JP2016151790A - Radio communication server rack and server aggregation using server rack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a server rack that can efficiently curb a delay wave in radio communication in a housing required for securing a passage of cooling air.SOLUTION: A server rack 70 includes housings 40, 42, 46 and 48 that define a space housing a plurality of server computers 60 inside. The housing of the server rack 70 includes a first half part that has an opening and a second half part that is closed, respectively. A plurality of servers 60 is housed inside the space, and thereby an inner space of the housing is separated into the first half part and the second half part by a case housing of a plurality of servers. The plurality of servers is arranged so that a case rear face directs at a second half part side. Each of the plurality of servers 60 has a mounting port which is provided in the case rear face, and to which a communication module is mounted. Of the inner face of the housing of the server rack and defining the first half part and second half part to be separated into by the plurality of servers, in at least one part excluding a face having the opening formed, radio wave absorption materials 80 and 82 are installed.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a server rack that accommodates a large number of servers, and in particular, from a server rack that enables wireless communication for high-speed data transmission in the server rack, and the server rack and a plurality of servers accommodated therein. Concerning the server aggregate.

  With the progress of cloud services, the number of data centers that store a large amount of data via a network is increasing. A number of devices such as servers are used in the data center. Due to the nature of the data center, it is necessary to operate 24 hours a day, 365 days a year, without breaks. As a result, each data center consumes a large amount of power throughout the year. For this reason, reducing the power consumption of the entire data center is an urgent issue. The server itself consumes power, and the server must be cooled to prevent the server from overheating and causing errors. Of the power consumed in the data center, not only the power consumed by devices such as servers, but also the proportion of air conditioning power used to cool servers is very large.

  In a general data center, in order to efficiently operate servers, a large number of server racks each accommodating a plurality of servers are densely installed. Typically, one server rack accommodates about 40 servers. Each server rack is arranged so that cooling air from the cooling device flows.

  For example, as shown in FIG. 1, a typical server rack 30 has a rectangular parallelepiped shape with a height of about 2.2 m, a width of about 0.7 m, and a depth of about 1.2 m. A large number of thin servers are accommodated in the interior. The entire server rack 30 includes a metal bottom plate 40, top plate 42, two side plates 44 and side plates 46, a rear door 48 and a front door 50. The front door 50 can be opened and closed, and an opening 52 is provided. In many cases, the opening 52 has a metal mesh shape. Although not shown, the same applies to the rear door 48. The cooling airflow is supplied into the server rack 30 through the opening 52 of the front door 50 and discharged to the outside through the opening of the rear door 48. The cooling airflow may be supplied through the reverse path.

  However, the operation of servers in such a data center has the following problems. In the server rack, it is necessary to connect each server and the switch for communication. This connection is made by a communication cable such as an Ethernet (registered trademark) cable. However, when there are a large number of servers, it is said that these cables are complicated and the maintenance of the server becomes complicated, and the cooling airflow is hindered by the cables, so that the cooling efficiency is greatly reduced.

  One way to solve these problems is to wirelessly communicate between the server and the switch in the data server. Then, the problem of a decrease in cooling efficiency due to the cable is improved, which can greatly contribute to the reduction in power consumption of the data server. Furthermore, the maintenance cost that has become complicated due to the presence of the communication cable can be reduced.

  However, there is a big problem in making all communication in the data center wireless. A large number of server racks are densely installed in the data center, and an enormous number of communication cables are used. Moreover, communication in the data center must be fast. For this reason, if all communication using cables is made wireless and a high communication speed is guaranteed, a necessary frequency band becomes an unrealistic value and cannot be realized. Therefore, it is realistic to confine communication radio waves for each server rack and share the same frequency band with all server racks.

  Server racks are usually made of metal, so it is relatively easy to confine radio waves. However, when wireless communication is performed in a space confined with metal, radio waves are multiple-reflected on a metal surface such as a wall surface in the server rack, which makes the environment extremely difficult for wireless communication. When multiple reflections exist, a large number of delayed waves are received in addition to the main wave. As a result, interference due to delayed waves occurs between modulation symbols arranged in time series.

  There is OFDM (Orthogonal Frequency Division Multiplexing) as a modulation scheme that is strong in modulation between symbols by a delayed wave. In OFDM modulation, a cyclic prefix is added to the beginning of each symbol to provide a guard interval period. As a result, interference of delayed waves that arrive within this period can be avoided. In particular, as one of the promising methods considered as a communication method in the server rack, there is OFDM modulation of the IEEE 802.11ad standard of 60 GHz band. In this OFDM modulation, the guard interval period is 48.4 ns. Therefore, if the delayed wave of a large level is delayed within 48.4 ns with respect to the main wave, communication can be performed ignoring intersymbol interference. However, IEEE 802.11ad is a standard that is intended for indoor use, and is not expected to be used in a narrow metal space such as a server rack. Therefore, when IEEE 802.11ad is used in a server rack, there is a concern about the presence of a long delay wave.

  The simplest countermeasure to solve this problem is to provide a radio wave absorber on the entire inner surface of the server rack. However, such a configuration has a problem that the cost of the server rack increases. Accordingly, an invention for reducing the problem of cost while solving the problem of long delay is disclosed in Patent Document 1 described later. The invention described in Patent Document 1 is to provide a radio wave absorber only on the surface of the inner surface of the housing that has the largest exposed area in order to suppress delayed waves in the narrow housing. It is said that this radio wave absorber can suppress reflected waves and reduce delayed waves.

JP2007-150256

  In the invention described in Patent Document 1, instead of providing a radio wave absorber on all inner surfaces, a radio wave absorber is provided only on the maximum surface, so that it can be installed inexpensively and easily, and effectively reduces delayed waves. It is. However, the present invention cannot be simply applied to server racks. When accommodating a plurality of servers in a server rack, the front surface 50 shown in FIG. 1 is the surface of the server rack that has the largest area exposed to the space inside the housing. However, normally, the front door 50 is formed with a mesh-shaped opening 52, which is a passage for cooling air. Therefore, it is unrealistic to install a radio wave absorber in the opening 52.

  Therefore, the present invention provides a server rack capable of efficiently suppressing a delayed wave in wireless communication in a housing that requires a passage of cooling air, such as a server rack, and the server rack, and the server rack. The object is to provide a server aggregate composed of a plurality of accommodated servers.

  The server rack according to the first aspect of the present invention has a housing that defines a space in which a plurality of server computers are accommodated. Each case has a front half and a rear half in which an opening is formed. The internal space of the housing is separated into a first half part and a second half part by housing a plurality of servers, by the case of the plurality of servers. The plurality of servers are arranged so that the back surface faces the rear half, and each of the plurality of servers has a mounting port provided on the back surface to which the communication module is mounted. A radio wave absorber is installed on at least a portion of the inner surface of the housing that defines the rear half separated from the front half by a plurality of servers, excluding the inner surface provided with the opening.

  Preferably, the casing has a rectangular parallelepiped shape including a top plate, a bottom plate, two side plates, and a front door and a rear door each having an opening, and having a hollow inside. The plurality of servers are housed and fixed inside the housing so as to be separated from the back door in an internal space defined by the housing, whereby the back door, the bottom plate and the top plate, and the two side plates The second half is defined by the case back of the plurality of servers. The radio wave absorber is disposed in a region in the rear half of at least one inner surface of the top plate, the bottom plate, and the two side plates.

  More preferably, all the openings are mesh-shaped, and the size of the mesh opening is smaller than the half wavelength of the radio wave used in the wireless communication performed in the rack.

  More preferably, no radio wave absorber is installed on the inner surface of any of the top plate, the bottom plate, and the two side plates in the first half.

  A server aggregate according to a second aspect of the present invention is defined by a server rack in a server rack having a housing that defines a space for accommodating a plurality of server computers therein and in a space defined by the server rack. A server aggregate including a plurality of servers accommodated so as to divide the space into a first half and a second half. Openings are formed in both the front half and the rear half of the housing. The plurality of servers are arranged so that the back of the case faces the rear half side, and each of the plurality of servers has a mounting port provided on the back of the case for mounting a communication module. Of the inner surface that defines the rear half of the housing, a radio wave absorber is provided on at least a portion of the inner surface that is provided with the opening. A communication module for performing wireless communication is mounted in a mounting port on the back of each case of the plurality of servers. The radio wave absorber is installed in a direction in which the antenna of the communication module mounted on the mounting port radiates radio waves.

  Preferably, the casing has a rectangular parallelepiped shape having a hollow inside, which includes a top plate, a bottom plate, two side plates, and a front door and a rear door each having an opening. The plurality of servers are housed and fixed inside the housing so as to be separated from the back door in an internal space defined by the housing, whereby the back door, the bottom plate and the top plate, and the two side plates The second half is defined by the back of the plurality of servers. The radio wave absorber is disposed in a region in the rear half of at least one inner surface of the top plate, the bottom plate, and the two side plates.

  More preferably, all the openings are mesh-shaped, and the size of the mesh opening is not smaller than the half wavelength of the radio wave used in the wireless communication performed by the communication module in the rack.

  More preferably, the antenna of the communication module includes a dipole antenna or a monopole antenna installed so that the antenna axis is perpendicular to the rear door.

  The antenna of the communication module may include a slot antenna formed such that the substrate on which the antenna is formed faces the member on which the radio wave absorber is installed among the top plate, the bottom plate, and the two side plates.

  Preferably, no radio wave absorber is installed on the inner surface of any of the top plate, the bottom plate, and the two side plates in the first half.

It is a perspective view from the front of a general server rack. It is a perspective view from the back of a server rack. It is a perspective view from the back of a server rack which shows arrangement | positioning of a server rack, a server, etc. which concern on the 1st Embodiment of this invention. It is a figure which shows the server mounted in the server rack shown in FIG. 3, and the communication module with which a server back is mounted | worn. It is a schematic diagram which shows the structure of a communication module. It is a block diagram which shows the structure of the circuit part of a communication module. It is a graph which shows the difference in the cumulative probability distribution of delay spread by the presence or absence of a radio wave absorber. It is a graph which shows the difference in the cumulative probability distribution of delay spread by the difference in antenna axial direction (main radiation direction). It is a perspective view from the back side which shows the structure of the server rack based on the 2nd Embodiment of this invention.

[First Embodiment]
In the following description and drawings, the same parts are denoted by the same reference numerals. Therefore, detailed description thereof will not be repeated.

  Referring to FIG. 2, when a large number of servers are accommodated in the server rack, a space 54 is formed between the back surface of the server and the inner surface of the back surface portion of the server rack. When performing wireless communication in a server rack, it is considered that radio waves are confined in this space and hardly leak to the outside. Therefore, in this embodiment, a radio wave absorber is provided at the following positions.

  FIG. 3 shows the inside of the server rack according to the first embodiment of the present invention, along with the inner surface of the server rack and the vicinity of the upper and lower centers of a large number of servers 60 housed in the server rack. An L2 / L3 switch (access point) 62 connected to each server is installed in the vicinity of the upper and lower centers of the server rack, and the servers 60 are installed on the upper and lower sides without a plurality of gaps. The server 60 is accommodated such that the rear surface thereof faces the rear surface side of the server rack, and a certain distance remains between the inner surface of the rear surface of the housing. With such an arrangement, a space (second half) is formed between the rear surface of the server and the inner surface of the rear portion of the server rack, and wireless communication is performed inside the space. The housing of the server rack 70 is made of metal, and a front door and a rear door each having an opening made of a metal mesh so that a cooling airflow flows are provided on the front surface and the back surface, respectively. In the present embodiment, the size of the mesh holes in the front door and the rear door are both less than half a wavelength so that the leakage of radio waves at the operating frequency is minimized. For example, when the operating frequency is 60 GHz, the size of the mesh hole is less than 2.5 mm.

  By accommodating the server and the L2 / L3 switch 62 in the server rack in this way, the internal space of the server rack is divided into a front half portion on the opening side and a closed rear half portion on the back side. The latter half space is defined by the bottom plate of the server rack, the top plate, the two side plates, and the rear door.

  As will be described later, on the back surface of the server 60 and the L2 / L3 switch 62, mounting terminals for communication modules that perform wireless communication are provided. In the present embodiment, the server rack 70 has a metal bottom plate, and is an inner surface of the bottom plate 40 and the top plate 42 (a surface facing the inside of the server rack) between the rear surface of the server and the inner surface of the rear portion of the server rack. Radio wave absorbers 80 and 82 are respectively provided in the area between them. When there is no bottom plate of the server rack 70 and the concrete floor is visible, the radio wave absorber 82 is provided only on the top plate 42 of the server rack. The portion where the radio wave absorber 82 is provided is not the maximum surface of the inner surface of the server rack. The same applies to the bottom plate 40. However, by providing the radio wave absorber 82 or the radio wave absorbers 80 and 82 as described above, the delay wave is greatly reduced as described later.

  Referring to FIG. 4, the communication module 94 has a USB interface. A USB terminal 92 is provided on the back surface 90 of the server 60 and a communication module 94 is mounted. A similar USB terminal is also provided on the back surface of the L2 / L3 switch 62. A communication module 94 is attached to each of the servers 60 and the USB terminal of the L2 / L3 switch 62.

  As a radio wave absorber, a radio wave absorber that absorbs radio waves by canceling both incident waves and reflected waves, and absorbs radio waves by converting radio waves into heat using dielectric loss or magnetic loss, etc. A radio wave absorber or the like can be used. For example, an electromagnetic wave absorber made into a sheet shape by mixing a magnetic material with a resin, an electromagnetic wave absorber made into a sheet shape by mixing iron powder with synthetic rubber, and a liquid material made by mixing a magnetic material and metal powder into a resin. A coated wave absorber, a wave absorber made of a resin such as urethane foam or styrene and impregnated with carbon to form a pyramid can be used.

  As shown in FIG. 5A, the communication module 94 is formed by forming a printed circuit board 108 made of resin in a resin housing 106 and mounting the circuit unit 100 and the dipole antenna 102 on the printed circuit board 108. is there. A USB terminal 104 is fixed to the circuit unit 100. The USB terminal 104 is attached to the USB terminal 92 of the server 60 in FIG.

  As shown in FIG. 6, the circuit unit 100 is functionally similar to a normal wireless communication module, and includes a USB interface circuit 110 connected to the USB terminal 104 and a baseband signal connected to the USB interface circuit 110. The processing circuit 112 includes an RF circuit 114 connected to the baseband signal processing circuit 112 and the dipole antenna 102. The antenna preferably has a main radiating direction that is not so much toward the rear door and the front door of the server rack. For example, the antenna is a dipole antenna as shown in FIG. It mounts so that it may become perpendicular | vertical, ie, a radiation direction may face the electromagnetic wave absorber 80 or 82. As shown in FIG. 5A, the antenna and the circuit unit 100 can be mounted on the same dipole antenna 102 using the existing printed circuit board technology.

  As described above, the antenna may be any antenna as long as it can be mounted on the rear surface of the server 60 so that the main radiation direction does not face the rear door or front door direction of the server rack. For example, as shown in FIG. 5B, a communication module 130 having a monopole antenna 140 formed so that the shaft 142 is perpendicular to the rear door of the server rack, or as shown in FIG. The communication module 150 having the slot antenna 160 formed so that 162 faces the direction connecting the left and right side surfaces of the server rack (the main radiation direction faces the radio wave absorbers 80 and 82) may be used. In this way, by connecting the communication module 94, 130, or 150 to the server 60 and the L2 / L3 switch 62 through the USB interface circuit 110, the server 60 or the L2 / L3 switch 62 is not changed. Communication cables can be wireless.

  The effect of the present embodiment will be seen with a delay spread, which is a general index representing the magnitude of the delay wave and the delay situation. If the delay spread is large, the level of the delayed wave is large and the amount of delay is large, indicating that the communication environment is bad.

  In the environment shown in FIGS. 2 and 3, the delay spread was obtained by simulation under the following conditions. That is, it is assumed that the transmission (access point) antenna is placed at the center of the server rack at the position of 4 cm from the back of the housing of the server 60. Assuming that the USB terminal of the server is in various positions, the receiving antenna was moved every 2 cm in the xy plane (see FIG. 4) at a distance of 4 cm from the back of the server housing. The communication frequency was 60 GHz. As shown in FIG. 3, it is assumed that the radio wave absorber is provided in a portion exposed to the wireless communication space on the upper surface of the bottom plate 40 and the lower side of the top plate 42.

  FIG. 7 shows a graph 180 of delay spread cumulative probability distribution when the radio wave absorber is arranged, and a graph 182 of delay spread cumulative probability distribution when the radio wave absorber is not arranged. By arranging the radio wave absorber, it is clear that the delay spread is reduced and the influence of the delayed wave can be reduced.

  In order to investigate the influence on the delay spread when the direction of the dipole antenna axis is changed with the radio wave absorber installed, the direction of the dipole antenna axis is set to the x-axis direction, the y-axis direction, and the z-axis direction (see FIG. FIG. 8 shows the result of calculating the cumulative probability distribution of the delay spread in the same manner. As can be easily understood with reference to FIG. 8, when the axis 120 of the dipole antenna 102 is in the y-axis direction, the delay spread is the largest as shown in the graph 192. When the axis 120 is in the x-axis direction, the delay spread becomes slightly smaller as shown by the graph 190. However, when the axis 120 is in the z-axis direction, as shown by the graph 180, the delay spread is greatly reduced as compared with both the y-axis direction and the x-axis direction. In the case of a dipole antenna, the case where the direction of the antenna axis is in the z-axis direction is a direction in which the direction of the antenna axis is perpendicular to the back surface of the server housing and the back door of the server rack. Therefore, when the arrangement shown in FIG. 4 and the communication module shown in FIG. 5A are used, the delay spread becomes the smallest.

  Note that the monopole antenna 140 (FIG. 5B) also exhibits the same behavior as the dipole antenna with respect to the radiation direction. Accordingly, in the case of a monopole antenna, it is preferable that the axis is formed so as to face the z-axis direction as in the case of the dipole antenna.

  In both the case of the monopole antenna and the case of the dipole antenna, radio waves are irradiated radially around the antenna axis. Therefore, no matter how the antennas are rotated around the z-axis shown in FIG. 4, the delay spread is not significantly affected. However, the situation is different in the case of the slot antenna shown in FIG. In the case of a slot antenna, the direction of radio wave radiation is perpendicular to the substrate surface on which the slot antenna is formed. In the case of the antenna shown in FIG. 5C, the radiation direction is a direction perpendicular to the paper surface. Therefore, in this case, it is necessary to adjust the communication module so that the substrate surface on which the slot antenna is formed faces the direction in which the radio wave absorber exists. For example, in the case of a communication module using a slot antenna, it is necessary to match the direction of the USB terminal of the server and the direction of the substrate surface of the communication module so that the direction of radio wave irradiation is the direction of the radio wave absorber. In such a case, for example, if there is a communication module capable of rotating the antenna substrate around the shaft 164 shown in FIG. 5C, irradiation is performed in accordance with the installation position of the electromagnetic wave absorber in the server rack when the server is installed. It is convenient to adjust the direction.

  As described above, the server rack, the server, and the communication module according to the present embodiment can efficiently reduce the influence of the delayed wave even in the metal space in the server rack, and can prevent the deterioration of the communication quality. . Most of the cables in the server rack can be removed. As a result, the cooling efficiency of the servers in the server rack is increased, and power consumption for cooling can be reduced.

[Second Embodiment]
In the above embodiment, the radio wave absorber is installed on the inner surface of the top plate 42 or on the inner surface of the top plate 42 and the upper surface of the bottom plate 40. However, the present invention is not limited to such an embodiment. A radio wave absorber is installed on a surface of the server rack other than the rear door having an opening in any one of the spaces formed by the back of the server and the inner surface of the rear half of the server rack (the space 54 shown in FIG. 2). Thus, the effect described in the first embodiment can be expected. The server rack 210 according to the second embodiment includes a bottom plate 40 and a top plate 42, side plates 46 and 48, a front door (not shown), and a rear door 48. As in the first embodiment, a plurality of servers 60 and L2 / L3 switches 62 installed at the upper and lower centers of the server rack 210 are accommodated in the space inside the server rack 210. A space 54 in which wireless communication is performed is formed by the back surface of the server 60, the inner surface of the back door 48 of the server rack 210, the bottom plate 40 and the top plate 42, and the two side plates 44 and 46. Radio wave absorbers 220 and 222 are respectively installed in areas defining the space 54 on the inner surfaces of the side plates 44 and 46.

  The server 60 and the communication module shown in FIG. 4 can be used. However, when a slot antenna is used, the antenna needs to be rotated 90 degrees around the axis 164 shown in FIG. 5C from the one shown in FIGS. 4 and 5C.

  Even when the server rack 210 according to the second embodiment is used, the same effect as that of the first embodiment can be obtained. In addition, when there was no bottom plate 40 in 1st Embodiment, the electromagnetic wave absorber was not installed in the bottom part. That is, the radio wave absorber is provided only on the top plate. Also in the second embodiment, a radio wave absorber may be provided on only one of the side plates 46 and 48, as in the first embodiment. In this case, the effect is inferior compared with the case where both are provided with radio wave absorbers, but wireless communication can still be realized and the number of cables can be reduced, so that the cooling efficiency of the server can be increased from the current level.

  Further, in the first embodiment, the radio wave absorber is provided only on the bottom plate 40 and the top plate 42, and in the second embodiment, the radio wave absorber is provided only on the side plates 46 and 48. However, the present invention is not limited to such an embodiment. For all of the bottom plate 40, the top plate 42, and the side plates 46 and 48, a radio wave absorber may be installed in a region that defines the space 54.

  The embodiment disclosed herein is merely an example, and the present invention is not limited to the above-described embodiment. The scope of the present invention is indicated by each claim of the claims after taking into account the description of the detailed description of the invention, and all modifications within the meaning and scope equivalent to the wording described therein are included. Including.

30, 70, 210 Server rack 40 Bottom plate 42 Top plate 44, 46 Side plate 48 Rear door 50 Front door 52 Opening 60 Server 62 L2 / L3 switch 80, 82, 220, 222 Radio wave absorber 92, 104 USB terminals 94, 130, 150 Communication Module 100 Circuit Unit 102 Dipole Antenna 104 USB Terminal 106 Resin Housing 108 Printed Circuit Board 140 Monopole Antenna 160 Slot Antenna

Claims (10)

A server rack having a housing that defines a space for accommodating a plurality of server computers therein,
Each of the housings has a front half and a rear half in which an opening is formed,
The internal space of the housing is separated into the front half and the rear half by the case of the plurality of servers by housing a plurality of servers therein, and the back of the plurality of servers is on the rear half side. And each of the plurality of servers has a mounting port provided on the back surface to which the communication module is mounted,
A radio wave absorber is provided on at least a part of the inner surface of the housing that defines the latter half separated from the front half by the plurality of servers, excluding the inner surface provided with the opening. , Server rack. The casing is composed of a top plate, a bottom plate, two side plates, and a front door and a rear door each provided with an opening, and has a rectangular parallelepiped shape with a hollow inside,
The plurality of servers are housed and fixed inside the housing so as to be separated from the back door in an internal space defined by the housing, thereby the back door, the bottom plate, and the top plate, The latter half is defined by the two side plates and the case back of the plurality of servers,
2. The server rack according to claim 1, wherein the radio wave absorber is installed in a region in the rear half of at least one inner surface of the top plate, the bottom plate, and the two side plates.   The server rack according to claim 1 or 2, wherein each of the openings has a mesh shape, and the size of the mesh opening is smaller than a half wavelength of a radio wave used in wireless communication performed in the rack. .   The server rack according to any one of claims 1 to 3, wherein a radio wave absorber is not installed on an inner surface of any of the top plate, the bottom plate, and the two side plates in the front half. A server rack having a housing for defining a space for accommodating a plurality of server computers therein;
A server aggregate including a plurality of servers accommodated in the space defined by the server rack so as to divide the space defined by the server rack into a first half and a second half,
An opening is formed in each of the front half and the rear half of the housing,
The plurality of servers are arranged so that the back of the case faces the rear half, and each of the plurality of servers has a mounting port provided on the back of the case to which a communication module is mounted.
Of the inner surface defining the latter half of the housing, a radio wave absorber is installed on at least part of the inner surface except for the inner surface provided with the opening,
A communication module for performing wireless communication is mounted on the mounting opening on the back of each case of the plurality of servers,
The radio wave absorber is a server aggregate that is installed in a direction in which an antenna of the communication module mounted in the mounting port radiates radio waves. The housing has a rectangular parallelepiped shape with a hollow inside, consisting of a top plate, a bottom plate, two side plates, and a front door and a rear door each provided with the opening.
The plurality of servers are housed and fixed inside the housing so as to be separated from the back door in an internal space defined by the housing, thereby the back door, the bottom plate, and the top plate, The second half is defined by the two side plates and the back surfaces of the plurality of servers.
The server assembly according to claim 5, wherein the radio wave absorber is installed in a region in the rear half of at least one inner surface of the top plate, the bottom plate, and the two side plates.   Each of the openings is mesh-shaped, and the size of the mesh opening is smaller than a half wavelength of a radio wave used in wireless communication performed by the communication module in the rack. The server aggregate described.   The server assembly according to claim 6 or 7, wherein the antenna of the communication module includes a dipole antenna or a monopole antenna installed so that an antenna axis is perpendicular to the rear door.   The antenna of the communication module is a slot formed so that a substrate on which the antenna is formed faces a member of the top plate, the bottom plate, and the two side plates on which the radio wave absorber is installed. The server aggregate according to claim 6 or 7, comprising an antenna.   The server aggregate according to any one of claims 5 to 9, wherein a radio wave absorber is not installed on any inner surface of the top plate, the bottom plate, or the two side plates in the front half.

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