Network node of mobile communication network and computer program

Abstract

To provide a technique for reducing imbalances in the processing load of NFs of the same type.SOLUTION: A network node of a mobile communication network includes selection means for selecting a third NF that will accommodate a target wireless device (WD) from a plurality of second NFs that can accommodate the target WD in response to receiving a first message regarding the target wireless device (WD) from a first network function (NF), and notification means for notifying the first NF of the third NF. The selection means selects the third NF from the plurality of second NFs on the basis of at least one of the number of WDs accommodated by each of the plurality of second NFs and a mobility parameter of each WD accommodated by each of the plurality of second NFs. The mobility parameter of the WD indicates the degree of movement of the WD.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a technique for accommodating a wireless device in a network function of a mobile communication network.

Background Art

[0002] A wireless device (WD) in a mobile communication network performs a registration process (Registration) for registering with the mobile communication network, for example, when powered on. As a result, the WD transitions from an unregistered state to a registered state. Also, in the registered state, the WD transitions between an active state and an idle state. The active state is a state in which the WD can communicate with a core network (CN) via a radio access network (RAN) of the mobile communication network. The idle state is a state in which the WD does not have a connection with the RAN, that is, a so-called standby state.

[0003] When data to be transmitted occurs in an idle state WD, the WD starts a random access procedure with the RAN to establish a radio link with the RAN, and transmits a service request message to the CN via the radio link to transition to the active state. Also, when an idle state WD is paged by the RAN, the WD also starts a random access procedure with the RAN to establish a radio link with the RAN, and transmits a service request message to the CN via the radio link to transition to the active state. Also, after transitioning to the active state, if the WD does not perform data transmission and reception for a period longer than that specified by a timer, the RAN releases the radio link with the WD, and as a result, the WD transitions to the idle state.

[0004] Also, the network function (NF) of the control plane (CP) in a mobile communication network manages data called the user equipment (UE) context regarding the WD in the registered state. In the following description, the UE context is simply denoted as "context". Also, unless it is clear from the context that it refers to the NF of the user plane, NF means the NF of the control plane.

[0005] When the WD is in the active state, the context of the WD is stored in the NF that provides services to the WD. As an example, the context of the active WD is stored in the access and mobility management function (AMF), session management function (SMF), control plane of the central unit (CU-CP), control plane of the distributed unit (DU-CP (Non-Patent Document 3)), etc. that provide services to the WD. Note that AMF and SMF are NFs of the CN, and CU-CP and DU-CP are NFs of the RAN. When the active WD transitions to the idle state, the context of the WD stored in the NF of the RAN is deleted. On the other hand, even when the active WD transitions to the idle state, the context of the WD stored in the NF of the CN is maintained. Note that when the WD transitions from the registered state to the unregistered state, the context of the WD is deleted from all NFs of the mobile communication network.

[0006] Normally, a plurality of NFs of the same type are provided in a mobile communication network. For example, when a plurality of AMFs and CU-CPs are provided, when the WD starts the registration process, the mobile communication network selects the AMF and CU-CP that provide services to the WD, and stores the context of the WD in the selected AMF and CU-CP. Also, when the idle WD sends a service request message to transition to the active state, the mobile communication network selects the CU-CP that provides services to the WD, and stores the context of the WD in the selected CU-CP. Note that initially, the AMF that stores the context of the WD provides services to the WD that has transitioned to the active state.

[0007] Non-Patent Documents 1 and 2 disclose selecting, based on the computer resources of each of a plurality of NFs of the same type, an NF that provides services to a WD from among the plurality of NFs, that is, an NF that stores the context of the WD. In the following description, an NF that provides services to a WD is referred to as an "NF that accommodates (or manages) the WD".

Prior Art Documents

Non-Patent Documents

[0008]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] Since the WD is movable, the mobile communication network monitors the movement of the WD and performs handover (HO) as necessary. When performing handover of the WD, the NF providing service to the WD transmits and receives control messages. Therefore, for example, in the case where there are two AMFs, i.e., AMF#1 and AMF#2, if only the fast-moving WDs are accommodated by AMF#1 and only the stationary or slow-moving WDs are accommodated by AMF#2, the number of control messages transmitted and received by AMF#1 is larger than the number of control messages transmitted and received by AMF#2. Therefore, the processing load of AMF#1 is higher than the processing load of AMF#2.

[0010] The present disclosure provides a technique for suppressing the bias in processing load among NFs of the same type.

Means for Solving the Problem

[0011] According to one aspect of the present disclosure, a network node of a mobile communication network includes: a selection means for selecting, in response to receiving a first message regarding a target wireless device (WD) from a first network function (NF), a third NF that accommodates the target WD from a plurality of second NFs capable of accommodating the target WD, wherein the selection means selects the third NF from the plurality of second NFs based on at least one of the number of WDs accommodated by each of the plurality of second NFs and the mobility parameter of each WD accommodated by each of the plurality of second NFs, and the mobility parameter of the WD indicates the degree of movement of the WD; and a notification means for notifying the first NF of the third NF.

Effect of the Invention

[0012] According to the present disclosure, it is possible to suppress the bias in processing load among NFs of the same type.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

[0014] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are essential for the invention. Two or more of the plurality of features described in the embodiments may be arbitrarily combined. Also, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0015] FIG. 1 is a configuration diagram of a mobile communication system according to the present embodiment. The mobile communication system includes a mobile communication network and one or more wireless devices (WDs) 1 connected to the mobile communication network. The wireless device is also referred to as a user equipment (UE). The mobile communication network includes a RAN 2 and a CN 3. The RAN 2 has one or more CU-CPs 22 and one or more DU-CPs 23. Although not shown, the RAN 2 includes a central unit data plane (CU-DP), a distributed unit data plane (DU-DP), a radio unit (RU), and the like. FIG. 1 shows a configuration when the base station is functionally divided into a CU, a DU, and an RU, but the present embodiment can also be applied to a base station that is not functionally divided. Furthermore, the method of functionally dividing the base station, such as dividing the base station into a baseband unit (BBU) and a remote radio unit (RRU), is also arbitrary. The CN includes various control plane NFs including an AMF 32 and a user plane function (UPF) which is a user plane NF. In FIG. 1, one or more NFs in the control plane different from the AMF 32 are collectively denoted as "other NFs 33".

[0016] Furthermore, the mobile communication network according to this embodiment includes a first controller 21 and a second controller 31. The first controller 21 is an NF of the RAN 2, and the second controller 31 is an NF of the CN 3.

[0017] FIG. 2 is a sequence diagram according to this embodiment. In S20, WD1 transmits an initial message to CU-CP 22. The initial message is an attach request message or a service request message. The attach request message is a message for an unregistered WD1 to request registration to the mobile communication network, and the service request message is a message for an idle WD1 to request a transition to the active state. Hereinafter, the sequence will be described assuming that the initial message in S20 is an attach request message. In this case, since WD1 is in an unregistered state at the time of S20, the context of the WD1 is not stored in any NF of the mobile communication network.

[0018] The initial message includes an identifier of the WD1 that transmitted the initial message and a mobility parameter of the WD1. The mobility parameter of WD1 is a parameter indicating the degree of movement of the WD1. In this embodiment, it is assumed that the higher the value, the faster the average movement speed of WD1. Therefore, WD1 is configured to measure the movement speed of the WD1 and maintain the value of the mobility parameter of the WD1. Note that WD1 can measure the movement speed of the WD1 by a positioning system such as a global positioning system (GPS), for example. Alternatively, WD1 can measure the movement speed of the WD1 by an acceleration sensor provided in the WD1.

[0019] Upon receiving the initial message, CU-CP22 transmits an AMF determination request message to the first controller 21 in S21. The AMF determination request message includes the identifier of WD1 and the mobility parameters of the WD1. In response to the AMF determination request message received in S21, the first controller 21 selects an AMF32 that accommodates WD1 from among a plurality of AMFs 32 capable of accommodating WD1. Note that a plurality of the same type of NFs (such as AMF32) capable of accommodating WD1 can be determined based on the current position of WD1 and the like. That is, all the same type of NFs provided in the mobile communication network are associated with a geographical area, and a plurality of the same type of NFs capable of accommodating WD1 are NFs associated with the area including the current position of WD1 among the same type of NFs provided in the mobile communication network. The method for selecting the AMF32 that accommodates WD1 will be described later. In S22, the first controller 21 notifies CU-CP22 of the selected AMF32. In S23, CU-CP22 transmits an initial message including the identifier and mobility parameters of WD1 to the AMF32 notified in S22.

[0020] Upon receiving the initial message, AMF32 creates and stores the context of WD1 in S24. The context of WD1 stored by AMF32 includes information indicating the mobility parameters of the WD1. Subsequently, in S25, AMF32 transmits a CU-CP determination request message to the first controller 21. The CU-CP determination request message includes the identifier and mobility parameters of WD1. The first controller 21 that receives the CU-CP determination request message selects a CU-CP22 that accommodates WD1 from among a plurality of CU-CP22s capable of accommodating WD1. The selection method will be described later. In S26, the first controller 21 notifies AMF32 of the selected CU-CP22.

[0021] In S27, AMF32 sends a context setup request message to CU-CP22 notified in S26. The context setup request message includes the identifier of WD1 and mobility parameters. The CU-CP22 that receives the context setup request message creates and stores the context of WD1 in S28. The context of WD1 stored by CU-CP22 includes information indicating the mobility parameters of the WD1. Note that in FIG. 2, the CU-CP22 that receives the initial message and the CU-CP22 that receives the context setup request message in S27 are considered the same, but the two CU-CP22s can be different.

[0022] Subsequently, in S29, CU-CP22 sends a DU-CP determination request message to the first controller 21. The DU-CP determination request message includes the identifier of WD1 and mobility parameters. The first controller 21 that receives the DU-CP determination request message selects a DU-CP23 that accommodates WD1 from among a plurality of DU-CP23s capable of accommodating WD1. The selection method will be described later. In S30, the first controller 21 notifies the selected DU-CP23 to CU-CP22.

[0023] In S31, CU-CP22 sends a context setup request message to DU-CP23 notified in S30. The context setup request message includes the identifier of WD1 and mobility parameters. The DU-CP23 that receives the context setup request message creates and stores the context of WD1 in S32. The context of WD1 stored by DU-CP23 includes information indicating the mobility parameters of the WD1.

[0024] Also, the AMF 32 that has received the initial message sends, at S33, a determination request message to the second controller 31 for another NF that accommodates WD1. In addition to the identifier of WD1 and the mobility parameters, this message indicates one or more types of other NFs 33. Hereinafter, it will be described assuming that the SMF is specified as one or more types of other NFs 33. The second controller 31 that has received the determination request message selects an SMF that accommodates WD1 from among a plurality of SMFs that can accommodate WD1. The selection method will be described later. The second controller 31 notifies the selected SMF to the AMF 32 at S34.

[0025] At S35, the AMF 32 transmits and receives control messages to and from the SMF notified at S34 to establish, for example, a PDU session for WD1 with the SMF. As a result, the SMF generates and stores the context of WD1 at S36. The context of WD1 stored by the SMF includes information indicating the mobility parameters of the WD1.

[0026] Subsequently, a method for the first controller 21 and the second controller 31 to select an NF that accommodates WD1 from among a plurality of NFs of the same type that can accommodate WD1 will be described. Note that the method for the first controller 21 and the second controller 31 to select an NF that accommodates WD1 from among a plurality of NFs is the same regardless of the type of NF (AMF, CU-CP, DU-CP, SMF, etc.). Therefore, hereinafter, a method for the first controller 21 to select an AMF 32 that accommodates WD1 from among a plurality of AMFs 32 will be described as an example.

[0027] In the following description, it is assumed that the mobility parameter of WD1 is an integer within the range of 0 to 100, and the higher the value, the higher the degree of movement of WD1. Also, WD1 that is the target for determining the destination AMF32 is referred to as the target WD. The first controller 21 and the second controller 22 are configured to be able to access each NF and obtain the number of WD1s currently accommodated in each NF and the mobility parameter of each WD1 currently accommodated in each NF. The mobility parameter of each WD1 is indicated in the context of the corresponding WD1.

[0028] <The First Selection Method> In the first selection method, the first controller 21 selects, as the AMF32 that accommodates the target WD, the AMF32 that currently has the smallest number of WD1s among the plurality of AMF32s. Note that if there are a plurality of AMF32s that have the smallest number of WD1s, the first controller 21 calculates the first evaluation value E1 for each of these AMF32s and selects the AMF32 that accommodates the target WD based on the first evaluation value E1.

[0029] The first evaluation value E1 is obtained as |A - M| based on the average value A of the mobility parameters of the WD1s accommodated in the AMF32 and the mobility parameter M of the target WD. That is, the first evaluation value E1 is the absolute value of the difference between the average value A of the mobility parameters of the WD1s accommodated in the AMF32 and the mobility parameter M of the target WD. In the following description, "the average value A of the mobility parameters of the WD1s accommodated in the AMF" is referred to as "the average value A associated with the AMF".

[0030] For example, as shown in FIG. 3, among the plurality of AMF32s that can accommodate WD1, assume that the AMF32s with the smallest number of WD1s are AMF#1, AMF#2, and AMF#3, and the number of WD1s they accommodate is 50. Further, as shown in FIG. 3, assume that the average value A associated with AMF#1 is 20, the average value A associated with AMF#2 is 50, and the average value A associated with AMF#3 is 80.

[0031] The first controller 21 determines to accommodate the target WD in the AMF 32 with the largest first evaluation value E1. For example, in the example of FIG. 3, when the mobility parameter of the target WD is 30, the first evaluation value E1 of AMF #1 is 10, the first evaluation value E1 of AMF #2 is 20, and the first evaluation value E1 of AMF #3 is 50. Therefore, the first controller 21 determines to accommodate the target WD in AMF #3 with the largest first evaluation value E1.

[0032] In the case of FIG. 3, when the mobility parameter of the target WD is within the range of 0 to 49, the first controller 21 determines to accommodate the target WD in AMF #3, and when the mobility parameter of the target WD is within the range of 51 to 100, the first controller 21 determines to accommodate the target WD in AMF #1. When the mobility parameter of the target WD is 50, the first evaluation values E1 of AMF #1 and AMF #3 are both 30, and are larger than 0 which is the first evaluation value E1 of AMF #2. In such a case, the first controller 21 selects the AMF that accommodates the target WD from AMF #1 and AMF #3 by an arbitrary method.

[0033] In this way, by selecting the AMF with the smallest number of accommodated WD1s as the AMF 32 that accommodates the target WD, the variation in the number of accommodated AMF32s can be suppressed. Since the number of control messages transmitted and received by an NF such as AMF 32 increases as the number of accommodated WD1s increases, by suppressing the variation in the number of WD1s accommodated by the NF, the imbalance in the processing load among NFs of the same type can be suppressed.

[0034] Also, when there are multiple AMF32s with the fewest accommodation numbers, the AMF32 with the largest first evaluation value E1 is selected as the AMF32 that accommodates the target WD. By accommodating the target WD in the AMF32 with the largest first evaluation value E1, the variation in the average values associated with the AMF32s with the fewest accommodation numbers can be reduced. Fig. 3 also shows the average value after accommodation when the target WD with a mobility parameter of 30 is accommodated in each of AMF#1, AMF#2, and AMF#3, and the variance of the average values associated with AMF#1, AMF#2, and AMF#3. As is clear from the variance in Fig. 3, the variance of the average values associated with AMF#1, AMF#2, and AMF#3 is minimized by accommodating the target WD in AMF#3.

[0035] For example, since a WD with a high mobility parameter performs frequent handovers, the AMF32 has to frequently transmit and receive control messages related to handovers. Therefore, the AMF32 with a high associated average value has to transmit and receive a large number of control messages on average, resulting in a high processing load. Therefore, by suppressing the variation in the average values associated with the NFs, the bias in the processing load among NFs of the same type can be suppressed.

[0036] Note that although the first evaluation value E1 of the NF is set as the absolute value of the difference between the average value A of the mobility parameters of the WD1s accommodated by the NF and the mobility parameter M of the target WD, the present embodiment is not limited to using the average value A. The average value A is an example of a value that increases as the mobility parameter of each WD1 accommodated by the NF increases, and any value calculated based on the mobility parameters of the WD1s accommodated by the NF can be used instead of the average value A as long as it increases as the mobility parameters of the WD1s accommodated by the NF increase on average.

[0037] <Second selection method> In the first selection method, first, an AMF32 that houses the target WD is selected based on the number of WDs1 in the AMF32. When there are multiple AMF32s with the smallest number of housed WDs, the AMF32 that houses the target WD is determined based on the first evaluation value E1 of the AMF32. In the present embodiment, a second evaluation value E2 represented by the following formula is obtained for each AMF32 based on the number N of WDs housed in the AMF32 and the first evaluation value E1. E2 = α×N + β×1 / E1

[0038] The second evaluation value E2 becomes smaller as the number N of WDs housed in the AMF32 becomes smaller, and also becomes smaller as the first evaluation value E1 becomes larger. The first controller 21 determines to house the target WD in the AMF32 with the smallest second evaluation value E2. When there are multiple AMF32s with the smallest second evaluation value E2, the first controller 21 determines an AMF32 that houses the target WD from the multiple AMF32s with the smallest second evaluation value E2 by an arbitrary method. For example, when α is 0, the first controller 21 obtains the first evaluation value E1 for all AMF32s capable of housing the target WD, and houses the target WD in the AMF32 with the largest first evaluation value E1. That is, when α is 0, it corresponds to determining the NF that houses WD1 using only the first evaluation value E1 without using the number of housed WDs N in the first selection method. On the other hand, when β is 0, the first controller 21 houses the target WD in the AMF32 with the smallest number of housed WDs. That is, when β is 0, it corresponds to determining the NF that houses WD1 using only the number of housed WDs N without using the first evaluation value E1 in the first selection method. α and β are weights determined based on which of the number of housed WDs N and the first evaluation value E1 is emphasized.

[0039] Values or initial values of α and β are set in advance for the first controller 21 and the second controller 31 by an operator of the mobile communication network. The values of α and β may be fixed or dynamically controlled. For example, the first controller 21 and the second controller 31 may be configured to dynamically control the values of α and β based on, for example, the computing resources of each NF or the number of WDs accommodated in the WD. Note that the values of α and β may be common values for different types of NFs such as the AMF 32 and the CU-CP 22, or may be different values for each type of NF.

[0040] In this embodiment, the second evaluation value E2 is set such that it becomes smaller as the number N of WDs accommodated in the NF becomes smaller, and becomes smaller as the first evaluation value E1 of the NF becomes larger. However, for example, the second evaluation value E2 may be set such that it becomes larger as the number N of WDs accommodated in the NF becomes smaller, and becomes larger as the first evaluation value E1 becomes larger. That is, the second evaluation value E2 can be E2 = α × 1 / N + β × E1 In this case, the first controller 21 and the second controller 31 determine to accommodate the target WD in the NF with the largest second evaluation value E2.

[0041] Subsequently, the difference between the case where the initial message of S20 is a service request message and the case where the initial message of S20 is an attach request message will be described. When it is a service request message, the NF of the CN 3 including the AMF holds the context of the WD1 that transmitted the service request message. Therefore, the processes of S21 and S23 in FIG. 4 are not performed, and the CU-CP 22 transmits an initial message to the AMF 32 that holds the context of the WD1 in S23. The same applies to other NFs 33, and the processes of S33 and S34 are not performed.

[0042] In the sequence of FIG. 4, WD1 determined the mobility parameters of the WD1 and notified the determined mobility parameters to the mobile communication network in the initial message. However, the configuration may also be such that the mobility parameters of WD1 are determined on the mobile communication network side. For example, the mobile communication network may be provided with a Network Data Analytics Function (NWDAF), which is an NF that provides a data analysis service. The NWDAF can collect various data from the NFs of the mobile communication network and provide the analysis results to other NFs. Further, the NWDAF can perform machine learning based on the collected data to generate a learning model, make a prediction based on the learning model, and provide the prediction result to other NFs. Therefore, by configuring the NWDAF to determine the mobility parameters of WD1, the first controller 21 and the second controller 22 can obtain the mobility parameters of WD1 from the NWDAF. In this case, when the first controller 21 and the second controller 22 receive a determination request message (S21, S25, S29, S33) from the NF, they obtain the mobility parameters of the target WD from the NWDAF.

[0043] In the present embodiment, the first controller 21 is provided in RAN2 and the second controller 31 is provided in CN3. However, the first controller 21 and the second controller 31 can also be combined into one controller. This one controller can be provided in RAN2 or CN3.

[0044] <Device Configuration> FIG. 4 is a configuration example of one controller including the functions of the above-described first controller 21, second controller 31, or both the first controller 21 and the second controller 31. Hereinafter, it will be generically referred to as the "controller". The controller is a network node of the mobile communication network.

[0045] The controller shown in FIG. 4 has, for example, one or more processors and one or more memory devices. The one or more memory devices may include a volatile memory device and a non-volatile memory device. By executing, by the one or more processors, a computer program stored in the one or more memory devices, each functional block shown in FIG. 4 can be realized. Also, the controller can be realized by a single device. Alternatively, the controller can be realized by a plurality of devices capable of communicating with each other. Further, the controller can be implemented within the same network node as other NFs. Note that FIG. 4 shows only the functional blocks necessary for understanding the present disclosure, and the controller may have functional blocks other than those shown in FIG. 4.

[0046] In response to receiving a determination request message regarding the target WD from the first NF, the selection unit 10 selects a third NF that accommodates the target WD from among a plurality of second NFs capable of accommodating the target WD. The selection method is as described as the first selection method and the second selection method above. For example, when the first NF is CU-CP22, the third NF is AMF32 or DU-CP23. Also, when the first NF is AMF32, the third NF is CU-CP22 or another NF33. The notification unit 12 notifies the first NF of the third NF selected by the selection unit 10. The acquisition unit 11 acquires the mobility parameters of the target WD. For example, the mobility parameters of the target WD are included in the determination request message, and the acquisition unit 11 acquires the mobility parameters of the target WD by receiving the determination request message. Alternatively, the acquisition unit 11 acquires the mobility parameters of the target WD from the NWDAF.

[0047] According to the present disclosure, when executed by the one or more processors of a device having one or more processors, a computer program that causes the device to function as the above-described controller (network node), and a computer-readable storage medium storing the computer program are provided. Further, according to the present disclosure, a method executed by a controller (network node) regarding the process shown in FIG. 2, a computer program that causes a device having one or more processors to execute the method, and a computer-readable storage medium storing the computer program are provided.

[0048] As described above, it is possible to suppress the bias in the processing load among the same type of NFs. Therefore, it becomes possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "build resilient infrastructure, promote sustainable industrialization, and foster innovation."

[0049] The invention is not limited to the above-described embodiments, and various modifications and changes are possible within the scope of the gist of the invention.

Explanation of Reference Numerals

[0050] 10: Determination unit, 12: Notification unit

Claims

1. A network node of a mobile communication network, comprising: selection means for selecting, in response to receiving a first message regarding a target wireless device (WD) from a first network function (NF), a third NF that accommodates the target WD from a plurality of second NFs capable of accommodating the target WD; notification means for notifying the first NF of the third NF; wherein the selection means selects the third NF from the plurality of second NFs based on at least one of the number of WDs accommodated by each of the plurality of second NFs and the mobility parameter of each WD accommodated by each of the plurality of second NFs; a network node, wherein the mobility parameter of the WD indicates the degree of movement of the WD.

2. The network node according to claim 1, wherein the selection means selects, as the third NF, the second NF having the smallest number of accommodated WDs among the plurality of second NFs.

3. When there are a plurality of second NFs having the smallest number of accommodated WDs, the selection means selects, as the third NF, the second NF having the largest first evaluation value among the second NFs having the smallest number of accommodated WDs; the first evaluation value of the second NF is the difference between a value based on the mobility parameter of each WD accommodated by the second NF and the mobility parameter of the target WD; the value based on the mobility parameter of each WD accommodated by the second NF increases as the mobility parameter of each WD accommodated by the second NF increases. The network node according to claim 2.

4. The selection means selects, as the third NF, the second NF having the largest first evaluation value among the plurality of second NFs; the first evaluation value of the second NF is the difference between a value based on the mobility parameter of each WD accommodated by the second NF and the mobility parameter of the target WD; the value based on the mobility parameter of each WD accommodated by the second NF increases as the mobility parameter of each WD accommodated by the second NF increases. The network node according to claim 1.

5. The selection means selects, as the third NF, the second NF having the smallest second evaluation value among the plurality of second NFs. The second evaluation value of the second NF increases as the accommodation number increases, and decreases as the difference between the value based on the mobility parameter of each of the WDs accommodated in the second NF and the mobility parameter of the target WD increases. The value based on the mobility parameter of each of the WDs accommodated in the second NF increases as the mobility parameter of each of the WDs accommodated in the second NF increases. The network node according to claim 1.

6. The selection means selects, as the third NF, the second NF having the largest second evaluation value among the plurality of second NFs. The second evaluation value of the second NF decreases as the accommodation number increases, and increases as the difference between the value based on the mobility parameter of each of the WDs accommodated in the second NF and the mobility parameter of the target WD increases. The value based on the mobility parameter of each of the WDs accommodated in the second NF increases as the mobility parameter of each of the WDs accommodated in the second NF increases. The network node according to claim 1.

7. The value based on the mobility parameter of each of the WDs accommodated in the second NF is the average value of the mobility parameters of each of the WDs accommodated in the second NF. The network node according to any one of claims 3 to 6.

8. The mobility parameter of the target WD is notified from the target WD. The network node according to any one of claims 1 to 6.

9. The network node according to any one of claims 1 to 6 further includes an acquisition means for acquiring the mobility parameter of the target WD from a fourth NF.

10. The fourth NF is a network data analysis function (NWDAF). The network node according to claim 9.

11. When the first NF is the control plane (CU-CP) of the central unit, the third NF is the access and mobility management function (AMF) or the control plane (DU-CP) of the distributed unit. When the first NF is an access and mobility management function (AMF), the third NF is a NF different from the control plane of the central unit (CU-CP) or the AMF of the core network of the mobile communication network, the network node according to any one of claims 1 to 6.

12. A computer program that, when executed by the one or more processors of a device having the one or more processors, causes the device to function as the network node according to any one of claims 1 to 6.

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