JP2003348128A - Call server and method for switching port thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a call server in a simple configuration having a small packet loss by quickly switching a standby port into an operating port on the occurrence of abnormality in an existing operating port. <P>SOLUTION: The call server is provided with a port switching means 2 for switching the operating port (port A) and the standby port (port B) by bus master control of a PCI (Peripheral Components Interconnect) bus, transmits a packet in compliance with the ARP (Address Resolution Protocol) protocol to a router 3 (opposite apparatus), allows the router 3 (opposite apparatus) to revise a routing table (MAC address stable), and executes port switching from a port C to a port D of the router 3. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a call server having a dual port structure of an operation port and a standby port for communicating with an opposing device via Ethernet, and more particularly to a PC.
The present invention relates to a call server that uses an I (Peripheral Components Interconnect) bus master to switch a standby port to an operation port and to switch a port of a partner device by using an ARP (Address Resolution Protocol) protocol packet to continue packet communication.

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Patent No. 2999089, when performing communication between host devices, two communication control devices are provided between a communication line and a host device. By using one of the communication control devices as a working system and the other communication control device as a standby system, the communication control device of the working system can be used at normal times to enable transmission and reception of a host device. It is known that when an abnormality occurs in the communication control device of the system, the communication control device of the standby system is switched to the active system and communication of the host device is continued.

The communication control device disclosed in Japanese Patent No. 2999089 has a configuration in which one unique address common to the active system and the standby system is set, and when an abnormality occurs, the standby system becomes the active system. Even after switching, it is used for communication as a unique address of the host device.

[0004] With this configuration, even if the active communication control device fails and the standby communication control device becomes the active system, the communication is continued at the unique address of the higher-level device. The device can continue communication using the unique address of the higher-level device before switching without being aware of the failure of the active communication control device and the switching of the standby communication control device to the active system.

[0005]

SUMMARY OF THE INVENTION Patent No. 2999089
The communication control means of the duplex configuration of the active system and the standby system disclosed in Japanese Patent Application Laid-Open Publication No. H10-157, is constituted by two pieces of hardware, and when a failure occurs and the standby system becomes the active system, a higher-level device is used. In the case where a repaired communication control device is used in a system composed of a plurality of higher-level devices and a communication control device, a unique address is externally set (written) from the outside to the active device. In order to prevent duplication, there is a problem that it is necessary to take a mechanical process or devise.

Further, the communication control device disclosed in Japanese Patent No. 2999089 executes initialization processing for the switched communication control device when a failure occurs in the active system and the system is switched from the standby system to the active system. A unique address must be set from the outside, and there is a problem that time is spent for the initialization process and communication loss of the spent time is caused.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to quickly switch from a standby port to an operation port when an operation port failure (abnormality) occurs, and to achieve a simple structure of packet loss. Is to provide a call server with a small number.

[0008]

In order to solve the above problems, a call server according to the present invention has an Ethernet operation port and a standby port, and when a failure occurs in the operation port, sets the standby port to the operation port. It is a call server that switches and continues communication, and is a PCI (Peripher
al Components Interconnect) By switching the bus master and the active port and the standby port,
Port switching means for transmitting a packet of an ARP (Address Resolution Protocol) protocol to the opposite device, and changing the routing table (MAC address table) of the opposite device to execute port switching is provided.

[0009] The call server according to the present invention is a PCI server.
(Peripheral Components Interconnect) By switching the operation port and standby port under the bus master control of the bus, the ARP (Address Resolution Protocol) protocol packet is transmitted to the opposite device, and the routing table (MAC address table) of the opposite device is changed. Since port switching means for executing port switching is provided, a standby port with a link established is set as an operation port, and a unique address (for example, a MAC address) is updated only for a partner device such as a hub, a router, or a communication device. It is possible to transmit and receive packets only with a simple configuration. With a simple configuration, switching from the standby port to the operation port is quick, and the packet loss of communication can be greatly improved.

Further, the port switching means according to the present invention comprises:
Communication processing means for performing bus master assignment control; storage means for storing a unique address;
ponents interconnect) bus master control means serving as a bus master on the bus, packet transmitting means for transmitting packets, packet receiving means for receiving packets, an operation port having a connector connected to Ethernet, and a standby port. .

[0011] The port switching means according to the present invention includes a communication processing means for performing bus master control, a storage means for storing a unique address, and a PCI (Peripheral Components Integrated).
rconnect) a bus master control unit serving as a bus master on the bus, a packet transmitting unit for transmitting a packet, a packet receiving unit for receiving a packet, an operation port having a connector for connecting to the Ethernet, and a standby port; If (abnormal) occurs, cancel the bus master control means of the operation port,
The standby port is switched from the standby port to the operation port by operating the bus master control means of the standby port, and the ARP (Addr
ess Resolution Protocol) packet is transmitted to the other device, and the routing table (MAC
By changing the address table), port switching of the partner device can also be executed, and by switching ports quickly, communication with less packet loss can be realized between the switched ports.

Further, the standby port according to the present invention is characterized in that a dedicated port, a plurality of ports, or a common port is provided for each of the plurality of operation ports.

The standby port according to the present invention has a dedicated port, a plurality of ports, or a common port for each of the plurality of operation ports, so that any failure of the operation port can be backed up by the standby port. Can be improved in reliability.

Further, the call server port switching method according to the present invention has an Ethernet operation port and a standby port, and switches the standby port to the operation port to continue communication when a failure occurs in the operation port. In the switching method, a step (S1) of detecting an abnormality of an operation port and a standby port are connected to a PCI (Peripheral Communicator).
(S2), a step of switching a standby port to an operation port (S3), and an ARP (Address Resolution P).
(S4) transmitting a packet of the (rotocol) protocol to the other device, and a routing table (M
Step (S5) of changing (AC address table)
And a step (S6) of switching the port of the opposing device to continue the packet communication.

[0015] A port switching method for a call server according to the present invention has an Ethernet operation port and a standby port, and switches a standby port to an operation port to continue communication when a failure occurs in the operation port. In the step (S1) of detecting an abnormality of the operation port, the standby port is set to a PCI (Peripheral Component).
(S2), a step of switching a standby port to an operation port (S3), and an ARP (Address Resolution Protocol).
ol) A step of transmitting a packet of the protocol to the opposite device (S4), a step of changing the routing table (MAC address table) of the opposite device (S5), and a step of switching the port of the opposite device to continue the packet communication. (S6), the standby port is set as the bus master and switched to the operation port, and the ARP (Address Reso
The port of the other device can be changed with a packet of the lution protocol), the switching from the standby port to the operation port is quick, and the packet loss of communication can be greatly improved.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a connection system diagram of a communication system to which a call server according to the present invention is applied.
In FIG. 1, the communication system includes a call server 1, a router 3 constituting an opposing device of the call server 1, and a communication device 4, and connects the call server 1 and the router 3 by Ethernet I1 and I2. The system is constructed by connecting the router 3 and the communication device 4 via the Ethernet I3.

The call server 1 normally has a port A
Is set as the operation port, port B is set as the standby port, and when the operation port (port A) fails, the port switching means 2 that sets port A as the standby port and switches port B (standby port) to the operation port is used. Prepare.

The port switching means 2 is a PCI (Peripheral
Switching between the operation port (port A) and the standby port (port B) by the bus master control of the Components Interconnect) bus, and the ARP (Address Resolution Pro)
Tocol) protocol packet is transmitted to the router 3 (opposite device), the routing table (MAC address table) of the router 3 (opposite device) is changed, and port switching from the port C to the port D of the router 3 is executed.

The router 3 has ports C and D for communicating packets with the call server 1, a port E for communicating packets with the communication device 4, and a port from port A of the call server 1 under the control of the port switching means 2. It has a switching function for switching between port C and port D when switched to B.

The communication device 4 has a port F for connecting to the Ethernet, connects to the port E of the router 3 via the Ethernet I3, and executes packet communication with the call server 1 via the router 3.

Port A of call server 1 (operation port)
And the port C of the router 3 are connected via the Ethernet I1, and the packet communication between the call server 1 and the router 3 is performed from the call server 1 via the route of port A (operation port) → Ethernet I1 → port C. The packet transmission to the router 3 and the packet transmission from the router 3 to the call server 1 are executed on the route of the port C → the Ethernet I1 → the port A.

The port B (standby port) of the call server 1 and the port D of the router 3 are connected via the Ethernet I2. When the port A (operation port) of the call server 1 is normal, the port B (standby port) is connected. Port) and port D
Is not executed, but a link is established.

When a failure occurs in port A (operating port) during packet communication using port A (operating port), port switching means 2 of call server 1 sets port A from the operating port to the standby port. With port B
From the standby port to the operation port.

Subsequently, the port switching means 2 transmits an ARP (Address Resolution Protocol) protocol packet from the port B to the router 3 and changes the unique address (MAC address) set in the routing table of the router 3. As a result, the port C is changed to the port D, and the packet communication between the call server 1 and the router 3 is performed from the port B (operation port) → the Ethernet I2 →
Execute on the path of port D.

Even if the port B is set as the standby port, since the link between the port B (standby port) and the port D is established, the port B is switched from the standby port to the operation port and the packet is switched. When communication is restarted, processing such as a power-up initialization sequence accompanying port switching becomes unnecessary, so that packet communication can be continued and packet loss can be suppressed.

Operation port of call server 1 (port A)
When a failure occurs in the port, the operation port (port A) is stopped, and the port B is switched from the standby port to the operation port.
By transmitting a packet of the RP (Address Resolution Protocol) protocol to the router 3 and changing the unique address (MAC address) of the routing table in the router 3 to switch from the port C to the port D, the packet transmission in the router 3 The route port C → port E can be set to port D → port E.

Since the communication device 4 is connected from the port F to the port E of the router 3 via the Ethernet I3, a failure occurs in the operation port (port A) of the call server 1, and the standby port (port B) is changed. Even when switching to the operation port and switching from port C to port D of the router 3, no change in connection or the like is required for packet communication.

Therefore, when the operation port of the call server 1 is configured to be duplicated, it is possible to cope with a failure of the operation port only by the internal processing of the call server 1 without preparing special processing in the counterpart device such as the router 3. can do.

In this embodiment, the call server 1
Although the router 3 is used as the opposite device, a general-purpose hub, switch or communication device 4 having a plurality of ports, a routing table and a switching function can be applied as the opposite device. Also, the call server may be referred to as a gatekeeper.

As described above, the call server 1 according to the present invention has a PCI (Peripheral Components Interconnect).
Operation port (Port A) by bus master control of the bus
And standby port (port B), and AR
Port switching means 2 for transmitting a packet of the P (Address Resolution Protocol) protocol to the opposite device (router 3), changing the routing table (MAC address table) of the opposite device (router 3), and executing port switching. Therefore, the standby port (port B) in which the link is established is set as the operation port, and only the opposite device such as a hub, a router, or a communication device has a unique address (for example, M
It is possible to transmit and receive packets only by updating the AC address, and the switching from the standby port to the operation port is quick with a simple configuration, and the packet loss of communication can be greatly improved.

FIG. 2 is a block diagram of a main part of an embodiment of the port switching means according to the present invention. In FIG.
The port switching means 2 includes a communication processing means 5, a storage means 6, a P
It has a CI bus 7, port A and port B.

The communication processing means 5 is constituted by a CPU (Central Processing Unit) and controls the storage means 6 and manages the ports A and B. The communication processing means 5 is a PC
It performs bus master assignment control of an I (Peripheral Components Interconnect) bus. By executing the bus master assignment control by the communication processing means 5, it is possible to control so that the port A or the port B does not become the bus master, and set the port A as the operation port and the port B as the standby port. Further, the communication processing unit 5 sets the port A as the standby port and the port B as the operation port by executing the bus master assignment control.

The storage means 6 is composed of a memory such as a ROM or a RAM, and has a MAC (Media Access Control) of the call server 1.
trol) address, an IP (Internet Protocol) address, and a fixed address of the router 3 which is the opposite device.

PCI (Peripheral Components Intercon)
nect) The bus 7 is formed by a bus for sharing addresses and data and a bus for control signals.
Alternatively, it transmits various addresses, data, and control signals exchanged between the communication processing means 5 and the port B.

Ports A and B are connected to PCs, respectively.
I bus interface, bus master control means 8a, 8
b, packet transmitting means 9a, 9b for transmitting a packet,
Receiving means 10a and 10b for receiving packets, connectors 11a and 11b connected to Ethernet I1 and I2, and link monitoring means 12a and 12b for monitoring link status.
Is provided.

When controlled by the bus master from the communication processing means 5 via the PCI bus 7, the bus master control means 8a and 8b respectively transmit packets supplied from the communication processing means 5 to the packet transmission means 9a and 9b, the connectors 11a and 1
1b to the Ethernet I1 and I2.

The bus master control means 8a, 8b
Connectors 11a, 11b from Ethernet I1, I2,
The packet supplied via the packet receiving means 10a and 10b is received, and the communication processing means 5 is received via the PCI bus 7.
To supply.

Further, the bus master control means 8a, 8b
Detects an abnormality (failure) in the port A and the port B, and notifies the communication processing unit 5 of the abnormality in the port via the PCI bus 7.

The link monitoring means 12a, 12b
Router 3 connected to Ethernet I1, I2 respectively
Establish a link with ports C and D.

When the bus master control means 8a or 8b is not set as a bus master under the control of the communication processing means 5, the Ethernet I1, I2
2 and packets received from Ethernets I1 and I2 are blocked.

Therefore, by setting the bus master control means 8a as a bus master and not setting the bus master control means 8b as a bus master, the port A can be used as an operation port and the port B can be used as a standby port.

Further, the bus master control means 8a
When the communication processing means 5 detects the abnormality (failure) of the bus master and notifies the communication processing means 5, the communication processing means 5 cancels the bus master of the bus master control means 8a and sets the bus master control means 8b to the bus master, so that the port A is on standby from the operation port. The port and the port B can be switched from the standby port to the operation port.

Next, the port A is set as the operating port. During the packet communication from the port A to the router 3 shown in FIG. 1 via the Ethernet I1, an error occurs in the port A, and the port B is set to the standby port. The operation of switching from the to the operation port to continue the packet communication with the router 3 will be described.

When a failure occurs in port A and communication processing means 5
Is sent from the communication processing means 5 to the bus master control means 8a via the PCI bus 7 to switch the port A from the operation port to the standby port.

Subsequently, the communication processing means 5 sends the PCI bus 7
A bus master setting command is supplied to the bus master control means 8b through the port B, and the port B is switched from the standby port to the operation port.

Further, the communication processing means 5 reads the IP address of the router 3 and the MAC address of the call server 1 from the storage means 6, and reads the ARP (Address Resolution Protocol).
col) protocol, and the packet is transmitted to the router 3 via the PCI bus 7 → port B (bus master control means 8b → packet transmitting means 9b → connector 11b) → Ethernet I2 → port D of the router 3.

ARP (Address Resolution Protocol)
The protocol is TCP / IP (Transmission Control
Protocol / Internet Protocol), and the call server 1 uses the MAC (Media Access
Control) Used to know the address. In Ethernet, a TCP / IP protocol is generally used, and a MAC address and an IP address are used in the TCP / IP protocol.

A packet including the IP address of the router 3 and the MAC address of the call server 1 is transmitted from the port B via the Ethernet I2. Ethernet I2 has
Other routers, hubs and the like are connected, and packets from the boat B are supplied.

After the port D of the router 3 responds to the IP address of the packet and receives the packet, the call server 1
Then, a packet obtained by adding the MAC address (unique address) of the router 3 to the IP packet is transmitted to the call server 1 via the Ethernet I2.

The call server 1 can know the MAC address (unique address) of the router 3 from the packet transmitted from the router 3, and sends a packet including a command to change the MAC address (unique address) of the router 3 to the router. Send to 3.

Upon receiving the MAC address (unique address) change instruction packet from the call server 1, the router 3 changes the unique address in the routing table shown in FIG. 4 according to the change instruction.

In the routing table of FIG. 4, an address and a port corresponding to the address are described. For example, the port C is changed to the port D corresponding to the unique address 0. Also, the port E is set to correspond to the unique address 5.

Therefore, by transmitting a packet including a change instruction of the unique address 0 from the call server 1 to the router 3, the port C of the router 3 can be switched to the port D, and the port B of the call server 1 and the router 3 can be switched. Packet communication can be executed between the ports D.

As described above, the port switching means 2 according to the present invention comprises a communication processing means 5 for performing bus master control, a storage means 6 for storing a unique address, and a PCI (Peripheral).
al Components Interconnect) Operation having bus master control means 8a and 8b serving as a bus master on the bus, packet transmitting means 9a and 9b for receiving packets, packet receiving means 10a and 10b for receiving packets, and connectors 11a and 11b for connecting to Ethernet. Since the port A and the standby port B are provided, if an abnormality occurs in the operation port A, the bus master control means 8 of the operation port A
a, the standby port B is switched to the active port by operating the bus master control means 8b of the standby port B, and the ARP (Address Resolution Protocol)
The protocol packet is transmitted to the other device (router 3),
By changing the routing table (MAC address table) of the opposing device (router 3), port switching of the opposing device can also be executed, and by switching ports quickly, switching between the switched ports (port B, port D) is possible. Communication with little packet loss can be realized.

FIG. 3 is an embodiment layout of the ports of the call server according to the present invention. (A) Operation port 2 in the figure
And two dedicated standby ports, (b) a diagram of two operation ports, two standby ports corresponding to the respective operation ports, and (c) a diagram of two operation ports. An arrangement diagram of two standby ports common to the ports, and FIG. 10D shows an arrangement diagram of two operation ports and one common standby port.

In FIG. 5A, a dedicated standby port Z corresponding to the operation port X is disposed at the operation ports X and Y, and a dedicated standby port W corresponding to the operation port Y is disposed. (B) In the figure, the operation port X and the operation port Y
And standby ports Z1 and Z2 corresponding to the operation port X, and standby ports W1 and W2 corresponding to the operation port Y.

In FIG. 5C, common standby ports K1 and K2 corresponding to the operation port X and the operation port Y are arranged in the operation port X and the operation port Y. (D) In the figure, a common standby port K is arranged for the operation port X and the operation port Y.

In this embodiment, the arrangement of the operation ports and the standby ports is shown in FIGS. 7A to 7D. However, the number of the operation ports may be three or more. May be set.

As described above, the standby ports Z, W, and K according to the present invention are provided with dedicated, multiple, or common ports for each of the plurality of operation ports X, Y. On the other hand, backup can be performed at the standby port, and communication reliability can be improved.

Next, a method of switching ports of the call server will be described. FIG. 5 is an operational flow chart of one embodiment of the call server port switching method according to the present invention.
The operation flow will be described with reference to FIGS.

In step S1, an abnormality in the operation port is detected during packet communication. The operation in step S1 is as follows.
This is executed by the link monitoring unit 12a of the operation port A. Subsequently, in step S2, the standby port is set to a PCI (Peripher
al Components Interconnect) Bus mastering is possible. The operation of step S2 is executed by the communication processing means 5 for the bus master control means 8b of the standby port B.

In step S3, the standby port is switched to the operation port. The operation of step S3 is executed by the communication processing unit 5. Next, in step S4, the ARP
(Address Resolution Protocol) protocol packet is transmitted to the other device. The operation in step S4 is as follows.
The communication processing means 5 and the bus master control means 8b
1b.

In step S5, the routing table (MAC address table) of the opposite device is changed. The operation of step S5 is executed by the communication processing means 5. In step S6, the port of the opposite device is switched and packet communication is continued. The operation in step S6 is executed by the opposite device (router 3) and the port switching unit 2.

As described above, the call server port switching method according to the present invention has an Ethernet operation port and a standby port, and when a failure occurs in the operation port, switches the standby port to the operation port to continue communication. A port switching method for detecting an abnormality in an operation port, and setting a standby port to a PCI (PeripheralCo
Step S2 of enabling bus mastering of an mponents interconnect (Mponents Interconnect) bus, step S3 of switching a standby port to an operation port, and ARP (Address Resolution Protocol)
l) Step S4 of transmitting a protocol packet to the opposite device, Step S5 of changing the routing table (MAC address table) of the opposite device, and Step S6 of switching the port of the opposite device to continue packet communication. Therefore, the standby port is set to the bus master and switched to the operation port, and the ARP (Address Resolution Protocol)
The port of the other device can be changed by the packet of the col) protocol, the switching from the standby port to the operation port is quick, and the packet loss of communication can be greatly improved.

[0065]

As described above, the call server according to the present invention is provided with a PCI (Peripheral Components Interc).
Onnect) By switching the operation port and the standby port by the bus master control of the bus, the ARP (Address Reso
lution Protocol) is equipped with port switching means for transmitting packets of the protocol to the other device and changing the routing table (MAC address table) of the other device to execute port switching. It is possible to send and receive packets only by setting the port and updating the unique address (for example, MAC address) only for the other device such as a hub, router or communication device.
With a simple configuration, switching from a standby port to an operation port is quick, and communication packet loss can be significantly improved.

Further, the port switching means according to the present invention comprises:
Communication processing means for performing bus master control, storage means for storing a unique address, and PCI (Peripheral Component
s Interconnect) bus master control means serving as a bus master on the bus, packet transmission means for transmitting packets, packet reception means for receiving packets, an operation port having a connector for connecting to the Ethernet, and a standby port. If something goes wrong,
The standby port is switched from the standby port to the active port by canceling the bus master control unit of the operation port and operating the bus master control unit of the standby port.
Resolution Protocol) protocol packets are transmitted to the other device, the routing table (MAC address table) of the other device is changed, and the port switching of the other device can be executed. Communication with little packet loss can be realized between them.

Further, the standby port according to the present invention has a dedicated port, a plurality of ports, or a common port for each of the plurality of operation ports, so that the standby port can back up any failure of the operation port. Thus, the reliability of communication can be improved.

A call server port switching method according to the present invention has an Ethernet operation port and a standby port, and switches a standby port to an operation port to continue communication when a failure occurs in the operation port. The switching method includes a step of detecting an abnormality of an operation port (S1), a step of enabling a standby port to be a bus master (S2), a step of switching a standby port to an operation port (S3), and an ARP (Address Resolution P).
(S4) transmitting a packet of the (rotocol) protocol to the other device, and a routing table (M
Step (S5) of changing (AC address table)
And the step (S6) of switching the port of the other device to continue the packet communication, so that the standby port is set as the bus master and switched to the operation port, and the ARP (Addres
s Resolution Protocol) packets can be used to change the port of the other device, switching from the standby port to the active port is quick, and communication packet loss can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a connection system diagram of a communication system according to an embodiment to which a call server according to the present invention is applied;

FIG. 2 is a block diagram of a main part of an embodiment of a port switching means according to the present invention;

FIG. 3 is a layout view of a call server port according to an embodiment of the present invention;

FIG. 4 is an image configuration diagram of a routing table of a partner device;

FIG. 5 is an operation flowchart of an embodiment of a call server port switching method according to the present invention;

[Explanation of symbols]

1 Call server 2 Port switching means 3 router 4 Communication equipment 5 Communication processing means 6 Storage means 7 PCI bus 8a, 8b bus master control means 9a, 9b Packet transmission means 10a, 10b packet receiving means 11a, 11b connector 12a, 12b link monitoring means

Claims (4)

[Claims] 1. A call server having an Ethernet (registered trademark) operation port and a standby port, wherein when a failure occurs in the operation port, the call server switches the standby port to an operation port and continues communication, and a PCI server. The operation port and the standby port are switched by the bus master control of the (Peripheral Components Interconnect) bus, and the ARP (Address Resolution P
A call server comprising: a port switching unit that transmits a packet of a (rotocol) protocol to a partner device and changes a routing table (MAC address table) of the partner device to execute port switching. 2. The port switching means includes communication processing means for performing bus master assignment control, storage means for storing a unique address, and PCI (Peripheral Components In).
terconnect) a bus master control unit serving as a bus master on the bus, a packet transmitting unit for transmitting a packet, a packet receiving unit for receiving a packet, an operation port having a connector connected to the Ethernet, and the standby port. The call server according to claim 1, wherein 3. The call server according to claim 2, wherein the standby port includes a dedicated port, a plurality of ports, or a common port for each of the plurality of operation ports. 4. A port switching method for a call server having an Ethernet operation port and a standby port, wherein when a failure occurs in the operation port, the standby port is switched to an operation port to continue communication. Step (S1) of detecting a port abnormality, and setting a standby port to a PCI (Peripheral Components Intercon
nect) Step of enabling bus mastering of bus (S2)
Switching the standby port to the operation port (S3)
Transmitting a packet of the ARP (Address Resolution Protocol) protocol to the other device (S4), changing the routing table (MAC address table) of the other device (S5), and switching the port of the other device. A step (S6) of continuing the packet communication.