Communication device

Abstract

This communication device comprises: an interface that, when a host communication device or a counterpart communication device executes a first state transition, which is a state transition from sleep to active, connects the host communication device and the counterpart communication device via a physical link on the basis of a physical link setting value, or when the host communication device or the counterpart communication device executes a second state transition, which is a state transition from active to sleep, disconnects the physical link; a storage unit that holds the physical link setting value; and a control unit that, when the host communication device or the counterpart communication device executes the second state transition, holds a logical link on the basis of the held physical link setting value and a logical link setting value, or when the host communication device or the counterpart communication device executes the first state transition, executes communication between the host communication device and the counterpart communication device by using the held logical link.

Description

communication equipment

[0001] The present invention relates to a communication device.

[0002] In a communication system including a plurality of communication devices, at least one of the communication devices may repeatedly transition between active and sleep states in order to save power (see Patent Document 1).

[0003] Hereinafter, a physical layer link connecting interfaces of communication devices is referred to as a "physical link." An example of an interface is an optical transceiver. Hereinafter, a setting value (parameter) that defines a physical link is referred to as a "physical link setting value." A physical link setting value indicates, for example, a communication speed and a communication mode (status) such as full-duplex communication.

[0004] When the interfaces are physically connected to each other, the interfaces of the communication devices are connected to each other using a physical link based on the physical link setting value. When a state transition to sleep is executed, the physical connection between the interfaces is cut off, and therefore the physical link connecting the interfaces is also cut off.

[0005] Hereinafter, a link in the logical layer that connects the control units of each communication device is referred to as a "logical link." The logical layer is a layer higher than the physical layer. Hereinafter, a setting value (parameter) that defines a logical link is referred to as a "logical link setting value." The logical link setting value represents identification information such as a MAC address and an IP address. The control units of the communication devices are connected to each other using a logical link based on the physical link setting value and the logical link setting value.

[0006] If the sleep time is controlled to be longer than the timeout time for further power saving, the physical and logical links will be disconnected due to the timeout, and in this case, the physical and logical links will need to be re-established when the state transitions from sleep to active.

[0007] Hirotaka Ujikawa, Tomoko Shibata, and Kenichi Suzuki, "Efforts to Reduce Power Consumption in Optical Access Networks," NTT Technical Journal, January 2015, pp. 32-35, January 2015.

[0008] However, every time the communication device executes a state transition from sleep to active, both the physical link and the logical link are re-established, which poses a problem in that power consumption cannot be reduced.

[0009] In view of the above circumstances, an object of the present invention is to provide a communication device that is capable of reducing power consumption.

[0010] One aspect of the present invention is a communication device comprising: an interface that, when the communication device itself or the opposite communication device executes a first state transition, which is a state transition from sleep to active, connects the communication device itself and the opposite communication device with a physical link based on a physical link setting value; and, when the communication device itself or the opposite communication device executes a second state transition, which is a state transition from active to sleep, disconnects the physical link; a memory unit that holds the physical link setting value; and, when the communication device itself or the opposite communication device executes the second state transition, holds a logical link based on the held physical link setting value and logical link setting value; and, when the communication device itself or the opposite communication device executes the first state transition, performs communication between the communication device itself and the opposite communication device using the held logical link.

[0011] The present invention makes it possible to reduce power consumption.

[0012] FIG. 1 is a diagram illustrating an example of the configuration of a communication system in an embodiment; FIG. 2 is a sequence diagram (first half) illustrating an example of the operation of the communication system in an embodiment; FIG. 3 is a sequence diagram (second half) illustrating an example of the operation of the communication system in an embodiment; FIG. 4 is a diagram illustrating an example of the configuration of a communication system in a comparative example; FIG. 5 is a sequence diagram (first half) illustrating an example of the operation of the communication system in a comparative example; and FIG. 6 is a sequence diagram (second half) illustrating an example of the operation of the communication system in a comparative example.

[0013] Before describing the embodiments of the present invention, an example (comparative example) to be compared with the embodiments will be described. (Comparative Example) Fig. 4 is a diagram showing an example configuration of a communication system 1a in the comparative example. The communication system 1a includes a first communication device 10a and a second communication device 20a. The first communication device 10a includes a first control unit 11a and a first interface 12a. The second communication device 20a includes a second control unit 21a and a second interface 22a.

[0014] To establish a physical link connecting the first interface 12a and the second interface 22a, a physical connection between the first interface 12a and the second interface 22a and a physical link setting value are required. To establish a logical link connecting the first control unit 11a and the second control unit 21a, a physical link setting value and a logical link setting value are required.

[0015] The first communication device 10a performs wired or wireless communication with the second communication device 20a. That is, the second communication device 20a performs wired or wireless communication with the first communication device 10a. In Fig. 4, for the purpose of power saving, at least one of the first communication device 10a and the second communication device 20a repeatedly transitions between active and sleep states.

[0016] Even during the sleep period, at least one of the first communication device 10a and the second communication device 20a may transition to the active state at a cycle shorter than the time it takes for the physical link setting value and the logical link setting value to time out, thereby preventing the physical link and the logical link between the first communication device 10a and the second communication device 20a from being disconnected due to a timeout.

[0017] However, in Fig. 4, for the purpose of further power saving, at least one of the first communication device 10a and the second communication device 20a repeatedly transitions between active and sleep states at a period longer than the time it takes for the physical link setting value and the logical link setting value to time out. As a result, the physical link and logical link between the first communication device 10a and the second communication device 20a are disconnected due to timeout during the sleep period. Furthermore, each time the state transitions from sleep to active, the physical link and the logical link are re-established. As a result, it takes a long time for main signal communication to become possible when the state transitions from sleep to active, making it impossible to reduce power consumption.

[0018] The configuration of the first communication device 10a may be the same as the configuration of the second communication device 20a. That is, the configuration of the first control unit 11a may be the same as the configuration of the second control unit 21a. The configuration of the first interface 12a may be the same as the configuration of the second interface 22a. Furthermore, the configuration of the first storage unit 13a may be the same as the configuration of the second storage unit 23a.

[0019] To avoid redundant explanation, the configuration of the second communication device 20a will be described below, out of the configuration of the first communication device 10a and the configuration of the second communication device 20a.

[0020] <Configuration Example of Second Control Unit 21a> When the second communication device 20a (own communication device) is started, the second control unit 21a starts the second interface 22a. The second control unit 21a repeats the process of reading the physical link setting value from the register of the second interface 22a until the physical link setting value is successfully read. Successful reading of the physical link setting value means that a physical link has been established.

[0021] When the second communication device 20a is started, the second control unit 21a determines the state of the physical link (e.g., communication speed, full-duplex communication, connected or disconnected) based on the physical link setting value read from the register of the second interface 22a. The second control unit 21a establishes a logical link based on the determination result of the physical link state based on the physical link setting value and the logical link setting value. The second control unit 21a performs main signal communication with the first control unit 11a using the logical link.

[0022] After the second communication device 20a is started up, the second control unit 21a controls the state transition between sleep and active of the second communication device 20a.

[0023] When the second communication device 20a transitions from active to sleep, the second control unit 21a detects the disconnection of the physical link by the second interface 22a. For example, the second control unit 21a detects the disconnection of the physical link based on a notification from the second interface 22a. For example, the second control unit 21a may determine that the physical link has been disconnected based on a physical link setting value read from a register. When the physical link is disconnected, the second control unit 21a disconnects the logical link. When the logical link is disconnected, the second control unit 21a invalidates (resets) the logical link setting value.

[0024] When the second communication device 20a transitions from sleep to active, the second control unit 21a determines the state of the physical link based on the physical link setting value read from the register. The second control unit 21a establishes a logical link based on the determination result of the physical link state based on the physical link setting value and the logical link setting value. The second control unit 21a performs main signal communication with the first communication device 10a (opposing communication device) using the logical link.

[0025] <Configuration Example of Second Interface 22a> When the second communication device 20a is started up and when the second communication device 20a transitions from sleep to active state, the second interface 22a establishes a physical link with the first interface 12a through physical layer negotiation. The second interface 22 performs main signal communication with the first communication device 10a (opposing communication device). The second interface 22a may perform I / O conversion. The second interface 22 may perform processing based on DHCP (Dynamic Host Configuration Protocol). The second interface 22a may perform processing based on ARP (Address Resolution Protocol). A register of the second interface 22a holds a physical link setting value while the physical link is established.

[0026] When the second communication device 20a transitions from an active state to a sleep state, the second interface 22a disconnects the physical link. When the physical link is disconnected, the second interface 22a invalidates (resets) the physical link setting value stored in the register.

[0027] Next, an example of the operation of the communication system 1a will be described. Fig. 5 is a sequence diagram (first half) showing an example of the operation of the communication system 1a in a comparative example. Fig. 6 is a sequence diagram (second half) showing an example of the operation of the communication system in a comparative example. In Figs. 5 and 6, solid arrows represent main signal communication. Dashed arrows represent control signal communication.

[0028] 5 and 6, for the purpose of power saving, the second communication device 20a, as an example, repeatedly transitions between active and sleep states. The first communication device 10a does not need to transition between active and sleep states.

[0029] When the first communication device 10a is started up, the first control unit 11a uses a control signal to start up the first interface 12a (step S301), which starts up the first interface 12a (step S302).

[0030] The first interface 12a performs negotiation with the second interface 22a as physical link control (step S303). The first control unit 11a repeatedly reads the physical link setting value from the register of the first interface 12a (step S304). The first interface 12a establishes a physical link with the second interface 22a (step S305).

[0031] The register of the first interface 12a holds the physical link setting value in a readable state (step S306). The first control unit 11a reads the physical link setting value from the register of the first interface 12a to confirm that the physical link has actually been established (step S307). The first control unit 11a executes negotiation with the second control unit 21a as logical link control (step S308). The first control unit 11a establishes a logical link based on the determination result of the physical link state based on the physical link setting value and the logical link setting value (step S309). The first control unit 11a executes main signal communication with the second control unit 21a (step S310).

[0032] When the second interface 22a goes to sleep, the first interface 12a disconnects the physical link (step S311). The second control unit 21a detects that the physical link has been disconnected (step S312). The second control unit 21a then disconnects the logical link (step S313).

[0033] The operations from step S314 to step S321 in the first communication device 10a are the same as the operations from step S303 to step S310 in the operation of the first communication device 10a.

[0034] Furthermore, the operations from step S401 to step S421 in the second communication device 20a are the same as the operations from step S301 to step S321 in the operation of the first communication device 10a.

[0035] As described above, in the comparative example described above, it takes a long time until main signal communication becomes possible when the state transitions from sleep to active, and therefore power consumption cannot be reduced.

[0036] Next, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a diagram showing an example of the configuration of a communication system 1 according to the embodiment. The communication system 1 includes a first communication device 10 and a second communication device 20. The first communication device 10 includes a first control unit 11, a first interface 12, and a first storage unit 13. The second communication device 20 includes a second control unit 21, a second interface 22, and a second storage unit 23.

[0037] The control unit provided in the device of the present invention can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network.

[0038] Each communication device is realized by software, with a processor such as a CPU (Central Processing Unit) executing a program stored in a storage unit having a non-volatile storage medium (non-transitory storage medium). The program may be recorded on a computer-readable storage medium. Examples of computer-readable storage media include portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), and CD-ROMs (Compact Disc Read Only Memory), and non-transitory storage media such as hard disks or solid-state drives (SSDs) built into computer systems. Each interface executes a predetermined communication process.

[0039] Each of the communication devices may be realized using hardware (accelerator) including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0040] To establish a physical link connecting the first interface 12 and the second interface 22, a physical connection between the first interface 12 and the second interface 22 and a physical link setting value are required. To establish a logical link connecting the first control unit 11 and the second control unit 21, a physical link setting value and a logical link setting value are required.

[0041] The first communication device 10 performs wired communication or wireless communication with the second communication device 20. That is, the second communication device 20 performs wired communication or wireless communication with the first communication device 10. In Fig. 1 , for the purpose of power saving, at least one of the first communication device 10 and the second communication device 20 repeatedly transitions between active and sleep states.

[0042] Even during the sleep period, at least one of the first communication device 10 and the second communication device 20 may transition to the active state at a cycle shorter than the time it takes for the physical link setting value and the logical link setting value to time out, thereby preventing the physical link and the logical link between the first communication device 10 and the second communication device 20 from being disconnected due to a timeout.

[0043] However, in FIG. 1, in order to further reduce power consumption, at least one of the first communication device 10 and the second communication device 20 repeatedly transitions between active and sleep states at a period longer than the time it takes for the physical link setting value and the logical link setting value to time out.

[0044] In this case, the physical link between the first interface 12 and the second interface 22 is disconnected due to a timeout during the sleep period. On the other hand, the logical link between the first control unit 11 and the second control unit 21 is maintained based on the physical link setting value and the logical link setting value stored in the storage unit.

[0045] Therefore, each time the state transitions from sleep to active, the physical link is re-established, but the logical link does not need to be re-established. As a result, in the embodiment, the time until main signal communication becomes possible when the state transitions from sleep to active is shortened, thereby making it possible to reduce power consumption.

[0046] The configuration of the first communication device 10 may be the same as the configuration of the second communication device 20. That is, the configuration of the first control unit 11 may be the same as the configuration of the second control unit 21. The configuration of the first interface 12 may be the same as the configuration of the second interface 22. Furthermore, the configuration of the first storage unit 13 may be the same as the configuration of the second storage unit 23.

[0047] To avoid redundant explanation, of the configuration of the first communication device 10 and the configuration of the second communication device 20, the configuration of the second communication device 20 will be explained below.

[0048] The second storage unit 23 stores, in advance, a physical link setting value that is, for example, a fixed value.

[0049] <Configuration Example of Second Control Unit 21> When the second communication device 20 (own communication device) is started, the second control unit 21 starts the second interface 22. The second control unit 21 repeats the process of reading the physical link setting value from the register of the second interface 22 until the physical link setting value is successfully read. Successful reading of the physical link setting value means that a physical link has been established.

[0050] When the second communication device 20 is started, the second control unit 21 determines the state of the physical link (e.g., communication speed, full-duplex communication, connected or disconnected) based on a physical link setting value, which is a constant value. The second control unit 21 establishes a logical link based on the determination result of the physical link state based on the physical link setting value and the logical link setting value. The second control unit 21 performs main signal communication with the first control unit 11 using the logical link.

[0051] After the second communication device 20 is started up, the second control unit 21 controls the state transition of the second communication device 20 between sleep and active states.

[0052] After the second communication device 20 is started up, the second control unit 21 reads out the stored physical link setting values ​​from the second storage unit 23. The second control unit 21 determines the state of the physical link based on the physical link setting values ​​read out from the second storage unit 23.

[0053] When the second communication device 20 transitions from an active state to a sleep state, the second control unit 21 holds a logical link setting value based on the physical link setting value held in the second storage unit 23. The second control unit 21 holds a logical link based on the held logical link setting value. Note that during the sleep period, the physical link is actually disconnected (the physical link is not held), but the second control unit 21 determines that the physical link is maintained (connection is maintained) based on the physical link setting value held in the second storage unit 23.

[0054] When the second communication device 20 transitions from a sleep state to an active state, the second control unit 21 holds a logical link setting value based on the physical link setting value held in the second storage unit 23. The second control unit 21 holds a logical link based on the held logical link setting value. The second control unit 21 executes main signal communication with the first communication device 10 (opposing communication device) using the held logical link based on the held logical link setting value.

[0055] <Configuration Example of Second Interface 22> When the second communication device 20 is started up and when the second communication device 20 transitions from sleep to active state, the second interface 22 establishes a physical link with the first interface 12 through physical layer negotiation. The second interface 22 performs main signal communication with the first communication device 10 (opposing communication device). The second interface 22 may perform I / O conversion. The second interface 22 may perform processing based on DHCP. The second interface 22 may perform processing based on ARP. A register of the second interface 22 holds a physical link setting value while the physical link is established.

[0056] When the second communication device 20 transitions from an active state to a sleep state, the second interface 22 disconnects the physical link. When the physical link is disconnected, the second interface 22 invalidates (resets) the physical link setting value held in the register.

[0057] Next, an example of the operation of the communication system 1 will be described. Fig. 2 is a sequence diagram (first half) showing an example of the operation of the communication system 1 in an embodiment. Fig. 3 is a sequence diagram (second half) showing an example of the operation of the communication system 1 in an embodiment. In Figs. 2 and 3, solid arrows represent main signal communication. Dashed arrows represent control signal communication.

[0058] 2 and 3, for the purpose of power saving, as an example, the second communication device 20 repeatedly transitions between active and sleep states. The first communication device 10 does not need to transition between active and sleep states.

[0059] When the first communication device 10 is started up, the first control unit 11 uses a control signal to start up the first interface 12 (step S101), which starts up the first interface 12 (step S102).

[0060] The first interface 12 performs negotiation with the second interface 22 as physical link control (step S103). The first control unit 11 repeatedly reads the physical link setting value from the register of the first interface 12 (step S104). The first interface 12 establishes a physical link with the second interface 22 (step S105).

[0061] The register of the first interface 12 holds the physical link setting value in a readable state (step S106). The first control unit 11 reads the physical link setting value from the register of the first interface 12 to confirm that the physical link has actually been established (step S107). The first storage unit 13 holds a fixed physical link setting value in advance (step S108). The first control unit 11 reads the physical link setting value from the first storage unit 13 (step S109).

[0062] Before reading the physical link setting value from the register of the first interface 12 , the first control unit 11 may read the physical link setting value, which is a predetermined constant value, from the first storage unit 13 .

[0063] The first control unit 11 performs logical link control by negotiating with the second control unit 21 (step S110). The first control unit 11 establishes a logical link based on the determination result of the physical link state based on the physical link setting value and the logical link setting value (step S111). The first control unit 11 performs main signal communication with the second control unit 21 (step S112).

[0064] When the second interface 22 goes to sleep, the first interface 12 disconnects the physical link (step S113). Here, the second control unit 21 holds the logical link setting value based on the physical link setting value held in the second storage unit 23. The second control unit 21 holds the logical link based on the held logical link setting value. Based on the physical link setting value held in the second storage unit 23, the second control unit 21 determines that the physical link is maintained.

[0065] The first interface 12 performs negotiation with the second interface 22 as physical link control (step S114). The first interface 12 establishes a physical link with the second interface 22 (step S115). The first control unit 11 uses the held logical link to perform main signal communication with the second control unit 21 (step S116).

[0066] Furthermore, the operations from step S201 to step S216 in the second communication device 20 are the same as the operations from step S101 to step S116 in the operation of the first communication device 10.

[0067] As described above, the first storage unit 13 stores a physical link setting value. The physical link setting value is, for example, a predetermined constant value. When the first communication device 10 (own communication device) or the second communication device 20 (opposing communication device) executes a state transition from sleep to active (first state transition), the first interface 12 connects the first communication device 10 and the second communication device 20 via a physical link based on the physical link setting value. When the first communication device 10 or the second communication device 20 executes a state transition from active to sleep (second state transition), the first interface 12 disconnects the physical link.

[0068] When the first communication device 10 and the second communication device 20 perform the second state transition, the first control unit 11 maintains a logical link based on the maintained physical link setting value and logical link setting value. When the first communication device 10 and the second communication device 20 perform the first state transition, the first control unit 11 performs communication between the first communication device 10 and the second communication device 20 using the maintained logical link.

[0069] In this way, the second communication device 20 goes to sleep while the logical link remains established, so the first control unit 11 executes main signal communication immediately after the state of the second communication device 20 transitions from sleep to active and a physical link is established by the first interface 12. Also, the second control unit 21 executes main signal communication immediately after the state of the second communication device 20 transitions from sleep to active and a physical link is established by the second interface 22.

[0070] This reduces the time until main signal communication becomes possible when the state transitions from sleep to active, thereby reducing power consumption.

[0071] (First Modification of the Embodiment) When the first communication device 10 is started up, the first interface 12 determines a physical link setting value through negotiation with the second interface 22. The first interface 12 determines the state of the physical link based on the physical link setting value read from the register of the first interface 12.

[0072] 2 , the first control unit 11 records the physical link setting value determined by the first interface 12 in the first storage unit 13, instead of reading out the fixed physical link setting value from the first storage unit 13. The first storage unit 13 holds the physical link setting value determined by the first interface 12.

[0073] When the second communication device 20 is started up, the second interface 22 determines a physical link setting value through negotiation with the first interface 12. That is, the physical link setting value is a value determined based on the negotiation executed by the second interface 22. The second control unit 21 determines the state of the physical link based on the physical link setting value read from the register of the second interface 22.

[0074] 2, the second control unit 21, instead of reading out a fixed physical link setting value, records the physical link setting value read out from the register of the second interface 22 in the second storage unit 23. The second storage unit 23 holds the physical link setting value determined by the second interface 22.

[0075] This reduces the time until main signal communication becomes possible when the state transitions from sleep to active, even if the physical link setting value of the first interface 12 does not match the physical link setting value of the second interface 22, thereby reducing power consumption.

[0076] (Second modified example of embodiment) When the state transitions from sleep to active, immediately after the completion of a FLP (Fast Link Pulse) burst in auto-negotiation between the first interface 12 and the second interface 22, the first control unit 11 and the second control unit 21 perform main signal communication via IP (Internet Protocol) communication and Ethernet (registered trademark) communication.

[0077] This eliminates the need for DHCP, ARP, and the process of resetting the control unit's settings, further shortening the time until main signal communication becomes possible when transitioning from sleep to active state, thereby making it possible to further reduce power consumption.

[0078] (Third Modification of the Embodiment) The first communication device 10 includes a switch (not shown) for arbitrarily switching the destination that the first control unit 11 refers to for the physical link setting value. The second communication device 20 includes a switch (not shown) for arbitrarily switching the destination that the second control unit 21 refers to for the physical link setting value.

[0079] This allows the physical link setting value and logical link setting value to be changed arbitrarily in the event of a failure in communication system 1 (device failure, communication path disconnection, etc.), making it easier to identify the cause of the failure in communication system 1.

[0080] (Fourth Modification of the Embodiment) The first control unit 11 refers to the physical link setting value stored in the first storage unit 13. If the main signal is not conducted for a certain period of time or more, the first control unit 11 refers to the physical link setting value stored in the register of the first interface 12. Similarly, the second control unit 21 refers to the physical link setting value stored in the second storage unit 23. If the main signal is not conducted for a certain period of time or more, the second control unit 21 refers to the physical link setting value stored in the register of the second interface 22.

[0081] This allows the physical link set values ​​and logical link set values ​​to be changed as desired in the event of a failure (such as a device failure or a disconnection of the communication path) in the communication system 1, thereby facilitating the identification of the cause of the failure in the communication system 1. Furthermore, because each control unit autonomously changes the reference destination for the physical link set values, it is possible to easily identify the cause of the failure in the communication system 1 without having to dispatch a worker or the like who changes the physical link set values, etc., to the installation location of each communication device.

[0082] (Fifth Modification of the Embodiment) The first interface 12 and the second interface 22 hold a physical link setting value, which is a constant value, in advance. When the second communication device 20 transitions from an active state to a sleep state, the first interface 12 and the second interface 22 establish a physical link in a short time based on the physical link setting value, which is a predetermined constant value, without performing negotiation.

[0083] As a result, when the first interface 12 and the second interface 22 transition to the sleep state, a physical link is established in a short time without performing negotiation, which makes it possible to further reduce power consumption.

[0084] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0085] The present invention is applicable to communication systems such as optical communication systems.

[0086] REFERENCE SIGNS 1, 1a...communication system, 10, 10a...first communication device, 11, 11a...first control unit, 12, 12a...first interface, 13, 13a...first storage unit, 20, 20a...second communication device, 21, 21a...second control unit, 22, 22a...second interface, 23, 23a...second storage unit

Claims

1. A communications device comprising: an interface that connects the own communication device and the opposed communication device with a physical link based on a physical link setting value when the own communication device or the opposed communication device executes a first state transition, which is a state transition from sleep to active, and disconnects the physical link when the own communication device or the opposed communication device executes a second state transition, which is a state transition from active to sleep; a memory unit that retains the physical link setting value; and a control unit that retains a logical link based on the retained physical link setting value and logical link setting value when the own communication device or the opposed communication device executes the second state transition, and performs communication between the own communication device and the opposed communication device using the retained logical link when the own communication device or the opposed communication device executes the first state transition.

2. A communication device as described in claim 1, wherein the memory unit holds the physical link setting value which is a predetermined constant value, or the physical link setting value which is determined based on a negotiation performed by the interface.

3. A communication device as described in claim 1 or claim 2, wherein the interface connects the self communication device and the opposite communication device via the physical link based on the physical link setting value, which is a predetermined constant value.

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