Communication device

Abstract

In life-and-death monitoring, there is a possibility that an active communication apparatus may be erroneously determined to be a lost communication apparatus due to congestion of a network. In the present invention, in a data link layer (L1), if a first packet (P1) is not received during a first period (T1), an outdoor control unit (39) determines that an indoor unit (20a-20c) has been lost in the data link layer (L1). In an application layer (L2), if a first response (RES1) to a first request (REQ1) is not received during a second period (T2), the outdoor control unit (39) determines that the indoor unit (20a-20c) has been lost in the application layer (L2). The first period (T1) is shorter than the second period (T2). The outdoor control unit (39), if determining that the indoor unit (20a-20c) has been lost in the data link layer (L1), stops periodic retransmission of a second packet (P2) that contains the first request (REQ1).

Description

Communication device

[0001] It relates to a communication device.

[0002] As shown in Patent Document 1 (International Publication No. 2011 / 074454), there is a technique for performing retransmission control of packets.

[0003] In Patent Document 1, since the congestion of the network due to retransmission control of packets is not considered, in the life-and-death monitoring, there is a risk that a live communication device cannot communicate and the live communication device is erroneously determined to have disappeared.

[0004] The communication device of the first aspect communicates with a plurality of communication devices via a first network. The plurality of communication devices includes 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 in which the communication function is divided. When the control unit does not receive the first packet during a first period, the control unit determines that the first communication device has disappeared in the first layer. Or, when the control unit does not receive the first packet continuously for a first number of times, the control unit determines that the first communication device has disappeared in the first layer. The control unit periodically transmits a first request to the first communication device in a second layer higher than 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 to the first communication device as a second packet 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 it receives a confirmation response packet for the second packet from the first communication device. When the control unit does not receive the first response during a second period, the control unit determines that the first communication device has disappeared in the second layer. Or, when the control unit does not receive the first response continuously for a second number of times, the control unit determines that the first communication device has disappeared in the second layer. The first period is shorter than the second period. Or, the first number of times is less than the second number of times. When the control unit determines that the first communication device has disappeared in the first layer, the control unit stops the periodic retransmission of the second packet.

[0005] The communication device in the first perspective 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, because the first period is shorter than the second period, and stops the periodic retransmission of the second packet. As a result, the communication device can prevent mistakenly determining that a live first communication device has been lost in the second layer due to the resolution of congestion in the first network.

[0006] The communication device in the second perspective is the communication device in the first perspective, and the control unit periodically transmits a third packet to multiple communication devices at the first layer, prompting them to join the first network. If the control unit determines that the first communication device has disappeared at the first layer, and then receives a fourth packet from the first communication device requesting to join the first network before determining that the first communication device has disappeared at the second layer, the control unit cancels the determination that the first communication device has disappeared at the first layer.

[0007] The third-perspective communication device is a first-perspective or second-perspective communication device, and the control unit, if it determines in the second layer that the first communication device has disappeared, increases the transmission interval of the first request.

[0008] The third-party communication device, with this configuration, can prevent congestion in the first network.

[0009] The communication device in the fourth perspective is a communication device from either the first or third perspective, and the communication device and multiple communication devices are air conditioners.

[0010] This is a schematic diagram of the air conditioner's configuration. This diagram illustrates the status monitoring in the data link layer. This diagram illustrates the status monitoring in the data link layer. This diagram illustrates the status monitoring in the application layer. This diagram illustrates the status monitoring in the application layer. This flowchart illustrates the status monitoring when the first period is longer than the second period. This flowchart illustrates the status monitoring when the first period is shorter than the second period.

[0011] (1) Overall configuration of the air conditioner The air conditioner 2 constitutes a vapor compression type refrigeration cycle and provides 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] Figure 1 is a schematic diagram of the air conditioner 2. As shown in Figure 1, the air conditioner 2 has one outdoor unit 30 (communication device) and multiple indoor units 20 (communication equipment). The outdoor unit 30 and the multiple indoor units 20 are connected by liquid refrigerant communication piping and gas refrigerant communication piping, forming a refrigerant circuit. The outdoor unit 30 and the multiple indoor units 20 are daisy-chained together by communication lines 90 (first network). The outdoor unit 30 communicates with the multiple indoor units 20 via the communication lines 90. The multiple indoor units 20 include indoor units 20a to 20c (first communication equipment).

[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 consists of 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 in low-pressure refrigerant from the suction pipe, compresses the refrigerant using a compression mechanism, and discharges the compressed refrigerant through the discharge pipe. The compressor's compression mechanism is driven by a compressor motor. The flow path switching valve is a mechanism that switches the refrigerant flow path between a first state and a second state. During cooling operation, the flow path switching valve sets the refrigerant flow path to the first state. At this time, the refrigerant discharged from the compressor flows through the refrigerant circuit in the order of outdoor heat exchanger, outdoor expansion valve, indoor expansion valve, and indoor heat exchanger, before returning to the compressor. In the first state, the outdoor heat exchanger functions as a condenser, and the indoor heat exchanger functions as an evaporator. During heating operation, the flow path switching valve sets the refrigerant flow path to the second state. At this time, the refrigerant discharged from the compressor flows through the refrigerant circuit in the order of indoor heat exchanger, indoor expansion valve, outdoor expansion valve, and outdoor heat exchanger, before returning 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 facilitates heat exchange between the refrigerant flowing through it and the outdoor air of 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 outdoor air to the outdoor heat exchanger. The outdoor fan is driven by an outdoor fan motor.

[0015] The outdoor control unit 39 controls the operation of each component of 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 arithmetic unit, a memory device, and a network interface device. The control arithmetic unit is a processor such as a CPU or GPU. The memory device is a storage medium such as RAM, ROM, or flash memory. The control arithmetic unit reads a program stored in the memory device and controls the operation of each component of the outdoor unit 30 by performing predetermined calculation processing according to the program. The control arithmetic unit can also write calculation results to the memory device or read information stored in the memory device according to the program. The outdoor control unit 39 exchanges various information, such as control signals or signals related to various settings, with the indoor control units 29a to 29c of the indoor units 20a to 20c via the communication line 90.

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

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

[0018] (2-2) Indoor units 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 comprises an indoor heat exchanger, an indoor fan, an indoor expansion valve, and indoor control units 29a to 29c.

[0019] The indoor heat exchanger facilitates heat exchange 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 drawn-in air to the target space. The indoor fan is driven by an indoor fan motor. The indoor expansion valve is a mechanism for regulating the pressure and flow rate of the refrigerant flowing through the refrigerant circuit.

[0020] The indoor control units 29a to 29c control the operation of each component of the indoor units 20a to 20c. The indoor control units 29a to 29c are communicatively connected to the indoor fan motor and the indoor expansion valve. The indoor control units 29a to 29c include a control arithmetic unit, a memory device, and a network interface device. The control arithmetic unit is a processor such as a CPU or GPU. The memory device is a storage medium such as RAM, ROM, or flash memory. The control arithmetic unit reads a program stored in the memory device and controls the operation of each component of the indoor units 20a to 20c by performing predetermined arithmetic processing according to the program. The control arithmetic unit can also write calculation results to the memory device and read information stored in the memory device according to the program. The indoor control units 29a to 29c are configured to receive various signals transmitted from the operating remote controls corresponding to the indoor units 20a to 20c. Furthermore, the indoor control units 29a to 29c exchange various information, such as control signals or signals related to various settings, with the outdoor control unit 39 of the outdoor unit 30 via the communication line 90.

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

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

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

[0024] Table 1 below is an example of the second list in the status monitoring at the application layer L2, where the outdoor control unit 39 determines that the indoor units 20a to 20c are operational. In Table 1, the "Status" of the indoor units 20a to 20c is "Operational," indicating that the indoor units 20a to 20c are operational.

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

[0026] (2-3-1) Status Monitoring at the Data Link Layer Figures 2A and 2B are diagrams illustrating status monitoring at the data link layer L1. As shown in Figures 2A and 2B, the outdoor control unit 39 periodically (transmission interval T3) receives the first packet P1 from the indoor units 20a to 20c at the data link layer L1. While the outdoor control unit 39 is periodically receiving the first packet 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 at the data link layer L1. For example, if the power to indoor unit 20a is turned OFF and the outdoor control unit 39 determines that indoor unit 20a has disappeared at the data link layer L1, it deletes the record corresponding to indoor unit 20a in 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 at the data link layer L1. In Table 3, compared to Table 1, the record corresponding to the indoor unit 20a has been deleted.

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

[0030] In this embodiment, the first period T1 in which the data link layer L1 determines that indoor units 20a to 20c have disappeared is shorter than the second period T2 in the application layer L2, which will be described later, in which the application layer L2 determines that indoor units 20a to 20c have disappeared. If the outdoor control unit 39 receives a fourth packet P4 from indoor unit 20a requesting to join the communication line 90 between the time it determines that indoor unit 20a has disappeared in the data link layer L1 and the time it determines that indoor unit 20a has disappeared in the application layer L2, it cancels the determination that indoor unit 20a has disappeared in the data link layer L1. When the outdoor control unit 39 cancels the determination that indoor unit 20a has disappeared in the data link layer L1, it adds a record corresponding to indoor unit 20a in 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. In Table 4, a record corresponding to the indoor unit 20a has been added compared to Table 3.

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

[0033] The outdoor control unit 39 receives an acknowledgment packet ACK for 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 for the second packet P2 from the indoor units 20a to 20c.

[0034] The outdoor control unit 39 receives a first response 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 response RES1 to the outdoor control unit 39 as a fifth packet P5 encapsulating the first response RES1 at the data link layer L1. The outdoor control unit 39 transmits an acknowledgment packet ACK to the indoor units 20a to 20c for the fifth packet P5. The outdoor control unit 39 determines that the indoor units 20a to 20c are alive as long as it is periodically receiving the first response RES1.

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

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

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

[0038] If the outdoor control unit 39 determines at 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 monitoring the status of the units when the first period is longer than the second period The issues with monitoring the status of the units when the first period T1 is longer than the second period T2 will be explained below using the flowchart in Figure 4. In Figure 4, the case where the power to indoor unit 20c remains ON while the power to indoor units 20a and 20b is turned OFF (when indoor units 20a and 20b disappear) is explained, and therefore indoor units 20a and 20b and indoor unit 20c are shown separately.

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

[0041] The power supplies of the indoor units 20a and 20b are turned off (step S1).

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

[0043] However, since the outdoor control unit 39 cannot receive an acknowledgement packet ACK for the second packet P2 from the indoor units 20a and 20b, until it receives the acknowledgement packet ACK for the second packet P2 from the indoor units 20a and 20b, it periodically re-transmits the second packet P2 to the indoor units 20a and 20b (step S4). As a result, the communication line 90 becomes congested.

[0044] Incidentally, after the power supplies of the indoor units 20a and 20b are turned off, since the outdoor control unit 39 cannot receive the first packet P1 from the indoor units 20a and 20b either, at the same time as starting the count of the second period T2, it starts counting the first period T1 for the indoor units 20a and 20b (step S5).

[0045] On the other hand, the outdoor control unit 39 transmits a first request REQ1 to the indoor unit 20c (step S6), and at the time of transmitting the first request REQ1, starts counting the second period T2 for the indoor unit 20c (step S7). However, due to congestion of the communication line 90, it cannot receive the acknowledgement packet ACK for the second packet P2 from the indoor unit 20c. Therefore, until the outdoor control unit 39 receives the acknowledgement packet ACK for the second packet P2 from the indoor unit 20c, it periodically re-transmits the second packet P2 to the indoor unit 20c (step S8). As a result, the communication line 90 becomes more congested.

[0046] Incidentally, since the outdoor control unit 39 cannot receive the first packet P1 from the indoor unit 20c either due to congestion of the communication line 90 (step S9), at the same time as starting the count of the second period T2, it starts counting the first period T1 for the indoor unit 20c (step S10).

[0047] Because the power to the indoor units 20a and 20b is OFF, the outdoor control unit 39 does not receive the first response RES1 from the indoor units 20a and 20b, and the second period T2 elapses. Therefore, the outdoor control unit 39 determines in the application layer L2 that the indoor units 20a and 20b have disappeared (step S11).

[0048] Due to congestion on the communication line 90, the second period T2 elapses 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 outdoor control unit 39 may mistakenly determine that a functioning indoor unit 20c has disappeared at the application layer L2 due to continued congestion of the communication line 90.

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

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

[0052] Because the power to the indoor units 20a and 20b is OFF, the outdoor control unit 39 does not receive the first packet P1 from the indoor units 20a and 20b, and the first period T1 elapses. Therefore, the outdoor control unit 39 determines that the indoor units 20a and 20b have disappeared at the data link layer L1 (step S13).

[0053] Due to congestion on the communication line 90, the first period T1 elapses 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 at the data link layer L1 (step S14).

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

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

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

[0057] In step S15, the periodic retransmission of the second packet P2 to indoor units 20a to 20c is stopped, and the congestion on the communication line 90 is resolved. Therefore, after the outdoor control unit 39 determines that indoor units 20a to 20c have disappeared at the data link layer L1, it receives the fourth packet P4 from indoor unit 20c before determining that indoor units 20a to 20c have disappeared at the application layer L2 (step S17). However, because the power to indoor units 20a and 20b is OFF, the outdoor control unit 39 does not receive the fourth packet P4 from indoor units 20a and 20b after determining that indoor units 20a to 20c have disappeared at the data link layer L1, and before determining that indoor units 20a to 20c have disappeared at the application layer L2.

[0058] The outdoor control unit 39 receives the fourth packet P4 from the indoor unit 20c and therefore cancels the determination that the indoor unit 20c has disappeared at the data link layer L1 (step S18).

[0059] Tables 9 and 10 below show the first and second lists at this stage, respectively. In particular, Table 10 has additional records corresponding to indoor unit 20c compared to Table 8.

[0060] Because the power to the indoor units 20a and 20b is OFF, the outdoor control unit 39 does not receive the first response RES1 from the indoor units 20a and 20b, and the second period T2 elapses. Therefore, the outdoor control unit 39 determines in the application layer L2 that the indoor units 20a and 20b have disappeared (step S19).

[0061] Tables 11 and 12 below show the first and second lists, respectively, 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 "Disappeared".

[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 disappeared before the application layer L2 determines that the indoor unit 20c has disappeared, and stops the periodic retransmission of the second packet P2. As a result, the outdoor control unit 39 can prevent mistakenly determining that a still-functioning indoor unit 20c has disappeared at the application layer L2 due to the resolution of congestion on the communication line 90.

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

[0064] If the outdoor control unit 39 determines at 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 is a technology that controls packet retransmission. Conventional technology does not take into account network congestion caused by packet retransmission control, so in liveness monitoring, it may not be able to communicate with live communication devices, and there is a risk that live communication devices will be mistakenly identified as lost communication devices.

[0066] In this embodiment, the outdoor unit 30 (communication device) communicates with a plurality of indoor units 20 (communication equipment) via a communication line 90 (first network). The plurality of indoor units 20 include indoor units 20a to 20c (first communication equipment). The outdoor unit 30 includes an outdoor control unit 39. The outdoor control unit 39 periodically receives a first packet P1 from the indoor units 20a to 20c in the data link layer L1 (first layer), one of the multiple layers in which the communication function is divided. If the outdoor control unit 39 does not receive a first packet P1 during the first period T1, it determines in the data link layer L1 that the indoor units 20a to 20c have disappeared. The outdoor control unit 39 periodically sends a first request REQ1 to the indoor units 20a to 20c in the application layer L2 (second layer), which is 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. At the data link layer L1, the outdoor control unit 39 transmits the first request REQ1 to the indoor units 20a to 20c as a second packet P2. The second packet P2 contains 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 acknowledgment packet ACK for the second packet P2 from the indoor units 20a to 20c. At the application layer L2, if the outdoor control unit 39 does not receive the first response RES1 during the second period T2, it determines that the indoor units 20a to 20c have disappeared. The first period T1 is shorter than the second period T2. If the outdoor control unit 39 determines that the indoor units 20a to 20c have disappeared at the data link layer L1, it stops the periodic retransmission of the second packet P2.

[0067] In this embodiment, because the first period T1 is shorter than the second period T2, the outdoor unit 30 determines that the indoor units 20a to 20c have disappeared at the data link layer L1 before determining that the indoor units 20a to 20c have disappeared at the application layer L2, and stops the periodic retransmission of the second packet P2. As a result, for example, even if the power to indoor unit 20c remains ON while the power to indoor units 20a and 20b are turned OFF, the outdoor unit 30 can prevent it from mistakenly determining that the still-functioning indoor unit 20c has disappeared at the application layer L2 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 a third packet P3 to the multiple indoor units 20 at the data link layer L1, prompting them to join the communication line 90. After the outdoor control unit 39 determines at the data link layer L1 that the indoor units 20a to 20c have disappeared, if it receives a fourth packet P4 from the indoor units 20a to 20c requesting them to join the communication line 90 before determining at the application layer L2 that the indoor units 20a to 20c have disappeared, the outdoor control unit 39 cancels the determination at 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, if 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 congestion of the communication line 90.

[0071] (3-4) In the outdoor unit 30 of this embodiment, the outdoor unit 30 and the multiple indoor units 20 constitute an air conditioner 2.

[0072] (4) Modifications (4-1) Modification 1A In this embodiment, the communication device and the first communication equipment were air conditioners 2. However, the communication device and the first communication equipment are not limited to air conditioners 2.

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

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

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

[0076] If a single refrigerant system has one outdoor unit and multiple indoor units, the communication device may be one outdoor unit belonging to a specific refrigerant system among the multiple refrigerant systems, and the multiple communication devices may be multiple indoor units belonging to that specific refrigerant system.

[0077] If a 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 multiple indoor units of each of the multiple refrigerant systems. In this case, each outdoor unit may be configured to periodically send a first request REQ1 to multiple indoor units of the same refrigerant system, and a specific outdoor unit among all the refrigerant systems may be configured to periodically receive a first packet P1 from all the indoor units within all the refrigerant systems.

[0078] (4-4) Modification 1D In this embodiment, the outdoor control unit 39 determined that the indoor units 20a to 20c had disappeared at the data link layer L1 if it did not receive the first packet P1 during the first period T1. However, the outdoor control unit 39 may also determine that the indoor units 20a to 20c have disappeared at the data link layer L1 if it does not receive the first packet P1 for a first consecutive number of times.

[0079] Furthermore, in this embodiment, the outdoor control unit 39 determined that the indoor units 20a to 20c had disappeared in the application layer L2 if it did not receive the first response RES1 during the second period T2 after sending the first request REQ1. However, the outdoor control unit 39 may also determine that the indoor units 20a to 20c have disappeared in the application layer L2 if it does not receive the first response RES1 for a second consecutive time after sending the first request REQ1.

[0080] In this case, the first count is less than the second count.

[0081] (4-5) Although embodiments of the present disclosure have been described above, it will be understood that various modifications to the form and details are possible without departing from the spirit and scope of the present disclosure as described in the claims.

[0082] 2 Air conditioner 20 Indoor unit (communication equipment) 20a-20c Indoor unit (first communication equipment) 30 Outdoor unit (communication device) 39 Outdoor control unit (control unit) 90 Communication line (first network) ACK Acknowledgment packet L1 Data link layer (Layer 1) L2 Application layer (Layer 2) P1-P4 First packet to fourth packet REQ1 First request RES1 First response T1 First period T2 Second period T4 Interval between sending the first request

[0083] International Publication No. 2011 / 074454

Claims

1. A communication device (30) that communicates with a plurality of communication devices (20), including a first communication device (20a to 20c), via a first network (90), comprising a control unit (39), the control unit periodically receives a first packet (P1) from the first communication device in the first layer (L1) of a plurality of layers in which the communication function is divided, determines that the first communication device has disappeared in the first layer if it does not receive the first packet during a first period (T1), or if it does not receive the first packet for a first consecutive number of times, and periodically sends a first request (REF1) to the first communication device in the second layer (L2) above the first layer, and receives a first response (RES1) to the first request from the first communication device. Communication device (30): At the first layer, transmits the first request to the first communication device as a second packet (P2) containing the first request, periodically retransmits the second packet to the first communication device until an acknowledgment packet (ACK) for the second packet is received from the first communication device, and at the second layer, determines that the first communication device has disappeared if the first response is not received during the second period (T2), or if the first response is not received for a second consecutive number of times, and the first period is shorter than the second period, or the first number of times is fewer than the second number of times, and the control unit stops the periodic retransmission of the second packet when it determines that the first communication device has disappeared at the first layer.

2. The communication device (30) according to claim 1, wherein the control unit periodically transmits a third packet (P3) to the plurality of communication devices in the first layer prompting them to join the first network, and if, after determining in the first layer that the first communication device has disappeared, the control unit receives a fourth packet (P4) from the first communication device requesting to join the first network before determining in the second layer that the first communication device has disappeared, the control unit cancels the determination that the first communication device has disappeared in the first layer.

3. The communication device (30) according to claim 1 or 2, wherein the control unit determines in the second layer that the first communication device has disappeared, and increases the transmission interval (T4) of the first request.

4. The communication device and the plurality of communication devices are an air conditioner (2), the communication device (30) according to any one of claims 1 to 3.

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