the functionality of the gNB5 (referred to herein as a "distributed" gNB) may be split into one or more distributed units (DUs) and a central unit (CU), where the CU typically performs higher level functions and communication with the next generation core, and the DU performs lower level functions and communication over the air interface with nearby UEs 3 (i.e., in the cell operated by the gNB5). In this example, the distributed gNB5 includes the following functional units or logical nodes: i) a gNB central unit (gNB-CU), which may be further split into a gNB-CU-Control Plane Unit 5C (gNB-CU-CP) and one or more gNB-CU-User Plane Units 5U (gNB-CU-UP), and ii) one or more gNB distributed units 5D (gNB-DUs).

[0033] The gNB-CU-CP5C and each gNB-CU-UP5U are connected via an E1 interface (E1AP). The gNB-CU and each gNB-DU5D are connected via an F1 interface (F1AP) between them. The gNB-CU-CP5C and gNB-DU5D are connected via an F1-C (F1 control plane) interface, while the gNB-CU-UP5U and each gNB-DU5D are connected via an F1-U (F1 user plane) interface.

[0034] The gNB-CU-CP 5C hosts the control plane parts of the RRC and PDCP protocols of the en-gNB or gNB-CU for a gNB. The gNB-CU-UP 5U hosts the user plane parts of the PDCP and SDAP protocols of the gNB-CU for a gNB (SDAP is not applicable for en-gNB). Each gNB-DU 5D supports at least one cell (however, each cell is supported by only one gNB-DU 5D).

[0035] The mobile device 3 and its serving base station 5 connect via an appropriate air interface (such as, for example, the so-called "NR" air interface and / or the "Uu" interface). Neighboring base stations 5 connect to each other via appropriate inter-base station interfaces (such as, for example, the so-called "Xn" interface and / or the "X2" interface). The base stations 5 also connect to core network nodes via appropriate interfaces (such as, for example, the so-called "NG-U" interface (for the user plane) and / or the so-called "NG-C" interface (for the control plane).

[0036] The core network 7 typically includes logical nodes (or "functions") for supporting communications in the telecommunications system 1. Typically, for example, the core network 7 of a "next generation" / 5G system includes, among other functions, a Control Plane Function (CPF) and a User Plane Function (UPF). For example, the core network 7 may include at least an Access and Mobility Management Function (AMF) 8 and a Session Management Function (SMF) 9. Connectivity to external IP networks 10 (such as the Internet) may also be provided from the core network 7.

[0037] Figure 2 shows diagrammatically the components and other nodes of a distributed base station, including the interfaces between them, when a restoration configuration is prepared. In more detail, the UE 3 is served by the DU 5D (at least one DU) using an appropriate air interface (in case of a wireless UE). The DU 5D connects to the CU-UP 5U via an F1-U interface (user plane) and to the associated (main or master) CU-CP 5C via an F1-C interface (control plane). The CU-CP 5C and the CU-UP 5U connect to each other via an E1 interface. The CU-CP 5C connects to the core network (AMF 8) via an NG interface (NGAP in Figure 2).

[0038] The main (or initial) CU-CP5C is hereinafter referred to as the master CU-CP5C. As mentioned above, the master CU-CP5C can be a single point of failure. To provide resiliency for this scenario, the system also sets up a further CU-CP5C' that acts as a backup node in case the master CU-CP5C fails. The further CU-CP5C' is hereinafter referred to as the second or secondary CU-CP5C'. Thus, as shown in FIG. 2, redundant F1 / E1 / NG connections are set up via the secondary CU-CP5C', although these connections may not be used initially. It will be appreciated that (at least some of) the redundant connections may be prepared before any UE 3 is connected to the main CU-CP5C (or during the procedure of connecting the first UE 3).

[0039] There are various ways in which these redundant connections may be established to the secondary CU-CP 5C'. For example, the master CU-CP 5C may configure a suitable resilient CU-CP 5C' as part of the E1 or F1 setup procedure (or E1 or F1 change procedure). The resilient configuration may beneficially include the address (TNL address) and name of the secondary CU-CP 5C' and the associated failure timer (or any other suitable aiding information for determining CU-CP failure). In this case, the address and name are used by the nodes (CU-UP 5U and DU 5D) to set up a suitable resilient connection with the secondary CU-CP 5C', and the failure time / aiding information is used during the operation to determine whether the resilient connection needs to be activated (i.e. in case of CU-CP failure).

[0040] Beneficially, the CU-UP 5U and DU 5D may obtain the address and name of the secondary CU-CP 5C' and associated failure timers from the master CU-CP 5C or another node (e.g., Operation and Management (OAM)). The CU-UP / DU and master CU-CP 5C may use existing messages with new information elements indicating at least one of the address, name, and failure timers associated with the secondary CU-CP 5C'. Alternatively, dedicated messages may be used to deliver some or all of this information to the CU-UP 5C and DU 5D.

[0041] To achieve timely and efficient recovery from a master CU-CP 5C failure, the related UE context is backed up so that it can be acquired and used by the secondary CU-CP 5C' without delay or data loss and without the need for excessive signaling. Specifically, the related UE context may be backed up in the secondary CU-CP (or AMF / SMF, etc.) when setting up / changing / releasing the UE context in the master CU-CP. Alternatively, a similar procedure may be used upon failure (or overload) of the master CU-CP to move the related UE context to the secondary CU-CP (optionally AMF / SMF). Thus, the backed up / moved UE context may be used by the secondary CU-CP 5C' and other nodes to restore UE services after failure (or overload) of the master CU-CP.

[0042] Beneficially, when one of the network entities (e.g. DU 5D or CU-UP 5U) detects a failure of the serving CU-CP 5C, it activates the CU-CP recovery by sending an appropriate activation message to the secondary CU-CP 5C', which takes over control of the UE 3 and informs the relevant entities so that the appropriate recovery configuration can be applied.

[0043] Beneficially, the above solution requires a relatively small amount of signaling to the UE and the network during gNB-CU-CP failure recovery, while at the same time, user plane interruption / service downtime from the end user's perspective is kept to a minimum with minimal control plane interruption.

[0044] Mobile Devices FIG. 3 is a block diagram illustrating the main components of the mobile device 3 (e.g., a mobile phone or Internet of Things (IoT) device) shown in FIG. 1. As shown, the mobile device 3 has a transceiver circuit 31 operable to transmit signals to and receive signals from a base station 5 via one or more antennas 33. The mobile device 3 has a controller 37 that controls the operation of the mobile device 3. The controller 37 is associated with a memory 39 and connects to the transceiver circuit 31. Although not necessary for its operation, the mobile device 3 may of course have all the usual features of a conventional mobile phone (such as a user interface 35), which may be suitably provided by any one or any combination of hardware, software, and firmware. The software may be pre-installed in the memory 39 and / or downloaded, for example, over a telecommunications network or from a removable data storage device (RMD).

[0045] The controller 37 is configured, in this example, to control the overall operation of the mobile device 3 by means of program or software instructions stored in memory 39. As shown, these software instructions include, among other things, an operating system 41 and a communications control module 43.

[0046] The communications control module 43 is operable to control communications between the mobile device 3 and its serving base station 5 (and other communications devices connected to the serving base station 5, e.g., other user equipment, core network nodes, etc.).

[0047] It will be appreciated that the communications control module 43 may include several sub-modules (or "layers") that support specific functions. For example, the communications control module 43 may include a Physical (PHY) layer sub-module, a Medium Access Control (MAC) sub-module, a Radio Link Control (RLC) sub-module, a Packet Data Convergence Protocol (PDCP) sub-module, a Service Data Adaptation Protocol (SDAP) sub-module, an Internet Protocol (IP) sub-module, a Radio Resource Control (RRC) sub-module, a Non-Access Stratum (NAS) sub-module, etc.

[0048] base station FIG. 4 is a block diagram illustrating the main components of the distributed base station 5 shown in FIG. 1. As shown, the base station 5 has a transceiver circuit 51 for transmitting signals to and receiving signals from user equipment (such as mobile device 3) via one or more antennas 53, a network interface 55 (e.g., NG-C / NG-U interface, etc.) for transmitting signals to and receiving signals from the core network 7, and a base station interface 56 (e.g., Xn interface, etc.) for transmitting signals to and receiving signals from neighboring base stations. The base station 5 has a controller 57 that controls the operation of the base station 5 according to software stored in a memory 59. The software may be pre-installed in the memory 59 and / or may be downloaded, for example, via the telecommunications network 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 61 and at least a communication control module 63. Although not shown in FIG. 3, the network interface 55 also typically includes an inter-base station interface module (e.g., Xn) and a core network interface module (e.g., NG-C / NG-U).

[0049] The communication control module 63 is responsible for handling (generating / sending / receiving) signaling between the base station 5 and other nodes, such as the UE 3 and core network nodes. Such signaling may include, for example, control data (e.g., NAS, RRC, paging, and / or system information, etc.) for managing the operation of the mobile device 3. It will be appreciated that the communication control module 63 may include several sub-modules (or "layers") that support specific functions. For example, the communication control module 63 may include a PHY sub-module, a MAC sub-module, an RLC sub-module, a PDCP sub-module, an SDAP sub-module, an IP sub-module, an RRC sub-module, etc.

[0050] When the base station 5 comprises a distributed gNB or en-gNB, the network interface 55 also comprises an E1 interface and an F1 interface (F1-C for control plane and F1-U for user plane) for communicating signals between the respective functions of the distributed gNB or en-gNB. In this case, the software also includes at least one of a gNB-CU-CP module 5C, a gNB-CU-UP module 5U, and a gNB-DU module 5D. If present, the gNB-CU-CP module 5C hosts the control plane portion of the RRC layer and the PDCP layer of the distributed gNB or en-gNB. If present, the gNB-CU-UP module 5U hosts the user plane portion of the PDCP layer and the SDAP layer of the distributed gNB or the user plane portion of the PDCP layer of the distributed en-gNB. If present, the gNB-DU module 5D hosts the RLC layer, the MAC layer, and the PHY layer of the distributed gNB or en-gNB.

[0051] It will be appreciated by those skilled in the art that the central units (e.g., 5C and / or 5U) may be implemented and physically collocated with the base stations, or may be implemented remotely, as a single physical entity, or as a cloud-based or virtualized system. It will also be appreciated that a single central unit may serve multiple base stations 5.

[0052] Core Network Node FIG. 5 is a block diagram illustrating the main components of a typical core network node (or function) shown in FIG. 1, e.g., AMF 8 or SMF 9. As shown, the core network node includes a transceiver circuit 71 operable to transmit signals to and receive signals from other nodes (including UE 3 and (R)AN node 5) via a network interface 75. A controller 77 controls the operation of the core network node according to software stored in memory 79. The software may be pre-installed in memory 79 and / or may be downloaded, for example, via the telecommunications network 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 81 and at least a communication control module 83. The communication control module 83 is responsible for handling (generating / sending / receiving) signaling between the core network node and other nodes, such as UE 3, (R)AN node 5, and other core network nodes.

[0053] operation As mentioned above, the system 1 includes a distributed base station apparatus 5 serving several UEs 3 via one or more distributed units 5D (labeled "gNB-DU" in FIG. 1 and "DU" in FIGS. 2 and 6). A central unit (CU) part of the distributed base station apparatus 5 is responsible for controlling the control plane and user plane operation related to the UEs 3. The user plane part of the central unit is called CU-UP 5U (or "gNB-CU-UP" in FIG. 1), which is effectively a logical node that hosts the user plane part of the PDCP protocol (and SDAP protocol, where appropriate) of the distributed base station apparatus 5. The control plane part of the central unit is called CU-CP 5C (or "gNB-CU-CP" in FIG. 1), which is effectively a logical node that hosts the control plane part of the RRC protocol and the PDCP protocol of the distributed base station apparatus 5.

[0054] A more detailed description will now be given (with reference to Figures 6 to 8) of various aspects of restoration in the systems shown in Figures 1 and 2. In more detail, Figure 6 illustrates generally an exemplary procedure for establishing a redundant connection to a secondary node (in this case an E1 / F1 / NG connection), Figure 7 illustrates generally an exemplary UE context backup procedure and Figure 8 illustrates generally an exemplary procedure for restoration activation.

[0055] Redundant Connection 6 illustrates, in schematic form, some possible ways in which a redundant connection to a secondary CU-CP5C' may be established. It will be appreciated that (at least part of) the procedure may be performed before any UE 3 is connected to the main CU-CP5C, or during the procedure of connecting the first (or second, etc.) UE 3.

[0056] In particular, the steps shown in Figure 6 may be applied to at least one of the following: i) establishing a redundant E1 connection between the CU-UP 5U and the secondary CU-CP 5C', ii) establishing a redundant F1 (control plane) connection between the DU 5D and the secondary CU-CP 5C', and iii) establishing a redundant NG connection between the AMF 8 and the secondary CU-CP 5C'. It will also be appreciated that the same (or similar) procedures may be used to modify or re-establish one or more existing connections as appropriate.

[0057] 6, an exemplary E1 setup procedure is shown at steps 1, 1a, 1b, 2, and 2a, an exemplary NG setup procedure is shown at steps 3 and 3a, and an exemplary F1 setup procedure is shown at steps 4, 4a, 4b, 5, and 5a. It will be appreciated that the E1 / NG / F1 procedures may be performed in different orders (and / or independently of each other).

[0058] In this example, the procedure begins with E1 setup between the CU-UP 5U and the master CU-CP 5C. As can be seen, in step 1, the CU-UP 5U generates and sends (using its associated communication control module 63) an appropriately formatted message to initiate E1 setup between the CU-UP 5U and the CU-CP 5C (acting as the master CU-CP). The CU-CP 5C may be selected based on information provided by the UE 3, the AMF 8, and / or any other nodes, where appropriate.

[0059] If the (master) CU-CP5C can accept this connection request, it generates and sends an appropriate response (e.g., an "E1 Setup Response") to the CU-UP5U. In one option, as generally shown in step 1a, the CU-CP5C may be configured to include in this message appropriate information relating to the appropriate redundant / secondary CU-CP5C'. For example, the E1 Setup Response message (or similar) may include one or more of the following: a name of at least one redundant / secondary CU-CP5C', a Transport Network Layer (TNL) address of each of the at least one redundant / secondary CU-CP5C', and information identifying a timer associated with the at least one redundant / secondary CU-CP5C'. In another option, as generally shown in step 1b, the CU-CP5C may be configured to include the above information in a different message (e.g., a message sent after the E1 Setup Response message). In this case, the E1 Setup Response message of step 1a need not include this information. However, it will be appreciated that the message sent in step 1b may be used to update or supplement any information included in the E1 setup response message. The message sent in step 1b may include a subsequent E1 setup response message, or a message related to an E1 reconfiguration or E1 modification (e.g., an E1 reconfiguration / modification request or related response message).

[0060] In step 2, the CU-UP5U initiates a procedure to establish a restoration E1 tunnel based on the information received in step 1a / 1b. Specifically, the CU-UP5U generates and transmits (using its associated communication control module 63) a properly formatted message to initiate an E1 setup between the CU-UP5U and the CU-CP5C' (acting as a secondary CU-CP for the CU-UP5U) identified in step 1a / 1b. The message may include information indicating that the E1 setup is to provide restoration (e.g., an appropriate "Restoration E1" indication, etc.). The restoration indication may be provided, for example, using an appropriate information element or flag. The message may also include information identifying the master CU-CP5C (not shown in FIG. 6) that may be used to establish / configure a connection (e.g., Xn) between the master CU-CP5C and the secondary CU-CP5C'.

[0061] In step 2a, the secondary CU-CP5C' accepts the E1 setup request and provides its own identifier (e.g., an appropriate "Master CU XnAP ID") associated with the master CU-CP5C for use by other nodes to identify the master CU-CP5C in the event of a failure and to activate a restoration connection if necessary.

[0062] Steps 3 and 3a show an exemplary procedure for connecting the secondary CU-CP5C' to the AMF8 (or another suitable AMF8) serving the master CU-CP5C. In this example, NG setup request / response messages are used, but it will be appreciated that other suitable messages (such as NG change request / response messages) may be used when appropriate. As can be seen, steps 3 and 3a may be performed in response to the establishment of the restoration E1 tunnel (after step 2) or at another time (after step 5) (e.g., as part of the procedure for connecting the secondary CU-CP5C' to the distributed unit 5D serving the master CU-CP5C). In other words, the connection establishment / change between the secondary CU-CP5C' and the AMF8 may be triggered by a message from the CU-UP5U or a message from the DU5D. Alternatively, although not shown in FIG. 6, the master CU-CP5C may be configured to send a message to the secondary CU-CP5C' (e.g., via Xn) to trigger the connection establishment / change between the secondary CU-CP5C' and the AMF8.

[0063] The following is a description of the procedures involved in establishing an F1 connection to support the recovery of a distributed base station device 5. As shown in step 4, the DU 5D initiates the setup of an appropriate connection with the first (master) CU-CP 5C by generating and sending an F1 setup request (using its associated communication control module 63) to the CU-CP 5C. This request may include an appropriate indication of whether the DU 5D requires (or supports) a redundant F1 tunnel, although it will be appreciated that such an indication may be entirely optional (or implicit).

[0064] As shown in step 4a, the first (master) CU-CP5C responds by generating and sending (using its associated communications control module 63) an appropriately formatted F1 setup response. In this case, the response may include one or more of the following: the name of at least one redundant / secondary CU-CP5C', the TNL address of each of the at least one redundant / secondary CU-CP5C', and information identifying a timer associated with the at least one redundant / secondary CU-CP5C'. Alternatively, as shown generally in step 4b, the CU-CP5C may be configured to include the above information in a different message adapted to provide an F1 recovery configuration (sent after the F1 setup response message). In this case, the F1 setup response message of step 4a need not include this information (or may only include a portion of it). However, it will be appreciated that the message sent in step 4b may be used to update or supplement any information included in the F1 setup response message. The message sent in step 4b may include a subsequent F1 setup response message, or a message related to an F1 reconfiguration or F1 modification (eg, an F1 reconfiguration / modification request or associated response message).

[0065] Based on the information received in step 4a / 4b, the DU5D initiates a procedure to establish a restoration F1 connection. Specifically, the DU5D generates and transmits (using its associated communication control module 63) a properly formatted message to initiate an F1 setup between the DU5D and the CU-CP5C' (acting as a secondary CU-CP for the DU5D) identified in step 4a / 4b. The message may include information indicating that the F1 setup is for providing restoration (e.g., an appropriate "Restoration F1" indication, etc.). The restoration indication may be provided, for example, using an appropriate information element or flag. The message may also include information identifying the master CU-CP5C (not shown in FIG. 6) that may be used to establish / configure a connection (e.g., Xn) between the master CU-CP5C and the secondary CU-CP5C'.

[0066] In step 5a, the secondary CU-CP 5C' accepts the F1 setup request and provides its own identifier associated with the master CU-CP 5C (eg, the appropriate "Master CU XnAP ID").

[0067] In summary, the above procedure allows for establishing / configuring an appropriate connection to a secondary CU-CP5C' that can act as a redundant node for the master CU-CP5C in the event that the master CU-CP5C fails (or becomes overloaded). Beneficially, the redundant E1 / F1 / NG connection to the secondary CU-CP5C' can be established before any UE 3 is connected to the master CU-CP5C (or in any case, before the master CU-CP5C fails or becomes overloaded).

[0068] For completeness, it will be appreciated that any establishment of redundant connections (E1 / NG / F1 in steps 2, 3, and 5, respectively) may be performed any time after the name / TNL address / failure timer of the secondary CU-CP5C' has been sent from the master CU-CP5C (or otherwise known). It will further be appreciated that steps 2, 3, and 5 need not be in any particular order. For example, the messages in steps 2 and 4 may be sent substantially simultaneously. As shown, step 3 (Restoration NG Setup) may be triggered by either or both of steps 2 or 5 (i.e., by any message that includes an indication associated with the restoration connection involving CU-CP5C'). It will also be appreciated that step 5 (Restoration F1 Establishment) may be triggered by the initial F1 establishment (i.e., steps 4 / 4a / 4b) even before the completion of the initial F1 establishment. As mentioned above, steps 1b and 4b are optional. They may be used when the messages in steps 1a and 3a do not include information related to the secondary CU-CP5C' or when such information needs to be updated.

[0069] With regard to the TNL address, secondary CU-CP name, and failure timer, it will be appreciated that the CU-CP 5C or DU 5D may obtain any of this information using messages forming part of the F1 / E1 set-up procedure (in the case of step 1 / 4) or any other suitable messages (in the case of step 1a / 4a). The information (or at least part of it) may also be obtained from other sources, for example the OAM.

[0070] UE Context Backup FIG. 7 is a schematic timing (signaling) diagram illustrating an example procedure for UE context backup to improve recovery of distributed base stations.

[0071] This procedure has the following objectives (among others): - backing up the UE context in a secondary CU-CP / AMF / SMF, e.g. when the UE context is set up / modified / released in the master CU-CP, in order to be able to restore the UE service in case of a failure (or overload) of the master CU-CP; and - moving all UE contexts associated with a serving (master) CU-CP to a secondary CU-CP (optionally AMF / SMF) when the serving CU-CP fails (or becomes overloaded); It can be used in at least one of the above.

[0072] It will be appreciated that the latter case may involve a relatively large amount of signaling messages at substantially the same time. Nevertheless, if the PDCP configuration is negotiated between the master CU-CP and the secondary CU-CP, sending an RRC reconfiguration message to the UE may not be necessary.

[0073] Turning now to the specific procedure shown in Figure 7, the main options are (among others): - the master CU-CP may initiate establishment or modification of a redundant UE context with the secondary CU-CP (step 2); - the CU-UP may initiate the establishment or modification of a redundant UE context with a secondary CU-CP (step 6); and - the DU may initiate establishment or modification of a redundant UE context with a secondary CU-CP (step 8); It is expected.

[0074] It will be appreciated that initially, at least one UE 3 is connected to the master CU-CP 5C (and other units of the distributed base station) after performing the appropriate UE attach procedure (as generally shown in step 1).

[0075] In step 2, after (or in response to) a UE attach / service request from the UE 3, the master CU-CP5C generates and sends (using its associated communication control module 63) an appropriately formatted signaling message to back up the UE context associated with the connected UE 3. In this example, the master CU-CP5C sends the signaling message via the base station to a base station interface, such as the Xn interface. It will be appreciated that step 2 may be performed for each newly connected UE 3, for a group of UEs (e.g. when a minimum number of UEs is reached), and / or periodically (e.g. after expiry of an associated timer). In this example, the master CU-CP5C sends a "UE recovery setup request" message (or a "UE recovery modification request" message) to the secondary CU-CP5C'. The message includes information identifying the UE (e.g. by its associated UE XnAP ID, etc.) and the corresponding UE context. It will also be appreciated that a similar UE context backup may be initiated by another node using a similar UE recovery setup / modification request message or any other suitable message, as described below with reference to steps 6 and 8.

[0076] If the secondary CU-CP5C' can accept the request from the master CU-CP5C, it generates and sends an appropriate response (e.g., "UE recovery setup response" or "UE recovery change response"). If the secondary CU-CP5C' cannot accept the request from the master CU-CP5C, it generates and sends an appropriate "UE recovery setup failed" or "UE recovery change failed" message to the master CU-CP5C, including an appropriate error cause (not shown in Figure 7).

[0077] When the master CU-CP5C sends the UE context to the secondary CU-CP5C' in step 2, the master CU-CP5C may also include the applicable PDCP configuration in the UE context (for each UE). However, if the secondary CU-CP5C' does not (or cannot) accept a UE context with a particular PDCP configuration, the secondary CU-CP5C' may be configured to return an appropriate message identifying that particular UE context (by its UE XnAP ID) and, if appropriate, including a modified (supported) UE context / PDCP configuration. For example, the secondary CU-CP5C' may determine that the secondary CU-CP5C' does not support a particular PDCP configuration (e.g., due to an unsupported encryption algorithm, header compression algorithm, etc.). In this case, the secondary CU-CP5C' may send a modified UE context with a supported PDCP configuration to the master CU-CP5C, as generally shown in step 2a. If the master CU-CP5C accepts the PDCP configuration provided in step 2a, it notifies the secondary CU-CP5C' (e.g., by sending a UE recovery setup / modification request accept message) and includes the associated UE XnAP ID and the accepted (modified) UE context. If the master CU-CP5C does not accept the PDCP configuration provided in step 2a, it sends a rejection message (e.g., a UE recovery setup / modification request reject message) to the secondary CU-CP5C' including the UE XnAP ID related to the rejected UE context. It will be appreciated that the PDCP configuration may also be referred to as an RRC context (including appropriate PDCP, RLC, MAC, PHY configurations). Although not shown in FIG. 7, the master CU-CP5C may be configured to select a different secondary node for rejected UE contexts to ensure recovery for those UEs as well (i.e., to back up such UE contexts at a different node).

[0078] After the secondary CU-CP5C' has been selected for recovery (backup / redundancy) for at least one UE 3 (at least one UE context), the secondary CU-CP5C' proceeds to generate and send (using its associated communication control module 63) an appropriately formatted signaling message to the AMF 8 in step 3. This message (e.g., "UE Recovery Setup Request" message) is to inform the AMF 8 (and other associated core network nodes, if any) about the selection of the secondary CU-CP5C' for recovery and to initiate the setup of an appropriate NG connection between the AMF 8 and the secondary CU-CP5C' (and the UE 3). This message may use UE-related signaling and may include an identifier associated with the UE 3 (e.g., a UE NGAP ID or similar identifier used by the secondary CU-CP5C'). The message may also include information related to a protocol data unit (PDU) session for the UE 3, although it will be appreciated that a default PDU session may be used instead (e.g., in the absence of PDU session information). Advantageously, each PDU session corresponds to a respective PDU session included in the received UE context. The secondary CU-CP5C' may need to establish these PDU sessions (or at least a default PDU session) so that the UE 3 can continue to communicate uninterrupted with the secondary CU-CP5C' if the master CU-CP5C fails.

[0079] As generally shown in step 4, the AMF 8 requests the SMF 9 to create the relevant session management context for recovery. The request (e.g., "Nsmf_PDUSession_CreateSMContext request") includes information identifying the UE 3 to which the request relates and information indicating the reason for this request (recovery). The indication may be provided, for example, using an appropriate information element or flag. As shown in step 4a, the SMF 9 confirms the creation of the session management context for recovery by sending an appropriately formatted response (e.g., "Nsmf_PDUSession_CreateSMContext response" etc.). In case the master CU-CP 5C fails, the SMF 9 switches the relevant path to the secondary CU-CP 5C' (e.g., as part of the procedure described with reference to Figure 8). The SMF 9 knows which CU-CP is the recovery node and which PDU session to use from the "UE recovery indication" included in message 4 of Figure 7.

[0080] The AMF 8 then generates and sends (using its communication control module 83) an appropriately formatted signaling message to the secondary CU-CP5C' in step 3a. This message (e.g., a "UE Recovery Setup Response" message) completes the setup of the NG connection between the AMF 8 and the secondary CU-CP5C' (and the UE 3). The message includes the appropriate UE identifier (UE NGAP ID). It will be appreciated that after step 3a, the secondary CU-CP5C' may also send an appropriate confirmation to the master CU-CP5C (similar to step 2a) indicating that it is prepared to serve the master CU-CP5C as a redundant node.

[0081] Turning now to the case of UE context backup initiated by the CU-UP 5U, it will be appreciated that the messages sent in step 6 are similar to those described above with reference to step 2. However, in this case the CU-UP 5U uses its own UE identifier, such as the so-called "UE E1AP ID". If the UE context backup was successful, the secondary CU-CP 5C' generates and sends an appropriate response to the CU-UP 5U in step 6a (the secondary CU-CP 5C' may also proceed to step 3, if applicable).

[0082] Finally, step 8 shows the UE context backup procedure initiated by the DU 5D. It will be appreciated that the messages sent in step 8 and the response in step 8a are similar to those described above with reference to steps 2 and 2a, respectively. However, in this case, the DU 5D uses its own UE identifier, such as the so-called "UE F1AP ID". After the UE context backup is successful, the secondary CU-CP 5C' may also proceed to step 3, if necessary.

[0083] For completeness, Figure 7 also shows an exemplary bearer context setup procedure (steps 5 and 5a) between the master CU-CP 5C and the CU-UP 5U to set up an appropriate bearer for the UE 3. Figure 7 also shows an exemplary UE context setup procedure (steps 7 and 7a) between the master CU-CP 5C and the DU 5D to set up the associated UE context in the distributed unit serving the UE 3.

[0084] It will be appreciated that step 2, step 5, and / or step 7 may be performed substantially simultaneously. In any case, the various procedures shown in FIG. 7 need not be performed in any particular order. UE recovery may be established (or modified) by either step 2, step 6, or step 8. In other words, UE recovery may be established and / or modified by the master CU-CP 5C, the CU-UP 5U, or the DU 5U. It will be appreciated that the message in steps 6 / 8 / 10 may be a UE recovery modification request if the UE context (e.g., data or signaling radio bearer) is modified. Step 3 (and subsequently step 4) may be triggered by either step 2, step 6, and step 8 (as they are alternatives). Thus, regardless of which node requests the secondary CU-CP 5C′ to act as a redundant unit for recovery, the secondary CU-CP 5C′ may update the relevant core network nodes accordingly.

[0085] CU-CP recovery activation FIG. 8 illustrates generally an exemplary procedure for activating a recovery CU-CP (and activating any backup UE context held by the recovery CU-CP) in the event of a serving CU-CP (master CU-CP) failure.

[0086] As generally shown in step 1, a failure of the master CU-CP 5C may be detected by either the associated DU 5D or CU-UP 5U due to a failure associated with the Stream Control Transmission Protocol (SCTP) for at least one UE 3. For example, the failure may be detected based on expiration of an associated timer, such as the "failure timer" described above with reference to Figure 6.

[0087] In this example, the DU5D determines in step 1 that a failure timer associated with the master CU-CP5C expired before the master CU-CP5C was able to recover from the SCTP failure. Thus, when the DU5D determines that the SCTP problem lasted longer than the maximum duration allowed by the associated failure timer, it generates and sends (using its associated communication control module 63) an appropriately formatted message to the secondary CU-CP5C' to activate recovery in step 2. Alternatively, as generally shown in step 3, the CU-UP5U may determine the failure of the master CU-CP5C (based on the associated failure timer) and send a message to the secondary CU-CP5C' to activate recovery.

[0088] The DU5D / CU-UP5U includes in the message an identifier of the master CU-CP5C (such as the master CU XnAP ID) to indicate which node is considered to have failed, so that the secondary CU-CP5C' can obtain the associated UE context. In steps 2a / 3a, the secondary CU-CP5C' indicates that it is now acting as the new serving CU-CP. Specifically, the secondary CU-CP5C' generates and sends an appropriate "Recovery Notification" message (and / or the like) to the CU-UP5U (if the message in step 2 is sent by the DU5D) or to the DU5D (if the message in step 3 is sent by the CU-UP5U). It will be appreciated that the secondary CU-CP5C' may notify both the DU5D and the CU-UP5U. In other words, both steps 2a and 3a may be performed after either step 2 or step 3. Effectively, the message of step 2a / 3a (which may be any suitable message) serves as an indication to corresponding nodes that restoration has been activated (and / or that the master node has failed), so that they can apply the relevant restoration configuration.

[0089] Effectively, from this point on, the secondary CU-CP behaves as the new master CU-CP for the associated UE 3. Where appropriate, the new master CU-CP may proceed to carry out any of the procedures described above with reference to Figures 6 and 7 to ensure that a new recovery CU-CP is prepared and to perform appropriate UE context backup. It will be appreciated that, although not shown in Figure 8, the SMF 9 switches the associated path / PDU session to the secondary CU-CP 5C', as configured in messages 4 and 4a of Figure 7.

[0090] If necessary, an RRC reconfiguration may take place between the new CU-CP 5C' and the UE 3. However, it will be appreciated that this step may be omitted if the master CU-CP and secondary CU-CP use the same PDCP configuration (e.g., if they both support the original PDCP configuration, or if they have agreed on the appropriate (supported) PDCP configuration / RRC context as described above with reference to steps 2a and 2b of Figure 7).

[0091] In summary, one of the network entities activates CU-CP recovery when it detects a failure of the serving CU-CP. The secondary CU-CP takes over control of the UE and informs the relevant entities so that they can apply the appropriate recovery configuration.

[0092] Modifications and Substitutions Detailed embodiments have been described above. Those skilled in the art will appreciate that several modifications and alternatives can be made to the above embodiments while still benefiting from the invention embodied therein. By way of example, only some of these alternatives and modifications are described herein.

[0093] With respect to step 1 of Figure 8, it will be appreciated that a relatively short SCTP error from which the DU / CU-UP can recover before the expiration of the failure timer may not trigger a CU-CP recovery procedure. Thus, by setting (agreeing on) the value of the failure timer, the DU / CU-UP and the master CU-CP can control how much data loss is tolerable before it becomes necessary to activate the backup UE context held by the secondary CU-CP.

[0094] Although the above description uses a distributed base station as an example, it will be appreciated that the above techniques for providing recovery and UE context backup / mobility may be applied to other similar communication devices comprising at least a control plane unit and a user plane unit (and appropriate interfaces between the relevant units), such communication devices (at least one unit of which) may be located in a (radio) access network or in a core network.

[0095] In the above description, for ease of understanding, the UE, (R)AN node (distributed base station), and core network node are described as having several separate modules (such as a communication control module). These modules may be provided in this way for certain applications, e.g., where an existing system is being modified to implement the invention, and in other applications, e.g., in systems designed from the beginning with the features of the invention in mind, but these modules may not be identifiable as separate entities because they may be incorporated into an overall operating system or code. These modules may be implemented in software, hardware, firmware, or a combination of these.

[0096] Each control unit may comprise any suitable form of processing circuitry including, but not limited to, one or more hardware-implemented computer processors, microprocessors, Central Processing Units (CPUs), Arithmetic Logic Units (ALUs), Input / Output (IO) circuitry, internal memory / cache (program and / or data), processing registers, communication buses (e.g., control buses, data buses, and / or address buses), Direct Memory Access (DMA) facilities, and / or hardware or software implemented counters, pointers, and / or timers.

[0097] In the above embodiment, several software modules have been described. Those skilled in the art will recognize that the software modules may be provided in compiled or uncompiled form and may be provided to the UE, the (units of) the distributed base station, and the core network node as a signal via a computer network or on a recording medium. Furthermore, the functions performed by part or all of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred as it makes it easier to update them to update the functionality of the UE, the distributed base station / (R)AN node, and the core network node.

[0098] User equipment (or "UE", "mobile station", "mobile device", or "wireless device") in this disclosure is an entity that connects to a network via a wireless interface.

[0099] It should be noted that the present disclosure is not limited to dedicated communication devices, but can be applied to any device having communication capabilities (and associated UE context). The terms "user equipment" or "UE" (as that term is used in 3GPP), "mobile station", "mobile device", and "wireless device" are generally intended to be synonymous with each other and include standalone mobile stations such as terminals, cell phones, smartphones, tablets, cellular IoT devices, IoT devices, and machines. It will be appreciated that the terms "mobile station" and "mobile device" also encompass devices that remain stationary for long periods of time.

[0100] For simplicity, the present application will often refer to mobile devices in the description, however, it will be appreciated that the described techniques may be implemented on any communications device (mobile and / or substantially fixed) capable of connecting to a communications network to send / receive data, regardless of whether such communications device is controlled by human input or by software instructions stored in memory.

[0101] The communication devices may be, for example, mobile communication devices such as mobile phones, smartphones, user equipment, personal digital assistants, laptop / tablet computers, web browsers, and / or e-book readers. Such mobile (or even substantially fixed) devices are typically operated by a user. However, the 3GPP standards also allow so-called "Internet of Things" (IoT) devices (e.g., Narrow-Band IoT (NB-IoT) devices) to be connected to the network, which typically includes various measurement equipment, telemetry equipment, monitoring systems, tracking and tracing devices, in-vehicle safety systems, vehicle maintenance systems, road sensors, digital billboards, point of sale (POS) terminals, and automated equipment such as remote control systems. Effectively, the Internet of Things is a network of devices (or "things") equipped with appropriate electronics, software, sensors, and / or network connectivity, etc., that enable these devices to collect and exchange data with each other and with other communication devices. It will be appreciated that IoT devices may also be referred to as Machine-Type Communication (MTC) communication devices or Machine-to-Machine (M2M) communication devices.

[0102] The information identifying the further control plane unit may be transmitted as part of at least one of a procedure for setting up a first interface (e.g., E1) between the control plane unit and a user plane unit, a procedure for setting up a second interface (e.g., F1) between the control plane unit and a distributed unit, a procedure for setting up a third interface (e.g., NG) between the control plane unit and a core network node, a procedure for modifying the first interface, a procedure for modifying the second interface, and a procedure for modifying the third interface. The information identifying the further control plane unit may include at least one of an address of the further control plane unit, a name of the further control plane unit, and an identifier of the further control plane unit.

[0103] The method performed by the control plane unit may further include initiating a procedure to set up at least one of a fourth interface (e.g., redundant E1) between the user plane unit and the further control plane unit, for use in case of a failure of the control plane unit, a fifth interface (e.g., redundant F1) between the distributed unit and the further control plane unit, for use in case of a failure of the control plane unit, and a sixth interface (e.g., redundant NG) between the core network node and the further control plane unit, for use in case of a failure of the control plane unit, based on the information identifying the further control plane unit.

[0104] The method performed by the control plane unit may further include transmitting, to at least one of the user plane unit and the distributed unit, assistance information for use in determining a failure of the control plane unit. The assistance information may identify or comprise a timer (value).

[0105] The method performed by the control plane unit may further include backing up, in the further control plane unit, at least one UE context associated with at least one UE served by the control plane unit.

[0106] The first interface (e.g., E1) may be provided between the control plane unit and the user plane unit, the second interface (e.g., F1) may be provided between the control plane unit and the distributed unit, and the third interface (e.g., NG) may be provided between the control plane unit and the core network node. In this case, the method performed by the communication device may further include initiating a procedure to set up at least one of a fourth interface (e.g., redundant E1) between the user plane unit and the further control plane unit to be used in case of a failure of the control plane unit, a fifth interface (e.g., redundant F1) between the distributed unit and the further control plane unit to be used in case of a failure of the control plane unit, and a sixth interface (e.g., redundant NG) between the core network node and the further control plane unit to be used in case of a failure of the control plane unit, based on the information identifying the further control plane unit. In this case, setting up the fourth, fifth, or sixth interface may include sending at least one message including an indication that the fourth, fifth, or sixth interface is being set up for restoration.

[0107] The method performed by the communications device may further include receiving information identifying a control plane unit for use in activating the further control plane unit if the control plane unit fails.

[0108] Configuring the further control plane unit may include setting up or modifying the further control plane unit to behave as a restoration node.

[0109] The at least one signaling message transmitted to the further control plane unit may include information identifying the UE (e.g., a UE ID) and a UE context associated with the UE. The at least one signaling message may be transmitted by the control plane unit. The at least one signaling message may be transmitted by the user plane unit. The at least one signaling message may be transmitted by the distributed unit.

[0110] The method performed by the communications device may further include sending at least one message to a core network node to establish a session for the restoration node based on the UE context.

[0111] The method performed by the communications device may further include receiving, from the further control plane unit, at least one message including information identifying the at least one change to the UE context, and determining whether to use the further control plane unit as a restoration node for the control plane unit based on the at least one change to the UE context, in which case the method may further include sending a message to the further control plane unit indicating that the at least one change to the UE context has been accepted, and using the further control plane unit as a restoration node for the control plane unit based on the modified UE context including the at least one change.

[0112] The at least one change to the UE context may include a change to a Packet Data Convergence Protocol (PDCP) configuration associated with the UE context.

[0113] The procedure of configuring the further control plane unit to act as a restoration node may include sending a request to a core network node to set up a Protocol Data Unit (PDU) session for the UE via the restoration node.

[0114] The method may further include initiating a procedure to switch over to a further control plane unit as a redundant unit upon failure of the control plane unit (e.g., by sending a message to initiate a procedure to activate the restored node).

[0115] The message for initiating the procedure to activate the restored node may include information identifying a control plane unit of the communication device.

[0116] The method performed by the control plane unit configured as the restoration node may further include sending at least one message to the user plane unit or the distributed unit to indicate that the restoration node has been activated.

[0117] The communication device may include a distributed base station device.

[0118] Various other modifications will be apparent to those skilled in the art and will not be described in further detail herein.

[0119] For example, all or a part of the exemplary embodiments disclosed above can be described as follows, but are not limited to these. (Appendix 1) A method performed by a control plane unit of a communication device including at least a control plane unit, a user plane unit, and a distribution unit, comprising: transmitting, to at least one of the user plane unit and the distributed unit, information identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit; A method comprising: (Appendix 2) The information identifying the further control plane unit may be a procedure for setting up a first interface between a control plane unit and a user plane unit; a procedure for setting up a second interface between the control plane unit and the distributed unit; a procedure for setting up a third interface between the control plane unit and a core network node; A procedure for modifying the first interface; A procedure for modifying the second interface; and Procedures for changing the third interface transmitted as part of at least one of The method described in Appendix 1. (Appendix 3) the information identifying the further control plane unit includes at least one of an address of the further control plane unit, a name of the further control plane unit, and an identifier of the further control plane unit; 3. The method according to claim 1 or 2. (Appendix 4) Based on the information identifying the further control plane unit, a fourth interface between the user plane unit and the further control plane unit, used in case of a failure of the control plane unit; a fifth interface between the distributed unit and the further control plane unit, used in case of a failure of the control plane unit; and A sixth interface between the core network node and the further control plane unit, used in case of failure of the control plane unit. and initiating a procedure for setting up at least one of the following: 4. The method according to any one of claims 1 to 3. (Appendix 5) and transmitting, to at least one of the user plane unit and the distributed unit, assistance information for use in determining a failure of the control plane unit. 5. The method according to any one of claims 1 to 4. (Appendix 6) The aiding information identifies a timer; The method described in Appendix 5. (Appendix 7) and, in the further control plane unit, backing up at least one UE context associated with at least one UE served by the control plane unit. 7. The method of any one of claims 1 to 6. (Appendix 8) A method performed by a communication device including a control plane unit, a user plane unit, and a distribution unit, comprising: receiving, from at least one of the control plane unit and the operation and maintenance node, information identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit; A method comprising: (Appendix 9) A first interface is provided between the control plane unit and the user plane unit, a second interface is provided between the control plane unit and the distributed unit, and a third interface is provided between the control plane unit and the core network node; The method further comprises the steps of: based on the information identifying the further control plane unit: a fourth interface between the user plane unit and the further control plane unit, used in case of a failure of the control plane unit; a fifth interface between the distributed unit and the further control plane unit, used in case of a failure of the control plane unit; and A sixth interface between the core network node and the further control plane unit, used in case of failure of the control plane unit. and initiating a procedure for setting up at least one of the following: The method described in Appendix 8. (Appendix 10) setting up the fourth, fifth, or sixth interface includes sending at least one message including an indication that the fourth, fifth, or sixth interface is being set up for restoration; 10. The method according to claim 9. (Appendix 11) receiving information identifying the control plane unit for use in activating the further control plane unit if the control plane unit fails; 11. The method according to claim 9 or 10. (Appendix 12) A method performed by a communication device including at least a control plane unit, a user plane unit, and a distribution unit, comprising: initiating a procedure for configuring the further control plane unit to act as a restoration node for the control plane unit by sending at least one signaling message to the further control plane unit; backing up, at a restoration node, user equipment (UE) contexts associated with UEs served by the control plane unit; A method comprising: (Appendix 13) Configuring the further control plane unit includes setting up or modifying the further control plane unit to behave as a restoration node; 13. The method according to claim 12. (Appendix 14) The at least one signaling message includes information identifying the UE and a UE context associated with the UE. 14. The method according to claim 12 or 13. (Appendix 15) At least one signaling message is transmitted by the control plane unit; 15. The method of any one of claims 12 to 14. (Appendix 16) At least one signaling message is transmitted by a user plane unit; 15. The method of any one of claims 12 to 14. (Appendix 17) At least one signaling message is transmitted by the distributed unit; 15. The method of any one of claims 12 to 14. (Appendix 18) and transmitting at least one message to a core network node to establish a session for the restoration node based on the UE context. 18. The method of any one of appendix 12 to 17. (Appendix 19) receiving at least one message from a further control plane unit, the message including information identifying at least one change to the UE context; determining whether to use a further control plane unit as a restoration node for the control plane unit based on at least one change to the UE context; Further comprising: 19. The method of any one of claims 12 to 18. (Appendix 20) sending a message to a further control plane unit indicating that the at least one change to the UE context has been accepted; using the further control plane unit as a restoration node for the control plane unit based on the modified UE context including the at least one modification; Further comprising: 19. The method according to claim 19. (Appendix 21) The at least one change to the UE context includes a change to a Packet Data Convergence Protocol (PDCP) configuration associated with the UE context; 21. The method according to claim 19 or 20. (Appendix 22) The procedure of configuring the further control plane unit to act as a restoration node includes sending a request to a core network node to set up a protocol data unit (PDU) session for the UE via the restoration node. 21. The method of any one of claims 1 to 20. (Appendix 23) and initiating a procedure for switching over to a further control plane unit as a redundant unit upon failure of the control plane unit. 23. The method of any one of claims 1 to 22. (Appendix 24) 1. A method executed by a communication device comprising at least a control plane unit configured as a control plane unit, a user plane unit and a distributed unit connecting to a further control plane unit configured as a restoration node for the control plane unit, the method comprising: determining a failure of a control plane unit; sending a message to the further control plane unit to initiate a procedure to activate the further control plane unit as a restoration node; A method comprising: (Appendix 25) 1. A method performed by a control plane unit configured as a restoration node for a control plane unit of a communication device comprising a user plane unit and a distributed unit, the method comprising: receiving, in case of a failure of a control plane unit of the communication device, from a user plane unit or a distributed unit, a message for initiating a procedure for activating a restoration node; communicating with at least one user equipment (UE) using a user plane unit or a distributed unit; A method comprising: (Appendix 26) The message includes information identifying a control plane unit of the communication device. 26. The method according to claim 24 or 25. (Appendix 27) and transmitting at least one message to the user plane unit or the distributed unit to indicate that the restored node has been activated. 27. The method of any one of claims 24 to 26. (Appendix 28) The communication device includes a distributed base station device. 28. The method of any one of appendix 1 to 27. (Appendix 29) A method performed by an operation and maintenance node, comprising: transmitting, to a node of a communication device including a control plane unit, a user plane unit, and a distributed unit, information identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit; A method comprising: (Appendix 30) A control plane unit for a communication device, the control plane unit including at least a control plane unit, a user plane unit, and a distribution unit, Means for transmitting information to at least one of the user plane unit and the distributed unit identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit. A control plane unit comprising: (Appendix 31) A communication device including a control plane unit, a user plane unit, and a distribution unit, means for receiving, from at least one of the control plane unit and the operation and maintenance node, information identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit; A communication device comprising: (Appendix 32) A communication device including at least a control plane unit, a user plane unit, and a distributed unit, means for initiating a procedure for configuring the further control plane unit to act as a restoration node for the control plane unit by sending at least one signaling message to the further control plane unit; Means for backing up user equipment (UE) context associated with a UE served by the control plane unit in a restoration node; A communication device comprising: (Appendix 33) A communication device comprising at least a control plane unit configured as a control plane unit, a user plane unit and a distributed unit connecting to a further control plane unit configured as a restoration node for the control plane unit, means for determining a failure of a control plane unit; means for transmitting a message to the further control plane unit to initiate a procedure for activating the further control plane unit as a restoration node; A communication device comprising: (Appendix 34) A control plane unit to be configured as a restoration node for a control plane unit of a communication device including a user plane unit and a distributed unit, the control plane unit comprising: means for receiving, in case of a failure of a control plane unit of the communication device, from a user plane unit or a distributed unit, a message for initiating a procedure for activating a restoration node; means for communicating with at least one User Equipment (UE) using a user plane unit or a distributed unit; A control plane unit comprising: (Appendix 35) Means for transmitting to a node of a communication device including a control plane unit, a user plane unit and a distributed unit information identifying a further control plane unit acting as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit. An operation and maintenance node comprising:

[0120] This application claims the benefit of priority to UK Patent Application No. 2202786.6, filed March 1, 2022, the disclosure of which is incorporated herein by reference in its entirety. [Explanation of symbols]

[0121] 1. Telecommunications Systems 3. Mobile Devices 5 base station 7 Core Network 8. Access and Mobility Management Functions 9 Session Management Function 10 External IP Networks 31 Transceiver Circuit 33 Antenna 35 User Interface 37 Control Unit 39 Memory 41 Operating Systems 43 Communication Control Module 51 Transceiver Circuit 53 Antenna 55 Network Interface 57 Control Unit 59 Memory 61 Operating Systems 63 Communication Control Module 5C gNB-CU-CP module 5U gNB-CU-UP module 5D gNB-DU module 71 Transceiver Circuit 75 Network Interface 77 Control Unit 79 Memory 81 Operating Systems 83 Communication Control Module

Claims

1. A method performed by a network node, comprising the steps of: transmitting to at least one of a user plane unit of a distributed base station and a distributed unit of the distributed base station information identifying a further control plane unit acting as a redundant unit for the control plane unit of the distributed base station for user equipment (UE) served by a control plane unit; the information being used to activate the further control plane unit to act as the redundant unit upon failure of the control plane unit. method.

2. The network node is the control plane unit. The method of claim 1.

3. The network node is an operation and maintenance (OAM) node. The method of claim 1.

4. transmitting, to the further control plane unit, a UE context associated with the UE for backup at the further control plane unit. The method of claim 2.

5. The UE context includes a Protocol Data Convergence Protocol (PDCP) configuration; The method comprises: receiving a rejection message from the further control plane unit indicating that the further control plane unit does not accept the UE context with the PDCP configuration and including a supported UE context with a PDCP configuration; determining whether the supported UE context with PDCP configuration is accepted; and Including, The method according to claim 4.

6. The transmitting of the UE context is performed when the UE context is set up / modified / released in the network node. The method according to claim 4 or 5.

7. The information is a procedure for setting up a first interface between the control plane unit and the user plane unit; a procedure for setting up a second interface between the control plane unit and the distributed unit; a procedure for setting up a third interface between the control plane unit and a core network node; a procedure for modifying said first interface; a procedure for modifying the second interface; and Procedures for changing the third interface transmitted as part of at least one of 7. The method according to any one of claims 1 to 6.

8. The information is an address of said further control plane unit, the name of said further control plane unit, and an identifier of said further control plane unit At least one of 8. The method according to any one of claims 1 to 7.

9. and transmitting to the at least one of the user plane unit and the distributed unit assistance information for determining a failure of the control plane unit.

9. The method according to any one of claims 1 to 8.

10. The aiding information includes a timer.

10. The method of claim 9.

11. 1. A method performed by a network unit in a distributed base station comprising a control plane unit, a user plane unit and a distributed unit connecting to a further control plane unit configured as a restoration node for said control plane unit, the method comprising: determining a failure of the control plane unit; and sending a message to the further control plane unit to initiate a procedure to activate the further control plane unit to behave as the restoration node; A method comprising:

12. receiving information identifying the further control plane unit from at least one of the control plane unit and an operation and maintenance (OAM) node. The method of claim 11.

13. based on the information identifying the further control plane unit, initiating a procedure for setting up an interface between the network unit and the further control plane unit, to be used in case of the failure of the control plane unit. The method of claim 12.

14. initiating the procedure for setting up the interface causes the further control plane unit to set up an interface between the further control plane unit and a core network node to be used in case of the failure of the control plane unit. The method of claim 13.

15. setting up the interface includes transmitting information indicating that the interface is being set up for restoration. The method of claim 14.

16. receiving information identifying the control plane unit for activating the further control plane unit if the control plane unit fails.

16. The method according to claim 14 or 15.

17. transmitting, for backup at the further control plane unit, a user equipment (UE) context associated with a UE served by the control plane unit.

17. The method according to any one of claims 11 to 16.

18. A method performed by a further control plane unit, comprising: receiving a message from a network unit in a distributed base station including the control plane unit and the network unit in case of a failure of the control plane unit, for initiating a procedure of activation to act as a restoration node for the control plane unit; communicating with a user equipment (UE) using said network unit; A method comprising:

19. based on information identifying the further control plane unit sent to the network unit, initiating a procedure for setting up an interface between the network unit and the further control plane unit, to be used in case of the failure of the control plane unit.

20. The method of claim 18.

20. based on initiating the procedure for setting up the interface between the network unit and the further control plane unit, initiating a procedure for setting up an interface between the further control plane unit and a core network node, to be used in case of the failure of the control plane unit.

20. The method of claim 19.

21. receiving a UE context associated with the UE for backup at the further control plane unit.

22. The method according to any one of claims 18 to 21.

22. The UE context includes a Protocol Data Convergence Protocol (PDCP) configuration; The method comprises: determining whether the UE context with the PDCP configuration is accepted; and sending a rejection message indicating that the further control plane unit does not accept the UE context with the PDCP configuration and including a supported UE context with PDCP configuration; Including, 22. The method of claim 21.

23. and sending a message to a core network node based on the UE context to establish a protocol data unit (PDU) session for the restoration node.

23. The method of claim 21 or 22.

24. the network unit is at least one of the user plane unit and the distribution unit; 23. The method according to any one of claims 11 to 22.

25. means for transmitting to at least one of the user plane unit of a distributed base station and the distributed units of the distributed base station information identifying a further control plane unit acting as a redundant unit for the control plane unit of the distributed base station for user equipment (UE) served by a control plane unit; Equipped with the information being used to activate the further control plane unit to act as the redundant unit upon failure of the control plane unit. Network node.

26. A network unit in a distributed base station comprising a control plane unit, a user plane unit and a distributed unit connecting to a further control plane unit configured as a restoration node for said control plane unit, means for determining a failure of the control plane unit; means for sending a message to the further control plane unit to initiate a procedure for activating the further control plane unit to behave as the restoration node; A network unit comprising:

27. means for receiving, in case of a failure of a control plane unit, from the network unit in a distributed base station including the control plane unit and the network unit, a message for initiating a procedure of activation to act as a restoration node for the control plane unit; means for communicating with a user equipment (UE) using said network unit; A further control plane unit comprising:

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