Central unit control plane device, central unit user plane device, and methods thereof

Abstract

A device configured to act as a central unit control plane (21) for a radio access network node (1) transmits to a central unit user plane (22) of the radio access network node (1) a control message that indicates that one or more packet data convergence protocol (PDCP) count values for an acknowledged mode (AM) data radio bearer (DRB) set for a radio terminal (4) need to be reset. This can contribute, for example, to facilitating reset of PDCP count values for an AM DRB by a radio access network node that employs an architecture that separates the control plane and the user plane.

Description

[Technical Field]

[0001] The present disclosure relates to wireless communication systems, and more particularly to an interface between a central unit control plane and a central unit user plane. [Background technology]

[0002] The 3rd Generation Partnership Project (3GPP®) provides specifications for the Fifth Generation System (5GS), including the architecture and signaling protocols of the NG Radio Access Network (NG-RAN). Non-Patent Document 1 specifies a 5G radio network layer signaling protocol for the E1 interface, i.e., the E1 Application Protocol (E1AP). The E1 interface provides a means for interconnecting the gNB Central Unit Control Plane (CU-CP) and the gNB Central Unit User Plane (CU-UP) of a gNB within the NG-RAN. Alternatively, the E1 interface provides a means for interconnecting the gNB-CU-CP and the gNB-CU-UP of an en-gNB within the Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN).

[0003] The gNB is a node that provides NR user plane and control plane protocol terminations to User Equipment (UE) and is connected to the 5G Core Network (5GC) via the NG interface, while the en-gNB is a node that provides NR user plane and control plane protocol terminations to UE and acts as a secondary node for E-UTRA-NR Dual Connectivity (EN-DC).

[0004] The gNB-CU is a logical node that hosts the Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) protocols of a gNB, or the RRC and PDCP protocols of an en-gNB, and controls the operation of one or more gNB Distributed Units (DUs). The gNB-CU terminates the F1 interface connected to the gNB-DU. The gNB-DU is 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 more cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected to the gNB-CU.

[0005] The gNB-CU-CP is a logical node that hosts the control plane portion of the RRC and PDCP protocols of the gNB-CU for the en-gNB or gNB. The gNB-CU-CP terminates the E1 interface connected to the gNB-CU-UP and the F1-C interface connected to the gNB-DU.

[0006] The gNB-CU-UP is a logical node that hosts the user plane part of the PDCP protocol of the gNB-CU for the en-gNB, or the user plane part of the PDCP protocol and the SDAP protocol 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 interface connected to the gNB-DU.

[0007] According to Non-Patent Document 1, the gNB-CU-CP can request Packet Data Convergence Protocol (PDCP) re-establishment for one or more Data Radio Bearers (DRBs) already configured for the UE from the gNB-CU-UP using a BEARER CONTEXT MODIFICATION REQUEST message. Specifically, the BEARER CONTEXT MODIFICATION REQUEST message can include a PDU Session Resource To Modify List IE. The PDU Session Resource To Modify List IE can include a DRB To Modify List IE. The DRB To Modify List IE includes a PDCP Configuration IE for each of the one or more DRBs to be modified. The PDCP Configuration IE can include a PDCP Re-establishment IE. The PDCP Re-establishment IE indicates that a PDCP entity re-establishment is triggered as defined in 3GPP TS 38.323 (Non-Patent Document 2).

[0008] According to Section 5.1.2 of Non-Patent Document 2, during PDCP re-establishment, the transmitting PDCP entity sets TX_NEXT to its initial value for Unacknowledged Mode (UM) DRBs and Signaling Radio Bearers (SRBs). Similarly, during PDCP re-establishment, the receiving PDCP entity sets RX_NEXT to its initial value for UM DRBs and SRBs. TX_NEXT is a state variable indicating the COUNT value of the next PDCP Service Data Unit (SDU) to be transmitted. The initial value of TX_NEXT for DRBs is zero. RX_NEXT is a state variable indicating the COUNT value of the next PDCP SDU expected to be received. The initial value of RX_NEXT for DRBs on the Uu interface between the UE and gNB is zero. The COUNT value consists of the Hyper Frame Number (HFN) and the PDCP Sequence Number (SN). [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] 3GPP TS 38.463 V16.8.0 (2021-12) "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NG-RAN; E1 Application Protocol (E1AP) (Release 16)", December 2021 [Non-patent document 2] 3GPP TS 38.323 V16.6.0 (2021-12) "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; Packet Data Convergence Protocol (PDCP) specification (Release 16)", December 2021 Summary of the Invention [Problem to be solved by the invention]

[0010] It is unclear how the gNB-CU-CP instructs the gNB-CU-UP, for example, using a BEARER CONTEXT MODIFICATION REQUEST message, to reset the PDCP counts for any one or more DRBs already configured for the UE, including Acknowledged Mode (AM) DRBs.

[0011] As mentioned above, according to the provisions of Non-Patent Document 1, the gNB-CU-CP can instruct the gNB-CU-UP to re-establish PDCP for a DRB by including a PDCP Re-establishment IE in the BEARER CONTEXT MODIFICATION REQUEST message. According to the provisions of Non-Patent Document 2, for a UM DRB, PDCP re-establishment includes resetting the PDCP count value, i.e., setting the PDCP count value to its initial value. A UM DRB is a data radio bearer that uses Unacknowledged Mode (UM) RLC. In other words, a UM DRB is a DRB in which Unacknowledged Mode (UM) is used in the RLC sublayer.

[0012] However, the gNB-CU-CP cannot instruct (or request) the gNB-CU-UP to reset the PDCP count values ​​of AM DRBs by a single control message (i.e., E1AP message). AM DRBs are data radio bearers that use Acknowledged Mode (AM) Radio Link Control (RLC). In other words, AM DRBs are DRBs for which Acknowledged Mode (AM) is used in the RLC sublayer.

[0013] One method is for the gNB-CU-CP to send a first BEARER CONTEXT MODIFICATION REQUEST message to the gNB-CU-UP requesting the release of the AM DRB, and then send a second BEARER CONTEXT MODIFICATION REQUEST message to the gNB-CU-UP requesting the re-establishment of the AM DRB. The gNB-CU-UP then releases the PDCP entity for the AM DRB in response to the first BEARER CONTEXT MODIFICATION REQUEST message, and then re-establishes the PDCP entity for the AM DRB in response to the second BEARER CONTEXT MODIFICATION REQUEST message. Establishing the PDCP entity includes setting the state variables of the PDCP entity, including TX_NEXT and RX_NEXT, to their initial values. Consequently, the PDCP count values ​​(i.e., TX_NEXT and RX_NEXT) for the AM DRB are reset. However, this procedure requires a first BEARER CONTEXT MODIFICATION procedure and a second BEARER CONTEXT MODIFICATION procedure. In other words, to reset the PDCP count value of the AM DRB, the gNB-CU-CP needs to send two BEARER CONTEXT MODIFICATION REQUEST messages to the gNB-CU-UP. This may increase the amount of signaling exchanged between the gNB-CU-CP and the gNB-CU-UP and may increase the time required to reset the PDCP count value of the AM DRB.

[0014] Such problems are not limited to 5G systems, but can also occur in wireless communication systems that employ architectures similar to those of 5G systems.

[0015] One of the objectives to be achieved by the embodiments disclosed in this specification is to provide an apparatus, a method, and a program that contribute to facilitating a radio access network node employing an architecture in which the control plane and the user plane are separated to reset the PDCP count value of an Acknowledged Mode (AM) data radio bearer. It should be noted that this objective is only one of multiple objectives to be achieved by multiple embodiments disclosed in this specification. Other objectives or problems and novel features will become apparent from the description of this specification or the accompanying drawings. [Means for solving the problem]

[0016] In a first aspect, an apparatus configured to operate as a central unit control plane of a radio access network node includes at least one memory and at least one processor coupled to the at least one memory, wherein the at least one processor is configured to send a control message to a central unit control plane of the radio access network node indicating that one or more PDCP count values ​​of configured AM data radio bearers for a wireless terminal need to be reset.

[0017] In a second aspect, an apparatus configured to operate as a central unit user plane of a radio access network node includes at least one memory and at least one processor coupled to the at least one memory, wherein the at least one processor is configured to receive a control message from the central unit control plane of the radio access network node indicating that one or more PDCP count values ​​of configured AM data radio bearers for a wireless terminal need to be reset.

[0018] In a third aspect, a method performed by a central unit control plane of a radio access network node comprises sending a control message to a central unit user plane of the radio access network node indicating that one or more PDCP count values ​​of AM data radio bearers configured for a wireless terminal need to be reset.

[0019] In a fourth aspect, a method performed by a central unit user plane of a radio access network node comprises receiving a control message from a central unit control plane of the radio access network node indicating that one or more PDCP count values ​​of AM data radio bearers configured for a wireless terminal need to be reset.

[0020] In a fifth aspect, a program includes a group of instructions (software code) that, when loaded into a computer, causes the computer to perform the method according to the third or fourth aspect described above. [Effects of the Invention]

[0021] According to the above-described aspects, it is possible to provide an apparatus, a method, and a program that contribute to facilitating a radio access network node employing a control plane / user plane separated architecture to reset the PDCP count value of an Acknowledged Mode (AM) data radio bearer. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram illustrating an example of the configuration of a wireless communication network according to an embodiment. [Figure 2] FIG. 10 is a sequence diagram illustrating an example of signaling according to an embodiment. [Figure 3] 10 is a flowchart illustrating an example of the operation of a central unit control plane according to an embodiment. [Figure 4]10 is a flowchart illustrating an example of an operation of a central unit user plane according to an embodiment. [Figure 5] FIG. 10 is a sequence diagram illustrating an example of signaling according to an embodiment. [Figure 6] 10 is a flowchart illustrating an example of the operation of a central unit control plane according to an embodiment. [Figure 7] 10 is a flowchart illustrating an example of an operation of a central unit user plane according to an embodiment. [Figure 8] FIG. 10 is a diagram illustrating an example of the format of a PDU Session Resource To Modify List information element according to an embodiment. [Figure 9] FIG. 10 is a sequence diagram illustrating an example of signaling according to an embodiment. [Figure 10] 10 is a flowchart illustrating an example of the operation of a central unit control plane according to an embodiment. [Figure 11] 10 is a flowchart illustrating an example of an operation of a central unit user plane according to an embodiment. [Figure 12] FIG. 10 is a diagram illustrating an example of the format of a PDU Session Resource To Modify List information element according to an embodiment. [Figure 13] FIG. 10 is a sequence diagram illustrating an example of signaling according to an embodiment. [Figure 14] 10 is a flowchart illustrating an example of the operation of a central unit control plane according to an embodiment. [Figure 15] 10 is a flowchart illustrating an example of an operation of a central unit user plane according to an embodiment. [Figure 16] FIG. 10 is a diagram illustrating an example of the format of a PDU Session Resource To Modify List information element according to an embodiment. [Figure 17] FIG. 10 is a sequence diagram illustrating an example of signaling according to an embodiment. [Figure 18]FIG. 2 is a block diagram illustrating an example configuration of a central unit control plane and a central unit user plane according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, specific embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and for clarity of explanation, duplicate explanations will be omitted as necessary.

[0024] The multiple embodiments described below can be implemented independently or in appropriate combination. These multiple embodiments have different novel features. Therefore, these multiple embodiments contribute to solving different purposes or problems and to achieving different effects.

[0025] The following embodiments are described primarily for the 3GPP 5G system. However, these embodiments may also be applied to other wireless communication systems employing an architecture similar to that of the 5G system. These embodiments may also be applied to other wireless communication systems including a radio access network node employing an architecture in which the control plane and the user plane are separated. More specifically, the radio access network node may be configured to communicate with one or more wireless terminals and may include a central unit control plane, one or more central unit user planes, and one or more distributed units. The embodiments described below may also be applied to such a radio access network node.

[0026] As used herein, depending on the context, "if" may be construed to mean "when," "at or around the time," "after," "upon," "in response to determining," "in accordance with a determination," or "in response to detecting." These expressions may be construed to have the same meaning, depending on the context.

[0027] First, the configurations and operations of multiple network elements common to multiple embodiments will be described. Figure 1 shows an example configuration of a wireless communication system according to multiple embodiments. Each element (network function) shown in Figure 1 can be implemented, for example, as a network element on dedicated hardware, as a software instance running on dedicated hardware, or as a virtualized function instantiated on an application platform.

[0028] The gNB1 is a node that provides NR user plane and control plane protocol termination to the User Equipment (UE) 4 and is connected to the 5G Core Network (5GC) via the NG interface. The NG interface includes the NG Control Plane (NG-C) interface and the NG User Plane (NG-U) interface. The NG-C interface is also called the N2 interface or reference point. The NG-U interface is also called the N3 interface or reference point. The NG-C interface uses the NG Application Protocol (NGAP) to communicate with control plane nodes in the core network (i.e., Access and Mobility management Function (AMF)). The NG-U interface uses the General Packet Radio Service Tunneling Protocol User Plane (GTP-U) tunnel and PDU Session user plane protocol to communicate with user plane nodes in the core network (i.e., User Plane Function (UPF)).

[0029] The gNB1 may be an en-gNB, which provides NR user plane and control plane protocol terminations to the UE and acts as a secondary node for E-UTRA-NR Dual Connectivity (EN-DC).

[0030] The gNB1 includes a gNB Central Unit (CU)2 and one or more gNB Distributed Units (DUs)3. The gNB-CU2 is a logical node that controls the operation of one or more gNB-DUs3. The gNB-CU2 hosts the Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) protocols of the gNB1. Note that if the gNB1 is an en-gNB, the gNB-CU2 hosts the RRC and PDCP protocols of the en-gNB.

[0031] The gNB-DU3 is a logical node that hosts the Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layers of the gNB1 (i.e., 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-DU3. The gNB-DU3 terminates the F1 interface connected to the gNB-CU2. The F1 interface includes the F1 Control Plane (F1-C) interface and the F1 User Plane (F1-U) interface.

[0032] The gNB-CU2 includes a gNB-CU Control Plane (CP) 21 and one or more gNB-CU User Planes (CU-UPs) 22. The gNB-CU-CP 21 is a logical node that hosts the control plane portion of the gNB-CU2's RRC and PDCP protocols. The gNB-CU-CP 21 terminates an E1 interface connected to each gNB-CU-UP 22 and an F1-C interface connected to each gNB-DU3. The E1 interface uses the E1 Application Protocol (E1AP). The F1-C interface uses the F1 Application Protocol (F1AP). The gNB-CU-CP 21 also terminates an NG-C interface connected to a control plane node (i.e., AMF) in the core network.

[0033] The gNB-CU-UP22 is a logical node that hosts the user plane portion of the PDCP protocol of the gNB-CU2 for the en-gNB, or the user plane portion of the PDCP protocol and the SDAP protocol of the gNB-CU2 for the gNB. The gNB-CU-UP22 terminates the E1 interface connected to the gNB-CU-CP21 and the F1-U interface connected to each gNB-DU3. The F1-U interface uses a GTP-U tunnel. The gNB-CU-UP22 also terminates the NG-U interface connected to the user plane node (i.e., UPF) in the core network.

[0034] The gNB1 shown in FIG. 1 is an example of a radio access network node. The UE4 shown in FIG. 1 is an example of a wireless terminal. The gNB-CU-CP21 shown in FIG. 1 is an example of a central unit control plane of a radio access network node. The gNB-CU-UP22 shown in FIG. 1 is an example of a central unit user plane of a radio access network node. The radio access network node communicates with one or more UEs or wireless terminals over the air interface. The radio access network node provides signaling with the core network and transfers user data to and from the core network, enabling these UEs or wireless terminals to communicate with the core network and data network. The radio access network node may also be referred to as a base station, radio station, or access point.

[0035] First Embodiment The configurations and operations of the wireless communication system and network elements (or apparatuses, nodes, devices, or network functions) according to this embodiment may be similar to those of the example described with reference to Fig. 1. This embodiment provides an improvement to E1AP signaling. Specifically, this embodiment provides an improvement that contributes to facilitating the gNB-CU-CP 21 and gNB-CU-UP 22 to reset the PDCP count values ​​of Acknowledged Mode (AM) Data Radio Bearers (DRBs).

[0036] 2 shows an example of signaling according to this embodiment. In step 201, the gNB-CU-CP 21 sends a control message to the gNB-CU-UP 22 indicating that the PDCP count values ​​of one or more AM DRBs configured for the UE 4 need to be reset. The control message may indicate that the PDCP count values ​​of multiple AM ​​DRBs need to be reset. The control message may be an E1AP message. More specifically, the control message may be a message sent to the gNB-CU-UP 22 to request modification of the bearer context. More specifically, the control message may be an E1AP BEARER CONTEXT MODIFICATION REQUEST message.

[0037] An AM DRB is a data radio bearer that uses Acknowledged Mode (AM) RLC. In other words, an AM DRB is a DRB in which Acknowledged Mode (AM) is used in the RLC sublayer (i.e., gNB-DU3). AM is one of three transmission modes supported by the RLC sublayer (i.e., AM, Unacknowledged Mode (UM), and Transparent Mode (TM)). In AM, the RLC sublayer provides automatic repeat request (ARQ). In this ARQ, an RLC entity (e.g., an RLC entity in a gNB-DU3) retransmits an RLC SDU or RLC SDU segments based on an RLC Control Protocol Data Unit (PDU) (i.e., a STATUS PDU) from a peer RLC entity (e.g., an RLC entity in a UE4).

[0038] The control message of step 201 causes the gNB-CU-UP 22 to reset the PDCP count values ​​of one or more AM DRBs. In response to receiving the control message, the gNB-CU-UP 22 may reset the PDCP count values ​​of one or more AM DRBs. Resetting the PDCP count values ​​means setting the PDCP count values ​​to their initial values.

[0039] In some implementations, one or more PDCP count values ​​of an AM DRB include TX_NEXT and RX_NEXT. TX_NEXT is a state variable indicating the COUNT value of the next PDCP Service Data Unit (SDU) to be transmitted. The initial value of TX_NEXT for DRBs is zero. RX_NEXT is a state variable indicating the COUNT value of the next PDCP SDU expected to be received. The initial value of RX_NEXT for DRBs on the Uu interface between the UE4 and the gNB1 is zero. Each COUNT value consists of a Hyper Frame Number (HFN) and a PDCP Sequence Number (SN).

[0040] The gNB-CU-CP21 may send a control message in step 201 to reset the PDCP count values ​​of one or more AM DRBs configured for the UE4.

[0041] In one example, the gNB-CU-CP21 may transmit a control message in step 201 during the preparation phase of an intra-CU inter-DU handover of the UE4. More specifically, the gNB-CU-CP21 may receive a control message from the gNB-DU3 (i.e., the target gNB-DU) that includes a cell group configuration created with full configuration. In other words, the gNB-CU-CP21 may receive a control message from the gNB-DU3 (i.e., the target gNB-DU) that includes a cell group configuration and indicates that the cell group configuration was created with full configuration. The cell group configuration includes configurations for the RLC sublayer, MAC sublayer, and PHY layer for the UE4. The full configuration means that delta signaling or delta configuration from the source cell group configuration of the source gNB-DU is not applied. In other words, the full configuration means that SDAP and PDCP delta signaling are not applied during an inter-DU handover. The target cell group configuration of the target gNB-DU generated in full configuration includes all cell group configurations, not just the differences from the source cell group configuration (i.e., delta configuration).

[0042] This control message between the CU and DU may be an F1AP message, or more specifically, an F1AP UE CONTEXT SETUP RESPONSE message. The F1AP UE CONTEXT SETUP RESPONSE message includes a DU To CU RRC Information information element (IE) including cell group configuration, and may also include a Full Configuration information element (IE). In response to receiving this control message (e.g., an F1AP UE CONTEXT SETUP RESPONSE message), the gNB-CU-CP21 may send a message of step 201 (e.g., an E1AP BEARER CONTEXT MODIFICATION REQUEST message).

[0043] In this case, the gNB-CU-CP21 may include the Downlink (DL) Transport Network Layer (TNL) address information received from the gNB-DU3 (i.e., target gNB-DU) via the F1AP UE CONTEXT SETUP RESPONSE message in the E1AP BEARER CONTEXT MODIFICATION REQUEST message of step 201. The DL TNL address information indicates the endpoint information of the gNB-DU3 (i.e., target gNB-DU) side of the GTP-U tunnel of the F1-U interface. The DL TNL address information may also be referred to as DL UP parameters. This allows the gNB-CU-CP21 to request the gNB-CU-UP22 to reset the PDCP count value of the AM DRB and to inform the gNB-CU-UP22 of the new DL TNL information of the AM DRB using a single control message.

[0044] In another example, the gNB-CU-CP21 may transmit the control message of step 201 when the PDCP count value of the AM DRB is about to wrap around, i.e., when the PDCP count value of the AM DRB is approaching its maximum value. In other words, the gNB-CU-CP21 may transmit the control message of step 201 when the PDCP count value of the AM DRB is about to wrap around. gNB In response to performing the refresh of the PDCP count value in step 201, the gNB-CU-CP 21 may transmit the control message of step 201. The gNB-CU-CP 21 may perform an RRC Counter check procedure to check the PDCP count value in the UE 4. Specifically, the gNB-CU-CP 21 may transmit a Counter Check message to the UE 4 and receive a Counter Check Response message from the UE 4 indicating the PDCP count value of the UE 4.

[0045] In yet another example, the gNB-CU-CP21 may determine whether or not K is being used based on other policies or triggers. gNB In response to the refresh of the UE, the control message of step 201 may be transmitted.

[0046] 3 shows an example of the operation of gNB-CU-CP21. In step 301, gNB-CU-CP21 generates a control message indicating that the PDCP count values ​​of one or more configured AM DRBs for UE4 need to be reset. The control message may indicate that the PDCP count values ​​of multiple AM ​​DRBs need to be reset. In step 302, gNB-CU-CP21 transmits the generated control message to gNB-CU-UP22.

[0047] 4 shows an example of the operation of gNB-CU-UP22. In step 401, gNB-CU-UP22 receives a control message from gNB-CU-CP21 indicating that the PDCP count values ​​of one or more AM DRBs configured for UE4 need to be reset. The control message may indicate that the PDCP count values ​​of multiple AM ​​DRBs need to be reset. In step 402, gNB-CU-UP22 resets the PDCP count values ​​of the one or more AM DRBs in response to receiving the control message.

[0048] According to the operations of gNB-CU-CP21 and gNB-CU-UP22 described in this embodiment, by sending one control message to gNB-CU-UP22, gNB-CU-CP21 can request gNB-CU-UP22 to reset the PDCP count values ​​of one or more AM DRBs, which can facilitate gNB-CU-CP21 and gNB-CU-UP22 to reset the PDCP count values ​​of the AM DRBs.

[0049] <Second embodiment> The configuration and operation of the wireless communication system and network elements (or apparatuses, nodes, devices, or network functions) according to this embodiment may be similar to the example described with reference to Fig. 1. This embodiment provides details of improvements to the E1AP signaling provided in the first embodiment.

[0050] 5 shows an example of signaling according to this embodiment. In step 501, the gNB-CU-CP 21 sends an E1AP BEARER CONTEXT MODIFICATION REQUEST message to the gNB-CU-UP 22. To indicate that one or more PDCP count values ​​for an AM DRB need to be reset, the BEARER CONTEXT MODIFICATION REQUEST message in step 501 includes a DRB to Setup List and a DRB to Remove List that indicate the same DRB identifier (DRB ID) for the AM DRB. To indicate that the PDCP count values ​​for multiple AM ​​DRBs need to be reset, the BEARER CONTEXT MODIFICATION REQUEST message may include a DRB to Setup List that indicates the DRB IDs of these DRBs and a DRB to Remove List that indicates the same DRB IDs.

[0051] The DRB to Setup List and DRB to Remove List indicating the same DRB identifier in a single BEARER CONTEXT MODIFICATION REQUEST message inform the gNB-CU-UP22 that the AM DRB needs to be newly set up after it is released. In response to receiving the DRB to Setup List and DRB to Remove List indicating the same DRB identifier, the gNB-CU-UP22 recognizes that the AM DRB identified by the DRB identifier needs to be newly set up after it is released. In response, the gNB-CU-UP22 releases the PDCP entity for the AM DRB and then re-establishes the PDCP entity for the AM DRB. Establishing the PDCP entity includes setting the state variables of the PDCP entity, including TX_NEXT and RX_NEXT, to their initial values. Consequently, the PDCP count values ​​(e.g., TX_NEXT and RX_NEXT) for the AM DRB are reset.

[0052] The gNB-CU-CP 21 may send a BEARER CONTEXT MODIFICATION REQUEST message in step 501 to reset the PDCP count values ​​of one or more AM DRBs configured for the UE 4. The triggers or conditions for sending the message in step 501 may be similar to those described with respect to the message in step 201 in the first embodiment.

[0053] 6 shows an example of the operation of gNB-CU-CP21. In step 601, gNB-CU-CP21 generates a BEARER CONTEXT MODIFICATION REQUEST message including a DRB to Setup List and a DRB to Remove List indicating the same DRB identifier of the AM DRB. In step 602, gNB-CU-CP21 sends the generated BEARER CONTEXT MODIFICATION REQUEST message to gNB-CU-UP22.

[0054] 7 shows an example of the operation of gNB-CU-UP22. In step 701, gNB-CU-UP22 receives a BEARER CONTEXT MODIFICATION REQUEST message from gNB-CU-CP21, which includes a DRB to Setup List and a DRB to Remove List indicating the same DRB identifier of an AM DRB. In step 702, in response to receiving the DRB to Setup List and the DRB to Remove List indicating the same DRB identifier, gNB-CU-UP22 recognizes that the AM DRB identified by the DRB identifier needs to be newly set up after being released.

[0055] The DRB to Setup List and the DRB to Remove List, which indicate the same DRB identifier of the AM DRB, may be included in the PDU Session Resource To Modify List information element (IE) in the BEARER CONTEXT MODIFICATION REQUEST message. The BEARER CONTEXT MODIFICATION REQUEST message is UE-associated signaling associated with a specific UE (e.g., UE 4).

[0056] FIG. 8 shows an example of the format of the PDU Session Resource To Modify List IE. In the example of FIG. 8, the PDU Session Resource To Modify List IE may include a DRB To Setup List IE801 and a DRB to Remove List IE802. The DRB To Setup List IE801 is a list of one or more DRBs to be set up for the UE 4 and includes the configuration of these one or more DRBs. The DRB to Remove List IE802 is a list of one or more DRBs to be released. The DRB To Setup List IE801 indicates a DRB ID 821 of each DRB to be set up. Similarly, the DRB to Remove List IE802 indicates a DRB ID 822 of each DRB to be released. If the DRB ID 821 is the same as the DRB ID 822, the gNB-CU-UP 22 recognizes that the DRB (e.g., AM DRB) identified by the DRB ID needs to be newly set up after being released.

[0057] As shown in Figure 8, the DRB To Setup List IE801 may include a DL UP parameters IE841. The DL UP parameters IE841 may indicate DL TNL address information of the gNB-DU3 (e.g., target gNB-DU) regarding the F1-U interface. For example, in the preparation phase of an intra-CU inter-DU handover, the gNB-CU-CP21 may receive DL TNL information from the target gNB-DU and include the DL TNL information in the DL UP parameters IE841.

[0058] Specifically, as described in Section 9.3.3.11 of 3GPP TS 23.100, the DRB To Setup List IE included in the existing PDU Session Resource To Modify List IE cannot include a DL UP parameters IE. Therefore, if the existing PDU Session Resource To Modify List IE format is used, the gNB-CU-CP21 needs to send an additional BEARER CONTEXT MODIFICATION REQUEST message including a DRB To Modify List IE indicating the DL TNL information of the target gNB-DU. In contrast, by using the DRB To Setup List IE801 modified to include a DL UP parameters IE841 as shown in Figure 8, the gNB-CU-CP21 can request the gNB-CU-UP22 to reset the PDCP count value of the AM DRB and inform the gNB-CU-UP22 of the new DL TNL information of the AM DRB using a single BEARER CONTEXT MODIFICATION REQUEST message.

[0059] Although omitted in Figure 8, the DRB To Setup List IE 801 may include other information items (or information elements). Similarly, the DRB to Remove List IE 802 may include other information items (or information elements). These information items (or information elements) may be the same as existing ones. The format and description of the existing PDU Session Resource To Modify List IE, including the existing DRB To Setup List IE and DRB to Remove List IE, are described in Non-Patent Document 1 (e.g., Sections 8.3.2.2, 9.2.2.4, and 9.3.3.11).

[0060] According to the operations of gNB-CU-CP21 and gNB-CU-UP22 described in this embodiment, by sending one control message, specifically a BEARER CONTEXT MODIFICATION REQUEST message, to gNB-CU-UP22, gNB-CU-CP21 can request gNB-CU-UP22 to reset the PDCP count values ​​of one or more AM DRBs. This makes it easy for gNB-CU-CP21 and gNB-CU-UP22 to reset the PDCP count values ​​of AM DRBs.

[0061] <Third embodiment> The configuration and operation of the wireless communication system and network elements (or apparatuses, nodes, devices, or network functions) according to this embodiment may be similar to the example described with reference to Fig. 1. This embodiment provides details of improvements to the E1AP signaling provided in the first embodiment.

[0062] 9 shows an example of signaling according to this embodiment. In step 901, the gNB-CU-CP 21 sends an E1AP BEARER CONTEXT MODIFICATION REQUEST message to the gNB-CU-UP 22. To indicate that the PDCP count values ​​of one or more AM DRBs need to be reset, the BEARER CONTEXT MODIFICATION REQUEST message in step 901 includes a DRB To Remove and Setup List containing one or more information items associated with the DRB identifiers (DRB IDs) of the AM DRBs. To indicate that the PDCP count values ​​of multiple AM ​​DRBs need to be reset, the DRB To Remove and Setup List may indicate the DRB IDs of these DRBs.

[0063] The DRB To Remove and Setup List in a BEARER CONTEXT MODIFICATION REQUEST message informs the gNB-CU-UP22 that DRBs (including AM DRB(s)) associated with one or more DRB IDs indicated in the list need to be newly set up after being released. In response to receiving the DRB To Remove and Setup List, the gNB-CU-UP22 recognizes that the DRBs (including AM DRB(s)) associated with one or more DRB IDs indicated in the list need to be newly set up after being released. In response, the gNB-CU-UP22 releases the PDCP entities for the AM DRB(s) and then re-establishes the PDCP entities for the AM DRB(s). Establishing the PDCP entities includes setting the state variables of the PDCP entities, including TX_NEXT and RX_NEXT, to their initial values. Consequently, the PDCP count values ​​(e.g., TX_NEXT and RX_NEXT) for the AM DRB(s) are reset.

[0064] The gNB-CU-CP 21 may send a BEARER CONTEXT MODIFICATION REQUEST message in step 901 to reset the PDCP count values ​​of one or more AM DRBs configured for the UE 4. The triggers or conditions for sending the message in step 901 may be similar to those described with respect to the message in step 201 in the first embodiment.

[0065] Figure 10 shows an example of the operation of gNB-CU-CP21. In step 1001, gNB-CU-CP21 generates a BEARER CONTEXT MODIFICATION REQUEST message including a DRB To Remove and Setup List containing information items associated with the DRB identifier of the AM DRB. In step 1002, gNB-CU-CP21 sends the generated BEARER CONTEXT MODIFICATION REQUEST message to gNB-CU-UP22.

[0066] Figure 11 shows an example of the operation of gNB-CU-UP22. In step 1101, gNB-CU-UP22 receives a BEARER CONTEXT MODIFICATION REQUEST message from gNB-CU-CP21, which includes a DRB To Remove and Setup List containing information items associated with the DRB identifiers of AM DRBs. In step 1102, in response to receiving the DRB To Remove and Setup List, gNB-CU-UP22 recognizes that the AM DRB(s) identified by the DRB identifiers included in the list need to be newly set up after being released.

[0067] The DRB To Remove and Setup List may be included in a PDU Session Resource To Modify List IE in a BEARER CONTEXT MODIFICATION REQUEST message. The BEARER CONTEXT MODIFICATION REQUEST message is UE-associated signaling associated with a specific UE (e.g., UE 4).

[0068] FIG. 12 shows an example of the format of the PDU Session Resource To Modify List IE. In the example of FIG. 12, the PDU Session Resource To Modify List IE may include a DRB To Remove and Setup List IE 1201. The DRB To Remove and Setup List IE 1201 corresponds to the DRB To Remove and Setup List described above. The DRB To Remove and Setup List IE 1201 indicates one or more DRB IDs of one or more DRBs that need to be released and re-setup. The DRB To Remove and Setup List IE 1201 may include settings 1221 for these one or more DRBs. If some or all of these settings 1221 are omitted, the gNB-CU-UP 22 may understand that the omitted settings are the same as the current settings before the DRB release. Alternatively, the DRB To Remove and Setup List IE 1201 may include the settings 1221 as a mandatory information element.

[0069] As shown in FIG. 12, the DRB To Remove and Setup List IE1201 may include a DL UP parameters IE1241. The DL UP parameters IE1241 may indicate DL TNL address information of the gNB-DU3 (e.g., target gNB-DU) related to the F1-U interface. For example, in the preparation phase of an intra-CU inter-DU handover, the gNB-CU-CP21 may receive DL TNL information from the target gNB-DU and include the DL TNL information in the DL UP parameters IE1241. This allows the gNB-CU-CP21 to request the gNB-CU-UP22 to reset the PDCP count value of the AM DRB and to inform the gNB-CU-UP22 of the new DL TNL information of the AM DRB using a single BEARER CONTEXT MODIFICATION REQUEST message.

[0070] Although omitted in Figure 12, the DRB To Remove and Setup List IE 1201 may include other information items (or information elements). These information items (or information elements) may be the same as those included in the existing DRB To Setup List IE or DRB To Modify List IE. The format and description of the existing PDU Session Resource To Modify List IE, including the existing DRB To Setup List IE and DRB to Modify List IE, are described in 3GPP TS 23.2.2 (e.g., sections 8.3.2.2, 9.2.2.4, and 9.3.3.11).

[0071] According to the operations of gNB-CU-CP21 and gNB-CU-UP22 described in this embodiment, by sending one control message, specifically a BEARER CONTEXT MODIFICATION REQUEST message, to gNB-CU-UP22, gNB-CU-CP21 can request gNB-CU-UP22 to reset the PDCP count values ​​of one or more AM DRBs. This makes it easy for gNB-CU-CP21 and gNB-CU-UP22 to reset the PDCP count values ​​of AM DRBs.

[0072] <Fourth embodiment> The configuration and operation of the wireless communication system and network elements (or apparatuses, nodes, devices, or network functions) according to this embodiment may be similar to the example described with reference to Fig. 1. This embodiment provides details of improvements to the E1AP signaling provided in the first embodiment.

[0073] Figure 13 shows an example of signaling according to this embodiment. In step 1301, the gNB-CU-CP 21 sends an E1AP BEARER CONTEXT MODIFICATION REQUEST message to the gNB-CU-UP 22. The BEARER CONTEXT MODIFICATION REQUEST message includes a DRB To Modify List containing one or more information items associated with the DRB identifiers of the AM DRBs. To indicate that the PDCP count values ​​of one or more AM DRBs need to be reset, one or more information items in the DRB To Modify List include an information item indicating that the PDCP count values ​​are to be reset. The name of the information item (or information element) indicating that the PDCP count values ​​are to be reset may be, for example, but is not limited to, "PDCP COUNT Not-Configuration." The information item (or information element) may also indicate that the PDCP count values ​​of one or more AM DRBs are not to be carried over.

[0074] An information item (or information element) indicating that the PDCP count value is to be reset informs the gNB-CU-UP22 that the PDCP count value of the DRB (e.g., AM DRB) identified by the DRB identifier associated with the information item needs to be reset. In response to receiving the information item (or information element), the gNB-CU-UP22 resets the PDCP count values ​​(e.g., TX_NEXT and RX_NEXT) of the DRB (e.g., AM DRB) identified by the DRB identifier associated with the information item.

[0075] The gNB-CU-CP 21 may send a BEARER CONTEXT MODIFICATION REQUEST message in step 1301 to reset the PDCP count values ​​of one or more AM DRBs configured for the UE 4. The triggers or conditions for sending the message in step 1301 may be similar to those described with respect to the message in step 201 in the first embodiment.

[0076] Figure 14 shows an example of the operation of gNB-CU-CP21. In step 1401, gNB-CU-CP21 generates a BEARER CONTEXT MODIFICATION REQUEST message including a DRB To Modify List that includes an information element indicating that the PDCP count value of the AM DRB is reset. The information element may also indicate that the PDCP count value of the AM DRB is not carried over. In step 1402, gNB-CU-CP21 sends the generated BEARER CONTEXT MODIFICATION REQUEST message to gNB-CU-UP22.

[0077] FIG. 15 shows an example of the operation of the gNB-CU-UP22. In step 1501, the gNB-CU-UP22 receives from the gNB-CU-CP21 a BEARER CONTEXT MODIFICATION REQUEST message including a DRB To Modify List that includes an information element indicating that the PDCP count value of the AM DRB is to be reset. The information element may indicate that the PDCP count value of the AM DRB is not to be carried over. In step 1502, in response to receiving the information element, the gNB-CU-UP22 recognizes that the PDCP count value of the AM DRB identified by the DRB ID associated with the information element needs to be reset. Alternatively, the gNB-CU-UP22 may recognize that the PDCP count value of the AM DRB identified by the DRB ID associated with the information element is not to be carried over, and reset the PDCP count value accordingly.

[0078] The DRB To Modify List may be included in a PDU Session Resource To Modify List IE in a BEARER CONTEXT MODIFICATION REQUEST message. The BEARER CONTEXT MODIFICATION REQUEST message is UE-associated signaling associated with a specific UE (e.g., UE 4).

[0079] FIG. 16 shows an example of the format of the PDU Session Resource To Modify List IE. In the example of FIG. 16, the PDU Session Resource To Modify List IE may include a DRB To Modify List IE 1601. The DRB To Modify List IE 1601 may include a PDCP COUNT Not-Configuration IE 1621. The name of the PDCP COUNT Not-Configuration IE 1621 is merely an example and is not limiting. The PDCP COUNT Not-Configuration IE 1621 indicates that the PDCP count value of the DRB (e.g., AM DRB) identified by the DRB ID indicated in the associated DRB ID IE 1622 needs to be reset. Alternatively, the PDCP COUNT Not-Configuration IE 1621 indicates that the PDCP count value of the DRB (e.g., AM DRB) identified by the associated DRB ID IE 1622 will not be carried over. The PDCP COUNT Not-Configuration IE 1621 may be an enumerated IE.

[0080] As shown in FIG. 16, the DRB To Modify List IE1601 may include a DL UP parameters IE1641. The DL UP parameters IE1641 may indicate DL TNL address information of the gNB-DU3 (e.g., target gNB-DU) related to the F1-U interface. For example, in the preparation phase of an intra-CU inter-DU handover, the gNB-CU-CP21 may receive DL TNL information from the target gNB-DU and include the DL TNL information in the DL UP parameters IE1641. This allows the gNB-CU-CP21 to request the gNB-CU-UP22 to reset the PDCP count value of the AM DRB and to inform the gNB-CU-UP22 of the new DL TNL information of the AM DRB using a single BEARER CONTEXT MODIFICATION REQUEST message.

[0081] Although omitted in Figure 16, the DRB To Modify List IE 1601 may include other information items (or information elements). These information items (or information elements) may be the same as those included in the existing DRB To Modify List IE. The format and description of the existing PDU Session Resource To Modify List IE, including the existing DRB to Modify List IE, are described in 3GPP TS 23.2.2, 23.2.2, 23.2.2.4, and 23.2.3.11.

[0082] According to the operations of gNB-CU-CP21 and gNB-CU-UP22 described in this embodiment, by sending one control message, specifically a BEARER CONTEXT MODIFICATION REQUEST message, to gNB-CU-UP22, gNB-CU-CP21 can request gNB-CU-UP22 to reset the PDCP count values ​​of one or more AM DRBs. This makes it easy for gNB-CU-CP21 and gNB-CU-UP22 to reset the PDCP count values ​​of AM DRBs.

[0083] <Fifth embodiment> The configuration and operation of the wireless communication system and network elements (or apparatuses, nodes, devices, or network functions) according to this embodiment may be similar to the example described with reference to Fig. 1. This embodiment provides details of improvements to the E1AP signaling provided in the first to fourth embodiments.

[0084] As already described, the gNB-CU-CP21 may transmit the control message of the first embodiment (e.g., step 201 of FIG. 2) to the gNB-CU-UP22 in the preparation phase of an intra-CU inter-DU handover of the UE4. Similarly, the gNB-CU-CP21 may transmit the BEARER CONTEXT MODIFICATION REQUEST message of the second, third, or fourth embodiment (e.g., step 501 of FIG. 5, step 901 of FIG. 9, or step 1301 of FIG. 13) to the gNB-CU-UP22 in the preparation phase of an intra-CU inter-DU handover of the UE4.

[0085] Figure 17 shows an example of signaling in the preparation phase of intra-CU inter-DU handover of UE 4. In step 1701, UE 4 sends a measurement report message (e.g., an RRC MeasurementReport message) to source gNB-DU 3A. In step 1702, the source gNB-DU 3A sends an UL RRC MESSAGE TRANSFER message to gNB-CU-CP 21 to pass the received measurement report message.

[0086] Before step 1703, the gNB-CU-CP21 may send an F1AP UE CONTEXT MODIFICATION REQUEST message to the source gNB-DU3A to inquire about the latest configuration. In this case, the source gNB-DU3A responds with a UE CONTEXT MODIFICATION RESPONSE message including full configuration information, i.e., the CellGroupConfig IE.

[0087] In step 1703, the UE sends a UE CONTEXT SETUP REQUEST message to the target gNB-DU3B to create a UE context and set up one or more DRBs. The UE CONTEXT SETUP REQUEST message includes handover preparation information (e.g., HandoverPreparationInformation IE).

[0088] In step 1704, the target gNB-DU3B responds to the gNB-CU-CP21 with a UE CONTEXT SETUP RESPONSE message indicating the DL TNL information of the target gNB-DU3B. The UE CONTEXT SETUP RESPONSE message may include the cell group configuration (i.e., CellGroupConfig IE) created in the full configuration.

[0089] In step 1705, the gNB-CU-UP 22 sends a BEARER CONTEXT MODIFICATION REQUEST message to modify or update the bearer context for UE 4. The BEARER CONTEXT MODIFICATION REQUEST message indicates that the PDCP count values ​​of one or more AM DRBs of UE 4 need to be reset. The BEARER CONTEXT MODIFICATION REQUEST message may include information that is the same as or similar to the information included in the control message of the first embodiment (e.g., step 201 of FIG. 2) or the BEARER CONTEXT MODIFICATION REQUEST message of the second, third, or fourth embodiments (e.g., step 501 of FIG. 5, step 901 of FIG. 9, or step 1301 of FIG. 13).

[0090] The BEARER CONTEXT MODIFICATION REQUEST message of step 1705 indicates the DL TNL information of the target gNB-DU3B. As described with reference to Figure 8, the gNB-CU-CP21 may include a DL UP parameters IE (841) indicating the DL TNL information of the target gNB-DU3B in the DRB To Setup List IE (801) within the PDU Session Resource To Modify List IE in the BEARER CONTEXT MODIFICATION REQUEST message. As described with reference to Figure 12, the gNB-CU-CP21 may include a DL UP parameters IE (1241) indicating the DL TNL information of the target gNB-DU3B in the DRB To Remove and Setup List IE (1201) within the PDU Session Resource To Modify List IE in the BEARER CONTEXT MODIFICATION REQUEST message. Alternatively, as described with reference to Figure 16, the gNB-CU-CP21 may include a DL UP parameters IE (1641) indicating the DL TNL information of the target gNB-DU3B in the DRB To Modify List IE (1601) in the PDU Session Resource To Modify List IE in the BEARER CONTEXT MODIFICATION REQUEST message.

[0091] In step 1706, gNB-CU-UP22 responds with a BEARER CONTEXT MODIFICATION RESPONSE message to gNB-CU-CP21. gNB-CU-CP21 generates an RRCReconfiguration message to be sent to UE4.

[0092] In step 1707, the gNB-CU-CP21 sends a UE CONTEXT MODIFICATION REQUEST message containing the generated RRCReconfiguration message to the source gNB-DU3A. The UE CONTEXT MODIFICATION REQUEST message may instruct the source gNB-DU3A to stop data transmission for the UE4.

[0093] In step 1708, the source gNB-DU3A forwards the received RRCReconfiguration message to the UE4.

[0094] In step 1709, the source gNB-DU3A responds to the gNB-CU-CP21 with a UE CONTEXT MODIFICATION RESPONSE message.

[0095] According to the procedure described with reference to Figure 17, in the preparation phase of UE4's intra-CU inter-DU handover, gNB-CU-CP21 can use one E1AP message (step 1705) to request gNB-CU-UP22 to reset the PDCP count value of UE4's AM DRB(s) and to inform gNB-CU-UP22 of the new DL TNL information of the AM DRB(s).

[0096] Next, configuration examples of the gNB-CU-CP21 and the gNB-CU-UP22 according to the above-described embodiments will be described below. Fig. 18 is a block diagram showing configuration examples of the gNB-CU-CP21 and the gNB-CU-UP22 according to the above-described embodiments.

[0097] Referring to Figure 18, the gNB-CU-CP21 or gNB-CU-UP22 includes a network interface 1801, a processor 1802, and a memory 1803. The network interface 1801 is used to communicate with network nodes (e.g., the gNB-CU-UP22 or gNB-CU-CP21, the gNB-DU3, and a control plane (CP) node or a user plane (UP) node in the core network). The network interface 1801 may include multiple interfaces. The network interface 1801 may include, for example, an optical fiber interface for communication between the CU and DU and a network interface compliant with the IEEE 802.3 series.

[0098] In the case of the gNB-CU-CP 21, the processor 1802 performs, for example, control plane processing, such as processing related to NGAP, RRC, E1AP, and F1AP signaling. In the case of the gNB-CU-UP 22, the processor 1802 performs, for example, termination of the NG-U interface, termination of the F1-U interface, and data processing for the SDAP and PDCP sublayers. The processor 1802 may include multiple processors.

[0099] The memory 1803 is configured by a combination of volatile memory and nonvolatile memory. The volatile memory is, for example, Static Random Access Memory (SRAM), Dynamic RAM (DRAM), or a combination thereof. The nonvolatile memory is, for example, Mask Read Only Memory (MROM), Electrically Erasable Programmable ROM (EEPROM), flash memory, or a hard disk drive, or any combination thereof. The memory 1803 may include storage located remotely from the processor 1802. In this case, the processor 1802 may access the memory 1803 via the network interface 1801 or another I / O interface.

[0100] The memory 1803 may store one or more software modules (computer programs) 1804 including instructions and data for performing processing by the gNB-CU-CP21 or gNB-CU-UP22 described in the above-described embodiments. In some implementations, the processor 1802 may be configured to read and execute the one or more software modules 1804 from the memory 1803 to perform processing by the gNB-CU-CP21 or gNB-CU-UP22 described in the above-described embodiments.

[0101] As described with reference to FIG. 18 , each of the processors included in the gNB-CU-CP21 and gNB-CU-UP22 according to the above-described embodiments can execute one or more programs including instructions for causing a computer to perform the algorithms described with reference to the drawings. The programs include instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The programs may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disk (DVD), Blu-ray (registered trademark) disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage, or other magnetic storage device. The programs may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0102] The above-described embodiments are merely examples of application of the technical ideas obtained by the inventors of the present invention. In other words, the technical ideas are not limited to the above-described embodiments, and various modifications are possible.

[0103] For example, some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes.

[0104] (Appendix 1) 1. An apparatus configured to operate as a central unit / control plane of a radio access network node, comprising: At least one memory; at least one processor coupled to the at least one memory; Equipped with the at least one processor is configured to send a control message to a central unit user plane of the radio access network node indicating that one or more Packet Data Convergence Protocol (PDCP) count values ​​of Acknowledged Mode (AM) Data Radio Bearers (DRBs) configured for the wireless terminal need to be reset. Device. (Appendix 2) The control message causes the central unit user plane to reset the one or more PDCP count values ​​of the AM DRB. 10. The apparatus described in Appendix 1. (Appendix 3) The central unit control plane is a gNB Central Unit Control Plane (CU-CP), The central unit user plane is a gNB Central Unit User Plane (CU-UP), 10. The apparatus of claim 1 or 2. (Appendix 4) The control message is a message sent to the central unit user plane to request modification of a bearer context. 4. The device according to any one of appendices 1 to 3. (Appendix 5) the control message is an E1 Application Protocol (E1AP) BEARER CONTEXT MODIFICATION REQUEST message; 5. The device according to any one of appendices 1 to 4. (Appendix 6) To indicate that the one or more PDCP count values ​​of the AM DRB need to be reset, the control message includes a DRB to Setup List and a DRB to Remove List indicating the same DRB identifier of the AM DRB; 6. The device according to any one of appendices 1 to 5. (Appendix 7) Inform the central unit user plane that the DRB to Setup List and the DRB to Remove List, which indicate the same DRB identifier, need to be newly set up after the AM DRB is released; 10. The apparatus described in Appendix 6. (Appendix 8) The at least one processor is configured to include downlink transport network layer address information for a user plane interface between the distributed unit and the central unit user plane received from the distributed unit of the radio access network node in one or more information items associated with the DRB identifier in the DRB to Setup List. 8. The apparatus of claim 6 or 7. (Appendix 9) To indicate that the one or more PDCP count values ​​of the AM DRB need to be reset, the control message includes a DRB To Remove and Setup List including one or more information items associated with a DRB identifier of the AM DRB. 6. The device according to any one of appendices 1 to 5. (Appendix 10) The DRB To Remove and Setup List informs the central unit user plane that the AM DRB needs to be newly set up after being released; 10. The apparatus described in Appendix 9. (Appendix 11) the at least one processor is configured to include downlink transport network layer address information for a user plane interface between the distributed unit and the central unit user plane received from a distributed unit of the radio access network node in the one or more information items of the DRB To Remove and Setup List; 11. The apparatus of claim 9 or 10. (Appendix 12) the control message includes a DRB To Modify List containing one or more information items associated with a DRB identifier of the AM DRB; To indicate that the one or more PDCP count values ​​of the AM DRB need to be reset, the one or more information items include an information item indicating that the one or more PDCP count values ​​are to be reset. 6. The device according to any one of appendices 1 to 5. (Appendix 13) the one or more PDCP count values ​​include a first count value of a PDCP Service Data Unit (SDU) to be transmitted next for the AM DRB, and a second count value of a PDCP SDU to be expected to be received next for the AM DRB; 13. The device according to any one of appendices 1 to 12. (Appendix 14) each of the one or more PDCP count values ​​comprises a Hyper Frame Number (HFN) and a PDCP Sequence Number (SN); 14. The device according to any one of appendices 1 to 13. (Appendix 15) the at least one processor is configured to transmit the control message to the central unit user plane in response to receiving a UE CONTEXT SETUP RESPONSE message from a distributed unit of the radio access network node, the UE CONTEXT SETUP RESPONSE message including a cell group configuration created in a full configuration. 15. The device according to any one of appendices 1 to 14. (Appendix 16) the at least one processor is configured to include in the control message downlink transport network layer address information for a user plane interface between the distributed unit and the central unit user plane received from the distributed unit via the UE CONTEXT SETUP RESPONSE message; 16. The apparatus of claim 15. (Appendix 17) 1. An apparatus configured to operate as a central unit user plane of a radio access network node, comprising: At least one memory; at least one processor coupled to the at least one memory; Equipped with the at least one processor is configured to receive a control message from a central unit control plane of the radio access network node indicating that one or more Packet Data Convergence Protocol (PDCP) count values ​​of Acknowledged Mode (AM) Data Radio Bearers (DRBs) configured for a wireless terminal need to be reset. Device. (Appendix 18) the at least one processor is configured to reset the one or more PDCP count values ​​of the AM DRB in response to receiving the control message. 18. The apparatus of claim 17. (Appendix 19) The central unit control plane is a gNB Central Unit Control Plane (CU-CP), The central unit user plane is a gNB Central Unit User Plane (CU-UP), 19. The apparatus of claim 17 or 18. (Appendix 20) The control message is a message sent to the central unit user plane to request modification of a bearer context. 20. The device according to any one of appendices 17 to 19. (Appendix 21) the control message is an E1 Application Protocol (E1AP) BEARER CONTEXT MODIFICATION REQUEST message; 21. The device according to any one of appendices 17 to 20. (Appendix 22) To indicate that the one or more PDCP count values ​​of the AM DRB need to be reset, the control message includes a DRB to Setup List and a DRB to Remove List indicating the same DRB identifier of the AM DRB; 22. The device according to any one of appendices 17 to 21. (Appendix 23) Inform the central unit user plane that the DRB to Setup List and the DRB to Remove List, which indicate the same DRB identifier, need to be newly set up after the AM DRB is released; 23. The apparatus of claim 22. (Appendix 24) The one or more information items associated with the DRB identifier in the DRB to Setup List include downlink transport network layer address information for a user plane interface between the distributed unit and the central unit user plane received by the central unit control plane from the distributed unit of the radio access network node, 24. The apparatus of claim 22 or 23. (Appendix 25) To indicate that the one or more PDCP count values ​​of the AM DRB need to be reset, the control message includes a DRB To Remove and Setup List including one or more information items associated with a DRB identifier of the AM DRB. 22. The device according to any one of appendices 17 to 21. (Appendix 26) The DRB To Remove and Setup List informs the central unit user plane that the AM DRB needs to be newly set up after being released; 26. The apparatus of claim 25. (Appendix 27) the one or more information items of the DRB To Remove and Setup List include downlink transport network layer address information for a user plane interface between the distributed unit and the central unit user plane received by the central unit control plane from a distributed unit of the radio access network node, 27. The apparatus of claim 25 or 26. (Appendix 28) the control message includes a DRB To Modify List containing one or more information items associated with a DRB identifier of the AM DRB; To indicate that the one or more PDCP count values ​​of the AM DRB need to be reset, the one or more information items include an information item indicating that the one or more PDCP count values ​​are to be reset. 22. The device according to any one of appendices 17 to 21. (Appendix 29) the one or more PDCP count values ​​include a first count value of a PDCP Service Data Unit (SDU) to be transmitted next for the AM DRB, and a second count value of a PDCP SDU to be expected to be received next for the AM DRB; 29. The device according to any one of appendices 17 to 28. (Appendix 30) each of the one or more PDCP count values ​​comprises a Hyper Frame Number (HFN) and a PDCP Sequence Number (SN); 30. The device according to any one of appendices 17 to 29. (Appendix 31) 1. A method performed by a central unit control plane of a radio access network node, comprising: transmitting a control message to a central unit user plane of the radio access network node indicating that one or more Packet Data Convergence Protocol (PDCP) count values ​​of Acknowledged Mode (AM) Data Radio Bearers (DRBs) configured for the wireless terminal need to be reset; method. (Appendix 32) 1. A method performed by a central unit user plane of a radio access network node, comprising: receiving a control message from a central unit control plane of the radio access network node indicating that one or more Packet Data Convergence Protocol (PDCP) count values ​​of Acknowledged Mode (AM) Data Radio Bearers (DRBs) configured for the wireless terminal need to be reset; method. (Appendix 33) A program for causing a computer to perform a method for a central unit control plane of a radio access network node, comprising: the method comprising: transmitting a control message to a central unit user plane of the radio access network node indicating that one or more Packet Data Convergence Protocol (PDCP) count values ​​of Acknowledged Mode (AM) Data Radio Bearers (DRBs) configured for the wireless terminal need to be reset; program. (Appendix 34) 1. A program for causing a computer to perform a method for a central unit user plane of a radio access network node, comprising: The method comprises receiving a control message from a central unit control plane of the radio access network node indicating that one or more Packet Data Convergence Protocol (PDCP) count values ​​of Acknowledged Mode (AM) Data Radio Bearers (DRBs) configured for a wireless terminal need to be reset. program.

[0105] This application claims priority based on Japanese Patent Application No. 2022-054841, filed on March 30, 2022, the disclosure of which is incorporated herein in its entirety. [Explanation of symbols]

[0106] 1 gNB 2 gNB-CU 3 gNB-DU 3A source gNB-DU 3B Target gNB-DU 4UE 21 gNB-CU-CP 22 gNB-CU-UP 1802 processor 1803 memory 1804 modules

Claims

1. 1. An apparatus configured to operate as a central unit / control plane of a radio access network node, comprising: means for transmitting a message including information explicitly indicating that one or more Packet Data Convergence Protocol (PDCP) count values ​​of a first Data Radio Bearer (DRB) established for a wireless terminal need to be reset to a central unit user plane of the radio access network node in a preparation phase of an intra-Central Unit (CU) inter-Distributed Unit (DU) handover; Device.

2. The message includes a list of one or more DRBs to be modified; The list includes a DRB identifier of the first DRB and the information; 10. The apparatus of claim 1.

3. The list is a DRB to Modify List.

3. The apparatus of claim 2.

4. The first DRB is an Acknowledged Mode (AM) DRB. The device according to any one of claims 1 to 3.

5. The message is a BEARER CONTEXT MODIFICATION REQUEST message. The device according to any one of claims 1 to 3.

6. the transmitting means is configured to transmit a UE CONTEXT SETUP RESPONSE message including a cell group configuration created in a full configuration to the central unit user plane in response to receiving the message from a distributed unit of the radio access network node. The device according to any one of claims 1 to 3.

7. the message includes a list of information for configuring one or more DRBs and a list of information for deleting one or more DRBs; The list of information for setting one or more DRBs and the list of information for deleting one or more DRBs include a DRB identifier of the first DRB; 10. The apparatus of claim 1.

8. 1. An apparatus configured to operate as a central unit user plane of a radio access network node, comprising: means for receiving, from a central unit control plane of the radio access network node, in a preparation phase of an intra-Central Unit (CU) inter-Distributed Unit (DU) handover, a message including information explicitly indicating that one or more Packet Data Convergence Protocol (PDCP) count values ​​of a first Data Radio Bearer (DRB) established for the radio terminal need to be reset; Device.

9. 1. A method performed by a central unit / control plane of a radio access network node, comprising: transmitting a message to a central unit user plane of the radio access network node in a preparation phase of an intra-Central Unit (CU) inter-Distributed Unit (DU) handover, the message including information explicitly indicating that one or more Packet Data Convergence Protocol (PDCP) count values ​​of a first Data Radio Bearer (DRB) configured for the radio terminal need to be reset; method.

10. 1. A method performed by a central unit user plane of a radio access network node, comprising: receiving, from a central unit control plane of the radio access network node, in a preparation phase of an intra-Central Unit (CU) inter-Distributed Unit (DU) handover, a message including information explicitly indicating that one or more Packet Data Convergence Protocol (PDCP) count values ​​of a first Data Radio Bearer (DRB) configured for the radio terminal need to be reset; method.

Images