JP2010226576A - Network, network communications apparatus, system switching method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a frame loss in system switching, in a network taking a redundant configuration for a transmission line between hosts, and to efficiently synchronize system switching between transmission-side and reception-side hosts. <P>SOLUTION: In system switching between transmission ports 124 and 128, a control section 118 of a transmission-side host 110 controls a branching section 120 so as to transfer a switching request frame to a transmission buffer of a transmission port of an active system and to transfer subsequent frames to a transmission buffer of a transmission port of a reserve system. Thereafter, when a switching completion frame, indicating reception of the switching request frame and completion of system switching in the transmission-side host itself is received from a reception-side host 160, the transmission port of the reserve system is switched to the active system. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a system switching technique in a network having a redundant configuration in a transmission path between network communication apparatuses.

  A network having a redundant configuration in a transmission path between network communication apparatuses and a communication device having a redundant configuration in an internal predetermined functional block are known, and techniques have been proposed from various viewpoints.

  For example, Patent Document 1 discloses a technique in which a transfer device is provided between layer 2 switches, and a plurality of operation transmission paths are provided between the transfer device and the layer 2 switch. This transfer apparatus includes a plurality of ports for connecting two systems of transmission paths to a layer 2 switch, and one of the ports is used as an operating system and the other system is used as a standby system. And when the failure occurs in the active system, the standby system is switched to the new active system.

  Patent Document 2 discloses a technique for preventing cell loss during system switching in an ATM (Asynchronous Transfer Mode) switch system (ATM switch) in which ATM switches are redundantly provided.

  In this method, a plurality of line corresponding units each receiving a cell from a corresponding input line and sending a cell to a corresponding output line, and first and second switching are performed for cells from each of the plurality of line corresponding units. In an ATM switch system including two switching circuits (ATM switches) and a system control unit that controls system switching in the first and second switching circuits, when a system switching factor occurs, the above-described plurality of lines are supported. A switch request signal is sent to the unit. A system switching response signal indicating that the transmission to the first and second switching circuits of the cells received and received from the plurality of line corresponding units in response to the switching request signal has been stopped is stopped. The system switching is received and the system switching in the first and second switch circuits is controlled according to the input status of the system switching response signal.

  According to this method, since it is possible to perform system switching after confirming that cell output from each line corresponding unit to the ATM switch is stopped, it is possible to prevent cell loss at the time of switching. ing. However, normally, an ATM switch is provided with a buffer for buffering cells, and cells may remain in the buffer even if there is no transmission from the line corresponding unit to the ATM switch. There may be a problem that the transmitted cell is not transmitted.

Patent Document 3 discloses an ATM switch system that takes into account ATM switch buffers and aims to prevent cell loss during system switching.
This ATM switch system includes an ATM active switch and a standby switch each having a buffer for temporarily storing cell data, a switching information insertion unit for writing switching information to a cell in input data, and switching information written therein. A branch circuit for allocating cells to be monitored and transferred to the active switch and the standby switch, a first monitoring control unit for controlling cell distribution of the branch circuit, and the active switch and the standby switch. A selection circuit that selects a cell to be read out and a second monitoring control unit that controls selection of the selection circuit are provided.

  The first monitoring control unit monitors the appearance of the switching control cell in which the switching information is written, and when the switching control cell appears, controls the branch circuit to switch from the active switch to the standby switch. As a result, the switching control cell accumulates at the end of the buffer of the active switch, and the cell immediately following the switching control cell accumulates in the buffer of the standby switch. When the second monitoring control unit receives the switching control cell while selecting the output signal from the active switch, the second monitoring control unit switches to the selection of the output signal from the standby switch. As a result, the switch can be switched without discarding the cells accumulated in the buffer of the active switch when switching information is received.

International Publication WO2006 / 114809 JP 2000-286850 A Japanese Patent Laid-Open No. 4-86043

  Consider the network 10 shown in FIG. The network 10 includes a network communication apparatus A and a network communication apparatus B, and two systems of transmission paths (transmission path 1 and transmission path 2) are provided between the network communication apparatus A and the network communication apparatus B. The network communication apparatus A transmits a frame to the network communication apparatus B via one of the transmission path 1 and the transmission path 2.

  In the network communication apparatus A, the transmission port 14 connected to the transmission path 1 transmits the frame buffered in the transmission buffer 12 to the network communication apparatus B when set to the active system. When the transmission port 14 is an active system, frames transmitted to the network communication apparatus B are buffered in the transmission buffer 12.

  Further, the transmission port 24 connected to the transmission path 2 also transmits the frame buffered in the transmission buffer 22 to the network communication apparatus B when set to the active system. When the transmission port 24 is an active system, frames transmitted to the network communication apparatus B are buffered in the transmission buffer 22.

  One of the transmission port 14 and the transmission port 24 is set as an active system and the other as a standby system.

  In the network communication apparatus B, the reception port 18 is connected to the transmission path 1, and the reception port 28 is connected to the transmission path 2. One of the reception port 18 and the reception port 28 is set as an active system and the other as a standby system.

  The transmission port and the reception port connected to both ends of the same route need to be set in the same system. That is, “the transmission port 14 and the reception port 18 are the active system, and the transmission port 24 and the reception port 28 are the standby system”, “the transmission port 14 and the reception port 18 are the standby system, and the transmission port 24 and the reception port 28 are the reception systems. Only one of the setting patterns “the port 28 is an active system” is possible.

  As an example, “transmission port 14 and reception port 18 are active, and transmission port 24 and reception port 28 are standby” is set. In this case, in the network communication apparatus A, frames to be transmitted to the network communication apparatus B are temporarily accumulated in the transmission buffer 12 and sequentially output to the transmission path 1 by the transmission port 14. In the network communication apparatus B, a frame transmitted from the transmission port 14 via the transmission path 1 is received by the reception port 18. The transmission port 24 and the reception port 28 are standby systems and are on standby.

  When performing system switching in this state, if switching is performed without considering whether there is a frame waiting for transmission in the transmission buffer 12, if frames remain in the transmission buffer 12, these frames are not transmitted, so-called Frame loss will occur.

  When the technique of Patent Document 3 is applied to the network communication device A in order to prevent frame loss, the flow of processing in the network communication device A is considered as follows.

  Switching information is written in a frame input to the transmission buffer 12 to become a switching control frame. When it is detected by monitoring that the frame input to the transmission buffer 12 is a switching control frame, the frame is input to the transmission buffer 22. When the output of the switching control frame is detected from the transmission port 14, the transmission port 24 is switched to the active system.

  This method always monitors whether the frame input to the buffer of the active transmission port is a switching control frame and whether the frame output from the active transmission port is a switching control frame. There is a problem that the processing is complicated and the circuit scale of the apparatus is increased.

  Further, in the network as shown in FIG. 8, communication cannot be established by simply switching the transmission port in the network communication apparatus A. For example, even if the transmission port 24 is switched to the active system, the frame cannot be transmitted from the network communication apparatus A to the network communication apparatus B unless the reception port 28 is switched to the active system. A mechanism for synchronizing the system switching between the network communication device A on the transmission side and the network communication device B on the reception side is desired.

  The present invention has been made in view of the above circumstances. In a network having a redundant configuration in a transmission path between network communication devices, the network device on the transmission side and the reception side is prevented while preventing frame loss during system switching. It is possible to efficiently synchronize the system switching between them.

  One aspect of the present invention is a network. This network includes a transmission-side network device, a reception-side network device, and two systems of transmission lines provided between the transmission-side and reception-side network devices.

  The network device on the transmission side includes two transmission ports, two transmission buffers, a branching unit, and a transmission side control unit.

  The two transmission ports are connected to two transmission lines, respectively, one is set as the active system and the other is set as the standby system, and the operating system transmits the frame to the network device on the receiving side.

Two transmission buffers are provided for two transmission ports, respectively, and buffer frames to be transmitted.
The branching unit transfers the frame to the transmission buffer of the active transmission port.

The transmission side control unit controls the system switching of the two transmission ports as follows.
First, a switching request frame that can indicate a switching request is transferred to the transmission buffer of the active transmission port, and the branching unit is controlled to transfer subsequent frames to the transmission buffer of the standby transmission port.

  Thereafter, when a switching completion frame indicating that the switching request frame has been received and the system switching in itself has been completed is received from the network communication device on the receiving side, the standby transmission port is switched to the active system.

  The network device on the reception side includes two reception ports and a reception side control unit that controls system switching between the two reception ports.

  The two receiving ports are connected to the two transmission lines, respectively, one is set as the active system and the other is set as the standby system, and the operating system receives a frame from the network device on the transmission side.

  When receiving a switching request frame that can indicate a switching request from the transmission-side network device, the receiving-side control unit switches the standby reception port to the active system and sends the switching completion frame to the transmission-side network communication device. Control to send.

  Note that the network of the above aspect is replaced with a method or system, the network communication device on the transmission side and the reception side included in the network, the system switching method in these communication devices, and executing these methods by executing a computer This program is also effective as an aspect of the present invention.

  According to the technology of the present invention, in a network having a redundant configuration in a transmission path between network communication devices, frame switching is prevented at the time of system switching, and system switching synchronization between the network device on the transmission side and the reception side is synchronized. Can be taken efficiently.

It is a figure which shows the network concerning the 1st Embodiment of this invention. It is a figure which shows the format of a LACP frame. It is a figure which shows the transmission side host in the network shown in FIG. It is a figure which shows the receiving side host in the network shown in FIG. It is a flowchart which shows the process at the time of the system switching in the 1st Embodiment of this invention. It is a figure which shows the transmission side host in the network concerning the 2nd Embodiment of this invention. It is a flowchart which shows the process at the time of the system switch in the 2nd Embodiment of this invention. It is a figure which shows the example of the network used in order to demonstrate the subject of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. For clarity of explanation, the following description and drawings are omitted and simplified as appropriate. Each element described in the drawings as a functional block for performing various processes can be configured by a CPU, a memory, and other circuits in terms of hardware, and a program loaded in the memory in terms of software. Etc. Therefore, it is understood by those skilled in the art that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof, and is not limited to any one.

<First Embodiment>
FIG. 1 shows a network 100 according to a first embodiment of the present invention. The network 100 conforms to Ethernet (registered trademark) as an example, and includes a transmission side host 110 and a reception side host 160, and a frame is transmitted from the transmission side host 110 to the reception side host 160.

  The transmission side host 110 and the reception side host 160 have a redundant configuration by Link Aggregation defined as IEEE P802.3ad. The two links 152 and 154 belong to the same Link Aggregation and are not used at the same time.

  Link Aggregation is established by executing Link Aggregation Control Protocol (LACP) defined by IEEE P802.3ad between two communication nodes. FIG. 2 shows the LACP frame format.

  FIG. 3 shows the sending host 110. The transmission side host 110 includes a management port 112, an input port 114, a command processing unit 116, a control unit 118, a branching unit 120, a transmission buffer 122, a transmission port 124, a transmission buffer 126, and a transmission port 128.

  The management port 112 is a port for managing the transmission side host 110, and the input port 114 receives a frame to be transmitted to the reception side host 160. The command processing unit 116 analyzes a command from the management port 112 and performs processing according to the command.

  The branching unit 120 transfers the frame from the input port 114 to one of the transmission buffer 122 and the transmission buffer 126. The control unit 118 controls which transmission buffer the frame is transferred to.

The transmission port 124 is connected to the link 152 and sequentially transmits the frames in the transmission buffer 122 to the reception-side host 160 via the link 152. The transmission port 128 is connected to the link 154 and sequentially transmits the frames in the transmission buffer 126 to the receiving host 160 via the link 154. The transmission port 124 and the transmission port 128 do not operate at the same time. When one of the transmission port 124 and the transmission port 128 is set and operated, the other is in the standby state set to the standby system.
The control unit 118 controls system switching between the two transmission ports.

  FIG. 4 shows the receiving host 160. The reception side host 160 includes a reception port 162, a reception port 164, a control unit 166, an aggregation unit 168, a transmission buffer 170, and an output port 172.

  The reception port 162 is connected to the link 152 and receives a frame transmitted from the transmission port 124 of the transmission side host 110. The reception port 164 is connected to the link 154 and receives a frame transmitted from the transmission port 128 of the transmission side host 110. The reception port 162 and the reception port 164 do not operate simultaneously, and when one is an active system, the other is a standby system.

  The control unit 166 controls system switching between the reception port 162 and the reception port 164. The aggregation unit 168 transmits the frames that have entered from the reception port 162 and the reception port 164 to the transmission buffer 170. The transmission buffer 170 buffers the data in the transmission buffer 170 and provides it to the output port 172. The output port 172 sequentially outputs the frames in the transmission buffer 170.

Here, for example, when system switching is necessary for system maintenance, processing in the network 100 will be described.
FIG. 5 is a flowchart showing processing performed by the transmission side host 110 and the reception side host 160 at the time of system switching.

  In the transmission side host 110, the management port 112 receives a switching command for instructing system switching (S10). The switching command is analyzed by the command processing unit 116 and output to the control unit 118. In response to this, the control unit 118 starts processing for system switching.

  First, the control unit 118 controls the branch unit 120 to transfer the frame to the standby transmission port. As a result, the frames transmitted to the receiving host 160 are buffered in the transmission buffer of the standby transmission port (S12).

  Further, the control unit 118 causes the branching unit 120 to transfer a switching frame for requesting system switching to the receiving host 160 to the active transmission port (S14). As a result, the switching frame is buffered at the end of the frame buffered in the transmission buffer of the active transmission port. The switching frame is, for example, a frame in which the first bit in the Reserve area (area indicated by an arrow in the figure) of the LACP frame shown in FIG.

  The active transmission port sequentially transmits frames buffered in its own transmission buffer. The switching frame is transmitted last (S16).

  While the above processes are being executed, in the receiving host 160, the active receiving port receives the frame and finally receives the switching frame (S30, S32).

  The switching frame received in step S32 is output to the aggregation unit 168. When the frame output to the aggregation unit 168 is a switching frame, the control unit 166 performs system switching between the reception port 162 and the reception port 164 (S34).

  When the receiving-side host 160 completes the system switching of the receiving port, a switching completion frame indicating completion of switching is transmitted from the receiving port of the new active system to the transmitting-side host 110 (S36).

In the transmission-side host 110, when the switch completion frame is received at the standby transmission port, the control unit 118 switches the standby transmission port to the active system. Thereby, a frame is transmitted from the transmission port of the new operation system (S18, S20). Correspondingly, the receiving host 160 receives the frame at the new active receiving port (S38).
According to the network 100 of this embodiment, the transmission port system is switched after all the frames remaining in the transmission buffer of the transmission port of the former operating system of the transmission side host are transmitted. Can be prevented. In addition, with the switching frame from the sending host, the transmission completion notification and switching request for the frame remaining in the transmission buffer of the old active transmission port are simultaneously sent to the receiving host, and the switching completion frame from the receiving host is also sent. With the simple processing and configuration, the transmission completion of the frame remaining in the transmission buffer of the transmission port of the old operational system and the completion of system switching at the reception host can be performed simultaneously to the transmission host. It is possible to efficiently synchronize the system switching between the transmission side host and the reception side host.

<Second Embodiment>
The second embodiment of the present invention is a network in which a transmission side host 210 shown in FIG. 6 is provided in place of the transmission side host 110 shown in FIG. 3 in the network 100 shown in FIG. Since it is the same as the network 100 shown in FIG. 1 except that the sending host is different, only the sending host 210 will be described here.

The transmission-side host 210 includes a management port 212, an input port 214, a command processing unit 216, a control unit 218, a branching unit 220, a transmission buffer 222, a transmission port 224, a transmission buffer 226, a transmission port 228, and a transfer buffer 230. .
The management port 212, the input port 214, the command processing unit 216, the branching unit 220, the transmission buffer 222, and the transmission buffer 226 are the management port 112, the input port 114, the command processing unit 116 in the transmission side host 110 shown in FIG. The same as branching unit 220, transmission buffer 122, and transmission buffer 126, respectively.

  The control unit 218 controls system switching. The transfer buffer 230 buffers frames remaining in the old active transmission buffer at the time of system switching.

  The transmission port 224 is connected to the link 152, and sequentially transmits the frames in the transmission buffer 222 to the reception-side host 160 via the link 152. The transmission port 228 is connected to the link 154 and transmits the frame in the transmission buffer 226 to the reception-side host 160 via the link 154. The transmission port 224 and the transmission port 228 do not operate at the same time. When one is operating, that is, when it is an active system, the other is in a standby state, that is, a standby system.

  When the frame is buffered in the transfer buffer 230, the transmission port 224 transmits all the frames in the transfer buffer 230 and then transmits the frames in the transmission buffer 222. Similarly, the transmission port 228 transmits all the frames in the transfer buffer 230 and then transmits the frames in the transmission buffer 226.

  FIG. 7 is a flowchart illustrating processing performed by the transmission-side host 110 and the reception-side host 160 when system switching is necessary due to system maintenance or the like.

  When the system is switched in the transmission-side host 210, the management port 212 receives a switching command (S110). The switching command is analyzed by the command processing unit 216 and output to the control unit 218. In response to this, the control unit 218 starts processing for system switching.

  First, the control unit 218 controls the branch unit 220 to transfer the frame to the standby transmission port. As a result, the frame transmitted to the receiving host 160 is buffered in the transmission buffer of the transmission port (S112).

  In addition, the control unit 118 controls the transmission buffer of the active transmission port, and causes the frame waiting for transmission buffered in the transmission buffer to be transferred to the transfer buffer 230 (S114).

  In addition, the control unit 118 causes the branching unit 220 to transfer a switching frame for requesting system switching to the receiving host 160 to the active transmission port (S116). As a result, the switching frame is buffered in the transmission buffer of the active transmission port.

  In the transmission side host 210, the active transmission port transmits the switching frame (S118), and in the reception side host 160, the active reception port receives the switching frame (S130).

  The switching frame received in step S130 is output to the aggregation unit 168. When the control unit 166 detects that the frame output to the aggregation unit 168 is a switching frame, the control unit 166 performs system switching between the reception port 162 and the reception port 164 (S132).

  In the receiving host 160, when the receiving port system switching is completed, a switching completion frame is transmitted from the new operating receiving port to the transmitting host 210 (S134).

  In the transmission-side host 210, when the switching completion frame is received at the standby transmission port, the control unit 218 switches the standby transmission port to the active system. Thereby, the frame is transmitted from the transmission port of the new operation system (S120, S122). The new active transmission port starts transmission from the frame buffered in the transfer buffer 230, and transmits the frame in its own transmission buffer after the frame in the transfer buffer 230 runs out.

  Correspondingly, the receiving host 160 receives the frame at the new active receiving port (S136).

  According to the network of the present embodiment, the frame in the transmission buffer of the old operational transmission port of the sending host is transferred to the transfer buffer 230, and after the system switchover, the new operational transmission port Since transmission is started from the frame in the buffer 230, frame loss at the time of switching can be prevented. In addition, other effects obtained by the network 100 of the first embodiment shown in FIG. 1 can be obtained.

  The present invention has been described above based on the embodiment. The embodiment is an exemplification, and various changes and increases / decreases may be added without departing from the gist of the present invention. It will be understood by those skilled in the art that modifications to which these changes and increases / decreases are also within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Transmission path 2 Transmission path 10 Network 12 Transmission buffer 14 Transmission port 18 Reception port 22 Transmission buffer 24 Transmission port 28 Reception port 100 Network 110 Transmission side host 112 Management port 114 Input port 116 Command processing part 118 Control part 120 Branch part 122 Transmission buffer 124 Transmission port 126 Transmission buffer 128 Transmission port 152 Link 154 Link 160 Reception side host 162 Reception port 164 Reception port 166 Control unit 168 Aggregation unit 170 Transmission buffer 172 Transmission port 210 Transmission side host 212 Management port 214 Input port 216 Command Processing unit 218 Control unit 220 Branch unit 222 Transmission buffer 224 Transmission port 230 Transfer buffer 226 Transmission buffer 228 Transmission port The

Claims (11)

Two transmission ports respectively connected to two transmission lines provided between the network communication apparatus on the reception side, one set as an active system and the other as a standby system, The two transmission ports for transmitting frames to a network device;
Two transmission buffers provided for the two transmission ports, each for buffering a frame to be transmitted;
A branch for transferring the frame to the transmission buffer of the active transmission port;
A control unit that controls system switching of the two transmission ports;
When the system is switched, the control unit
A switching request frame that can indicate a switching request is transferred to the transmission buffer of the active transmission port, and the branching unit is controlled to transfer the subsequent frames to the transmission buffer of the standby transmission port;
After that, when a switching completion frame indicating that the switching request frame has been received and system switching in itself has been completed is received from the network communication device on the receiving side, the standby transmission port is switched to the operating system. A network communication device. A transfer buffer;
In the system switching, the control unit further transfers the frame in the transmission buffer to the transfer buffer before the switch request frame is transferred to the transmission buffer of the active transmission port. Let
2. The network communication apparatus according to claim 1, wherein the transmission port switched from the standby system to the active system transmits the frame in the transfer buffer before the frame in its transmission buffer. Two receiving ports respectively connected to two transmission lines provided between the network communication device on the transmitting side, one is set as an active system and the other is set as a standby system. The two receiving ports for receiving frames from the network device;
A control unit for controlling system switching of the two receiving ports,
When the control unit receives a switching request frame that can indicate a switching request from the network device on the transmission side, the control unit switches the standby reception port to the active system, and receives the switching request frame; A network communication device, characterized in that control is performed so as to transmit a switching completion frame indicating completion of system switching to the network communication device on the transmission side. A network device on the sending side;
A network device on the receiving side;
In a network having two transmission lines provided between the transmission-side and reception-side network devices,
The network device on the transmission side is:
Two transmission ports respectively connected to the two transmission paths, one of which is set as an active system and the other as a standby system, and the two transmission ports for transmitting frames to the receiving-side network device by the active system When,
Two transmission buffers provided for the two transmission ports, each for buffering a frame to be transmitted;
A branch for transferring the frame to the transmission buffer of the active transmission port;
A transmission-side controller that controls system switching of the two transmission ports;
The transmission side control unit, when switching the system,
A switching request frame that may indicate a switching request is transferred to the transmission buffer of the active transmission port, and the branching unit is controlled to transfer subsequent frames to the transmission buffer of the standby transmission port;
After that, when the switching completion frame indicating that the switching request frame is received and the system switching in itself is completed is received from the network communication device on the receiving side, the standby transmission port is switched to the operating system. ,
The network device on the receiving side is:
The two reception ports respectively connected to the two transmission paths, one of which is set as an active system and the other as a standby system, and the two reception ports for receiving frames from the network device on the transmission side by the active system Port,
A receiving-side controller that controls system switching of the two receiving ports;
When the receiving side control unit receives a switching request frame that can indicate a switching request from the transmitting side network device, the receiving side control unit switches the standby receiving port to the active system, and transmits the switching completion frame to the transmitting side. A network characterized by performing control to transmit to a network communication device. The network device on the transmission side further includes a transfer buffer,
The transmission side control unit further transfers the frame in the transmission buffer to the transfer buffer before the switching request frame is transferred to the transmission buffer of the active transmission port at the time of system switching. Let
5. The network according to claim 4, wherein the transmission port switched from the standby system to the active system transmits the frame in the transfer buffer earlier than the frame in its own transmission buffer. Two transmission ports respectively connected to two transmission lines provided between the network communication apparatus on the reception side, one set as an active system and the other as a standby system, The two transmission ports for transmitting frames to a network device;
Two transmission buffers provided for the two transmission ports, each for buffering a frame to be transmitted;
In the network communication device on the transmission side comprising a branching unit that transfers the frame to the transmission buffer of the active transmission port,
When switching between the two transmission ports,
A switching request frame that can indicate a switching request is transferred to the transmission buffer of the active transmission port, and the branching unit is controlled to transfer the subsequent frames to the transmission buffer of the standby transmission port;
After that, when a switching completion frame indicating that the switching request frame has been received and system switching in itself has been completed is received from the network communication device on the receiving side, the standby transmission port is switched to the operating system. A system switching method characterized by that. The network device on the transmission side further includes a transfer buffer,
At the time of system switching, before the switching request frame is transferred to the transmission buffer of the transmission port of the active system, the branching unit is further configured to transfer the frame in the transmission buffer to the transfer buffer,
7. The system switching method according to claim 6, wherein the transmission port switched from the standby system to the active system is controlled to transmit the frame in the transfer buffer earlier than the frame in its own transmission buffer. . Two receiving ports respectively connected to two transmission lines provided between the network communication device on the transmitting side, one is set as an active system and the other is set as a standby system. In the receiving-side network device having the two receiving ports for receiving frames from the network device,
When a switching request frame that can indicate a switching request is received from the network device on the transmission side, the standby reception port is switched to the active system, and the switching request frame is received and the system switching in itself is completed. A system switching method comprising: performing control so as to transmit a switching completion frame indicating that the switching has been performed to the network communication device on the transmission side. Two transmission ports respectively connected to two transmission lines provided between the network communication apparatus on the reception side, one set as an active system and the other as a standby system, The two transmission ports for transmitting frames to a network device;
Two transmission buffers provided for the two transmission ports, each for buffering a frame to be transmitted;
In the network communication device on the transmission side comprising a branching unit that transfers the frame to the transmission buffer of the active transmission port,
When switching between the two transmission ports,
A switching request frame that can indicate a switching request is transferred to the transmission buffer of the active transmission port, and the branching unit is controlled to transfer the subsequent frames to the transmission buffer of the standby transmission port;
After that, when a switching completion frame indicating that the switching request frame has been received and system switching in itself has been completed is received from the network communication device on the receiving side, the standby transmission port is switched to the operating system. A program characterized by causing a computer to execute the above. The network device on the transmission side further includes a transfer buffer,
At the time of system switching, before the switching request frame is transferred to the transmission buffer of the transmission port of the active system, the branching unit is further configured to transfer the frame in the transmission buffer to the transfer buffer,
The computer further executes control so that the transmission port switched from the standby system to the active system transmits the frame in the transfer buffer earlier than the frame in the transmission buffer of the transmission port. 9. The program according to 9. Two receiving ports respectively connected to two transmission lines provided between the network communication device on the transmitting side, one is set as an active system and the other is set as a standby system. In the receiving-side network device having the two receiving ports for receiving frames from the network device,
When a switching request frame that can indicate a switching request is received from the network device on the transmission side, the standby reception port is switched to the active system, and the switching request frame is received and the system switching in itself is completed. A program for causing a computer to perform control so as to transmit a switching completion frame indicating that the switching has been performed to the network communication device on the transmission side.

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