Patent Publication Number: US-2021176744-A1

Title: Communication apparatus and radio communication system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of International Application PCT/JP2018/035454 filed on Sep. 25, 2018 and designated the U.S., the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The embodiments discussed herein are related to a communication apparatus and a radio communication system. 
     BACKGROUND 
     At present, in the 3rd Generation Partnership Project (3GPP) which is a standardization organization, an element technology of a radio access network that satisfies demand conditions of the fifth generation mobile communication system (5G) has been studied for early introduction of the 5G. 
     In the 5G mobile network, concentration and distribution of processing in a base station have been studied in order to cope with an increase in message traffic. For example, central unit (CU) and distributed unit (DU) split has been studied as a method of concentrating and distributing the processing in the base station. For example, a next generation Node B (gNB) that is a logical base station is constituted by one combination, a N to 1 combination, or N combinations of the CU and the DU. In the CU and DU split, processing of messages is split for each node in a hierarchy of protocols, a higher-level protocol is processed by the CU, and a lower-level protocol is processed by the DU. 
     In the gNB, when a Public Warning System (PWS) message such as a Write-Replace Warning Request is received from Access and Mobility Management Function (AMF) of a higher-level apparatus, information for identifying the PWS messages is not notified from the CU to the DU. For example, when the Write-Replace Warning Request is received, the CU aggregates pieces of information into one piece of information such that the DU transmits the message with no change to a radio section. When a PWS Cancel Request is received, the CU deletes the information for identifying the PWS message from the information to be notified to the DU. 
     Examples of the related art include the following references: [PTL 1] International Publication Pamphlet No. WO 2015/186291; [PTL 2] Japanese Laid-open Patent Publication No. 2012-165197; [PTL 3] Japanese Laid-open Patent Publication No. 2004-274693; [NPL 1] 3GPP TR 38.801 V14.0.0 (2017-03); and [NPL 2] 3GPP TDoc R3-183486 (2018-05). 
     SUMMARY 
     According to an aspect of the embodiments, provided is a communication apparatus configured to perform processing, the processing including: executing an addition processing configured to add identification information for identifying report information to processed report information obtained by performing processing corresponding to a type of the report information on the report information received from a higher-level network; and executing a transmission processing configured to transmit the processed report information to which the identification information is added by the addition unit to a second communication apparatus coupled to a radio link. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a configuration example of a radio communication system according to a first embodiment; 
         FIG. 2  is a diagram for describing an example of processing of a PWS message in the embodiment; 
         FIGS. 3A to 3D  illustrate a diagram for describing specific examples of the processing of the PWS message in the radio communication system according to the embodiment; 
         FIG. 4  illustrates an example of a functional configuration of a gNE according to the embodiment; 
         FIG. 5  illustrates an example of a data configuration of priority information in the embodiment; 
         FIG. 6  is a diagram for describing a specific example of an operation of a CU in the embodiment; 
         FIG. 7  is a diagram for describing a specific example of an operation of the gNE in the embodiment; 
         FIG. 8  illustrates an example of a data configuration of an RRC transmission PWS list in the embodiment; 
         FIG. 9  is a sequence diagram for describing an example of an operation of the radio communication system in the embodiment; 
         FIG. 10  is a flowchart for describing an example of an operation of a DU in the embodiment; 
         FIG. 11  is a flowchart for describing an example of the operation of the DU in the embodiment; and 
         FIG. 12  illustrates a hardware configuration example of the gNE. 
     
    
    
     DESCRIPTION OF EMBODIMENT(S) 
     Incidentally, when the gNB receives a plurality of PWS messages, it is important that the DU does not transmit information on duplicate PWS messages to the radio section or stops transmission of information on a low-priority PWS message to the radio section according to a resource of the radio section. When an instruction to stop a part of the plurality of PWS messages being received by the gNB is given, it is important that the DU specifies the PWS message to be stopped. 
     However, when the DU transmits one piece of information aggregated by the CU with no change to the radio section, it is difficult for the DU to perform duplication determination and priority determination of the plurality of PWS messages. It is difficult for the DU to specify the PWS message to be stopped without the information for identifying the PWS message. 
     An object of a disclosed technology is to provide a communication apparatus and a radio communication system that are capable of identifying and processing a plurality of PWS messages. 
     Hereinafter, embodiments of a communication apparatus and a radio communication system disclosed in the present application are described in detail with reference to the drawings. The following embodiments are not intended to limit the disclosed technology. Configurations having equivalent functions in the embodiments are denoted by the same reference numerals, and redundant description thereof will be omitted. 
     Embodiments 
       FIG. 1  illustrates a configuration example of a radio communication system  1  according to an embodiment. The radio communication system  1  illustrated in  FIG. 1  includes a Cell Broadcast Center (CBC)  2 , an AMF  3 , a gNB  4 , and user equipment (UE)  5 . The CBC  2  is a broadcast distribution apparatus that distributes report information such as an Earthquake Early Warning, receives information provided by an information distribution source such as the Weather Management Agency, creates a message, and decides a distribution destination. The AMF  3  controls mobility management, and transmits a PWS message to the gNB  4  in the area. 
     The gNB  4  is a logical radio base station, and includes a CU  10  and a DU  20 . The CU  10  processes a higher-level protocol of a message received from the AMF  3  or the DU  20 . In the present embodiment, the CU  10  processes Radio Resource Control (RRC) and Packet Data Convergence Protocol (PDCP). The DU  20  processes a lower-level protocol of a message received from the CU  10  or the UE  5 . In the present embodiment, the DU  20  processes Radio Link Control (RLC), Medium Access Control (MAC), and PHYsical layer (PHY). An interface between the CU  10  and the DU  20  is referred to as F1. An interface between the AMF  3  and the CU  10  is referred to as N2. 
       FIG. 2  is a diagram for describing an example of processing of the PWS message in the embodiment. In  FIG. 2 , a Write-Replace Warning Request is illustrated as the PWS message. A Write-Replace Warning Response, a PWS Cancel Request, a PWS Cancel Response, a PWS Restart Indication, a PWS Failure Indication, and the like are used as other PWS messages. 
     As illustrated in  FIG. 2 , in the gNB  4 , the CU  10  aggregates pieces of information of the RRC level which include a Message Identifier and a Serial Number among information elements of the Write-Replace Warning Request received from the AMF  3  to PWS System Information. The DU  20  distributes the message to the UE  5  by transmitting the PWS System Information received from the DU  20  with no change to a radio section (see NPL 2). 
     Here, the Message Identifier is information indicating a message type, and the Serial Number is identification information for identifying a message among messages of the same type. For example, the PWS message may be identified by a combination of the Message Identifier and the Serial Number. 
     On the other hand, in Long-Term Evolution (LTE) of a 4G standard, a radio base station (eNB) receives a plurality of PWS messages from the Mobility Management Entity (MME) in some cases. For example, an eNB in which S1-Flex coupled in a full mesh is implemented with a plurality of MMEs receives an identical PWS message from different MMEs in some cases. In some cases, the identical PWS message is transmitted from an identical MME by multiple times in order to suppress transmission and reception failures. 
     When a plurality of identical Write-Replace Warning Requests is received in duplicate, the eNB performs duplication determination by using the combination of the Message Identifier and the Serial Number, and does not transmit the second and subsequent identical messages to the radio section. 
     When a plurality of different Write-Replace Warning Requests is received, the eNB determines priorities by using the combination of the Message Identifier and the Serial Number, and transmits the messages to the radio section in descending order of priority according to a resource of the radio section. 
     In contrast, in the radio communication system  1  according to the embodiment, when the gNB  4  receives the plurality of Write-Replace Warning Requests, in the processing illustrated in  FIG. 2 , since the DU  20  does not know the Message Identifier and the Serial Number, it is difficult to perform the duplication determination and importance determination. 
     In the radio communication system  1  according to the embodiment, when the gNB  4  receives a PWS Cancel Request for giving an instruction to stop a part of the plurality of Write-Replace Warning Requests while receiving the plurality of Write-Replace Warning Requests, it is important that the DU  20  specifies the PWS message to be stopped. 
     Thus, in the radio communication system  1  according to the embodiment, as will be described below, the CU  10  includes a PWS identifier for identifying the PWS message such as the Message Identifier or the Serial Number in the PWS message to be transmitted to the DU  20 . Accordingly, in the radio communication system  1  according to the embodiment, for example, the DU  20  performs the duplication determination of the plurality of received Write-Replace Warning Requests, and may suppress transmission of an unnecessary message to the radio section. For example, the DU  20  may specify the PWS message to be stopped by the received PWS Cancel Request. 
     The CU  10  includes an information element (Priority Indicator) for easily determining the priority in the PWS message to be transmitted to the DU  20 . Accordingly, for example, the DU  20  determines the priorities of the plurality of received Write-Replace Warning Requests, and may reliably transmit a high-priority message according to the resource of the radio section. 
       FIG. 3  (i.e.  FIGS. 3A to 3D ) is a diagram for describing specific examples of processing of the PWS message in the radio communication system  1  according to the embodiment. As illustrated in  FIG. 3A , the CU  10  in which N2-Flex is implemented with the AMFs  3  receives the identical PWS messages in duplicate from different AMFs  3  in some cases. As illustrated in  FIG. 3B , the DU  20  in which F1-Flex is implemented with the CUs  10  receives the identical PWS message in duplicate from different CUs  10  in some cases. In such a case, the DU  20  may perform the duplication determination by using the PWS identifier. 
     As illustrated in  FIG. 3C , when the plurality of different PWS messages is simultaneously received, the DU  20  may perform the priority determination by using the PWS identifier and the Priority Indicator. 
       FIG. 3D  illustrates a case where the DU  20  further receives the PWS Cancel Request for giving the instruction to stop the transmission of a part of the PWS messages to the radio section while simultaneously receiving the plurality of different PWS messages (Write-Replace Warning Requests). In this case, the DU  20  specifies the message to be stopped by using the PWS identifier included in the PWS Cancel Request received from the CU  10 , and may stop the transmission of the message to the radio section. 
     Next,  FIG. 4  illustrates an example of a functional configuration of the gNB  4  according to the embodiment. As illustrated in  FIG. 4 , the gNB  4  includes the CU  10  and the DU  20 . 
     The CU  10  includes an inter-AMF-CU message transmission and reception unit  11 , a message determination unit  12 , an AMF-CU and CU-DU message conversion unit  13 , and an inter-CU-DU message transmission and reception unit  15 . The CU  10  stores a priority list  16  in a memory. 
       FIG. 5  illustrates an example of a data configuration of the priority list  16 . As illustrated in  FIG. 5 , the priority list  16  is information indicating a correspondence between the PWS identifier and the priority (PWS priority).  FIG. 5  illustrates that, for example, a priority of a PWS message with a PWS identifier “11, aa” is “2”. In the example illustrated in  FIG. 5 , the PWS identifier is represented by the combination of the Message Identifier and the Serial Number of the PWS message. For example, the PWS identifier “11, aa” indicates that the Message Identifier is “11” and the Serial Number is “aa”. 
     The PWS identifier is not limited to the combination of the Message Identifier and the Serial Number of the PWS message, and may be, for example, a hash value as long as the PWS message may be identified. The priority will be described later. 
     Referring back to  FIG. 4 , the description will be continued. The inter-AMF-CU message transmission and reception unit  11  controls communication between the CU  10  and the AMF  3  of a higher-level network. The message determination unit  12  determines the processing corresponding to the message type for each PWS message received from the AMF  3 , and delivers the PWS message to be transmitted to the DU  30  to the AMF-CU and CU-DU message conversion unit  13 . 
     The AMF-CU and CU-DU message conversion unit  13  performs the processing corresponding to the message type on the message received from the message determination unit  12 . The AMF-CU and CU-DU message conversion unit  13  includes a PWS message processing unit  14 . 
     The PWS message processing unit  14  functions as an addition unit. For example, the PWS message processing unit  14  adds the PWS identifier that is the identification information for identifying the PWS message to the processed PWS message obtained by performing processing corresponding to the message type of the PWS message on the PWS message that is report information received from a higher-level network. 
     The PWS message processing unit  14  further adds, to the processed PWS message, predetermined priority information for each PWS message which indicates a priority order in which the DU  20  coupled to a radio link transmits the message by using the radio link. 
       FIG. 6  is a diagram for describing a specific example of an operation of the CU  10  in the embodiment.  FIG. 6  illustrates a case where the CU  10  receives the Write-Replace Warning Request as the PWS message from the AMF  3 . As illustrated in  FIG. 6 , in the CU  10 , the AMF-CU and CU-DU message conversion unit  13  performs processing specialized for the Write-Replace Warning Request and creates the processed PWS message. For example, the AMF-CU and CU-DU message conversion unit  13  aggregates the pieces of information of the RRC level which includes the Message Identifier and the Serial Number among the information elements of the received Write-Replace Warning Request to the PWS System Information. 
     The PWS message processing unit  14  adds the Message Identifier and the Serial Number to the processed PWS message. The PWS message processing unit  14  also adds the Priority Indicator as the priority information. The Priority Indicator is the information elements indicating the priority corresponding to the Message Identifier and the Serial Number. The PWS message processing unit  14  specifies the priority corresponding to the Message Identifier and the Serial Number while referring to the priority list  16 , and sets a value of the specified priority to the Priority Indicator. 
     As will be described later, the priority is a value that designates the priority order in which the DU  20  transmits the processed PWS message to the radio link, and is a value set in advance for each PWS message. The CU  10  sets the priority of each PWS message in advance in cooperation with an operation and maintenance (O&amp;M) apparatus or a higher-level apparatus such as the AMF  3 , and stores the priority as the priority list  16 . As stated above, the priority information is used, and thus, the DU  20  may easily determine the priority as will be described later. 
     For example, the PWS message processing unit  14  may not add the priority information to the PWS Cancel Request. 
     The CU  10  negotiates the setting of the priority information in advance with the DU  20 . For example, the CU  10  and the DU  20  share a method relating to the set value of the Priority Indicator in advance. For example, the DU  20  designates a method of setting the priority to be notified to the DU to 5 stages, or designates a method of setting the PWS message with a low priority not to be notified. In this case, for example, the CU  10  stores the priority list  16  for each method, and adds the priority information by using the priority list  16  corresponding to the method designated by the DU  20 . 
       FIG. 7  is a diagram for describing a specific example of an operation of the gNB  4  in the embodiment.  FIG. 7  illustrates a case where the CU  10  and the DU  20  negotiate the setting of the priority information by using an F1 Setup Procedure. As illustrated in  FIG. 7 , the DU  20  adds a Priority Indicator Request to an F1 Setup Request. The Priority Indicator Request is, for example, an information element for designating the above method. 
     The CU  10  adds the Priority Information to an F1 Setup Response to be returned to the DU  20 . The Priority Information is an information element indicating a response to the Priority Indicator Request, and for example, information indicating the decided method is set. 
     After the F1 Setup Request is received from the DU  20 , the CU  10  may set the priority of each PWS message in cooperation with the O&amp;M apparatus or the higher-level apparatus. For example, the CU  10  creates the priority list  16  corresponding to the method designated by the DU  20 . 
     The negotiation on the setting of the priority information between the CU  10  and the DU  20  is not limited to a case of using the F1 Setup Procedure. For example, the negotiation of the setting of the priority information may be performed or changed by using a GNB-DU Configuration Update Procedure between the CU  10  and the DU  20 . In this case, the DU  20  adds the Priority Indicator Request to a GNB-DU Configuration Update. The CU  10  adds the Priority Information to a GNB-DU Configuration Acknowledge to be returned to the DU  20 . After the GNB-DU Configuration Update is received from the DU  20 , the CU  10  may set the priority of each PWS message in cooperation with the O&amp;M apparatus or the higher-level apparatus. 
     Alternatively, the negotiation of the setting of the priority information may be performed or changed by using a GNB-CU Configuration Update Procedure between the CU  10  and the DU  20 . In this case, the CU  10  sets the priority of each PWS message in advance in cooperation with the O&amp;M apparatus or the higher-level apparatus. The CU  10  adds the Priority Indicator Request to a GNB-CU Configuration Update. The DU  20  adds the Priority Information to GNB-CU Configuration Acknowledge to be returned to the CU  10 . 
     Referring back to  FIG. 4 , the description will be continued. The inter-CU-DU message transmission and reception unit  15  controls communication between the CU  10  and the DU  20 . For example, the inter-CU-DU message transmission and reception unit  15  functions as a transmission unit. For example, the inter-CU-DU message transmission and reception unit  15  transmits the processed PWS message to which the PWS identifier is added by the PWS message processing unit  14  to the DU  20  that is another communication apparatus coupled to the radio link. 
     The DU  20  includes an inter-CU-DU message transmission and reception unit  21 , a message determination unit  22 , a CU-DU and DU-RRC message conversion unit  23 , and an inter-DU-RRC message transmission and reception unit  25 . The DU  20  stores an RRC transmission PWS list  26  in a memory. 
       FIG. 8  illustrates an example of a data configuration of the RRC transmission PWS list  26 . The RRC transmission PWS list  26  is information for managing the PWS message (Write-Replace Warning Request) being received by the DU  20 , and includes the PWS identifier and the PWS priority of the Write-Replace Warning Request being received as illustrated in  FIG. 8 . For example,  FIG. 8  illustrates that the DU  20  is receiving a message with a PWS identifier “11, aa” and a priority “2” as a target to be transmitted to the radio section. 
     Referring back to  FIG. 4 , the description will be continued. The inter-CU-DU message transmission and reception unit  21  controls communication between the CU  10  and the DU  20 . For example, the inter-CU-DU message transmission and reception unit  21  functions as a reception unit. For example, the inter-CU-DU message transmission and reception unit  21  receives the processed PWS message obtained by adding the PWS identifier for identifying the PWS message to the PWS message transmitted from the higher-level network and performing the processing corresponding to the message type of the PWS message on the PWS message. 
     The message determination unit  22  determines the processing corresponding to the message type for each processed PWS message received from the CU  10 , and delivers the processed PWS message to be transmitted to the radio link to the CU-DU and DU-RRC message conversion unit  23 . 
     The CU-DU and DU-RRC message conversion unit  23  performs the processing corresponding to the message type on the processed PWS message received from the message determination unit  22 . The CU-DU and DU-RRC message conversion unit  23  includes a PWS message processing unit  24 . 
     The PWS message processing unit  24  functions as an identification unit. For example, the PWS message processing unit  24  identifies the processed PWS message by using the PWS identifier added to each of the plurality of processed PWS messages received from the CU  10 . 
     For example, the PWS message processing unit  24  identifies the message to be stopped by using the PWS identifier included in the PWS Cancel Request received from the CU  10 . Accordingly, for example, when the DU  20  receives the PWS Cancel Request having, as targets, a part of the plurality of different Write-Replace Warning Requests while simultaneously receiving the plurality of different Write-Replace Warning Requests, the DU  20  specifies the message to be stopped, and may stop the transmission of the message to the radio section (see  FIG. 3( d ) ). 
     The PWS message processing unit  24  performs the duplication determination for controlling the duplicate processed PWS messages among the plurality of received processed PWS messages. For example, the PWS message processing unit  24  determines that the messages of which the PWS identifiers coincide with each other among the plurality of received Write-Replace Warning Requests are duplicated while referring to the RRC transmission PWS list  26 . The DU  20  may suppress the transmission of the unnecessary message to the radio section by stopping the transmission of the second and subsequent identical Write-Replace Warning Requests to the radio section. 
     The PWS message processing unit  24  further performs priority determination processing of controlling the priority order in which the DU transmits the message by using the radio link by using predetermined priority information for each PWS message which is added to the processed PWS message and indicates the priority order in which the DU transmits the message by using the radio link. For example, the PWS message processing unit  24  transmits the messages to the radio section in descending order of priority in a range in which there is an available resource in the radio section by using the value of the Priority Indicator added to each of the plurality of received Write-Replace Warning Requests. 
     For example, the PWS message processing unit  24  transmits, to the radio section, the messages in descending order of priority among the Write-Replace Warning Requests being received as a target to be transmitted to the radio section while referring to the RRC transmission PWS list  26 . When there is no available resource in the radio section, the transmission of a low-priority message is stopped. Accordingly, the DU  20  determines the priority of the PWS message with simple processing, and may reliably transmit the high-priority message to the radio section even when there are a few resources in the radio section. 
     The PWS message processing unit  24  adds the Message Identifier and the Serial Number to the PWS message to be transmitted to the CU  10 . For example, the PWS message processing unit  24  adds the same Message Identifier and Serial Number as the Message Identifier and Serial Number of the PWS message such as the PWS Cancel Request received from the CU  10  to the PWS message as the response such as the PWS Cancel Response to be returned to the CU  10 . At this time, the PWS message processing unit  24  may add the Priority Indicator with no change. Neither the Message Identifier, the Serial Number, nor the Priority Indicator may be added to the PWS message indicating a state of a cell such as the PWS Restart Indication. 
     Referring back to  FIG. 4 , the description will be continued. The inter-DU-RRC message transmission and reception unit  25  controls communication between the DU  20  and the UE  5 . For example, the inter-DU-RRC message transmission and reception unit  25  distributes the message to the UE  5  by transmitting the PWS System Information of the Write-Replace Warning Request to the radio link. 
     Next, an operation of the radio communication system  1  according to the present embodiment will be described.  FIG. 9  is a sequence diagram for describing an example of the operation of the radio communication system  1  according to the embodiment. 
     First, the CU  10  and the DU  20  negotiate the setting of the priority information by using the F1 Setup Procedure (step S 1 ). The CU  10  creates the priority list  16  for setting the priority information of the PWS to be notified to the DU  20  according to the negotiation (step S 2 ). When the negotiation of the setting of the priority information is changed, the CU  10  uses, for example, the GNB-CU Configuration Update Procedure (step S 3 ). 
     In the CU  10 , when the Write-Replace Warning Request is received from the AMF  3  (step S 4 ), the PWS message processing unit  14  sets an intended information element (IE) (step S 5 ). For example, the PWS message processing unit  14  adds the Message Identifier and the Serial Number to the Write-Replace Warning Request processed by the AMF-CU and CU-DU message conversion unit  13 . The PWS message processing unit  14  adds the Priority Indicator as the priority information by using the priority list  16 . The inter-CU-DU message transmission and reception unit  15  transmits, to the DU  20 , the processed Write-Replace Warning Request to which the intended information element is added (step S 6 ). 
     In the DU  20 , the PWS message processing unit  24  identifies the Write-Replace Warning Request by using the Message Identifier and the Serial Number added to each of the plurality of processed Write-Replace Warning Requests received from the CU  10 . First, the PWS message processing unit  24  performs the duplication determination for determining that there are the duplicate messages among the plurality of received processed Write-Replace Warning Requests (step S 7 ). 
     When it is determined that there are the duplicate messages as a result of the duplication determination (No in step S 8 ), the PWS message processing unit  24  advances the processing to step S 13 . In the processing of step S 13 , the PWS message processing unit  24  returns the Write-Replace Warning Response indicating that the message is not transmitted to the radio section due to the duplication to the CU  10  and the AMF  3  via the inter-CU-DU message transmission and reception unit  21  and the CU  10 . 
     On the other hand, when it is determined that there are no duplicate messages as the result of the duplication determination (Yes in step S 8 ), the PWS message processing unit  24  performs the priority determination by using the Priority Indicator added to each of the plurality of received processed Write-Replace Warning Requests (step S 9 ). 
     When the transmission (RRC notification) of the message to the radio section is not executable as a result of the priority determination (No in step S 11 ), the PWS message processing unit  24  advances the processing to step S 14 . In the processing of step S 14 , the PWS message processing unit  24  returns the Write-Replace Warning Response indicating that the message is not transmitted to the radio section due to the low priority to the CU  10  and the AMF  3  via the inter-CU-DU message transmission and reception unit  21  and the CU  10 . 
     On the other hand, when the transmission of the message to the radio section is executable as the result of the priority determination (Yes in step S 11 ), the inter-DU-RRC message transmission and reception unit  25  transmits the PWS System Information of the Write-Replace Warning Request to the radio link (RRC transmission, step S 12 ). The PWS message processing unit  24  advances the processing to step S 15 . In the processing of step S 15 , the PWS message processing unit returns the Write-Replace Warning Response indicating that the transmission of the message to the radio section is completed to the CU  10  and the AMF  3  via the inter-CU-DU message transmission and reception unit  21  and the CU  10 . 
     Next,  FIGS. 10 and 11  are flowcharts for describing an example of an operation of the DU  20 . First,  FIG. 10  illustrates a processing procedure of the duplication determination of step S 7  described above. The inter-CU-DU message transmission and reception unit  21  receives, from the CU  10 , the processed PWS message to which the PWS identifier and the priority information are added by the CU  10  and on which the processing corresponding to the message type is performed (step S 71 ). 
     The PWS message processing unit  24  reads the PWS identifier added to the received processed PWS message (step S 72 ). The PWS message processing unit  24  checks whether or not there is the PWS identifier coinciding with the read PWS identifier while referring to the RRC transmission PWS list  26  (steps S 73  to S 74 ). 
     When there is the PWS identifier coinciding with the read PWS identifier in the RRC transmission PWS list  26  (Yes in step S 74 ), the PWS message processing unit  24  determines that there are the duplicate messages (step S 75 ). On the other hand, when there is no PWS identifier coinciding with the read PWS identifier in the RRC transmission PWS list  26  (No in step S 74 ), the PWS message processing unit  24  determines that there are no duplicate messages (step S 76 ). 
       FIG. 11  illustrates a processing procedure of the priority determination of step S 9  described above. First, when the PWS message to be processed is received (step S 91 ), the PWS message processing unit  24  checks whether or not there is the available resource in the radio section (step S 92 ). When there is no available resource in the radio section (Yes in step S 92 ), the PWS message processing unit  24  advances the processing to step S 98 . On the other hand, when there is no available resource in the radio section (No in step S 92 ), the PWS message processing unit advances the processing to step S 93 . 
     In the processing of step S 93 , the PWS message processing unit  24  reads the PWS priority from the Priority Indicator added to the received PWS message processed by the CU  10 . The PWS message processing unit  24  checks whether or not there is the PWS message with the PWS priority lower than the read PWS priority while referring to the RRC transmission PWS list  26  (steps S 94  to S 95 ). 
     When there is no PWS message with the PWS priority lower than the read PWS priority (No in step S 95 ), the PWS message processing unit  24  determines that the transmission (RRC notification) of the message to the radio section is not executable (step S 100 ). 
     On the other hand, when there is the PWS message with the PWS priority lower than the read PWS priority (Yes in step S 95 ), the PWS message processing unit  24  stops the transmission (RRC transmission) of the PWS message with the PWS priority lower than the read PWS priority to the radio section (step S 96 ). The PWS message processing unit  24  deletes the PWS message with the PWS priority lower than the read PWS priority from the RRC transmission PWS list  26  (step S 97 ). 
     The PWS message processing unit  24  adds the received PWS message processed by the CU  10  to the RRC transmission PWS list  26  (step S 98 ), and determines that the transmission (RRC notification) of the message to the radio section is executable (step S 99 ). 
     As described above, according to the present embodiment, the CU  10  adds the PWS identifier for identifying the PWS message to the processed PWS message obtained by performing the processing corresponding to the message type of the PWS message on the PWS message received from the higher-level network. The CU  10  transmits the processed PWS message to which the PWS identifier is added to the DU  20 . 
     In this case, the DU  20  may receive the processed PWS message obtained by adding the PWS identifier for identifying the PWS message to the PWS message transmitted from the higher-level network and performing the processing corresponding to the message type of the PWS message. The DU  20  may identify the processed PWS message by using the PWS identifier added to each of the plurality of received processed PWS messages. 
     Accordingly, for example, when the gNB  4  receives the PWS Cancel Request for giving the instruction to stop a part of the plurality of Write-Replace Warning Requests while receiving the plurality of Write-Replace Warning Requests, the DU  20  may specify the PWS message to be stopped. As stated above, the DU  20  that does not have a function of reading the information on the RRC level identifies the plurality of PWS messages, and may perform the processing. 
     The DU  20  may control the duplicate processed PWS messages among the plurality of received processed PWS messages. Accordingly, for example, the DU  20  performs the duplication determination of the plurality of received Write-Replace Warning Requests, and may suppress the transmission of the unnecessary message to the radio section. 
     According to the present embodiment, the CU  10  further adds, to the processed PWS message, the predetermined priority information for each PWS message which indicates the priority order in which the DU  20  transmits the message by using the radio link. In this case, the DU  20  may control the priority order in which the DU transmits the message by using the radio link by using the priority information added to the processed PWS message. 
     Accordingly, for example, the DU  20  may easily determine the priorities of the plurality of received Write-Replace Warning Requests without using the PWS identifier or cooperating with the O&amp;M apparatus or the higher-level apparatus. As a result, the DU  20  may reliably transmit the high-priority message according to the resource of the radio section. 
     [Hardware Configuration] 
     The CU  10  and the DU  20  in the above-described embodiment may be achieved by, for example, the following hardware configuration.  FIG. 13  illustrates a hardware configuration example of the CU  10  and the DU  20 . As illustrated in  FIG. 13 , the CU  10  includes a processor  10   a , a memory  10   b , and a transfer path interface (IF)  10   c . The processor  10   a  includes, for example, a central processing unit (CPU), a field-programmable gate array (FPGA), a digital signal processor (DSP), and the like. The memory  10   b  includes a random-access memory (RAM) such as, for example, a synchronous dynamic random-access memory (SDRAM), a read-only memory (ROM), and a flash memory. The transfer path IF  10   c  is a circuit that communicates with other apparatuses such as the AMF  3  and the DU  20 . The inter-AMF-CU message transmission and reception unit  11 , the message determination unit  12 , the AMF-CU and CU-DU message conversion unit  13 , the PWS message processing unit  14 , and the inter-CU-DU message transmission and reception unit  15  are achieved by, for example, the processor  10   a.    
     The DU  20  includes a processor  20   a , a memory  20   b , a transfer path interface (IF)  20   c , and a radio transfer IF  20   d . The processor  20   a  includes, for example, a central processing unit (CPU), a field programmable gate array (FPGA), a digital signal processor (DSP), and the like. The memory  20   b  includes a RAM such as, for example, a synchronous dynamic random-access memory (SDRAM), a read-only memory (ROM), and a flash memory. The transfer path IF  20   c  is a circuit that communicates with another apparatus such as the CU  10 . The radio transfer IF  20   d  is a circuit that performs radio communication with the UE  5  via an antenna. The inter-CU-DU message transmission and reception unit  21 , the message determination unit  22 , the CU-DU and DU-RRC message conversion unit  23 , the PWS message processing unit  24 , and the inter-DU-RRC message transmission and reception unit  25  are achieved by, for example, the processor  20   a.    
     All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.