Communication control system, control method for communication control system, and control program for communication control system

Abstract

This communication control system is for controlling optical wireless communication between rack-mounted servers stored in server racks and comprises: a reception unit for receiving designation of servers that perform communication with each other; a specifying unit for specifying whether the server racks in which the servers performing communication with each other are stored are the same server rack or different server racks on the basis of information that is stored in a storage unit and pertains to the server racks in which a plurality of servers stored in individual server racks are stored and the positions at which the servers are stored in the server racks; and a setting unit that sets a first optical frequency for use in communication between servers stored in the same server rack and a second optical frequency for use in communication between servers stored in different server racks, (1) sets first optical frequencies that are different from each other and not near each other when optical wireless communication between two or more sets of different servers occurs in the same server rack, (2) sets second optical frequencies that are different from each other and not near each other when optical wireless communication between two or more different sets of servers occurs between servers stored in different server racks, and (3) sets an optical frequency that does not overlap with the first optical frequencies and the second optical frequencies.

Description

COMMUNICATION CONTROL SYSTEM, CONTROL METHOD FOR COMMUNICATION CONTROL SYSTEM, AND CONTROL PROGRAM FOR COMMUNICATION CONTROL SYSTEM

[0001] The present invention relates to a communication control system, a control method for a communication control system, and a control program for a communication control system.

[0002] Connections between server racks in data centers are typically made using physical methods such as optical fiber, coaxial cables, and Ethernet cables. This has led to problems such as cumbersome cable installation, time-consuming management of installation conditions, space taken up by stubborn excess cable, the risk of tripping, and the need for organization within the rack. In response to these issues, a system has been disclosed in which optical connection devices are installed in individual installation units for data exchange between devices, enabling mutual communication between devices via optical signals (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2000-31913

[0004] When communicating between servers located in a server rack, there is a need for a highly accurate communication method that can simultaneously communicate between servers located in the same server rack and between servers located in different server racks without causing crosstalk.

[0005] A communication control system according to one embodiment of the present invention is a communication control system for controlling optical wireless communication between rack-mounted servers stored in a server rack, and includes: a reception unit that receives designation of servers that will communicate with each other; an identification unit that identifies whether the server racks in which the servers that communicate with each other are stored are the same or different, based on information stored in a predetermined memory unit about the server racks in which the multiple servers stored in each server rack are stored and their positions in the server racks; and a setting unit that sets a first optical frequency to be used for communication between the servers stored in the same server rack and a second optical frequency to be used for communication between the servers stored in different server racks, wherein: (1) when optical wireless communication occurs between two or more sets of different servers in the same server rack, the setting unit sets optical frequencies that are different from each other and not adjacent to each other for each first optical frequency; (2) when optical wireless communication occurs between two or more sets of different servers stored in different server racks, the setting unit sets optical frequencies that are different from each other and not adjacent to each other for each second optical frequency; and (3) sets optical frequencies that do not overlap with the first optical frequency and the second optical frequency.

[0006] In the communication control system according to one embodiment of the present invention, the setting unit may use a coarse wavelength division multiplexing (CWDM) method among wavelength division multiplexing methods as the optical wireless communication.

[0007] In the communication control system according to one embodiment of the present invention, the setting unit may use a DWDM (Dense Wavelength Division Multiplexing) method among wavelength division multiplexing methods as the optical wireless communication.

[0008] In a communication control system according to one embodiment of the present invention, each server rack is provided with a wavelength selective tunable device (ADM: Add Drop Multiplexer), and the communication control system may further include a command unit that generates a command to the wavelength selective tunable device installed in the server rack in which the servers communicating with each other are located to drop light of an optical frequency used between the servers communicating with each other into the server rack.

[0009] In the communication control system according to one embodiment of the present invention, the setting unit may set the first optical frequency and the second optical frequency based on an optical frequency used in communication between a plurality of servers.

[0010] In a communication control system according to one embodiment of the present invention, each server rack may include a wavelength conversion device that converts the optical frequency of light dropped onto the server rack into an optical frequency compatible with the server.

[0011] A control method for a communication control system according to one embodiment of the present invention is a control method for a communication control system that controls optical wireless communication between rack-mounted servers stored in a server rack, and includes the steps of: receiving designation of servers that will communicate with each other; identifying whether the server racks in which the servers that will communicate with each other are stored are the same or different, based on information stored in a predetermined memory unit about the server racks in which the multiple servers stored in each server rack are stored and their positions in the server racks; and setting a first optical frequency to be used for communication between the servers stored in the same server rack and a second optical frequency to be used for communication between the servers stored in different server racks, in which (1) when optical wireless communication occurs between two or more sets of different servers in the same server rack, different and non-adjacent optical frequencies are set for each of the first optical frequencies; (2) when optical wireless communication occurs between two or more sets of different servers stored in different server racks, different and non-adjacent optical frequencies are set for each of the second optical frequencies; and (3) setting optical frequencies that do not overlap with the first optical frequency and the second optical frequency.

[0012] A control program for a communication control device according to one embodiment of the present invention is a control program for a communication control system that controls optical wireless communication between rack-mounted servers stored in a server rack, and provides an information processing device with the following functions: accepting designation of servers that will communicate with each other; identifying whether the server racks in which the servers that will communicate with each other are stored are the same or different, based on information stored in a specified memory unit about the server rack in which the multiple servers stored in each server rack are stored and their positions in the server rack; and setting a first optical frequency to be used for communication between servers stored in the same server rack and a second optical frequency to be used for communication between servers stored in different server racks, wherein: (1) when optical wireless communication occurs between two or more sets of different servers in the same server rack, the first optical frequencies are set to optical frequencies that are different from each other and that are not adjacent to each other; (2) when optical wireless communication occurs between two or more sets of different servers stored in different server racks, the second optical frequencies are set to optical frequencies that are different from each other and that are not adjacent to each other; and (3) setting optical frequencies that do not overlap with the first optical frequency and the second optical frequency.

[0013] When communicating between servers located in a server rack, it is possible to provide a highly accurate communication method that allows communication between servers located in the same server rack and between servers located in different server racks simultaneously, without crosstalk.

[0014] FIG. 1(a) is a schematic diagram of a communication control system configuration according to one embodiment of the present invention, FIG. 1(b) is an explanatory diagram of wavelength multiplexing division, and FIG. 1(c) is a schematic diagram of a server rack configuration according to one embodiment of the present invention. FIG. 2 is an example of a functional block diagram of a communication control device and a transmitting device according to one embodiment of the present invention. FIG. 3 is an example of a data table in a communication control system according to one embodiment of the present invention. FIG. 4 is a schematic diagram explaining a communication control system according to one embodiment of the present invention. FIG. 5 is a flowchart showing an example of the operation of a communication control device according to one embodiment of the present invention. FIGS. 6(a) to 6(c) are schematic diagrams explaining a communication control system according to one embodiment of the present invention.

[0015] Hereinafter, an embodiment of the invention according to the present disclosure (also referred to as the present invention) will be described using the drawings. Note that the drawings are merely examples, and the present invention is not limited to those shown in the drawings. For example, the illustrated communication control devices, transmission devices, server racks, and number of servers, server rack configurations, frequencies, functional block diagrams, flowcharts, and data tables are merely examples, and the present invention is not limited to these.

[0016] <System Configuration> FIG. 1A is a diagram illustrating an example configuration of a communication control system according to an embodiment of the present invention. The communication control system 600 is a communication control system that controls optical wireless communication between rack-mounted servers 20 housed in server racks 10 (10a, 10b, 10c, 10d, ..., 10x; hereinafter, simply referred to as "server racks 10" unless otherwise specified). In a collection 30 of multiple server racks 10, a communication control device 300 controls optical wireless communication using optical signals between servers 20 located in the same server rack 10 and between servers 20 located in different server racks 10. Optical wireless communication is being researched and developed as a new communication medium for mobile communication systems beyond 5G (5th generation), 6G (6th generation), and beyond. Optical wireless communication may refer to communication using infrared light, visible light, laser light, or the like, which are in the THz (terahertz) frequency band of several hundred nanometers to several micrometers.

[0017] FIG. 1(b) is a schematic diagram illustrating wavelength division multiplexing (WDM) used in optical wireless communication. In WDM, optical signals of different wavelengths (channels) are transmitted together. Wavelength division multiplexing methods include coarse wavelength division multiplexing (CWDM) and dense wavelength division multiplexing (DWDM). FIG. 1(b) shows the wavelength allocation diagram for CWDM, which uses a wide wavelength band of 0.7 to 1.6 μm with wavelength spacing of approximately 20 nm or more. In the case of DWDM, the wavelength spacing is approximately 0.8 nm (equivalent to a frequency of 100 GHz in the 1.55 μm band), and the number of channels is approximately 40. In recent years, DWDM with 50 GHz spacing and 80 channels has also been used.

[0018] FIG. 1C is a schematic diagram of the configuration of a server rack 10. The server rack 10 houses multiple rack-mounted servers (hereinafter simply referred to as "servers") 20 and includes an optical communication unit 11 and a wavelength conversion device 12. The optical communication unit 11 includes a wavelength-selective tunable device (ADM: Add Drop Multiplexer) that can select, using an optical switch, whether to extract or pass a specific wavelength signal from an optical signal OP multiplexed using wavelength division multiplexing. The wavelength conversion device 12 converts the frequency of an optical signal that passes through the optical communication unit 11 and arrives at the device itself to a frequency compatible with (operating at) each server 20 and passes the converted signal to the server 20. Conversely, the wavelength conversion device 12 converts the frequency of an optical signal containing information transmitted from each server 20 into an optical signal having a frequency according to the setting of a setting unit 113 (described later). The optical communication unit 11 and the wavelength conversion device 12 may be connected to a communication control device 100 (not shown) via wire or wireless (including optical wireless).

[0019] <Communication Control Device> Next, the hardware configuration and functional configuration of the communication control device 100 will be described with reference to Fig. 2. (1) Hardware Configuration of Communication Control Device The communication control device 100 includes a control unit 110, a communication unit 120, an input / output unit 130, and a storage unit 170.

[0020] The control unit 110 is typically a processor, including a central processing unit (CPU), a microprocessing unit (MPU), a graphics processing unit (GPU), a microprocessor, etc., and is realized by a logic circuit (hardware) or a dedicated circuit formed in an integrated circuit (IC (Integrated Circuit) chip, LSI (Large Scale Integration)), etc. The control unit 110 reads out a program (software) stored in the storage unit 170 and executes the code and instructions included in the program, thereby performing the functions and methods described in each embodiment.

[0021] The storage unit 170 stores various programs and data required for the operation of the communication control device 100. The storage unit 170 may include, for example, a hard disk drive (HDD), a solid state drive (SSD), a flash memory, etc. The storage unit 170 may also include memory (random access memory (RAM), read only memory (ROM), etc.) that provides a working area for the control unit 110.

[0022] The storage unit 170 stores (contains) information about the server racks 10 in which the multiple servers 20 are stored and their locations in the server racks 10. FIG. 3 is an example of a table related to the storage locations of each server 20. The data table TB10 stores a server identifier that uniquely identifies each server 20, associated with the identifier of the server rack 20 in which the server 20 is stored (rack identifier), and the location of the server 10 in the server rack 20 (rack storage location). Note that the figure is an example, and the information stored in the data table TB10 may be more or less than this.

[0023] The communication unit 120 is implemented as hardware such as a network adapter, communication software, or a combination of these. The communication unit 120 is connected to an external information processing device (not shown) and receives a designation of the server 20 with which to communicate.

[0024] The input / output unit 130 includes an input device that accepts various operations on the communication control device 100 from an administrator or the like, and an output unit that outputs processing results processed by the communication control device 100. The input device may include, for example, a keyboard or a microphone, and the output device may include, for example, a display or a speaker. The input / output unit 130 may also be a connection interface with the optical signal transmitting device 200. The transmitting device 200 is a typical optical signal generating device and includes a signal conversion processing unit 210 and a light source 220. The signal conversion processing unit 210 converts (superimposes) data to be transmitted to the server 20 into an optical signal. The light source 220 may be a single light source or multiple light sources, and may be, for example, a laser diode (LD) or a light-emitting diode (LED), but is not limited to these.

[0025] (2) Functional Configuration of the Communication Control Device The communication control device 100 includes a reception unit 111, an identification unit 112, a setting unit 113, and a command unit 114 as functions realized by the control unit 110. Note that, among the functional units shown in FIG. 2 , functional units that are not essential in the embodiments described below may be omitted. Furthermore, the functions or processes of the functional units may be realized by machine learning (ML) or artificial intelligence (AI) to the extent feasible.

[0026] The processing of each functional unit of the communication control device 100 according to one embodiment of the present invention will be described with reference to FIG. 4 , which is a schematic diagram illustrating a case in which servers 20 located in multiple server racks 10 are connected by optical signals. The reception unit 111 receives designation of the servers 20 that will communicate with each other. The designation of the servers 20 may be transmitted from an external information processing device (not shown). In the example of FIG. 4 , the combinations of servers stored in different racks are designated as follows: server 20a1 stored in rack A 10a and server 20e1 stored in rack E 10e, and server 20d1 stored in rack D 10d and server 20e2 stored in rack E 10e. Furthermore, the combinations of servers stored in the same rack are designated as follows: server 20a2 and server 20a3 stored in rack A 10a, server 20d2 and server 20d3 stored in rack D 10d, server 20c1 and server 20c2 stored in rack C 10c, and server 20c3 and server 20c4 stored in rack C 10c. The server 20 may be designated by its server identifier, for example. The identifying unit 112 identifies, based on the data table TB10, whether the servers communicating with each other are stored in the same server rack or different server racks.

[0027] The setting unit 113 sets the frequency of the optical signal used for communication between the servers 20 for each combination of servers 20. The setting unit 113 sets a first optical frequency to be used for communication between the servers 20 stored in the same server rack 10 and a second optical frequency to be used for communication between the servers 20 stored in different server racks 10. At this time, when optical wireless communication occurs between two or more sets of different servers in the same server rack 10, the setting unit 113 sets optical frequencies that are different from each other and are not adjacent to each other for each first optical frequency. That is, in the example of FIG. 4 , different optical frequencies are used for "servers 20c1-20c2" and "servers 20c3-20c4" stored in the same rack C 10C. Specifically, a frequency band with a center frequency of 810 nm is used for communication between "servers 20c1-server 20c2," and a frequency band with a center frequency of 900 nm is used for communication between "servers 20c3-server 20c4."

[0028] When the received optical signal contains information addressed to a server 20 stored in the server rack 10 in which the optical communication unit 11 is installed, the optical communication unit 11 drops (extracts) the optical signal of the frequency containing that information and takes it into the server rack 10. When the received optical signal does not contain information addressed to a server 20 stored in the server rack 10 in which the optical communication unit 11 is installed, the optical communication unit 11 passes the signal as is.

[0029] Furthermore, when optical wireless communication occurs between two or more sets of different servers 20 stored in different server racks 10, the setting unit 113 sets different and non-adjacent optical frequencies for the respective second optical frequencies. That is, in the example of FIG. 4 , the optical frequencies for "server 20a1-server 20e1" stored in different racks A 10a and E 10e, and "server 20d1-server 20e2" stored in racks D 10d and E 10e are set to be different. Specifically, a frequency band with a center frequency of 900 nm is used for communication between "server 20a1-server 20e1," and a frequency band with a center frequency of 810 nm is used for communication between "server 20d1-server 20e2." The setting unit 113 then sets optical frequencies that do not overlap with the first optical frequency and the second optical frequency. That is, the frequencies used by the same server are set to be different. Specifically, in the rack A 10A, the "server 20a1-server 20e1" and the "server 20a2-20a3" use the frequency bands of 900 nm and 810 nm, respectively.

[0030] Thus, according to one embodiment of the present invention, cabling is no longer necessary, and broadband, highly compressed optical communications between and within racks can be realized, compatible with future advances in inter-server bandwidth, from several gigabits to several terabits per second. Furthermore, freeing up space for excess cable length within server racks improves air conditioning efficiency and reduces thermal runaway of equipment.

[0031] The command unit 114 generates a command to the wavelength-selective variable device included in the optical communication unit 11 installed in the server rack 10 where the servers 20 communicating with each other are located, to drop the light of the optical frequency used between the servers 20 communicating with each other to the server rack 10. This allows information to be transmitted to the servers 20 reliably without crosstalk of optical signals.

[0032] Here, the setting unit 113 sets the first optical frequency and the second optical frequency based on the optical frequencies used in communication between the multiple servers 20. That is, when a designation for communication between new servers is received, the setting unit 113 extracts an optical signal frequency that is not used in communication between the servers 20 and that does not overlap within the server rack 10, i.e., does not cause crosstalk. Note that this processing by the setting unit 113 may be realized by AI (artificial intelligence).

[0033] In addition, when CWDM is used as the wavelength multiplexing division method, the wavelength setting precision of the optical device can be relaxed compared to DWDM, so the load on the control system can be reduced. In other words, since the wavelength spacing is wide and wavelength control is not required, it is economical and power consumption can be reduced.

[0034] Furthermore, when DWDM is used as the wavelength multiplexing division method, a large number of channels are available, making it possible to accommodate communication between many servers.

[0035] <Control Flow of Communication Control Device> The control flow of the communication control device 100 described above will be described with reference to FIG. 5 . First, the storage unit 170 stores information (data table TB10) about the server racks 10 in which the multiple servers 20 are stored and their locations within the server racks 10 (step S11). Next, the reception unit 111 receives designations of the servers 20 that will communicate with each other (step S12). The setting unit 113 determines whether the server racks 10 storing the servers 20 that will communicate with each other are the same (step S13). If it is determined that the server racks 10 are the same ("YES" in step S13), the setting unit 113 sets different but not adjacent first optical frequencies for use in communication between the servers 20 when optical wireless communication occurs between two or more sets of different servers 20 (step S14). If it is determined that the server racks 10 are different from each other ("NO" in step S13), when optical wireless communication occurs between two or more sets of different servers 20, the setting unit 113 sets the second optical frequency used for communication between each server 20 to an optical frequency that is different from each other and not close to each other (step S15).

[0036] While the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art would readily be able to make various modifications and alterations based on the present disclosure. Therefore, it should be noted that these modifications and alterations are within the scope of the present invention. For example, the functions included in each component, step, etc. may be rearranged so as not to cause logical inconsistencies, and multiple components, steps, etc. may be combined or separated into one. Furthermore, the configurations described in the above embodiments may be appropriately combined. For example, each component described as being included in the communication control device 100 may be realized in a distributed manner by multiple communication control devices. Furthermore, the processing described above as being performed by the communication control device 100 may be performed by the transmitting device 200.

[0037] For example, in the above description, the server racks 10 are arranged in a row as a set 30 of server racks 10. However, the present invention may be applicable to various arrangements of server racks 10. An example is shown in FIGS. 6(a) to 6(c). Each figure is a schematic diagram showing an example of the formation of an optical communication path when multiple rows of server racks 10 are arranged. Note that in each figure, the server rack 10 is viewed from above the server rack 10.

[0038] FIG. 6( a ) shows a case where communication between servers is performed independently for each row of server racks 10. In this case, the above-described communication control may be performed for each row of server racks 10. That is, the frequencies of optical signals may overlap for each server rack 10. In contrast, in FIG. 6( b ), the server rack located at the end of each row of server racks 10 may be used as a hub, and frequencies may be set to prevent crosstalk, including for optical wireless communication between each row of server racks 10. Furthermore, in FIG. 6( c ), frequencies may be set to prevent crosstalk while connecting all server racks 10 in a matrix. In this case, the optical signal is preferably divided using wavelength division multiplexing, which can generate many channels.

[0039] Although the above description has been given using a 5G mobile communication system as an example, the present invention is not limited thereto and may also be applied to mobile communication systems such as 4G (fourth generation), 6G (sixth generation), and LTE. For example, optical wireless communication is being researched and developed as a new communication medium for radio access networks (RANs) in 5G (fifth generation), 6G (sixth generation), and later mobile communication systems. 5G and later mobile communication systems include a RAN Intelligent Controller (RIC), which is defined as a logical node that designs and configures base station parameters and automates and optimizes operations. As the computational load on the RIC increases, the load on the server also increases. According to one embodiment of the present invention, the number of physical cables laid between servers can be reduced, thereby reducing heat generated by the cables compared to conventional systems.

[0040] The programs of the embodiments of the present disclosure may be provided in a state stored in a storage medium readable by the communication control device. The storage medium may store the programs in a "non-transitory tangible medium." The programs include, for example, software programs and control programs. When the functional units of the communication control device 100 are realized by software, the communication control device 100 functions as the reception unit 111, the identification unit 112, the setting unit 113, and the command unit 114 by the processor executing the programs loaded into the memory.

[0041] The storage medium may, where appropriate, comprise one or more semiconductor-based or other integrated circuits (ICs) (e.g., field programmable gate arrays (FPGAs), application specific ICs (ASICs), etc.), hard disk drives (HDDs), hybrid hard drives (HHDs), optical disks, optical disk drives (ODDs), magneto-optical disks, magneto-optical drives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes, solid state drives (SSDs), RAM drives, secure digital cards or drives, any other suitable storage media, or any suitable combination of two or more of these. The storage medium may, where appropriate, be volatile, non-volatile, or a combination of volatile and non-volatile.

[0042] Furthermore, the program of the present disclosure may be provided to the communication control device 100 via any transmission medium (such as a communication network or broadcast waves) capable of transmitting the program.

[0043] Furthermore, each embodiment of the present disclosure may be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission. Note that the program of the present disclosure may be implemented using, for example, a scripting language such as JavaScript (registered trademark) or Python, or the C language, Go language, Swift, Koltin, Java (registered trademark), or the like.

[0044] According to each aspect of the present disclosure described above, the load on the server room is reduced and heat generation is suppressed, thereby contributing to the achievement of Goal 11 of the Sustainable Development Goals (SDGs), "Sustainable cities and communities."

[0045] REFERENCE SIGNS LIST 100 Communication control device 110 Control unit 111 Reception unit 112 Identification unit 113 Setting unit 114 Command unit 120 Communication unit 130 Input / output unit 170 Storage unit 200 Transmission device 210 Signal conversion processing unit 220 Light source 600 Communication control system 10 Server rack 11 Optical communication unit 12 Wavelength conversion device 20 Server OP Optical signal

Claims

1. A communication control system for controlling optical wireless communication between rack-mounted servers stored in a server rack, comprising: a reception unit that receives designation of servers that will communicate with each other; an identification unit that identifies whether the server racks in which the servers that will communicate with each other are stored are the same or different, based on information stored in a predetermined memory unit about the server rack in which the multiple servers stored in each server rack are stored and their positions in the server rack; and a setting unit that sets a first optical frequency to be used for communication between servers stored in the same server rack and a second optical frequency to be used for communication between servers stored in different server racks, the setting unit being: (1) when optical wireless communication occurs between two or more sets of different servers in the same server rack, the setting unit sets optical frequencies that are different from each other and not adjacent to each other for each of the first optical frequencies; (2) when optical wireless communication occurs between two or more sets of different servers stored in the different server racks, the setting unit sets optical frequencies that are different from each other and not adjacent to each other for each of the second optical frequencies; and (3) when optical wireless communication occurs between two or more sets of different servers stored in the different server racks, the setting unit sets optical frequencies that do not overlap with each other for the first optical frequency and the second optical frequency.

2. The communication control system according to claim 1, wherein the setting unit uses a CWDM (Coarse Wavelength Division Multiplexing) method among wavelength division multiplexing methods as the optical wireless communication.

3. The communication control system according to claim 1, wherein the setting unit uses a DWDM (Dense Wavelength Division Multiplexing) method among wavelength division multiplexing methods as the optical wireless communication.

4. The communication control system according to claim 1, wherein each of the server racks is equipped with a wavelength selective tunable device (ADM: Add Drop Multiplexer), and the communication control system further comprises a command unit that generates a command to the wavelength selective tunable device installed in the server rack in which the servers communicating with each other are located to drop light of the optical frequency used between the servers communicating with each other to the server rack.

5. The communication control system according to claim 1, wherein the setting unit sets the first optical frequency and the second optical frequency based on optical frequencies used in communications between the plurality of servers.

6. The communication control system according to claim 4, wherein each of the server racks is provided with a wavelength conversion device that converts the optical frequency of light dropped onto the server rack into an optical frequency compatible with the server.

7. A control method for a communication control system that controls optical wireless communication between rack-mounted servers stored in a server rack, the control method comprising the steps of: receiving designation of servers that will communicate with each other; determining whether the server racks storing the servers that will communicate with each other are the same or different, based on information stored in a predetermined memory unit about the server rack in which the multiple servers stored in each server rack are stored and their positions in the server rack; and setting a first optical frequency to be used for communication between servers stored in the same server rack and a second optical frequency to be used for communication between servers stored in different server racks, the steps comprising: (1) when optical wireless communication occurs between two or more sets of different servers in the same server rack, setting optical frequencies that are different from each other and not adjacent to each other for each of the first optical frequencies; (2) when optical wireless communication occurs between two or more sets of different servers stored in the different server racks, setting optical frequencies that are different from each other and not adjacent to each other for each of the second optical frequencies; and (3) setting optical frequencies that do not overlap with the first optical frequency and the second optical frequency.

8. A control program for a communication control system that controls optical wireless communication between rack-mounted servers stored in a server rack, the control program causing an information processing device to realize the following functions: a function for accepting designation of servers that will communicate with each other; a function for identifying whether the server racks in which the servers that will communicate with each other are stored are the same or different, based on information stored in a specified memory unit about the server rack in which the multiple servers stored in each server rack are stored and their positions in the server rack; and a function for setting a first optical frequency to be used for communication between servers stored in the same server rack and a second optical frequency to be used for communication between servers stored in different server racks, the function comprising: (1) when optical wireless communication occurs between two or more sets of different servers in the same server rack, setting optical frequencies that are different from each other and not adjacent to each other for each of the first optical frequencies; (2) when optical wireless communication occurs between two or more sets of different servers stored in the different server racks, setting optical frequencies that are different from each other and not adjacent to each other for each of the second optical frequencies; and (3) setting optical frequencies that do not overlap with the first optical frequency and the second optical frequency.

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