JP2019176521A - Communication device and control method - Google Patents

Abstract

To provide a technique for suppressing communication stop of the whole communication system, even if a cable fails.SOLUTION: A communication device 20 transmits a frame, received at a reception side port 60, from a transmission side port 60. A first detector 68 detects linking-up at the transmission side port 60. When linking-up is detected, a second detector 70 detects approach to overflow in a transmission buffer 66 for storing the frame that must be transmitted by the transmission side port 60. When approach to overflow is detected, a control section 72 executes flow control via the reception side port 60, if transmission failure in the transmission side port 60 is not detected, and the control section does not execute flow control via the reception side port 60 if the transmission failure in the transmission side port 60 is detected.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a communication technique, and more particularly to a communication apparatus and a control method for transferring a frame.

The layer 2 switch connects stations on a LAN (Local Area Network) to each other. When a bit error or a buffer full state occurs in the data link layer of layer 2, the receiving apparatus only discards an abnormal received frame. The layer 2 switch can avoid frame loss due to a shortage of buffer resources by performing flow control. Flow control is a control mechanism that prevents the transmission apparatus from transmitting data frames at a higher rate than the data frame rate that can be received by the reception apparatus. In the flow control, transmission feedback control is performed from the receiving device side to the transmitting device side, and the transmission rate on the transmitting device side is adjusted according to the buffer status on the receiving device side (see, for example, Patent Document 1). .

JP 2004-289744 A

The communication system is formed, for example, by connecting a plurality of layer 2 switches in a pyramid shape. In such a configuration, when a failure occurs in the cable connected to the port of the layer 2 switch near the end, if the layer 2 switch executes flow control, communication of the entire communication system may be stopped. is there.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique for suppressing communication stoppage of the entire communication system even when a failure occurs in a cable.

In order to solve the above problem, a communication apparatus according to an aspect of the present invention is a communication apparatus that transmits a frame received at a first interface from a second interface, and detects a link-up at the second interface. When the detection unit and the first detection unit detect a link up, the second detection unit detects an approach to overflow in a buffer that accumulates frames to be transmitted by the second interface, and the second detection unit A control unit that detects a transmission failure in the second interface when the difference between the value of the reception counter in the first interface and the value of the transmission counter in the second interface is greater than or equal to a threshold value when an approach is detected; When the transmission unit detects a transmission failure, the second interface that detected the transmission failure Comprising a display unit that notifies the failure of the cable connected to the chair, the.

Another aspect of the present invention is a control method. This method is a control method in a communication device that transmits a frame received at a first interface from a second interface, and includes a step of detecting a link up at the second interface, A step of detecting an approach to an overflow in a buffer for storing frames to be transmitted by an interface; and a difference between a value of a reception counter in the first interface and a value of a transmission counter in a second interface when an approach to the overflow is detected Detecting a transmission failure in the second interface due to the threshold being equal to or greater than a threshold; and, if detecting a transmission failure, notifying the occurrence of a failure in the cable connected to the second interface that has detected the transmission failure; Is provided.

It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

ADVANTAGE OF THE INVENTION According to this invention, even if a failure generate | occur | produces in a cable, the communication stop of the whole communication system can be suppressed.

It is a figure which shows the structure of the communication system which concerns on the Example of this invention. It is a figure which shows the structure of the communication apparatus of FIG. It is a flowchart which shows the execution procedure of the flow control by the communication apparatus of FIG.

Before describing the present invention specifically, an outline will be given first. An embodiment of the present invention relates to a communication system formed by connecting a plurality of communication devices in a pyramid shape. The communication device is, for example, a layer 2 switch or a switching hub. Flow control is effective for buffer overflow in a communication device, but as described above, communication of the entire communication system may be stopped by flow control. In order to cope with this, when the communication device in the present embodiment detects an approach to the buffer overflow, the communication device executes flow control if there is no failure in the cable, but there is a failure in the cable. If so, flow control is not executed.

FIG. 1 shows a configuration of a communication system 100 according to an embodiment of the present invention. Communication system 100
Are the first communication device 20a, the second communication device 20b, which are collectively referred to as the server 10 and the communication device 20,
The third communication device 20c, the fourth communication device 20d, the fifth communication device 20e, the sixth communication device 20f,
7th communication apparatus 20g, 8th communication apparatus 20h, 9th communication apparatus 20i, 10th communication apparatus 20j
, Eleventh communication device 20k, twelfth communication device 20l, first terminal device 30a, second terminal device 30b, third terminal device 30c, fourth terminal device 30d, fifth terminal device 30e, collectively referred to as terminal device 30, It includes a sixth terminal device 30f, a seventh terminal device 30g, an eighth terminal device 30h, a ninth terminal device 30i, a tenth terminal device 30j, an eleventh terminal device 30k, and a twelfth terminal device 30l.

The communication system 100 is formed by connecting a plurality of communication devices 20 in a pyramid shape. The apex portion of the communication system 100 formed in a pyramid shape includes a server 1
0 is placed. The server 10 is connected to a first communication device 20a and a second communication device 20b. Further, the first communication device 20a and the second communication device 20b include a third communication device 20c.
The sixth communication device 20f is connected to the third communication device 20c to the sixth communication device 20f.
The communication device 20g to the twelfth communication device 20l are connected. Therefore, the seventh communication device 20g ~
The twelfth communication device 20l is connected to the server 10 via “two” communication devices 20, and the third communication device 20l
The communication device 20 c to the sixth communication device 20 f are connected to the server 10 via “1” communication device 20. On the other hand, since the first communication device 20a and the second communication device 20b are directly connected to the server 10, it can be said that they are connected to the server 10 via the communication device 20 of “0”.

Here, communication devices 20 having the same number of communication devices 20 connected to the server 10 can be said to be communication devices 20 in the same hierarchy. Further, a hierarchy having a smaller number of communication devices 20 connected to the server 10 is “upper”, and a hierarchy having a larger number of communication devices 20 is “lower”. In the case of FIG. 1, the first communication device 20 a and the second communication device 20 b are included in the upper layer next to the layer of the server 10, and the seventh communication device 20 g to the twelfth communication device 20 l are in the lowest layer. included. Furthermore, a plurality of terminal devices 30 are connected to the seventh communication device 20g to the twelfth communication device 20l. Note that the number of layers of the communication devices 20 connected in a pyramid shape is not limited to “3”. Further, the number of communication devices 20 included in each layer may be different from that in FIG. Furthermore, the terminal device 30 may be connected to the communication device 20 included in the higher hierarchy.

The server 10 transmits a frame including data. The data may be arbitrary, and the final destination of the frame is the terminal device 30. The transmission may be unicast transmission, multicast transmission, or broadcast transmission. As described above, the communication device 20 is a layer 2 switch and a switching hub, and has a function of transferring a frame. The communication device 20 can execute flow control. Flow control is a process for managing a data rate so as to prevent a high-speed transmission side from overrunning a low-speed reception side between two nodes, and one example is back pressure. The back pressure is a method of intentionally transmitting a collision signal to the transmission source and suppressing transmission of the frame to the transmission source when the buffer in the communication device 20 is about to overflow. The terminal device 30 is an electronic device that is operated by a user or the like, and receives a frame from the server 10 via the communication device 20. The terminal device 30 executes a process according to the data included in the received frame.

In such a configuration of the communication system 100, it is assumed that a broadcast frame is transmitted from the server 10 to the terminal device 30 via the communication device 20. For example, server 1
0 transmits a broadcast frame to the first communication device 20a, and the first communication device 20a transmits the received broadcast frame to the third communication device 20c. The third communication device 20c transmits the received broadcast frame to the seventh communication device 20g, and
The communication device 20g transmits the received broadcast frame to the first terminal device 30a. When the processing capability is reduced in the first terminal device 30a, the receivable data rate is reduced.

As a result, the seventh communication device 20g receives the broadcast frame from the third communication device 20c only at a low data rate, even though the seventh communication device 20g receives the broadcast frame at a high data rate. Cannot send. As a result, the transmission buffer of the seventh communication device 20g is likely to overflow, so the seventh communication device 20g executes back pressure on the third communication device 20c to lower the data rate of the third communication device 20c. Let After that, when the decrease in processing capacity in the first terminal device 30a is recovered,
The seventh communication device 20g releases the back pressure for the third communication device 20c. As a result, the return to the original data rate is realized.

Here, even when a failure, for example, a short circuit occurs in the cable between the seventh communication device 20g and the first terminal device 30a, the transmission buffer of the seventh communication device 20g is likely to overflow, so the seventh communication device 20g The back pressure is executed on the third communication device 20c.
Unlike the case where the processing capability of the first terminal device 30a is reduced, the cable failure is not recovered. Therefore, the transmission buffer of the third communication device 20c is likely to overflow due to the execution of the back pressure, and the third communication device 20c executes the back pressure on the first communication device 20a. As described above, the overflow of the transmission buffer propagates to the upper layer, and the server 10 cannot transmit the broadcast frame. As a result, communication of the entire communication system 100 is stopped. In order to suppress the occurrence of such a situation, the communication device 20 executes the following processing.

FIG. 2 shows the configuration of the communication device 20. The communication device 20 is connected to a first lower device 50a, a second lower device 50b, a third lower device 50c, and an (N-1) th lower device 50n-1 collectively referred to as an upper device 40 and a lower device 50. The communication device 20 includes a first port 6 collectively referred to as a port 60.
0a, 2nd port 60b, 3rd port 60c, 4th port 60d, Nth port 60n, switch part 62, and display part 64 are included. The switch unit 62 includes a first transmission buffer 66a, a second transmission buffer 66b, a third transmission buffer 66c, a fourth transmission buffer 66d, an Nth transmission buffer 66n, a first detection unit 68, a second transmission buffer 66, and a second transmission buffer 66b. Detection unit 70, control unit 72
including.

The higher-level device 40 is another communication device 20 or the server 10 arranged at a higher level than the communication device 20, and the lower-level device 50 is another communication device 20 arranged at a lower level than the communication device 20. Alternatively, the terminal device 30 is used. A LAN cable can be connected to the port 60, and the upper device 40 or the lower device 50 is connected via the LAN cable. Therefore, it can be said that the port 60 is an interface for inputting / outputting a frame to / from the external upper device 40 or the lower device 50. Each port 60 includes a transmission pin (TD pin) used when transmitting a frame and a reception pin (RD pin) used when receiving a frame.

The switch unit 62 determines the transmission destination port 60 based on the destination MAC address of the frame input at one port 60, and transfers the frame to the determined port 60.
In the case of a broadcast frame, the switch unit 62 transfers the broadcast frame to a port 60 other than the input port 60. For example, when a broadcast frame is input from the first port 60a, the switch unit 62 transfers the broadcast frame from the second port 60b to the Nth port 60n. When a broadcast frame is input from the fourth port 60d, the switch unit 62 transfers the broadcast frame from the first port 60a to the third port 60c and the Nth port 60n. Here, when transferring, the frame to be transferred is temporarily stored in the transmission buffer 66. The transmission buffer 66 is arranged in one-to-one correspondence with the port 60. For example, the first transmission buffer 66a is provided so as to correspond to the first port 60a. The same applies to the other transmission buffers 66.

The first detection unit 68 detects link-up of each port 60. This corresponds to detecting the link up of the port 60 used for frame transmission. For example, the detection of link up is determined based on whether or not a link pulse signal is received at the RD pin. If it is received, link up is detected. When the first detection unit 68 detects a link-up for each port 60, the first detection unit 68 notifies the second detection unit 70 of it.

When the second detection unit 70 receives the notification from the first detection unit 68, the second detection unit 70 checks the free capacity of the transmission buffer 66 corresponding to the port 60 in which the link up is detected. For example, when the link up of the second port 60b is detected, the second detection unit 70 sets the second transmission buffer 66b.
Check the free space of. When the free space is smaller than the first threshold, the second detection unit 70
An approach to overflow in the transmission buffer 66 is detected. The second detection unit 70
When an approach to overflow in the transmission buffer 66 is detected, this is notified to the control unit 72.

When the control unit 72 receives the notification from the second detection unit 70, the control unit 72 checks whether or not a transmission failure is detected in the port 60 corresponding to the transmission buffer 66 in which the approach to the overflow is detected. In order to detect a transmission failure, the control unit 72 includes a transmission counter and a reception counter for each port 60. The transmission counter counts the number of frames transmitted from the port 60 during a certain period, for example, 100 msec. On the other hand, the reception counter counts the number of frames received at the port 60 during the same fixed period. When a broadcast frame is targeted as a frame, each communication device 20 transfers a broadcast frame from the remaining port 60 when it receives the broadcast frame at one port 60.

When the port 60 for which transmission failure is to be confirmed is the second port 60b, if no transmission failure has occurred, the total value of the reception counters at the ports 60 other than the second port 60b and the transmission at the second port 60b The counter values should be equal. Using this, the control unit 72
Is a port 60 other than the port 60 subject to confirmation of transmission failure (hereinafter referred to as “reception-side port 60”).
And the difference between the total value of the reception counters at the port 60 for which transmission failure is to be confirmed (hereinafter referred to as “transmission side port 60”) is smaller than the second threshold value. Then, it is determined that the transmission failure is not detected in the port 60 on the transmission side.

On the other hand, when the difference is greater than or equal to the second threshold, particularly when the total value of the reception counter is greater than the value of the transmission counter, the control unit 72 detects a transmission failure at the port 60 on the transmission side. When a failure such as a short circuit occurs in the cable, even if a broadcast frame is transmitted from the port 60 on the transmission side, the broadcast frame is reflected at the failure location, so transmission is not completed and the value of the transmission counter does not increase. Because. In addition, the control part 72 does not need to detect transmission failure immediately, when a difference is more than a 2nd threshold value. For example, the control unit 72
May detect a transmission failure when the difference is equal to or greater than a second threshold value for a predetermined number of times. An example of the predetermined number of times is “4”.

Thereafter, when it is determined that the transmission failure is not detected in the transmission-side port 60, the control unit 72 performs flow control such as back pressure via the reception-side port 60. In addition, since a well-known technique should just be used for flow control, description is abbreviate | omitted here. On the other hand, when a transmission failure is detected at the port 60 on the transmission side, the control unit 72 does not execute the flow control via the port 60 on the reception side. In this case, the control unit 72 sends the port 6 on the transmission side.
Discard the frame to be transmitted from 0. If a cable failure occurs, the data rate will not recover unless the cable is replaced. For this reason, even if flow control is executed, a frame for flow control is only transmitted from the receiving port 60 unnecessarily, and bandwidth is consumed by such a frame. In addition, the host apparatus 40 that has been subjected to flow control.
Since the same frame is retransmitted after waiting for transmission, this also consumes bandwidth, and the higher-level device 4
An overflow at 0 leads to a communication stop of the entire communication system 100. In order to suppress these, when a transmission failure is detected in the port 60 on the transmission side, that is, when the occurrence of a cable failure is estimated, the control unit 72 does not execute flow control.

Further, when the control unit 72 does not execute the flow control via the port 60 on the receiving side,
Unless the communication device 20 is restarted, the non-execution of flow control is continued. In other words, the control unit 72 does not execute the flow control without executing the detection of the link up to the port 60 on the transmission side, the detection of the approach to the overflow, and the detection of the transmission failure. This is because the failure of the cable is not recovered unless the cable is replaced as described above. Note that the control unit 72 executes the above-described processing while changing the port 60 on the transmission side and the port 60 on the reception side according to the notification from the second detection unit 70.

The display unit 64 receives a notification from the control unit 72 when the control unit 72 detects a transmission failure. The display unit 64 includes LEDs (Light Em corresponding to the plurality of ports 60).
LED corresponding to port 60 indicated in the notification.
Lights up or blinks. This corresponds to notifying that a failure such as a short circuit has occurred in the cable connected to the port 60 indicated by the LED.

In terms of hardware, this configuration is arbitrary computer CPU, memory, other L
Although it can be realized by SI and is realized by a program loaded in a memory or the like in terms of software, here, functional blocks realized by their cooperation are illustrated. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

The operation of the communication system 100 configured as above will be described. FIG. 3 is a flowchart illustrating a flow control execution procedure performed by the communication device 20. When the first detection unit 68 detects the link up of the port 60 (Y in S10), the second detection unit 70 checks the free capacity of the transmission buffer 66 corresponding to the port 60 (S12). When the overflow approaches (Y in S14) and no transmission failure is detected (N in S16), the control unit 72 executes flow control (S18). On the other hand, when transmission failure is detected (Y of S16), the control part 72 does not perform flow control (S20). If the first detection unit 68 does not detect the link up of the port 60 (N in S10) or is not approaching the overflow (N in S14), the process is terminated.

According to the present embodiment, even if an approach to overflow is detected, if a transmission failure is detected, flow control is not executed, so that useless frame transmission can be stopped. In addition, since transmission of useless frames is stopped, communication stop of the entire communication system can be suppressed even if a failure occurs in the cable. Further, when non-execution of flow control is determined, non-execution of flow control is maintained, so that processing for determining link-up, approach to overflow, and transmission failure can be made unnecessary. Moreover, since these processes are unnecessary, the processing amount can be suppressed. Moreover, since the failure of the cable is notified by the LED, the replacement of the cable can be prompted. In addition, since flow control is not executed, it is possible to avoid waiting for retransmission in the host device. In addition, since a standby for retransmission in the host device is avoided, overflow in the host device can be suppressed.

In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

10 server, 20 communication device, 30 terminal device, 40 upper device, 50 lower device, 60 port, 62 switch unit, 64 display unit, 66 transmission buffer, 68 first detection unit, 70 second detection unit, 72 control unit, 100 Communication system.

Claims (2)

A communication device for transmitting a frame received at a first interface from a second interface,
A first detection unit for detecting link-up at the second interface;
A second detector for detecting an approach to an overflow in a buffer for accumulating frames to be transmitted by the second interface when the first detector detects a link up;
When the second detection unit detects an approach to overflow, the difference between the value of the reception counter at the first interface and the value of the transmission counter at the second interface is greater than or equal to a threshold value, A controller that detects a transmission failure on the interface;
When the control unit detects a transmission failure, a display unit that notifies the occurrence of a failure in the cable connected to the second interface that has detected the transmission failure;
A communication apparatus comprising: A control method in a communication apparatus for transmitting a frame received at a first interface from a second interface,
Detecting link up at the second interface;
Detecting link up, detecting an approach to overflow in a buffer storing frames to be transmitted by the second interface;
When an approach to overflow is detected, a transmission failure in the second interface is detected when a difference between a reception counter value in the first interface and a transmission counter value in the second interface is equal to or greater than a threshold value. And steps to
If a transmission failure is detected, notifying the failure of the cable connected to the second interface that detected the transmission failure;
A control method comprising:

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