communication equipment

Abstract

When the network becomes congested, there is a risk that an active communication device may be mistakenly determined as a lost communication device during alive monitoring. [Solution] When an outdoor control unit 39 does not receive a first packet P1 in a first period T1 in a data link layer L1, it determines that the indoor units 20a to 20c have been lost in the data link layer L1. When an outdoor control unit 39 does not receive a first response RES1 to a first request REQ1 in an application layer L2 in a second period T2, it determines that the indoor units 20a to 20c have been lost in the application layer L2. The first period T1 is shorter than the second period T2. When the outdoor control unit 39 determines that the indoor units 20a to 20c have been lost in the data link layer L1, it stops periodic retransmission of a second packet P2 including the first request REQ1.

Description

[Technical Field]

[0001] Related to communication devices. [Background technology]

[0002] As disclosed in Patent Document 1 (International Publication No. 2011 / 074454), there is a technique for controlling packet retransmission. Summary of the Invention [Problem to be solved by the invention]

[0003] Patent Document 1 does not take into account network congestion caused by packet retransmission control, so there is a risk that during health monitoring, communication with an active communication device may not be possible and the active communication device may be mistakenly determined to have been lost. [Means for solving the problem]

[0004] A communication device according to a first aspect communicates with a plurality of communication devices via a first network. The plurality of communication devices include a first communication device. The communication device includes a control unit. The control unit periodically receives a first packet from the first communication device in a first layer among a plurality of layers into which communication functions are divided. The control unit determines that the first communication device has been lost in the first layer if the first packet is not received for a first period of time. Alternatively, the control unit determines that the first communication device has been lost in the first layer if the first packet is not received a first number of times in succession. The control unit periodically transmits a first request to the first communication device in a second layer above the first layer. The control unit receives a first response to the first request from the first communication device. The control unit transmits the first request as a second packet to the first communication device in the first layer. The second packet includes the first request. The control unit periodically retransmits the second packet to the first communication device until an acknowledgment packet for the second packet is received from the first communication device. The control unit determines that the first communication device has been lost in the second layer if the first response is not received for a second period. Alternatively, the control unit determines that the first communication device has been lost in the second layer if the first response is not received a second number of times in a row. The first period is shorter than the second period. Alternatively, the first number of times is less than the second number of times. If the control unit determines that the first communication device has been lost in the first layer, it stops periodically retransmitting the second packet.

[0005] In the communication device of the first aspect, because the first period is shorter than the second period, the communication device determines that the first communication device has been lost in the first layer before determining that the first communication device has been lost in the second layer, and stops periodic retransmission of the second packet. As a result, the communication device can prevent erroneous determination that the first communication device, which is still active, has been lost in the second layer due to the elimination of congestion in the first network.

[0006] A communication device of a second aspect is the communication device of the first aspect, wherein the control unit periodically transmits, in a first layer, a third packet prompting a plurality of communication devices to join the first network. After determining that the first communication device has disappeared in the first layer, if the control unit receives a fourth packet requesting participation in the first network from the first communication device before determining that the first communication device has disappeared in the second layer, the control unit cancels the determination that the first communication device has disappeared in the first layer.

[0007] A communication device according to a third aspect is the communication device according to the first or second aspect, wherein the control unit increases the transmission interval of the first request when it is determined in the second layer that the first communication device has disappeared.

[0008] With such a configuration, the communication device according to the third aspect can prevent congestion in the first network.

[0009] A communication device according to a fourth aspect is the communication device according to any one of the first aspect to the third aspect, in which the communication device and the plurality of communication devices are air conditioners. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an air conditioner; [Figure 2A] FIG. 1 is a diagram for explaining alive monitoring in the data link layer. [Figure 2B] FIG. 1 is a diagram for explaining alive monitoring in the data link layer. [Figure 3A] FIG. 10 is a diagram for explaining alive monitoring in the application layer. [Figure 3B] FIG. 10 is a diagram for explaining alive monitoring in the application layer. [Figure 4] FIG. 10 is a flow diagram for explaining alive-or-dead monitoring when the first period is longer than the second period. [Figure 5] FIG. 10 is a flow diagram for explaining alive-or-dead monitoring when the first period is shorter than the second period. DETAILED DESCRIPTION OF THE INVENTION

[0011] (1) Overall configuration of air conditioner The air conditioner 2 is configured with a vapor compression refrigeration cycle and performs air conditioning for one or more target spaces within a building. The air conditioner 2 is a so-called multi-type air conditioning system for buildings.

[0012] FIG. 1 is a schematic configuration diagram of an air conditioner 2. As shown in FIG. 1, the air conditioner 2 has one outdoor unit 30 (communication device) and multiple indoor units 20 (communication devices). The outdoor unit 30 and the multiple indoor units 20 are connected by a liquid refrigerant communication pipe and a gas refrigerant communication pipe to form a refrigerant circuit. The outdoor unit 30 and the multiple indoor units 20 are daisy-chain connected by a communication line 90 (first network). The outdoor unit 30 communicates with the multiple indoor units 20 via the communication line 90. The multiple indoor units 20 include indoor units 20a to 20c (first communication devices).

[0013] (2) Detailed configuration of the air conditioner (2-1) Outdoor unit The outdoor unit 30 is installed, for example, on the roof of a building. The outdoor unit 30 mainly includes a compressor, a flow path switching valve, an outdoor heat exchanger, an outdoor expansion valve, an outdoor fan, and an outdoor control unit 39 (control unit).

[0014] The compressor draws low-pressure refrigerant through the suction pipe, compresses it using the compression mechanism, and discharges the compressed refrigerant through the discharge pipe. The compressor's compression mechanism is driven by the compressor motor. The flow path switching valve switches the refrigerant flow path between a first state and a second state. The flow path switching valve sets the refrigerant flow path to the first state during cooling operation. At this time, the refrigerant discharged from the compressor flows through the refrigerant circuit in the following order: outdoor heat exchanger, outdoor expansion valve, indoor expansion valve, indoor heat exchanger, and then back to the compressor. In the first state, the outdoor heat exchanger functions as a condenser, and the indoor heat exchanger functions as an evaporator. The flow path switching valve sets the refrigerant flow path to the second state during heating operation. At this time, the refrigerant discharged from the compressor flows through the refrigerant circuit in the following order: indoor heat exchanger, indoor expansion valve, outdoor expansion valve, outdoor heat exchanger, and then back to the compressor. In the second state, the outdoor heat exchanger functions as an evaporator, and the indoor heat exchanger functions as a condenser. The outdoor heat exchanger exchanges heat between the refrigerant flowing through it and the air outside the building. The outdoor expansion valve is a mechanism for regulating the pressure and flow rate of the refrigerant flowing through the refrigerant circuit. The outdoor fan supplies the air outside the building to the outdoor heat exchanger. The outdoor fan is driven by the outdoor fan motor.

[0015] The outdoor control unit 39 controls the operation of each component constituting the outdoor unit 30. The outdoor control unit 39 is communicatively connected to the compressor motor, flow path switching valve, outdoor expansion valve, and outdoor fan motor. The outdoor control unit 39 has a control and arithmetic device, a storage device, and a network interface device. The control and arithmetic device is a processor such as a CPU or a GPU. The storage device is a storage medium such as RAM, ROM, or flash memory. The control and arithmetic device reads programs stored in the storage device and performs predetermined arithmetic processing in accordance with the programs, thereby controlling the operation of each component constituting the outdoor unit 30. The control and arithmetic device can also write arithmetic results to the storage device and read information stored in the storage device in accordance with the programs. The outdoor control unit 39 exchanges various information, such as control signals and signals related to various settings, with the indoor control units 29a to 29c of the indoor units 20a to 20c via a communication line 90.

[0016] The outdoor control unit 39 has multiple layers into which communication functions are divided. In this embodiment, the multiple layers into which communication functions are divided are multiple layers in the OSI reference model. The multiple layers into which communication functions are divided may also be multiple layers in the TCP / IP model, for example.

[0017] The multiple layers into which the communication functions are divided mainly include a data link layer L1 (first layer) and an application layer L2 (second layer) that is higher than the data link layer L1.

[0018] (2-2) Indoor unit The indoor units 20a to 20c are installed, for example, on the ceiling of the target space. Each of the indoor units 20a to 20c mainly includes an indoor heat exchanger, an indoor fan, an indoor expansion valve, and an indoor control unit 29a to 29c.

[0019] The indoor heat exchanger exchanges heat between the refrigerant flowing through it and the air in the target space. The indoor fan draws air from the target space into the indoor units 20a to 20c, exchanges heat with the refrigerant in the indoor heat exchanger, and supplies the air to the target space. The indoor fan is driven by an indoor fan motor. The indoor expansion valve is a mechanism for adjusting the pressure and flow rate of the refrigerant flowing through the refrigerant circuit.

[0020] The indoor control units 29a-29c control the operation of each component constituting the indoor units 20a-20c. The indoor control units 29a-29c are connected to the indoor fan motors and indoor expansion valves so as to be able to communicate with them. The indoor control units 29a-29c include a control and arithmetic device, a storage device, and a network interface device. The control and arithmetic device is a processor such as a CPU or a GPU. The storage device is a storage medium such as a RAM, a ROM, or a flash memory. The control and arithmetic device reads programs stored in the storage device and performs predetermined arithmetic processing in accordance with the programs, thereby controlling the operation of each component constituting the indoor units 20a-20c. The control and arithmetic device can also write arithmetic results to the storage device and read information stored in the storage device in accordance with the programs. The indoor control units 29a-29c are configured to be able to receive various signals transmitted from operation remote controls corresponding to the indoor units 20a-20c. The indoor control units 29a-29c also exchange various information, such as control signals and signals related to various settings, with the outdoor control unit 39 of the outdoor unit 30 via a communication line 90.

[0021] Like the outdoor control unit 39, the indoor control units 29a to 29c have multiple layers into which communication functions are divided. The multiple layers into which communication functions are divided mainly include a data link layer L1 and an application layer L2.

[0022] (2-3) Life and death monitoring The outdoor control unit 39 monitors the alive status of the indoor units 20a to 20c in the data link layer L1 and the application layer L2. Hereinafter, for example, if the indoor unit 20a is dead, it may be described as the indoor unit 20a being missing.

[0023] As a premise, the outdoor control unit 39 has a first list indicating addresses and alive status in the data link layer L1 of the indoor units 20a to 20c, which is used during communication between the data link layer L1. The outdoor control unit 39 also has a second list indicating addresses and alive status in the application layer L2 of the indoor units 20a to 20c, which is used during communication between the application layer L2.

[0024] The following Table 1 is an example of the second list when the outdoor control unit 39 determines that the indoor units 20a to 20c are alive in alive monitoring in the application layer L2. In Table 1, the "status" of the indoor units 20a to 20c is "alive", which indicates that the indoor units 20a to 20c are alive. [Table 1]

[0025] Table 2 below is an example of the first list when the outdoor control unit 39 determines that the indoor units 20a to 20c are alive in alive monitoring at the data link layer L1. Table 2 shows the correspondence between the addresses at the application layer L2 and the addresses at the data link layer L1 for each of the indoor units 20a to 20c. Unlike Table 1, Table 2 shows that the indoor units 20a to 20c are alive because there are records corresponding to each of the indoor units 20a to 20c. [Table 2]

[0026] (2-3-1) Alive monitoring in the data link layer 2A and 2B are diagrams for explaining alive monitoring in the data link layer L1. As shown in Figures 2A and 2B, the outdoor control unit 39 periodically (at transmission intervals T3) receives first packets P1 from the indoor units 20a to 20c in the data link layer L1. While the outdoor control unit 39 is periodically receiving the first packets P1, it determines that the indoor units 20a to 20c are alive.

[0027] On the other hand, if the outdoor control unit 39 does not receive the first packet P1 during the first period T1, it determines that the indoor units 20a to 20c have disappeared in the data link layer L1. For example, if the power of the indoor unit 20a is turned off and the outdoor control unit 39 determines that the indoor unit 20a has disappeared in the data link layer L1, it deletes the record corresponding to the indoor unit 20a from the first list.

[0028] Table 3 below is an example of the first list when the outdoor control unit 39 determines that the indoor unit 20a has disappeared in the data link layer L1. Compared to Table 1, Table 3 has deleted the record corresponding to the indoor unit 20a. [Table 3]

[0029] The outdoor control unit 39 periodically transmits (broadcasts) a third packet P3 to the multiple indoor units 20 in the data link layer L1, urging them to join the communication line 90.

[0030] In this embodiment, the first period T1 during which it is determined in the data link layer L1 that the indoor units 20a to 20c have been lost is shorter than the second period T2 during which it is determined in the application layer L2, described below, that the indoor units 20a to 20c have been lost. After determining in the data link layer L1 that the indoor unit 20a has been lost, if the outdoor control unit 39 receives a fourth packet P4 from the indoor unit 20a requesting participation in the communication line 90 before determining in the application layer L2 that the indoor unit 20a has been lost, the outdoor control unit 39 cancels the determination in the data link layer L1 that the indoor unit 20a has been lost. When the outdoor control unit 39 cancels the determination in the data link layer L1 that the indoor unit 20a has been lost, it adds a record corresponding to the indoor unit 20a to the first list.

[0031] Table 4 below is an example of the first list when the outdoor control unit 39 cancels the determination that the indoor unit 20a has disappeared in the data link layer L1. Compared to Table 3, Table 4 adds a record corresponding to the indoor unit 20a. [Table 4]

[0032] (2-3-2) Application layer health monitoring 3A and 3B are diagrams for explaining alive monitoring in the application layer L2. As shown in FIGS. 3A and 3B, the outdoor control unit 39 periodically (at transmission intervals T4) transmits a first request REQ1 to the indoor units 20a to 20c in the application layer L2. At this time, the outdoor control unit 39 transmits the first request REQ1 as a second packet P2 to the indoor units 20a to 20c in the data link layer L1. The second packet P2 includes the first request REQ1. Specifically, for example, when the outdoor control unit 39 transmits the first request REQ1 to the indoor unit 20a, the outdoor control unit 39 transmits the first request REQ1 in the application layer L2 with the destination address set to "aaa" according to Table 1. Next, the outdoor control unit 39 transmits the second packet P2, in which the first request REQ1 is encapsulated, with the destination address set to "111" according to Table 2 in the data link layer L1.

[0033] The outdoor control unit 39 receives an acknowledgment packet ACK in response to the second packet P2 from the indoor units 20a to 20c. The outdoor control unit 39 periodically retransmits the second packet P2 to the indoor units 20a to 20c until it receives an acknowledgment packet ACK in response to the second packet P2 from the indoor units 20a to 20c.

[0034] The outdoor control unit 39 receives first responses RES1 to the first request REQ1 from the indoor units 20a to 20c. At this time, the indoor units 20a to 20c transmit the first responses RES1 to the outdoor control unit 39 as fifth packets P5 that encapsulate the first responses RES1 in the data link layer L1. The outdoor control unit 39 transmits acknowledgement packets ACK to the indoor units 20a to 20c in response to the fifth packet P5. While the outdoor control unit 39 is periodically receiving the first responses RES1, it determines that the indoor units 20a to 20c are alive.

[0035] On the other hand, if the outdoor control unit 39 does not receive a first response RES1 for a second period T2 after sending the first request REQ1, it determines in the application layer L2 that the indoor units 20a-20c have disappeared. The first period T1 is shorter than the second period T2. For example, if the outdoor control unit 39 determines in the application layer L2 that the indoor unit 20a has disappeared, it changes the "status" of the record in the second list corresponding to the indoor unit 20a to "disappeared."

[0036] Table 5 below is an example of the second list when the outdoor control unit 39 determines in the application layer L2 that the indoor unit 20a has disappeared. In Table 5, compared to Table 1, the "Status" of the record corresponding to the indoor unit 20a has been changed to "Disappeared." [Table 5]

[0037] If the outdoor control unit 39 determines that the indoor unit 20a has disappeared in the data link layer L1 (because the first period T1 is shorter than the second period T2), the address of the indoor unit 20a in the data link layer L1 is unknown, so the outdoor control unit 39 stops periodically retransmitting the second packet P2 to the indoor unit 20a.

[0038] If the outdoor control unit 39 determines in the application layer L2 that the indoor unit 20a has disappeared, it lengthens the transmission interval T4 of the first request REQ1 and broadcasts the second packet P2 to the indoor units 20a to 20c.

[0039] (2-3-3) Issues with life-or-death monitoring that arise when the first period is longer than the second period Below, the issue of alive monitoring that arises when the first period T1 is longer than the second period T2 will be explained using the flowchart in Fig. 4. In Fig. 4, the indoor units 20a and 20b are shown separately from the indoor unit 20c in order to explain the case where the indoor units 20a and 20b are powered off while the indoor unit 20c remains powered on (the case where the indoor units 20a and 20b are lost).

[0040] As a premise, the outdoor control unit 39 has determined that the indoor units 20a to 20c are alive in both the data link layer L1 and the application layer L2. In other words, the first list is in the state of Table 2, and the second list is in the state of Table 1.

[0041] The indoor units 20a and 20b are powered off (step S1).

[0042] After the indoor units 20a, 20b are powered off, the outdoor control unit 39 sends a first request REQ1 to the indoor units 20a, 20b (step S2), and starts counting the second period T2 for the indoor units 20a, 20b at the time of sending the first request REQ1 (step S3).

[0043] However, because the outdoor control unit 39 is unable to receive the acknowledgment packet ACK for the second packet P2 from the indoor units 20a and 20b, it periodically retransmits the second packet P2 to the indoor units 20a and 20b until it receives the acknowledgment packet ACK for the second packet P2 from the indoor units 20a and 20b (step S4), which causes congestion on the communication line 90.

[0044] After the indoor units 20a, 20b are powered off, the outdoor control unit 39 is unable to receive the first packet P1 from the indoor units 20a, 20b, and therefore starts counting the first period T1 for the indoor units 20a, 20b at the same time as starting counting the second period T2 (step S5).

[0045] Meanwhile, the outdoor control unit 39 sends a first request REQ1 to the indoor unit 20c (step S6) and starts counting the second period T2 for the indoor unit 20c at the time of sending the first request REQ1 (step S7). However, due to congestion on the communication line 90, the outdoor control unit 39 is unable to receive an acknowledgment packet ACK for the second packet P2 from the indoor unit 20c. Therefore, the outdoor control unit 39 periodically resends the second packet P2 to the indoor unit 20c until it receives an acknowledgment packet ACK for the second packet P2 from the indoor unit 20c (step S8). This causes further congestion on the communication line 90.

[0046] In addition, because the outdoor control unit 39 is unable to receive the first packet P1 from the indoor unit 20c due to congestion on the communication line 90 (step S9), it starts counting the first period T1 for the indoor unit 20c at the same time as it starts counting the second period T2 (step S10).

[0047] Because the indoor units 20a, 20b are powered off, the second period T2 passes without the outdoor control unit 39 receiving the first response RES1 from the indoor units 20a, 20b. Therefore, the outdoor control unit 39 determines in the application layer L2 that the indoor units 20a, 20b have disappeared (step S11).

[0048] Due to congestion on the communication line 90, the second period T2 passes without the outdoor control unit 39 receiving the first response RES1 from the indoor unit 20c. Therefore, the outdoor control unit 39 determines in the application layer L2 that the indoor unit 20c has disappeared (step S12).

[0049] As a result, if the first period T1 is longer than the second period T2, the congestion on the communication line 90 continues, causing the outdoor control unit 39 to mistakenly determine that an active indoor unit 20c has disappeared in the application layer L2.

[0050] The following Table 6 shows the second list at this stage. In Table 6, compared to Table 1, the "status" of the records corresponding to the indoor units 20a to 20c has been changed to "lost." [Table 6]

[0051] (2-3-4) Alive / death monitoring when the first period is shorter than the second period In this embodiment, in order to solve the above-mentioned problem, the first period T1 is shorter than the second period T2. Hereinafter, it will be explained using the flowchart in Figure 5 that when the first period T1 is shorter than the second period T2, the above-mentioned problem does not occur. Steps S1 to S9 in Figure 5 are the same as those in Figure 4, except that the first period T1 is shorter than the second period T2.

[0052] Because the indoor units 20a, 20b are powered off, the first period T1 passes without the outdoor control unit 39 receiving the first packet P1 from the indoor units 20a, 20b. Therefore, the outdoor control unit 39 determines that the indoor units 20a, 20b have disappeared in the data link layer L1 (step S13).

[0053] Due to congestion on the communication line 90, the first period T1 passes without the outdoor control unit 39 receiving the first packet P1 from the indoor unit 20c. Therefore, the outdoor control unit 39 determines that the indoor unit 20c has disappeared in the data link layer L1 (step S14).

[0054] The following Tables 7 and 8 respectively show the first and second lists at this stage. In particular, compared to Table 2, in Table 8, the records corresponding to the indoor units 20a to 20c have been deleted. [Table 7] [Table 8]

[0055] The outdoor control unit 39 determines in the data link layer L1 that the indoor units 20a to 20c have been lost, and therefore stops the periodic retransmission of the second packet P2 to the indoor units 20a to 20c (step S15). This relieves the congestion on the communication line 90.

[0056] The outdoor control unit 39 periodically transmits (broadcasts) a third packet P3 to the indoor units 20a to 20c in the data link layer L1 (step S16).

[0057] Because step S15 has stopped the periodic retransmission of the second packet P2 to the indoor units 20a to 20c and eliminated the congestion on the communication line 90, the outdoor control unit 39 receives a fourth packet P4 from the indoor unit 20c after determining in the data link layer L1 that the indoor units 20a to 20c have been lost and before determining in the application layer L2 that the indoor units 20a to 20c have been lost (step S17). Note that because the power to the indoor units 20a, 20b is OFF, the outdoor control unit 39 does not receive the fourth packet P4 from the indoor units 20a, 20b after determining in the data link layer L1 that the indoor units 20a to 20c have been lost and before determining in the application layer L2 that the indoor units 20a to 20c have been lost.

[0058] The outdoor control unit 39, having received the fourth packet P4 from the indoor unit 20c, cancels the determination that the indoor unit 20c has been lost in the data link layer L1 (step S18).

[0059] The following Tables 9 and 10 respectively show the first and second lists at this stage. In particular, compared to Table 8, Table 10 adds a record corresponding to indoor unit 20c. [Table 9] [Table 10]

[0060] Because the indoor units 20a, 20b are powered off, the second period T2 passes without the outdoor control unit 39 receiving the first response RES1 from the indoor units 20a, 20b. Therefore, the outdoor control unit 39 determines in the application layer L2 that the indoor units 20a, 20b have disappeared (step S19).

[0061] The following Tables 11 and 12 respectively show the first and second lists at this stage. In particular, in Table 11, compared to Table 9, the "Status" of the records corresponding to indoor units 20a and 20b has been changed to "Lost." [Table 11] [Table 12]

[0062] If the first period T1 is shorter than the second period T2, the data link layer L1 determines that the indoor unit 20c has been lost before the application layer L2 determines that the indoor unit 20c has been lost, and the periodic retransmission of the second packet P2 is stopped. As a result, the outdoor control unit 39 can prevent itself from erroneously determining that the indoor unit 20c, which is still active, has been lost in the application layer L2 due to the elimination of congestion on the communication line 90.

[0063] Furthermore, as shown in Tables 1, 7 to 12, when the first period T1 is shorter than the second period T2, the outdoor control unit 39 can create the first list and the second list that reflect the actual situation while maintaining the state in which the indoor unit 20c is determined to be "alive" in the application layer L2.

[0064] If the outdoor control unit 39 determines in the application layer L2 that the indoor units 20a and 20b have disappeared, it lengthens the transmission interval T4 of the first request REQ1 and broadcasts the second packet P2 to the indoor units 20a to 20c (step S20).

[0065] (3) Features (3-1) Conventionally, there are technologies for controlling packet retransmission. However, these conventional technologies do not take into consideration network congestion caused by packet retransmission control, and therefore there is a risk that during alive monitoring, communication with an alive communication device will be lost and the alive communication device will be mistakenly determined to be a lost communication device.

[0066] In this embodiment, the outdoor unit 30 (communication device) communicates with multiple indoor units 20 (communication devices) via a communication line 90 (first network). The multiple indoor units 20 include indoor units 20a to 20c (first communication devices). The outdoor unit 30 is equipped with an outdoor control unit 39. The outdoor control unit 39 periodically receives a first packet P1 from the indoor units 20a to 20c in a data link layer L1 (first layer) among multiple layers into which communication functions are divided. If the outdoor control unit 39 does not receive the first packet P1 during a first period T1, it determines that the indoor units 20a to 20c have been lost in the data link layer L1. The outdoor control unit 39 periodically transmits a first request REQ1 to the indoor units 20a to 20c in an application layer L2 (second layer) higher than the data link layer L1. The outdoor control unit 39 receives a first response RES1 to the first request REQ1 from the indoor units 20a to 20c. The outdoor control unit 39 transmits the first request REQ1 to the indoor units 20a to 20c as a second packet P2 in the data link layer L1. The second packet P2 includes the first request REQ1. The outdoor control unit 39 periodically retransmits the second packet P2 to the indoor units 20a to 20c until it receives an acknowledgement packet ACK in response to the second packet P2 from the indoor units 20a to 20c. If the outdoor control unit 39 does not receive the first response RES1 during the second period T2, it determines in the application layer L2 that the indoor units 20a to 20c have been lost. The first period T1 is shorter than the second period T2. If the outdoor control unit 39 determines in the data link layer L1 that the indoor units 20a to 20c have been lost, it stops periodically retransmitting the second packet P2.

[0067] Because the first period T1 is shorter than the second period T2, the outdoor unit 30 of this embodiment determines in the data link layer L1 that the indoor units 20a-20c have been lost before determining in the application layer L2 that the indoor units 20a-20c have been lost, and stops periodic retransmission of the second packet P2. As a result, even if, for example, the indoor units 20a and 20b are powered off while the indoor unit 20c remains powered on, the outdoor unit 30 can prevent erroneous determination in the application layer L2 that the indoor unit 20c, which is still active, has been lost because the congestion on the communication line 90 has been resolved.

[0068] (3-2) In the outdoor unit 30 of this embodiment, the outdoor control unit 39 periodically transmits, in the data link layer L1, a third packet P3 to the multiple indoor units 20, urging them to join the communication line 90. After determining in the data link layer L1 that the indoor units 20a to 20c have disappeared, if the outdoor control unit 39 receives a fourth packet P4 requesting participation in the communication line 90 from the indoor units 20a to 20c before determining in the application layer L2 that the indoor units 20a to 20c have disappeared, the outdoor control unit 39 cancels its determination in the data link layer L1 that the indoor units 20a to 20c have disappeared.

[0069] (3-3) In the outdoor unit 30 of this embodiment, when the outdoor control unit 39 determines in the application layer L2 that the indoor units 20a to 20c have disappeared, it lengthens the transmission interval T4 of the first request REQ1.

[0070] As a result, the outdoor unit 30 can prevent the communication line 90 from becoming congested.

[0071] (3-4) In the outdoor unit 30 of this embodiment, the outdoor unit 30 and the plurality of indoor units 20 are air conditioners 2.

[0072] (4) Variations (4-1) Variation 1A In this embodiment, the communication device and the first communication device are the air conditioner 2. However, the communication device and the first communication device are not limited to the air conditioner 2.

[0073] (4-2) Variation 1B In this embodiment, the first network is the communication line 90. However, the first network is not limited to a wired network, and may be a wireless network.

[0074] (4-3) Variation 1C In this embodiment, the air conditioner 2 has three indoor units 20a to 20c as the plurality of communication devices. However, the number of indoor units that the air conditioner 2 has as the plurality of communication devices is not limited to three.

[0075] In this embodiment, the air conditioner 2 has one refrigerant system. However, the air conditioner 2 may have multiple refrigerant systems.

[0076] When one refrigerant system has one outdoor unit and multiple indoor units, the communication device may be one outdoor unit of a specific refrigerant system among the multiple refrigerant systems, and the multiple communication devices may be multiple indoor units of the specific refrigerant system.

[0077] If one refrigerant system has one outdoor unit and multiple indoor units, the communication device may be the outdoor unit of each of the multiple refrigerant systems, and the multiple communication devices may be the indoor units of each of the multiple refrigerant systems. In this case, each outdoor unit may be configured to periodically transmit a first request REQ1 to the multiple indoor units in the same refrigerant system, and one specific outdoor unit in all of the refrigerant systems may be configured to periodically receive first packets P1 from all indoor units in all of the refrigerant systems.

[0078] (4-4) Variation 1D In this embodiment, the outdoor control unit 39 determines in the data link layer L1 that the indoor units 20a to 20c have been lost if the outdoor control unit 39 does not receive the first packet P1 during the first period T1. However, the outdoor control unit 39 may also determine in the data link layer L1 that the indoor units 20a to 20c have been lost if the outdoor control unit 39 does not receive the first packet P1 a first number of times in a row.

[0079] Furthermore, in this embodiment, the outdoor control unit 39 determines in the application layer L2 that the indoor units 20a to 20c have disappeared if the first response RES1 is not received during the second period T2 after transmitting the first request REQ1. However, the outdoor control unit 39 may also determine in the application layer L2 that the indoor units 20a to 20c have disappeared if the first response RES1 is not received a second number of times in succession after transmitting the first request REQ1.

[0080] In this case, the first number of times is less than the second number of times.

[0081] (4-5) Although the embodiments of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the present disclosure as defined in the claims. [Explanation of symbols]

[0082] 2. Air conditioners 20 Indoor unit (communication equipment) 20a~20c Indoor unit (1st communication equipment) 30 Outdoor unit (communication device) 39 Outdoor control unit (control unit) 90 Communication Line (1st Network) ACK acknowledgement packet L1 Data Link Layer (Layer 1) L2 Application Layer (Layer 2) P1~P4 1st packet to 4th packet REQ1 First request RES1 First response T1 1st period T2 2nd period T4 First request transmission interval [Prior art documents] [Patent documents]

[0083] [Patent Document 1] International Publication No. 2011 / 074454

Claims

1. A communication device (30) that communicates with a plurality of communication devices (20) including first communication devices (20a to 20c) via a first network (90), A control unit (39) is provided, The control unit periodically receiving a first packet (P1) from the first communication device in a first layer (L1) of a plurality of layers into which a communication function is divided; determining that the first communication device has been lost in the first layer when the first packet is not received during a first period (T1) or when the first packet is not received a first number of times in succession; In a second layer (L2) higher than the first layer, a first request (REQ1) is periodically transmitted to the first communication device, and a first response (RES1) to the first request is received from the first communication device; In the first layer, transmitting the first request to the first communication device as a second packet (P2) including the first request, and periodically retransmitting the second packet to the first communication device until receiving an acknowledgement packet (ACK) for the second packet from the first communication device; If the first response is not received during a second period (T2), or if the first response is not received a second number of times in succession, the second layer determines that the first communication device has been lost; The first period is shorter than the second period, or the first number of times is less than the second number of times; the control unit, when determining that the first communication device has been lost in the first layer, stops periodic retransmission of the second packet. A communication device (30).

2. The control unit In the first layer, a third packet (P3) is periodically transmitted to the plurality of communication devices to prompt them to join the first network; canceling the determination in the first layer that the first communication device has disappeared, if a fourth packet (P4) requesting participation in the first network is received from the first communication device after it has been determined in the first layer that the first communication device has disappeared, until it is determined in the second layer that the first communication device has disappeared; The communication device (30) of claim 1.

3. When the control unit determines that the first communication device has been lost in the second layer, the control unit lengthens a transmission interval (T4) of the first request. A communication device (30) according to claim 1 or 2.

4. The communication device and the plurality of communication devices are air conditioners (2). A communication device (30) according to claim 1 or 2.

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