Network node, network unit, further control plane unit, and method

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 a communication system.

Background Art

[0002] The present invention relates to, although not exclusively, wireless communication systems and devices operating according to 3rd Generation Partnership Project (3GPP (registered trademark)) standards or their equivalents or derivatives, and in particular to the recovery of distributed devices such as distributed base stations in so-called "5G" (or "New Radio") systems.

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

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

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

[0006] Specifically, the gNB (referred to herein as the "distributed" gNB) may include the following functional units. gNB Central Unit (gNB-CU): A logical node that hosts the Radio Resource Control (RRC) layer, the Service Data Adaptation Protocol (SDAP) layer, and the Packet Data Convergence Protocol (PDCP) layer (or the RRC layer and PDCP layer of the en-gNB) of the gNB, which 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) layer, Medium Access Control (MAC) layer, and Physical (PHY) layer of a gNB or en-gNB, and its operation is partially controlled by the gNB-CU. One gNB-DU supports one or more 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 gNB-CU for an en-gNB or 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 an en-gNB, and the user plane parts of the PDCP protocol and SDAP protocol of the gNB-CU for a 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 uses the terms mobile device, user device, or UE to refer to any communication device that can be connected to the core network via one or more base stations.

[0008] When using the above-described distributed architecture, the split between gNB-CU and gNB-DU enables the deployment of highly centralized gNB-CUs with a wide coverage area for each gNB-CU, especially from the perspective 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 that affects many users. Therefore, 3GPP believes that the recovery of gNB-CU (-CP) is of high importance and there is ongoing research on possible recovery enhancements with the following objectives: - Solutions for gNB-CU-CP failure recovery should minimize the signaling load to the UE and the network. - Solutions for gNB-CU-CP failure recovery should minimize the user plane interruption, i.e., minimize the service downtime from the end-user perspective. - Solutions for minimizing control plane interruption should also be targeted.

Prior Art Documents

Non-Patent Documents

[0009]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The inventors have identified several problems that need to be addressed in order to provide improved recovery to distributed base stations. For example, even before a first UE is connected to the network via a distributed base station device, redundant interfaces (E1 / F1 / NG) of the secondary CU-CP should be established in advance. Also, in order to avoid a situation where all UE contexts affected by a failure of the main unit have to be reconfigured, it is necessary to back up / move UE contexts from the main unit to the secondary unit in a timely and efficient manner. Further, when one of the network entities detects a 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 relevant entities have to apply an appropriate configuration for using the new (secondary) CU-CP. However, it is not yet known how such recovery activation / notification and reconfiguration are realized.

Means for Solving the Problems

[0011] Therefore, a preferred embodiment of the present invention aims to provide a method and apparatus that address or at least partially address one or more of the above problems while meeting the above objectives.

[0012] For the efficiency of those skilled in the art, the present invention is described in detail in the context of a 3GPP system (NR), but the principles of the present invention can be applied to other systems that employ similar distributed devices.

[0013] In one aspect, the present invention provides 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 distributed unit, the method including transmitting information identifying an additional control plane unit that acts as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit to at least one of the user plane unit and the distributed unit.

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

[0015] In one aspect, the present invention provides a method performed by a communication device including at least a control plane unit, a user plane unit, and a distributed unit, the method including starting a procedure to configure an additional control plane unit to act as a recovery node for the control plane unit by transmitting at least one signaling message to the additional control plane unit, and backing up a UE context associated with a user equipment (UE) served by the control plane unit at the recovery node.

[0016] In one aspect, the present invention provides a method executed by a communication device including at least a control plane unit configured as a control plane unit, a user plane unit, and a distributed unit connected to a further control plane unit configured as a recovery node for the control plane unit, the method including determining a failure of the control plane unit and transmitting a message for starting a procedure to activate the further control plane unit as a recovery node to the further control plane unit.

[0017] In one aspect, the present invention provides a method executed by a control plane unit configured as a recovery node for a control plane unit of a communication device including a user plane unit and a distributed unit, the method including receiving, in the event of a failure of the control plane unit of the communication device, a message for starting a procedure to activate the recovery node from the user plane unit or the distributed unit, 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 executed by an operation and maintenance node, the method including transmitting information for identifying a further control plane unit that acts as a redundant unit for a control plane unit for at least one user equipment (UE) served by the control plane unit to a node of a communication device including a control plane unit, a user plane unit, and a distributed unit.

[0019] In one aspect, the present invention provides a control plane unit for a communication 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 control unit, and a transceiver) for transmitting information identifying a further control plane unit that acts as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit to at least one of the user plane unit and the distributed unit.

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

[0021] In one aspect, the present invention provides a communication device including at least a control plane unit, a user plane unit, and a distributed unit, the communication device comprising means (e.g., a memory, a control unit, and a transceiver) for starting a procedure for configuring a further control plane unit to act as a recovery node for the control plane unit by transmitting at least one signaling message to the further control plane unit, and means for backing up a UE context associated with a user equipment (UE) served by the control plane unit at the recovery node.

[0022] In one aspect, the present invention provides a communication device including at least a control plane unit configured as a control plane unit, a user plane unit, and a distributed unit connected to a further control plane unit configured as a recovery node for the control plane unit, the communication device comprising means (e.g., memory, control unit, and transceiver) for determining a failure of the control plane unit, and means for transmitting a message for starting a procedure for activating the further control plane unit as a recovery node to the further control plane unit.

[0023] In one aspect, the present invention provides a control plane unit configured as a recovery 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 (e.g., memory, control unit, and transceiver) for receiving, in the event of a failure of the control plane unit of the communication device, a message for starting a procedure for activating the recovery node from the user plane unit or the distributed unit, 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., memory, control unit, and transceiver) for transmitting information for identifying a further control plane unit that acts as a redundant unit for a control plane unit for at least one user equipment (UE) served by the control plane unit to a node of a communication device including a control plane unit, a user plane unit, and a distributed unit.

[0025] Aspects of the invention extend to corresponding systems, and computer program products such as computer-readable storage media storing instructions, which are operable to program a programmable processor to perform the methods described above or as described in the claims and / or to provide the 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 invention independently of (or in combination with) any other disclosed and / or shown feature. In particular, without limitation, any feature of any dependent claim falling under a particular independent claim may be introduced into that independent claim in any combination or individually.

[0027] Hereinafter, embodiments of the present invention will be described by way of example with reference to the accompanying drawings.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

[0029] Overview FIG. 1 schematically shows a mobile (cellular or wireless) telecommunications system 1 to which embodiments of the present invention are applicable.

[0030] In this network, users of mobile devices 3 (UEs) can communicate with each other and with other users via respective base stations 5 and core networks 7 using an appropriate 3GPP radio access technology (RAT), such as 5G RAT. It will be appreciated that several base stations 5 form a (radio) access network or (R)AN. As will be understood by those skilled in the art, for illustrative purposes, FIG. 1 shows one mobile device 3 and one base station 5, but when implemented, the system typically includes other base stations and mobile devices (UEs).

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

[0032] As shown in FIG. 1, the functions of the gNB 5 (referred to as a “distributed” gNB in this specification) may be split into one or more distributed units (DUs) and a central unit (CU). The CU typically performs higher-level functions and communication with the next-generation core, while the DU performs lower-level functions and communication via the air interface with UEs 3 in the vicinity (i.e., within the cell operated by the gNB 5). In this example, the distributed gNB 5 includes the following functional units or logical nodes: i) a gNB central unit (gNB-CU) that 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-DU).

[0033] The gNB-CU-CP 5C and each gNB-CU-UP 5U are connected via an E1 interface (E1AP). The gNB-CU and each gNB-DU 5D are connected via an F1 interface (F1AP) therebetween. The gNB-CU-CP 5C and the gNB-DU 5D are connected via an F1-C (F1 control plane) interface, while the gNB-CU-UP 5U and each respective gNB-DU 5D are connected via an F1-U (F1 user plane) interface.

[0034] The gNB-CU-CP 5C hosts the control plane portion of the RRC protocol and the PDCP protocol for the en-gNB or gNB-CU for the gNB. The gNB-CU-UP 5U hosts the user plane portion of the PDCP protocol and the SDAP protocol for the gNB-CU for the gNB (SDAP is not applicable in the case of the 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 are connected via an appropriate air interface (e.g., the so-called "NR" air interface and / or "Uu" interface, etc.). Adjacent base stations 5 are connected to each other via an appropriate inter-base-station interface (e.g., the so-called "Xn" interface and / or "X2" interface, etc.). The base station 5 is also connected to the core network node via an appropriate interface (e.g., the so-called "NG-U" interface (for the user plane) and / or the so-called "NG-C" interface (for the control plane), etc.).

[0036] The core network 7 typically includes logical nodes (or "functions") for supporting communications in the telecommunication 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 at least include an Access and Mobility Management Function (AMF) 8 and a Session Management Function (SMF) 9. A connection to an external IP network 10 (such as the Internet) may also be provided from the core network 7.

[0037] Figure 2 schematically shows the components of the distributed base station and other nodes, including the interfaces between them, when the recovery configuration is prepared. More specifically, UE3 is served by DU5D (at least one DU) using an appropriate air interface (in the case of a wireless UE). DU5D is connected to CU-UP5U via the F1-U interface (user plane) and to the associated (main or master) CU-CP5C via the F1-C interface (control plane). CU-CP5C and CU-UP5U are connected via the E1 interface. CU-CP5C is connected to the core network (AMF8) via the NG interface (NGAP in Figure 2).

[0038] The main (or initial) CU-CP5C is hereinafter referred to as the master CU-CP5C. As described above, the master CU-CP5C can be a single point of failure. To provide resiliency for this scenario, in this system, an additional CU-CP5C’, which acts as a backup node in the event of the failure of the master CU-CP5C, is also set up. The additional CU-CP5C’ is hereinafter referred to as the second or secondary CU-CP5C’. Thus, as shown in Figure 2, redundant F1 / E1 / NG connections are set up via the secondary CU-CP5C’, although these connections may not be used initially. It should be recognized that the redundant connections (at least some of them) may be prepared before any UE3 is connected to the main CU-CP5C (or during the procedure of connecting the first UE3).

[0039] There are various ways to establish these redundant connections to the secondary CU-CP5C'. For example, the master CU-CP5C may configure a resilient CU-CP5C' as part of an E1 setup procedure or an F1 setup procedure (or an E1 or F1 change procedure). The resilient configuration may beneficially include the address (TNL address) and name of the secondary CU-CP5C' as well as the associated failure timer (or any other suitable assistance information for determining CU-CP failure). In this case, the address and name are used by the nodes (CU-UP5U and DU5D) to set up an appropriate resilient connection to the secondary CU-CP5C', and the failure time / assistance information is used during the operation to determine whether it is necessary to activate the resilient connection (i.e., in the case of CU-CP failure).

[0040] Beneficially, the CU-UP5U and DU5D may obtain the address and name of the secondary CU-CP5C' and obtain the associated failure timer from the master CU-CP5C or another node (e.g., Operation and Management: OAM). The CU-UP / DU and the master CU-CP5C may use an existing message having a new information element indicating at least one of the address, name, and failure timer associated with the secondary CU-CP5C'. Alternatively, a dedicated message may be used to deliver some or all of this information to the CU-UP5C and DU5D.

[0041] To achieve timely and efficient recovery from the failure of the master CU-CP5C, the related UE context is backed up so that it can be obtained and used by the secondary CU-CP5C' without delay or data loss and without requiring excessive signaling. Specifically, the related UE context can 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 when the master CU-CP fails (or is overloaded) to move the related UE context to the secondary CU-CP (optionally AMF / SMF). Therefore, the backed-up / moved UE context can be used by the secondary CU-CP5C' and other nodes to recover the UE service after the failure (or overload) of the master CU-CP.

[0042] Advantageously, when one of the network entities (e.g., DU5D or CU-UP5U) detects the failure of the serving CU-CP5C, it activates CU-CP recovery by sending an appropriate activation message to the secondary CU-CP5C'. The secondary CU-CP5C' takes over the control of UE3 and notifies the related entities so that an appropriate recovery configuration can be applied.

[0043] Advantageously, the above solution requires relatively little signaling to the UE and the network during gNB-CU-CP failure recovery. At the same time, the user plane interruption / service downtime from the end-user perspective is minimized with minimal control plane interruption.

[0044] Mobile device Figure 3 is a block diagram showing the main components of the mobile device 3 (e.g., a mobile phone or an 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 the base station 5 via one or more antennas 33. The mobile device 3 has a control unit 37 that controls the operation of the mobile device 3. The control unit 37 is associated with a memory 39 and is connected to the transceiver circuit 31. Although not necessarily required for its operation, the mobile device 3 may of course have all the normal functions of a conventional mobile phone (such as a user interface 35), which may be appropriately 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, via a telecommunications network or from a removable data storage device (RMD).

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

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

[0047] It should be recognized that the communication control module 43 may include several sub-modules (or "layers") that support specific functions. For example, the communication 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, and so on.

[0048] Base station FIG. 4 is a block diagram showing the main components of the distributed base station 5 shown in FIG. 1. As shown, the base station 5 includes a transceiver circuit 51 for signaling to a user equipment (such as the mobile device 3) via one or more antennas 53 and receiving signals from the user equipment, a network interface 55 (such as an NG-C / NG-U interface, etc.) for transmitting signals to the core network 7 and receiving signals from the core network 7, and a base station interface 56 (such as an Xn interface, etc.) for transmitting signals to an adjacent base station and receiving signals from the adjacent base station. The base station 5 has a control unit 57 that controls the operation of the base station 5 according to software stored in the 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 typically also includes an inter-base station interface module (such as Xn) and a core network interface module (such as NG-C / NG-U).

[0049] The communication control module 63 is responsible for processing (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 (such as 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") to 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 includes a distributed gNB or an en-gNB, the network interface 55 also includes an E1 interface and an F1 interface (F1-C for the control plane and F1-U for the 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 the gNB-CU-CP module 5C, the gNB-CU-UP module 5U, and the gNB-DU module 5D. If present, the gNB-CU-CP module 5C hosts the control plane portions 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] Those skilled in the art will understand that the central unit (e.g., 5C and / or 5U) may be implemented and physically located together with the base station, or remotely, as a single physical element, or as a cloud-based or virtualized system. It will also be understood that a single central unit may serve multiple base stations 5.

[0052] Core network node FIG. 5 is a block diagram showing the main components of a general core network node (or function) shown in FIG. 1, such as AMF 8 or SMF 9. As shown, the core network node includes a transceiver circuit 71 operable to transmit signals to other nodes (including UE 3 and (R) AN node 5) via a network interface 75 and receive signals from other nodes. A control unit 77 controls the operation of the core network node according to software stored in a memory 79. The software may be pre-installed in the memory 79 and / or may be downloaded, for example, via a 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 processing (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 described above, the system 1 includes a distributed base station device 5 that serves several UEs 3 via one or more distributed units 5D (denoted as "gNB-DU" in FIG. 1 and "DU" in FIGS. 2 and 6). The central unit (CU) part of the distributed base station device 5 is responsible for controlling the control plane and user plane operations related to the UE 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 the SDAP protocol if appropriate) of the distributed base station device 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 parts of the RRC protocol and the PDCP protocol of the distributed base station device 5.

[0054] Here, a more detailed description will be given of various aspects of recovery in the systems shown in FIGS. 1 and 2 (see FIGS. 6 to 8). More specifically, FIG. 6 schematically shows an exemplary procedure for establishing a redundant connection to a secondary node (in this case, an E1 / F1 / NG connection), FIG. 7 schematically shows an exemplary UE context backup procedure, and FIG. 8 schematically shows an exemplary procedure for activating recovery.

[0055] Redundant connection FIG. 6 schematically shows some possible ways to establish a redundant connection to a secondary CU-CP 5C'. It will be appreciated that the procedure (at least in part) may be executed before any UE 3 is connected to the main CU-CP 5C, or during the procedure of connecting the first (or second, etc.) UE 3.

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

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

[0058] In this example, the procedure starts with an E1 setup between CU-UP5U and the master CU-CP5C. As can be seen from the figure, in step 1, CU-UP5U generates and transmits (using its associated communication control module 63) a properly formatted message to initiate an E1 setup between CU-UP5U and CU-CP5C (acting as the master CU-CP). CU-CP5C can be selected based on information provided by UE3, AMF8, and / or any other node, if appropriate.

[0059] (Master) CU-CP5C, if it can accept this connection request, generates an appropriate response (e.g., "E1 setup response") and transmits it to CU-UP5U. In one option, as generally shown in step 1a, CU-CP5C can be configured to include appropriate information related to a suitable redundant / secondary CU-CP5C' in this message. For example, the E1 setup response message (or similar) may include one or more of the following: the name of at least one redundant / secondary CU-CP5C', the respective transport network layer (TNL) address of at least one redundant / secondary CU-CP5C', and information identifying a timer associated with at least one redundant / secondary CU-CP5C'. In another option, as generally shown in step 1b, CU-CP5C can 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 in step 1a need not include this information. However, it should be recognized that the message sent in step 1b can be used to update or supplement any information included in the E1 setup response message. The message sent in step 1b may include subsequent E1 setup response messages, or messages related to E1 reconfiguration or E1 change (e.g., E1 reconfiguration / change request, or related response messages).

[0060] In step 2, CU-UP5U starts the procedure to establish a recovery E1 tunnel based on the information received in step 1a / 1b. Specifically, CU-UP5U generates (using its associated communication control module 63) and transmits a properly formatted message to start an E1 setup between CU-UP5U and CU-CP5C’ which was identified in step 1a / 1b and acts as a secondary CU-CP for CU-UP5U. The message may include information indicating that the E1 setup is for providing recovery (e.g., an appropriate “Recovery E1” indication, etc.). The recovery indication may be provided using, for example, an appropriate information element or flag. The message may also include information identifying the master CU-CP5C (not shown in FIG. 6) that can be used to establish / configure the 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, identifies the master CU-CP5C in case of failure, and provides its own identifier (e.g., an appropriate “Master CU XnAP ID”, etc.) associated with the master CU-CP5C for use by other nodes to activate the recovery connection if necessary.

[0062] Steps 3 and 3a illustrate 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 should be recognized that other suitable messages (such as NG change request / response messages) may be used when appropriate. As can be seen from the figure, steps 3 and 3a can be executed in response to the establishment of the recovery E1 tunnel (after step 2) or at another time (for example, 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 establishment / change of the connection between the secondary CU-CP5C' and the AMF8 can 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 (for example, via Xn) to the secondary CU-CP5C' to trigger the establishment / change of the connection between the secondary CU-CP5C' and the AMF8.

[0063] The following is an explanation of the procedure related to the establishment of the F1 connection that supports the recovery of the distributed base station device 5. As shown in step 4, the DU5D starts the setup of an appropriate connection with the first (master) CU-CP5C by generating an F1 setup request (using its associated communication control module 63) and sending it to the CU-CP5C. This request may include an appropriate indication of whether the DU5D requires (or supports) a redundant F1 tunnel, but it should be recognized that such an indication may be entirely optional (or implicit).

[0064] As shown in step 4a, the first (master) CU-CP 5C responds by generating and sending a properly formatted F1 setup response (using its associated communication control module 63). In this case, the response may include one or more of the following, i.e., at least the name of at least one redundant / secondary CU-CP 5C', the respective TNL address of at least one redundant / secondary CU-CP 5C', and information identifying the timer associated with at least one redundant / secondary CU-CP 5C'. As another option, as generally shown in step 4b, the CU-CP 5C 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 in step 4a need not include this information (or may include only a part thereof). However, it should be recognized 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 subsequent F1 setup response messages, or messages related to F1 reconfiguration or F1 change (e.g., F1 reconfiguration / change requests, or related response messages).

[0065] Based on the information received in step 4a / 4b, the DU 5D starts the procedure to establish a recovery F1 connection. Specifically, the DU 5D generates and sends (using its associated communication control module 63) a properly formatted message to start an F1 setup between the DU 5D and the CU-CP 5C' (acting as a secondary CU-CP for the DU 5D) identified in step 4a / 4b. The message may include information indicating that the F1 setup is for providing recovery (e.g., an appropriate "recovery F1" indication, etc.). The recovery indication may be provided, for example, using an appropriate information element or flag. The message may also include information identifying the master CU-CP 5C (not shown in FIG. 6) that may be used to establish / configure the connection (e.g., Xn) between the master CU-CP 5C and the secondary CU-CP 5C'.

[0066] In step 5a, the secondary CU-CP 5C’ accepts the F1 setup request and provides its own identifier (e.g., an appropriate “master CU XnAP ID”, etc.) associated with the master CU-CP 5C.

[0067] In summary, the above procedure enables the establishment / configuration of an appropriate connection to a secondary CU-CP 5C’ that can act as a redundant node for the master CU-CP 5C in case the master CU-CP 5C fails (or becomes overloaded). Advantageously, the redundant E1 / F1 / NG connection to the secondary CU-CP 5C’ can be established before any UE3 connects to the master CU-CP 5C (or in any case, before the master CU-CP 5C fails or becomes overloaded).

[0068] For completeness, it should be recognized that the establishment of any of the redundant connections (E1 / NG / F1 in steps 2, 3, and 5 respectively) may be performed at any time after the name / TNL address / failure timer of the secondary CU-CP 5C’ has been sent from the master CU-CP 5C (or is otherwise known). Further, it should be recognized that steps 2, 3, and 5 need not be in a particular order. For example, the messages in steps 2 and 4 may be sent substantially simultaneously. As shown, step 3 (recovery NG setup) may be triggered by either or both of steps 2 or 5 (i.e., by any message including an instruction associated with the recovery connection involving CU-CP 5C’). It should also be recognized that step 5 (recovery 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 described above, steps 1b and 4b are optional. These may be used when the messages in steps 1a and 3a do not include information related to the secondary CU-CP 5C’, or when such information needs to be updated.

[0069] Regarding the TNL address, the secondary CU-CP name, and the failure timer, it should be recognized that the CU-CP 5C or the DU 5D may obtain any of this information using a message that forms part of the F1 / E1 setup procedure (in the case of step 1 / 4) or any other suitable message (in the case of step 1a / 4a). The information (or at least a part thereof) may be obtained from other sources, for example, OAM.

[0070] UE Context Backup Figure 7 is a schematic timing (signaling) diagram showing an exemplary procedure for UE context backup to improve the recovery of a distributed base station.

[0071] This procedure is for (among other things) the following purposes, namely, - To be able to recover UE services in case of failure (or overload) of the master CU-CP. For example, when the UE context is set up / modified / released at the master CU-CP, back up the UE context at the secondary CU-CP / AMF / SMF, and - Move all UE contexts associated with the serving (master) CU-CP to the secondary CU-CP (optionally AMF / SMF) when the serving CU-CP has failed (or become overloaded). It can be used for at least one of the above.

[0072] In the latter case, it should be recognized that it may contain a relatively large number of signaling messages, substantially simultaneously. Nevertheless, when the PDCP configuration is negotiated between the master CU-CP and the secondary CU-CP, it may not be necessary to send an RRC reconfiguration message to the UE.

[0073] Looking at the specific procedure shown in Figure 7 here, (among other things) the following main options, namely, - The master CU-CP may initiate the establishment or modification of a redundant UE context using the secondary CU-CP (step 2). - CU-UP may initiate the establishment or modification of the redundant UE context using the secondary CU-CP (step 6), and - DU may initiate the establishment or modification of the redundant UE context using the secondary CU-CP (step 8), is assumed.

[0074] First, it will be recognized that after at least one UE3 executes an appropriate UE attachment procedure (as generally shown in step 1), it is connected to the master CU-CP 5C (and other units of the distributed base station).

[0075] In step 2, after (or in response to) a UE attachment / service request from UE3, the master CU-CP 5C generates and sends a properly formatted signaling message (using its associated communication control module 63) to back up the UE context associated with the connected UE3. In this example, the master CU-CP 5C sends the signaling message to a base station interface such as the Xn interface via the base station. It will be recognized that step 2 can be executed for each newly connected UE3, for a group of UEs (e.g., when the minimum number of UEs is reached), and / or periodically (e.g., after the expiration of a related timer). In this example, the master CU-CP 5C sends a "UE recovery setup request" message (or "UE recovery change request" message) to the secondary CU-CP 5C'. 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 recognized that a similar UE context backup may be initiated by another node using a similar UE recovery setup / change request message or any other appropriate message, as will be described later with reference to steps 6 and 8.

[0076] If the secondary CU-CP5C’ can accept a 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 a request from the master CU-CP5C, it generates and sends an appropriate "UE recovery setup failure" or "UE recovery change failure" message to the master CU-CP5C, including an appropriate error cause (not shown in FIG. 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 accept (or is unable to accept) the UE context with a specific PDCP configuration, the secondary CU-CP5C' may be configured to return an appropriate message that identifies the specific UE context (by its UE XnAP ID), and may include the modified (supported) UE context / PDCP configuration if appropriate. For example, the secondary CU-CP5C' may determine that it does not support a specific PDCP configuration (due to, for example, an unsupported encryption algorithm, header compression algorithm, etc.). In this case, as generally shown in step 2a, the secondary CU-CP5C' may send a modified UE context with the supported PDCP configuration to the master CU-CP5C. 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 / change request acceptance message), including 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 / change request rejection message) to the secondary CU-CP5C' that includes the UE XnAP ID related to the rejected UE context. It should be recognized that the PDCP configuration may also be referred to as the RRC context (including the appropriate PDCP, RLC, MAC, PHY configurations). Although not shown in Figure 7, the master CU-CP5C may be configured to select a different secondary node for the rejected UE context in order to guarantee recovery for those UEs (i.e., to back up such UE contexts at different nodes).

[0078] After the secondary CU-CP5C’ is selected for recovery (backup / redundancy) for at least one UE3 (at least one UE context), the secondary CU-CP5C’ proceeds in step 3 to generate a signaling message properly formatted (using its associated communication control module 63) and send it to the AMF8. This message (e.g., a “UE Recovery Setup Request” message) notifies the AMF8 (and if any other related core network nodes) regarding the selection of the secondary CU-CP5C’ for recovery and is for starting the setup of an appropriate NG connection between the AMF8 and the secondary CU-CP5C’ (and UE3). This message may use UE-related signaling and may include an identifier associated with UE3 (e.g., the UE NGAP ID or a similar identifier used by the secondary CU-CP5C’). The message may also include information related to the protocol data unit (PDU) session for UE3, although it is recognized that the default PDU session may be used instead (e.g., in the case where there is no PDU session information). Effectively, each PDU session corresponds to each PDU session included in the received UE context. The secondary CU-CP5C’ may need to establish these PDU sessions (or at least the default PDU session) so that UE3 can continue communication using the secondary CU-CP5C’ without interruption if the master CU-CP5C fails.

[0079] As generally shown in step 4, AMF 8 requests SMF 9 to create a relevant session management context for recovery. The request (e.g., "Nsmf_PDUSession_CreateSMContext request") includes information identifying the UE 3 related to the request 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, SMF 9 confirms that it has created a session management context for recovery by sending an appropriately formatted response (e.g., "Nsmf_PDUSession_CreateSMContext response", etc.). If the master CU-CP 5C fails, SMF 9 switches the relevant path to the secondary CU-CP 5C' (as part of the procedure described, for example, with reference to FIG. 8). SMF 9 knows from the "UE Recovery Indication" included in message 4 of FIG. 7 which CU-CP is the recovery node and which PDU session to use.

[0080] Next, in step 3a, AMF 8 generates a properly formatted signaling message (using its communication control module 83) and sends it to the secondary CU-CP 5C'. This message (e.g., "UE Recovery Setup Response" message) completes the setup of the NG connection between AMF 8 and the secondary CU-CP 5C' (and UE 3). The message includes an appropriate UE identifier (UE NGAP ID). After step 3a, it should be recognized that the secondary CU-CP 5C' may also send an appropriate confirmation (similar to step 2a) to the master CU-CP 5C indicating that it is ready to serve as a redundant node for the master CU-CP 5C.

[0081] Now, looking at the case of UE context backup initiated by CU-UP5U, it will be recognized that the message sent in step 6 is the same as the message described above with reference to step 2. However, in this case, CU-UP5U uses its own UE identifier such as the so-called "UE E1AP ID". If the UE context backup is successful, the secondary CU-CP5C' generates an appropriate response in step 6a and sends it to CU-UP5U (the secondary CU-CP5C' may also proceed to step 3 if applicable).

[0082] Finally, step 8 shows the UE context backup procedure initiated by DU5D. It will be recognized that the message sent in step 8 and the response in step 8a are the same as the messages described above with reference to steps 2 and 2a respectively. However, in this case, DU5D uses its own UE identifier such as the so-called "UE F1AP ID". After the UE context backup is successful, the secondary CU-CP5C' 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-CP5C and CU-UP5U to set up an appropriate bearer for UE3. Figure 7 also shows an exemplary UE context setup procedure (steps 7 and 7a) between the master CU-CP5C and DU5D to set up the relevant UE context in the distributed unit serving UE3.

[0084] It will be appreciated that Step 2, Step 5, and / or Step 7 may be executed substantially simultaneously. In either case, the various procedures shown in FIG. 7 do not need to be executed in a specific order. UE recovery may be established (or changed) by any of Step 2, Step 6, or Step 8. In other words, UE recovery may be established and / or changed by the master CU-CP 5C, CU-UP 5U, or DU 5U. It will be appreciated that if the UE context (e.g., (data or signaling radio bearer) is changed, the message in Step 6 / 8 / 10 may be a UE recovery change request. Step 3 (and subsequent Step 4) may be triggered by any of Step 2, Step 6, and Step 8 (since it is an alternative). Thus, regardless of which node requests the secondary CU-CP 5C' to act as a redundant unit for recovery, the secondary CU-CP 5C' can update the associated core network node accordingly.

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

[0086] As generally shown in Step 1, a failure of the master CU-CP 5C can 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 can be detected based on the expiration of an associated timer such as the "failure timer" described above with reference to FIG. 6.

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

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

[0089] Effectively, from this point on, the secondary CU-CP acts as the new master CU-CP for the associated UE3. If appropriate, the new master CU-CP may proceed to execute any of the procedures described above with reference to FIGS. 6 and 7 to ensure that a new recovery CU-CP is prepared and to perform an appropriate UE context backup. Although not shown in FIG. 8, it will be appreciated that the SMF9 switches the associated path / PDU session to the secondary CU-CP5C' as configured by messages 4 and 4a in FIG. 7.

[0090] If necessary, an RRC reconfiguration may be performed between the new CU-CP5C' and UE3. However, it will be appreciated that this step may be omitted if the master CU-CP and the secondary CU-CP use the same PDCP configuration (e.g., if both support the original PDCP configuration or if they agree on an appropriate (supported) PDCP configuration / RRC context as described above with reference to steps 2a and 2b in FIG. 7).

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

[0092] Changes and Alternatives Detailed embodiments have been described above. Those skilled in the art will understand that some changes and alternatives can be made to the above embodiments while still obtaining benefits from the invention embodied therein. By way of example, only some of these alternatives and changes are described here.

[0093] Regarding step 1 of FIG. 8, it will be recognized that relatively short SCTP errors for which DU / CU-UP can recover before the expiration of the failure timer may not be able to trigger the CU-CP recovery procedure. Thus, by setting (agreeing on) the value of the failure timer, DU / CU-UP and the master CU-CP can control how much data loss is acceptable before they need to activate the backup UE context held by the secondary CU-CP.

[0094] The above description uses a distributed base station as an example, but it will be recognized that the above techniques for providing recovery and UE context backup / migration can be applied to other similar communication devices having at least a control plane unit and a user plane unit (and appropriate interfaces between related units). Such communication devices (at least one of its units) may be arranged in a (radio) access network or 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 individual modules (such as a communication control module). These modules may be provided in this way in certain application examples, for example, when an existing system is modified to implement the present invention, or in other application examples, for example, in a system designed from the beginning with the features of the present invention in mind. However, since these modules can be incorporated into the overall operating system or code, these modules may not be distinguishable as individual entities. These modules may be implemented in software, hardware, firmware, or a combination thereof.

[0096] Each control unit may include, for example, any suitable form of processing circuit including, but not limited to, one or more hardware-implemented computer processors, microprocessors, central processing units (CPUs), arithmetic logic units (ALUs), input / output (I / O) circuits, internal memory / cache (program and / or data), processing registers, communication buses (e.g., control bus, data bus, and / or address bus), direct memory access (DMA) functions, and / or hardware or software-implemented counters, pointers, and / or timers.

[0097] In the above embodiments, several software modules have been described. Those skilled in the art will recognize that the software modules may be provided in a compiled or uncompiled form, and may be supplied to the UE, distributed base station (units), and core network nodes via a computer network or as a signal on a recording medium. Further, the functions executed by some or all of this software may be executed using one or more dedicated hardware circuits. However, the use of software modules is preferred as it facilitates updating the UE, distributed base station / (R)AN nodes, and core network nodes to update their functions.

[0098] The user equipment (or "UE", "mobile station", "mobile device", or "wireless device") in the present disclosure is an entity connected to a network via a wireless interface.

[0099] It should be noted that the present disclosure is not limited to dedicated communication devices and can be applied to any device having a communication function (and related UE context). The terms "user equipment" or "UE" (when this term is used in 3GPP), "mobile station", "mobile device", and "wireless device" are generally intended to be synonymous with each other and include stand-alone 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 include devices that remain stationary for long periods of time.

[0100] For simplicity, this application often refers to mobile devices in the description, but it will be recognized that the described techniques can be implemented on any (mobile and / or substantially stationary) communication device that can connect to a communication network to send / receive data, regardless of whether such a communication device is controlled by human input or software instructions stored in memory.

[0101] The communication device may be, for example, a mobile communication device such as a mobile phone, smartphone, user equipment, personal digital assistant, laptop / tablet computer, web browser, and / or e-book reader. Such mobile (or even semi-fixed) devices are typically operated by a user. However, the 3GPP standard also enables connecting so-called "Internet of Things" (IoT) devices (e.g., Narrow-Band IoT (NB-IoT) devices) to the network, which typically includes various automated devices such as measurement devices, telemetry devices, monitoring systems, tracking and tracing devices, in-vehicle safety systems, vehicle maintenance systems, road sensors, digital billboards, point of sale (POS) terminals, and remote control systems. Effectively, the Internet of Things is a network of devices (or "things") equipped with appropriate electronic devices, software, sensors, and / or network connectivity, which enables these devices to collect data and exchange data with each other and with other communication devices. It will be recognized that IoT devices may also be referred to as Machine-Type Communication (MTC) communication devices or Machine-to-Machine (M2M) communication devices.

[0102] Information for identifying an additional 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 the user plane unit, a procedure for setting up a second interface (e.g., F1) between the control plane unit and the distributed unit, a procedure for setting up a third interface (e.g., NG) between the control plane unit and the core network node, a procedure for changing the first interface, a procedure for changing the second interface, and a procedure for changing the third interface. Information for identifying an additional control plane unit may include at least one of an address of the additional control plane unit, a name of the additional control plane unit, and an identifier of the additional control plane unit.

[0103] A method executed by the control plane unit may further include starting a procedure for setting up at least one of a fourth interface (e.g., redundant E1) between the user plane unit and an additional control plane unit, a fifth interface (e.g., redundant F1) between the distributed unit and the additional control plane unit, and a sixth interface (e.g., redundant NG) between the core network node and the additional control plane unit, which are used in the event of a failure of the control plane unit, based on the information for identifying the additional control plane unit.

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

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

[0106] A first interface (e.g., E1) may be provided between the control plane unit and the user plane unit, a second interface (e.g., F1) may be provided between the control plane unit and the distributed unit, and a 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 a further control plane unit, a fifth interface (e.g., redundant F1) between the distributed unit and a further control plane unit, and a sixth interface (e.g., redundant NG) between the core network node and a further control plane unit, which are used in case of failure of the control plane unit, based on information identifying the further control plane unit. In this case, the setup of the fourth, fifth, or sixth interface may include transmitting at least one message including an indication that the fourth, fifth, or sixth interface is being set up for recovery.

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

[0108] Configuring an additional control plane unit may include setting up or modifying an additional control plane unit to act as a recovery node.

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

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

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

[0112] At least one change to the UE context may include a change to the packet data convergence protocol (PDCP) configuration associated with the UE context.

[0113] The procedure for configuring an additional control plane unit to act as a recovery 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 recovery node.

[0114] The method may further include initiating a procedure to switch to an additional 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 recovery node).

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

[0116] The method executed by a control plane unit configured as a recovery node may further include sending at least one message to a user plane unit or a distributed unit to indicate that the recovery 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 are not described in further detail herein.

[0119] For example, all or part of the exemplary embodiments disclosed above can be described as follows in the appendices, but are not limited thereto. (Appendix 1) A method executed by a control plane unit of a communication device including at least a control plane unit, a user plane unit, and a distributed unit, Transmitting information for identifying an additional control plane unit that acts as a redundant unit for a control plane unit for at least one user equipment (UE) served by the control plane unit to at least one of a user plane unit and a distributed unit A method comprising: (Appendix 2) The information for identifying the additional control plane unit 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 the core network node, a procedure for changing the first interface, a procedure for changing the second interface, and a procedure for changing the third interface transmitted as at least a part of at least one of the method according to Appendix 1. (Appendix 3) The information for identifying the additional control plane unit includes at least one of an address of the additional control plane unit, a name of the additional control plane unit, and an identifier of the additional control plane unit the method according to Appendix 1 or 2. (Appendix 4) Based on the information for identifying the additional control plane unit, a fourth interface between the user plane unit and the additional control plane unit used in case of failure of the control plane unit, a fifth interface between the distributed unit and the additional control plane unit used in case of failure of the control plane unit, and A sixth interface between a core network node and a further control plane unit, which is used in the event of failure of a control plane unit further comprising starting a procedure for setting up at least one of the method according to any one of appendices 1 to 3 (Appendix 5) further comprising transmitting assistance information for use in determining a failure of a control plane unit to at least one of a user plane unit and a distributed unit the method according to any one of appendices 1 to 4 (Appendix 6) the assistance information identifies a timer the method according to appendix 5 (Appendix 7) further comprising, in a further control plane unit, backing up at least one UE context associated with at least one UE served by the control plane unit the method according to any one of appendices 1 to 6 (Appendix 8) A method performed by a communication device including a control plane unit, a user plane unit, and a distributed unit, comprising receiving, from at least one of a control plane unit and an operation and maintenance node, information identifying a further control plane unit to act as a redundant unit for the control plane unit for at least one user equipment (UE) served by the control plane unit including, a method (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 includes starting a procedure to set up at least one of: a fourth interface between a user plane unit and a further control plane unit, to be used in case of failure of a control plane unit; a fifth interface between a distributed unit and a further control plane unit, to be used in case of failure of a control plane unit; and a sixth interface between a core network node and a further control plane unit, to be used in case of failure of a control plane unit based on information identifying the further control plane unit. The method according to 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 recovery. The method according to appendix 9. (Appendix 11) The method further includes receiving information identifying a control plane unit for use in activating a further control plane unit when a control plane unit has failed. The method according to appendix 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 distributed unit, the method including: starting a procedure to configure a further control plane unit to act as a recovery node for a control plane unit by sending at least one signaling message to the further control plane unit; backing up a UE context associated with a user equipment (UE) served by the control plane unit at the recovery node; and The method as described above. (Appendix 13) Configuring an additional control plane unit includes setting up or modifying an additional control plane unit to act as a recovery node, the method described in Appendix 12. (Appendix 14) At least one signaling message includes information identifying the UE and the UE context associated with the UE, the method described in Appendix 12 or 13. (Appendix 15) At least one signaling message is sent by a control plane unit, the method described in any one of Appendices 12 to 14. (Appendix 16) At least one signaling message is sent by a user plane unit, the method described in any one of Appendices 12 to 14. (Appendix 17) At least one signaling message is sent by a distributed unit, the method described in any one of Appendices 12 to 14. (Appendix 18) Further includes sending at least one message for establishing a session for the recovery node to a core network node based on the UE context, the method described in any one of Appendices 12 to 17. (Appendix 19) Receiving at least one message including information identifying at least one change to the UE context from an additional control plane unit; and Determining whether to use an additional control plane unit as a recovery node for the control plane unit based on at least one change to the UE context; and further includes, the method described in any one of Appendices 12 to 18. (Appendix 20) Sending a message indicating that at least one change to the UE context has been accepted to a further control plane unit, Using a further control plane unit as a recovery node for the control plane unit based on the changed UE context including at least one change, Further comprising, The method described in Appendix 19. (Appendix 21) At least one change to the UE context includes a change to the packet data convergence protocol (PDCP) configuration associated with the UE context, The method described in Appendix 19 or 20. (Appendix 22) The procedure for configuring a further control plane unit to act as a recovery node includes sending a request to a core network node to set up a protocol data unit (PDU) session for the UE via the recovery node, The method described in any one of Appendices 1 to 20. (Appendix 23) Further comprising starting a procedure to switch to a further control plane unit as a redundant unit upon failure of the control plane unit, The method described in any one of Appendices 1 to 22. (Appendix 24) A method executed by a communication device including at least a control plane unit configured as a control plane unit, a user plane unit, and a distributed unit connected to a further control plane unit configured as a recovery node for the control plane unit, Determining the failure of the control plane unit, Sending a message to a further control plane unit to start a procedure for activating a further control plane unit as a recovery node, Including, a method. (Appendix 25) A method executed by a control plane unit configured as a recovery node for a control plane unit of a communication device including a user plane unit and a distributed unit, comprising: Receiving, from a user plane unit or a distributed unit, a message for starting a procedure to activate the recovery node in case of failure of the control plane unit of the communication device; Communicating with at least one user equipment (UE) using the user plane unit or the distributed unit; A method comprising the above. (Appendix 26) The message includes information for identifying the control plane unit of the communication device. The method according to Appendix 24 or 25. (Appendix 27) Further comprising transmitting at least one message to the user plane unit or the distributed unit to indicate that the recovery node has been activated. The method according to any one of Appendices 24 to 26. (Appendix 28) The communication device includes a distributed base station device. The method according to any one of Appendices 1 to 27. (Appendix 29) A method executed by an operation and maintenance node, comprising: Transmitting information for identifying an additional control plane unit that acts as a redundant unit for a control plane unit for at least one user equipment (UE) served by the control plane unit to a node of a communication device including the control plane unit, the user plane unit, and the distributed unit. A method comprising the above. (Appendix 30) A control plane unit for a communication device including at least a control plane unit, a user plane unit, and a distributed unit, Means for transmitting information for identifying an additional control plane unit that acts as a redundant unit for a control plane unit for at least one user equipment (UE) served by the control plane unit to at least one of a user plane unit and a distributed unit A control plane unit comprising the same. (Appendix 31) A communication device including a control plane unit, a user plane unit, and a distributed unit, Means for receiving information for identifying an additional control plane unit that acts as a redundant unit for a control plane unit for at least one user equipment (UE) served by the control plane unit from at least one of the control plane unit and an operation and maintenance node A communication device comprising the same. (Appendix 32) A communication device including at least a control plane unit, a user plane unit, and a distributed unit, Means for starting a procedure for configuring an additional control plane unit to act as a recovery node for the control plane unit by transmitting at least one signaling message to the additional control plane unit; and Means for backing up a UE context associated with a user equipment (UE) served by the control plane unit at the recovery node A communication device comprising the same. (Appendix 33) A communication device including at least a control plane unit configured as a control plane unit, a user plane unit, and a distributed unit connected to an additional control plane unit configured as a recovery node for the control plane unit, Means for determining a failure of the control plane unit Means for sending a message to a further control plane unit to initiate a procedure for activating a further control plane unit as a recovery node, A communication device comprising the same. (Appendix 34) A control plane unit configured to be a recovery node for a control plane unit of a communication device including a user plane unit and a distributed unit, Means for receiving, from the user plane unit or the distributed unit, a message for initiating a procedure for activating a recovery node in the event of a failure of the control plane unit of the communication device, Means for communicating with at least one user equipment (UE) using the user plane unit or the distributed unit, A control plane unit comprising the same. (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 for identifying a further control plane unit that acts 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 the same.

[0120] This application claims the benefit of priority based on UK Patent Application No. 2202786.6 filed on March 1, 2022. The entire disclosure thereof is incorporated herein by reference.

Description of Reference Numerals

[0121] 1 Telecommunication system 3 Mobile device 5 Base station 7 Core network 8 Access and Mobility Management Function 9 Session Management Function 10 External IP network 31 Transceiver circuit 33 Antenna 35 User Interface 37 Control Unit 39 Memory 41 Operating System 43 Communication Control Module 51 Transceiver Circuit 53 Antenna 55 Network Interface 57 Control Unit 59 Memory 61 Operating System 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 System 83 Communication Control Module

Claims

1. A network node, before any connection is established between one or more user equipments (UEs) and the network node, means for transmitting information for identifying a further control plane unit that acts as a redundant unit for a control plane unit of a distributed base station for serving a certain UE to at least one of a user plane unit of the distributed base station and a distributed unit of the distributed base station, wherein the information is used to activate the further control plane unit as the redundant unit due to a failure of the control plane unit, the network node.

2. The network node is the control plane unit, and comprises means for transmitting a UE context associated with the UE to the further control plane unit for backup at the further control plane unit, The network node according to claim 1.

3. The UE context includes a Protocol Data Convergence Protocol (PDCP) configuration, means for receiving, from the further control plane unit, 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 the PDCP configuration, means for determining whether the supported UE context with the PDCP configuration is accepted, The network node according to claim 2.

4. The means for transmitting the UE context transmits the UE context when the UE context is set up, changed, and / or released in the network node, The network node according to claim 3.

5. 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, ​ Procedure for setting up a third interface between the control plane unit and the core network node Procedure for changing the first interface Procedure for changing the second interface, or Procedure for changing the third interface is transmitted as at least a part of one of The network node according to claim 1

6. Transmitting assistance information for determining a failure of the control plane unit to at least one of the user plane unit and the distributed unit The network node according to claim 1

7. A network unit in a distributed base station that includes a control plane unit, a user plane unit, and a distributed unit, and is connected to a further control plane unit configured as a recovery node for the control plane unit, Means for determining a failure of the 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 the recovery node comprising The further control plane unit is configured as the recovery node before any connection is established by one or more user equipments (UEs) at the distributed base station Network unit

8. A further control plane unit, Means for receiving a message for initiating a procedure for activating as a recovery node for the control plane unit in the event of a failure of the control plane unit from a network unit in a distributed base station including a control plane unit, a user plane unit, and a distributed unit Means for communicating with a user equipment (UE) using the network unit comprising The further control plane unit is configured as the recovery node before any connection is established by one or more UEs at the distributed base station Further control plane unit

9. A method in a network node, Before any connection is established between one or more user equipments (UEs) and the network node, information identifying an additional control plane unit that acts as a redundant unit for the control plane unit of the distributed base station serving a certain UE is transmitted to at least one of the user plane unit of the distributed base station and the distributed unit of the distributed base station, wherein the information is used to activate the additional control plane unit as the redundant unit due to a failure of the control plane unit, Method. **Claim 10** A method in a network unit in a distributed base station, including a control plane unit, a user plane unit, and a distributed unit, and connecting to an additional control plane unit configured as a recovery node of the control plane unit, comprising: determining a failure of the control plane unit; transmitting a message to the additional control plane unit to start a procedure for activating the additional control plane unit as the recovery node; and the additional control plane unit is configured as the recovery node before any connection is established by one or more user equipments (UEs) in the distributed base station. Method. **Claim 11** A method in an additional control plane unit, comprising: receiving, from a network unit in a distributed base station including a control plane unit, a user plane unit, and a distributed unit, a message for starting a procedure for activating the control plane unit as a recovery node in the event of a failure of the control plane unit; communicating with a user equipment (UE) using the network unit; and the additional control plane unit is configured as the recovery node before any connection is established by one or more UEs in the distributed base station. Method.

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