Network relay system and control method thereof

1. A network relay device that carries out data transmission to and from an opposite device, the network relay device comprising:

multiple ports connecting with corresponding multiple ports of the opposite device via multiple-physical lines; and

a link aggregation control module that aggregates the multiple physical lines to establish a link aggregation, which is regarded as one logic link, and carries out transmission of a control frame signal including a synchronization bit, as well as data transmission, at each port via the physical lines,

in response to detection of occurrence of a trouble in communication of at least one of the aggregated multiple physical lines, the link aggregation control module causing all ports that connect with a normal physical line without the trouble among the multiple ports to stop the data transmission and send the control frame signal including the synchronization bit set equal to a first value,

where the first value functions to stop the data transmission at corresponding ports of the opposite device connecting with the normal physical lines.

2. A network relay device in accordance with claim 1 , wherein the link aggregation control module causes at least the port connecting with the normal physical line to send the control frame signal including the synchronization bit set equal to a second value, which is different from the first value, in the case of recovery of communication of the at least one physical line from the trouble,

where the second value functions to start the data transmission at the corresponding port of the opposite device connecting with the normal link.

3. A network relay device in accordance with claim 2 , wherein the link aggregation control module starts the data transmission at the port that has sent the control frame signal including the synchronization bit set equal to the second value, in response to reception of the control frame signal including the synchronization bit, which is set equal to a value representing either of a start standby state and a start of the data transmission, from the corresponding port of the opposite device.

4. A network relay device in accordance with claim 1 , wherein the link aggregation control module causes at least the port connecting with the normal physical line to send the control frame signal including the synchronization bit set equal to a second value, which is different from the first value, when the trouble in communication of the at least one physical line has been fixed and when all the multiple ports have received the control frame signal including the synchronization bit, which is set equal to a value representing a start standby state of the data transmission, from respective corresponding ports of the opposite device,

where the second value functions to start the data transmission at the corresponding port of the opposite device connecting with the normal link.

5. A network relay device in accordance with claim 4 , wherein the link aggregation control module starts the data transmission at the port that has sent the control frame signal including the synchronization bit set equal to the second value, in response to reception of the control frame signal including the synchronization bit, which is set equal to a value representing either of a start standby state and a start of the data transmission, from the corresponding port of the opposite device.

6. A network relay device in accordance with claim 1 , wherein the opposite device is a network relay device in conformity with IEEE (Institute of Electrical and Electronic Engineers) 802.3.

7. A network relay device in accordance with claim 1 , wherein the network relay device is either one of a switch and a router.

8. A network relay device that carries out data transmission to and from an opposite device, the network relay device comprising:

multiple ports connecting with corresponding multiple ports of the opposite device via multiple physical lines; and

a link aggregation control module that aggregates the multiple physical lines to establish a link aggregation, which is regarded as one logic link, and carries out transmission of a control frame signal including a synchronization bit, as well as data transmission, at each port via the physical lines,

the link aggregation control module allowing each of the multiple ports to take one of first through fourth states as an operating state,

the link aggregation control module causing the port set in the first state to carry out data transmission, as well as transmission of the control frame signal, where the control frame signal sent from the port in the first state includes the synchronization bit set equal to a value ‘1’,

the link aggregation control module causing the port set in either of the second state and the third state to carry out transmission of only the control frame signal, where the control frame signal sent from the port in either of the second state and the third state includes the synchronization bit set equal to a value ‘0’,

the link aggregation control module causing the port set in the fourth state to carry out transmission of only the control frame signal, where the control frame signal sent from the port in the fourth state includes the synchronization bit set equal to the value ‘1’,

in response to detection of occurrence of a trouble in communication of physical line other than a physical line connecting with the port in the first state, among the aggregated multiple physical lines, the link aggregation control module allowing for a transition of the operating state of all ports that connect with normal physical lines without the trouble from the first state to the second state

the link aggregation control module allowing for a transition of the operating state from the second state to the third state, when the port in the second state receives the control frame signal from a corresponding port of the opposite device,

the link aggregation control module allowing for a transition of the operating state from the third state to the fourth state, in response to recovery of communication of the physical line from the trouble,

the link aggregation control module allowing for a transition of the operating state from the fourth state to the first state, when the port in the fourth state receives the control frame signal including the synchronization bit set equal to 1 from a corresponding port of the opposite device,

the link aggregation control module allowing for a transition of the operating state from the first state to the fourth state, when the port in the first state receives the control frame signal including the synchronization bit set equal to 0 from a corresponding port of the opposite device.

9. A network relay device in accordance with claim 8 , wherein the link aggregation control module allows for the transition of the operating state from the third state to the fourth state, when the trouble has been fixed in communication of the physical line and when all the multiple ports have received the control frame signal including the synchronization bit set equal to 1 from respective corresponding ports of the opposite device.

10. A network relay device in accordance with claim 8 , wherein the opposite device is a network relay device in conformity with IEEE (Institute of Electrical and Electronic Engineers) 802.3.

11. A network relay device in accordance with claim 8 , wherein the network relay device is either one of a switch and a router.

12. A control method of controlling a network relay device, the network relay device having multiple ports that connect with corresponding multiple ports of an opposite device via multiple physical lines and carrying out data transmission to and from the opposite device, the control method comprising the steps of:

(a) aggregating the multiple physical lines to establish a link aggregation, which is regarded as one logic link, and carrying out transmission of a control frame signal including a synchronization bit, as well as data transmission, at each port via the physical line; and

(b) in response to detection of occurrence of a trouble in communication of at least one of the aggregated multiple physical lines, causing all ports that connect with normal physical lines without the trouble among the multiple ports to stop the data transmission and send the control frame signal including the synchronization bit set equal to a preset value, where the preset value functions to stop the data transmission at corresponding ports of the opposite device connecting with the normal physical lines.