JP3209622B2 - Communications system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system in which a plurality of computer networks such as LANs are connected by a network connection device via a path which is connected only during communication such as an ISDN line.

[0002]

BACKGROUND ART Generally, LAN (Local Area Network) or the like workstations in the transmission path in a computer network, printer, various nodes such as the display device is connected. And usually this one LA
Various communications are performed between nodes connected to the N transmission paths. Further, a plurality of LANs can be connected to each other by a dedicated line, and communication can be performed between nodes belonging to different LANs.

FIG. 12 is a schematic diagram showing a schematic configuration of a communication system composed of, for example, four LANs connected by a dedicated line. Independent transmission lines 2a, 2b, 2c, 2d are laid in the respective LANs 1a, 1b, 1c, 1d. A plurality of nodes 3a (A1, A2,..., An), 3b (B1, B2,...) Are respectively provided on the transmission lines 2a, 2b, 2c, 2d of the LANs 1a, 1b, 1c, 1d.
..), 3c (C1, C2,...), 3d (D1, D2,.
…) Is connected.

[0004] Each of the transmission paths 2a, 2b, 2c, 2d
Are routers 4a1, 4a2, 4a3.4b, 4c1, 4c2, 4d as one or a plurality of network connection devices, respectively.
Is connected. For example, three routers 4a1 to 4a3 are connected to the LAN 1a. In this case, the LAN 1a is a network provided at the head office of the company, and the other LA
N1b to 1d are networks arranged in each branch.

[0005] Then, for example, the LAN 1
a for each of the routers 4a1, 4a2, and 4a3 via dedicated lines 5ac1, 5ac2, 5ad, and 5ab, respectively.
1c, 1d. Each router 4c1, 4c2, 4d, 4b of 1b is connected. Also, the router 4c2 of the LAN 1c and the LA
A dedicated line 5cd is also connected to the router 4d of N1d.

When each of the nodes 3a to 3d transmits data to a node of another LAN to which the nodes 3a to 3d do not belong, TC
In the P / IP communication, for example, data is embedded in an Ethernet packet shown in FIG. 4 and transmitted to a router incorporated in the own LAN. Each router extracts an IP packet consisting of an IP header and data from the Ethernet packet,
The IP packet is transmitted to a dedicated line connected to the LAN specified by the IP header . The router on the receiving LAN that has received the IP packet incorporates the IP packet into an Ethernet packet and transmits it to the node specified by the IP packet.

In such a communication system, each router stores information (route information) indicating which LAN is connected to which LAN through each router for each communication line, that is, for each route. A table is provided.

Each of the routers 4a1 to 4d sends out the route information stored in its own internal table to each dedicated line to which it is connected by a broadcast method at regular intervals. Also, each route information in its own internal table is updated with the route information received from another router via the dedicated line. Each route information in the internal table of each router is grasped by each node of the LAN to which the router belongs by receiving the broadcast communication.

[0009]

However, FIG.
However, the communication system shown in (1) has the following problems to be improved.

That is, the LANs 1a to 1d are connected to each other by dedicated lines 5ac1, 5ac2, 5ad, 5ab, and 5cd, respectively. Naturally, dedicated lines 5ac1, 5ac2, 5ab,
In order to communicate between LANs where 5ab and 5cd are not installed, a router or dedicated line is required. It is necessary to adopt a method of connecting using a plurality of transmission paths. Specifically, for example, to perform communication between the node 3d of the LAN 1d of one branch and the node 3b of each LAN 1b of the other branch,
[Node 3d ~ Transmission line 2d ~ Router 4d ~ Dedicated line 5
ad ~ router 4a2 ~ transmission line 2a ~ router 4a3 ~ dedicated line 5
ab-router 4b-transmission path 2b-node 3b].

As described above, other L which is not directly related to the communication
Since the transmission path 2a of the AN 1a is used, this relay LA
There is a concern that the communication load on the transmission path 2a of N1a will increase significantly.

Further, even if two dedicated lines 5ac1 and 5ac2 are laid between the head office LAN 1a and the branch LAN 1c, for example, each node 3 of the LAN 1a
When a designates the node 3c of the LAN 1c to execute communication, it communicates with the node 3c of the communication destination LAN 1c via, for example, a preset router 4a2 and a dedicated line 5ac2 which are regarded as optimal. Therefore, the router 4c2 of the communication destination LAN 1c is connected to another LAN 1d by another dedicated line 5cd.
When the communication is being performed via the communication, the line connection by the later communication request is not successful. Therefore, the router 4c2 of the communication destination LAN 1c ends the communication with the other LAN 1d,
It is necessary to wait until it shifts to the communication standby state.

Further, when the router 4a2 of the own LAN 1a is communicating with the other LAN 1d, the line connection by the later communication request will not be successful.

As described above, even if each LAN is connected to each other by a plurality of dedicated lines and a plurality of communication paths are formed between the LANs, there is a problem that these paths cannot be effectively used.

The present invention has been made in view of such circumstances, and by adding a metric value that changes according to the use status of a corresponding route to the route information of each route stored in an internal table, When there is a route that is communicating with another network, another free route can be automatically searched and communication can be performed, each route can be used effectively, and each route that is not actually performing communication can be used. An object of the present invention is to provide a communication system that can be shut down and that can reduce the maintenance cost of the entire system.

[0016]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides connection destination information and optimality of a corresponding route for each network connection device of each computer network constituting a communication system. Table storing route information including a metric value indicating the degree of the route, and route information updating each route information in the internal table with the route information transmitted at a specified period via the corresponding route during line connection of each route An updating unit and a metric value lowering unit that lowers the metric value of the route information corresponding to the route connected to the line in the internal table during the line connection period are added.

Further, in response to a communication request to a node of another computer network during a line disconnection period of a route to each node of each computer network, an internal table of a network connection device of the computer network to which the node belongs is provided. Path information searching means for searching for path information including connection destination information specifying the communication destination computer network, and for each path specified by the searched path information, the line connection succeeds in ascending order of the metric value. Up to this point, line connection attempt means for sequentially attempting line connection, and metric value increasing means for increasing the metric value of a path in the internal table for which the line connection has not been successful for a predetermined time are added.

[0018]

According to the network connection device configured as described above, the connection destination information and the metric value indicating the degree of optimality of the route are stored in the internal table provided in the network connection device for each route. The stored route information is stored. Then, when the path shifts to the line connection state by communication, the metric value of the path information corresponding to the path in the internal table decreases. Therefore, as long as the route is in the line connection state, even if there are a plurality of routes that match the communication route condition, the node selects and sets this route, so that the route is not changed during communication. When the line connection state is released, the metric value returns to the original metric value preset for this route.

When a communication request is issued, a node first searches for route information up to the destination node. When a plurality of pieces of route information are retrieved, the node attempts to connect the line to the route having the smallest metric value. If the destination network connection device is communicating using another route, the line connection naturally fails. In this case, the node attempts a circuit connection to the route having the next lower metric value. In this way, the circuit connection is tried in order from the path with the smaller metric value to the path with the larger metric value until the circuit connection is successful.

Since each route for which the line connection has failed is communicating, the metric value for a predetermined time determined by the average communication time increases. Therefore, when starting a new communication, the node does not select and set a communication route.

As described above, when executing communication with a node of another computer network, the node can efficiently use the path when there are a plurality of paths that match the communication path condition.

[0022]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 is a schematic configuration diagram of the communication system of the embodiment. The same parts as those of the conventional communication system shown in FIG. Therefore, the detailed description of the overlapping part is omitted.

In the communication system of this embodiment, three routers 6a1, 6a2, 6a3 as network connection devices are connected to a transmission path 2a of a LAN 1a as a computer network provided at a head office of a company, for example. Also, one router 6b, 6d is connected to each transmission line 2b, 2d of each LAN 1b, 1d provided in each branch.
Is connected, and two routers 6c are connected to LAN1c of another branch.
1, 6c2 are connected.

Each of the routers 6a1, 6a2, 6a3, 6b, 6c1,
6c2 and 6d can be connected to the ISDN network 7. More specifically, the routers 6b, 6c1, 6c2, and 6d of the LANs 1b, 1c, and 1d at each branch are connected to the routers 6a1, 6a2, and 6a3 of the LAN 1a at the head office via the ISDN lines 8 of the ISDN line network 7, respectively. Is done. In addition, L of the branch
Another ISDN line 8 connects between the router 6c2 of the AN 1c and the router 6d of the LAN 1d of another branch.

The router 6a1 of the LAN 1a of the head office is connected to the routers 6b, 6c1, 6c2 of the LANs 1b, 1c, 1d of the respective branches.
6d are connected via individual ISDN lines 8, respectively. Therefore, this router 6a1 has four routes connected to each LAN. Similarly, another router 6a
Each of 2, 6a3 also has four paths. Each router 6b, 6c1, 6c2, 6d of each branch has three routes connected to each router 6a1, 6a2, 6a3 of the LAN 1a at the head office, and the router 6c2 and the router 6d also have another route connecting each other. .

FIG. 1 is a block diagram showing a schematic configuration of the router 6a1. The other routers 6a2 to 6d have substantially the same configuration.

The router 6a1 is constituted by a kind of information processing device such as a microcomputer. CPU 1 that performs various types of information processing on bus line 10
1, ROM for storing various control programs and fixed data
12, a dedicated line interface (hereinafter abbreviated as a dedicated line IF) 13 connected to the dedicated line 9,
Ethernet IN connected to transmission line 2a of AN1a
Interface 14, the four ISDs of the ISDN network 7
Four ISDN interfaces (hereinafter abbreviated as ISDN IF) 15a, 15b, 1 connected to the N line 8
5c and 15d are connected.

The dedicated line 9 connected to the dedicated line IF 13 is a line that maintains the always-connected state in FIG. 12, and the router of this embodiment is always connected to the ISDN line 8 that is not always connected. This indicates that two types of dedicated lines 9 can be connected. FIG.
In the communication system of the embodiment shown, the dedicated line I
The dedicated line 9 is not connected to F13. This dedicated line 9 also constitutes one or more paths on the control program.

Further, the bus line 10 has its own L
Data buffer 1 for temporarily storing information to be transmitted from each node 3a of AN 1a to each node of another LAN and information to be transmitted from each node of other LAN to each node of own LAN
7. Internal table 19 and emulation table 20
Are connected, a clock circuit 21 for counting elapsed time, and the like.

As shown in FIG. 2, an internal table 19 formed in the RAM 18 stores
For each path indicated by each ISDN line 8 connected to 5a to 15d and a dedicated line 9 connected to the Ethernet IF 13, an interface No. for specifying an interface to which the corresponding path is connected, and a LAN for specifying a connection destination LAN network address NTA, router address RA specifying the destination router, the metric value MA indicating the optimal degree of the corresponding path (ISDN lines 8, a dedicated line 9), the route information indicating various information of the route from reception timer T _R, etc. 19
a is stored.

In this embodiment, N pieces of route information 1
9a can be stored, but in practice, in this router 6a1, the number of connectable ISDN lines 8 is 4 and the number of dedicated lines 9 is 0, so that at least four Information 19a is stored. Of course, when the number of connected ISDN lines increases or when the dedicated line 9 is laid, the number of stored path information 19a also increases.

The metric value MA is a value indicating the degree of optimality of the corresponding route. The smaller the metric value MA, the higher the degree of optimality. The degree of optimality is a value that can be set in advance by an administrator in consideration of, for example, the communication cost when the ISDN line 8 is used, the degree of line congestion, the frequency of use of the partner router, and the like.

Further, the reception timer T _R is gradually counted up by the clock of the clock circuit 21 described above. The reception timer T _R is cleared when the corresponding path information 19a via the route described above is received (T _R =
0). The reception timer T _R is set in advance three permissible time T ₁ (= 120 seconds), T ₂ (= 180 seconds), T ₃
(= 270 seconds), a reception timeout is set.

As shown in FIG. 3, N pieces of path information 20a can be set in the emulation table 20 formed in the RAM 18. Each piece of route information 20a has the same configuration as each piece of route information 19a set in the internal table 19 shown in FIG. FIG. 4 shows an Ethernet packet 2 transmitted on a transmission path of each LAN (Ethernet).
It is a figure which shows the structure of 1a. When all the destination addresses DA of the Ethernet packet 21a are [1], the Ethernet packet 21a is treated as a broadcast communication.

Similarly, in an IP packet 21b transmitted on the ISDN line 8 or the dedicated line 9, which is composed of an IP header and data in the Ethernet packet 21a,
When all 6 bits of the host in the destination address DA of the P packet 21b are [1], it is treated as a broadcast.

Each node 3a of each LAN 1a to 1d
3d, the same table as the internal table 19 formed in each router 6a1-6d of the LAN to which it belongs is formed. Then, by the broadcast communication from each of the routers 6a1 to 6d, each route information 19a stored in the table is transmitted.
Is always updated to the latest value.

The CPU 11 of each of the routers 6a1-6d
The program is configured to execute a transmission process of transmitting each piece of route information 19a stored in the internal table 19 to another router according to the flowchart of FIG.

When the specified period T ₀ for performing the broadcast communication has elapsed, the leased line IF 13 and the ISDN IFs 15 a to 15 a
Select one interface (IF) from 5d (P
1) If the selected interface is an ISDN-type interface (P3), the selected ISDN IF
It is checked whether or not 15a to 15d are currently connected to the ISDN line 8 (P4). In the case of the line cutoff state, the process returns to P1, and another interface is selected.

When the line is connected (P4) and when the interface type is the dedicated line IF 13 which is always connected to the line (P3), one piece of route information 19a is read from the internal table 19 in P5. The interface No. of the read path information 19a is checked, and this interface No.
If this matches the selected interface, there is no need to transmit this routing information 19a, so the process returns to P5 and reads the next routing information 19a. Then, at P8, the read path information 19a is additionally set in the data area of the Ethernet packet 21 shown in FIG. Note that a broadcast communication is set for the destination address DA.

[0041] When the setting processing for the Ethernet packet 21a of the destination interface of the routing information of all the non 19a route information 19a in the internal table 19 is completed, the interface select this Ethernet packet 21a above as the path information packet 13,15a ~ 1
The transmission is made to the dedicated line 9 or the ISDN line 8 via 5d.

One interface 13, 15a-15
When the transmission processing of each piece of route information 19a for d is completed,
The transmission process of each piece of route information 19a to the next interface 13, 15a to 15d is started.

As described above, each time the prescribed period T ₀ elapses, each of the route information 19 a stored in the internal table 19 from each of the interfaces 13, 15 a to 15 d is transferred via the dedicated line 9 or each of the ISDN lines 8. The data is transmitted to the routers 6a1 to 6d of the other LAN. However, the route information 19a is not transmitted to the ISDN line 8 in the line cutoff state.

When the CPU 11 receives the path information packet shown in FIG. 4 from the leased line IF 13 or each of the ISDN IFs 15a to 15d, the CPU 11 is configured to perform a receiving process shown in the flowchart of FIG.

When the flow chart is started and a route information packet is received in P10, one piece of route information set in the data area of the packet is extracted (P11).
Next, the type of the interface that has received the route information packet is checked (P12). ISDN / IF15a-15
In the case of d, the extracted route information is written into the emulation table 20 for the moment. Specifically, to update the routing information 20a of the corresponding path that is stored in the emulation table 20 in this path information, and resets the reception timer T _R of the path information 20a after update to 0 (P1
3).

If the type of the received interface is a dedicated line I
In the case of F13, the metric value MA of the extracted route information
Add the received interface metric value ifm to R. Then, it is set as a new metric value MAR (P
14).

Next, it is checked whether the network address NTA of the extracted route information exists in each route information 19a of the internal table 19 (P15). If it does not exist, the route information received this time is completely new route information,
This route information is newly registered in the internal table 19 (P16).

If the corresponding network address NTA exists, each metric value MA of each piece of route information 19a to which the corresponding network address NTA belongs is compared with the metric value MAR of the received route information (P17). The recorded metric value MA is the received metric value MAR.
Nothing is performed for the smaller route information 19a. If there is the route information 19a having the large metric value MA, the route information 19a is rewritten to the route information having the small metric value received this time (P18).

Route information 19a of equal metric value MA
Exists, the router address R of the corresponding route information 19a
It is checked whether or not A matches the router address RA of the received route information (P20). If it matches, the received route information this time it corresponds to the corresponding path information 19a, and resets the reception timer T _R of the path information 19a to 0 (P
21).

[0050] While the metric value MA and the network address NA is consistent with P20, if there is a path information 19a to the router address RA do not match, examine the reception timer T _R of the corresponding route information 19a (P22). If the reception timer T _R has exceeded the allowable time T ₁ (= 120 seconds), it is determined that the dedicated line 9 has not been normally formed with this router, and the relevant route information 19a has been received this time. Rewrite with the route information (P23). If the reception timer T _R has not reached the allowable time T ₁ (= 120 seconds), nothing is performed.

When the updating and setting processing of one piece of path information included in the received path information packet to the internal table 19 and the emulation table 20 is completed, the updating and setting processing for the next path information is started.

As described above, the internal table 19 and the emulation table 20 are stored on the basis of each piece of route information included in the route information packet received via the dedicated line 9 or the ISDN line 8 connected to the line at the specified period T _0. Each of the route information 19a and 20a being updated is updated.

FIG. 8 is a flowchart showing a time interruption process for the emulation table 20 in the CPU 11.

When a short time ΔT such as one second elapses (S1), one piece of route information 20a in the emulation table 20 is read (S2). And at the moment I
I the SDN · IF15a~15d is in line connection, and to specify the interface No of the read route information 20a
If SDN · IF15a~15d is in line connection (S3), the process proceeds to S4, examining the reception timer T _R of the read route information 20a.

[0055] The reception timer T _R is permissible time T ₂ (= 1
If the time is less than 80 seconds, it is determined to be normal and the process returns to S2 without doing anything, and the next path information 20a is read.

[0056] reception timer T _R is permissible time T ₂ (= 180
If it is longer than (seconds) and less than or equal to the limit allowable time T ₃ (= 270 seconds), the metric value MA of the corresponding path information 20a is changed to infinity (S5). Reception timer T _R is a limit allowable time T ₃
If it exceeds (= 270 seconds), the corresponding route information 20a is deleted from the emulation table 20 (S6).

In S3, the read path information 2
ISDN IF1 specified by interface No. 0a
If 5a to 15d are not in line connection, nothing is done and S2
Then, the next route information 20a is read from the emulation table 20.

As described above, in the time interruption processing shown in FIG. 8, in each of the ISDN lines 8, the pertinent route information 20a indicates the allowable time during the line connection period even though the corresponding ISDN line 8 is in the line connection state. T ₂ (= 180 seconds)
If not updated, the route destination router is
It is determined that a call is being made with the router of the AN, and the metric value M
Let A be infinite so that the node does not select it. further,
If the update is not performed for the limit allowable time T ₃ (= 270 seconds) or more, the router or IS corresponding to the corresponding route information 19a
Check whether any abnormality has occurred in the DN line 8 or the corresponding IS
It is determined that the DN line 8 has been removed, and
a is deleted from the emulation table 20.

The CPU 11 sets each path information 2 stored in the emulation table 20 in accordance with the flowchart of FIG.
An update process is performed on each piece of route information 19a in the internal table 19 using 0a.

In S7, when the specified time T ₀ has elapsed, one piece of route information 20a stored in the emulation table 20 is read (S8). Next,
It is checked whether or not each of the ISDN IFs 15a to 15d is connected to a line (S9). If during the line connection, ISDN line 8 which is specified by the interface No in the read path information 20a checks whether or not the currently line connection (S10). If the ISDN line 8 of the read route information 20a is in line connection, the metric value MAR of the read route information 20a is replaced by the interface metric value ifmc (==
Add 0). That is, the metric value M is set so that the node unconditionally selects the path information 20a in the line connection state.
The AR is corrected to the minimum (S11). It should be noted that the interface metric value ifmc at the time of line connection must be set to a predetermined interface metric value or less.

Interface of read path information 20a
If No does not match the ISDN line 8 currently connected to the line, the metric value MAR of the route information 20a is changed to infinity (S12). That is, the metric value MA is set so that the path information 20a is not selected by the node.
Make R infinite. Currently, each ISDN / IF 15a
If No. to 15d are not connected to the line, the process proceeds to S13, where the interface metric value ifm predetermined for the interface is added to the metric value MAR of the read path information 20a.

Then, the process proceeds to S14, where the network address NTA of the read path information 20a is stored in the internal table 1
It is checked whether or not each of the pieces of path information 19a of No. 9 exists. If it does not exist, the route information 20a read this time is completely new.
Since the route information is the route information, the route information 20a is newly registered in the internal table 19 (S15).

If the corresponding network address NTA exists, each metric value MA of each path information 19a to which the corresponding network address NTA belongs is compared with the corrected metric value MAR of the read path information 20a (S16). Nothing is done for the route information 19a where the recorded metric value MA is smaller than the corrected metric value MAR. Route information 19 with a large metric value
If a exists, the path information 19a is rewritten to the path information having the smaller metric value read this time (S17).

Route information 19a of equal metric value MA
Exists, the router address R of the corresponding route information 19a
It is checked whether or not A matches the router address RA of the read path information (S18). If they match, the route information 20a read this time corresponds to the corresponding route information 19a.
The reception timer T _R of the corresponding route information 19a is reset to 0 (S19).

At S18, if there is route information 19a in which the metric value MA and the network address NA match but the router address RA does not match, the route information 1
Check reception timer T _R of 9a (S20). If the reception timer T _R has exceeded the allowable time T ₁ (= 120 seconds), it is determined that the ISDN line 8 has not been normally formed with this router, and the corresponding route information 19a has been read this time. Rewrite with the route information 20a (S21). If the reception timer T _R has not reached the allowable time T ₁ (= 120 seconds), nothing is performed.

When the updating and setting processing of one piece of path information 20a read from the emulation table 20 to each piece of path information 19a stored in the internal table 19 is completed, the updating and setting processing for the next path information 20a is started. .

As described above, each ISDN stored in the internal table 19 based on each path information 20a stored in the emulation table 20 at a constant period T _0.
The route information 19a corresponding to the line 8 is updated.

In this case, during the line connection period for the ISDN line 8, the metric value MA of the route information 19a corresponding to the ISDN line 8 being connected is set to [minimum], and the other ISDN lines are set. 8, the metric value MA of each piece of the route information 19a is set to [infinity].

On the other hand, when all ISDN lines 8 are in the line cutoff period, the metric value MA of the route information 19a corresponding to the ISDN line 8 and the leased line 9 that are currently connected to the line.
Is set to the interface metric value ifm set in advance for each route.

FIG. 10 is a flowchart showing a time interruption process for the internal table 19 in the CPU 11.

When a short time ΔT such as one second elapses (Q1), one piece of route information 19a in the internal table 19 is obtained.
Is read (Q2). Check reception timer T _R of the read path information 19a (Q3). Reception timer T _R is the allowable time T
If it is less than ₂ (= 180 seconds), the process returns to Q2 without doing anything and reads the next route information 19a.

[0072] reception timer T _R is permissible time T ₂ (= 180
If it is longer than (seconds) and equal to or shorter than the limit allowable time T ₃ (= 270 seconds), the metric value MA of the corresponding path information 19a is changed to [infinity] (Q4). If reception timer T _R is exceeding the limit allowable time T ₃ (= 270 seconds), the corresponding path information 1
9a is deleted from the internal table 19 (Q5).

As described above, in the time interruption process shown in FIG.
If 9a is not updated for more than the permissible time T ₂ (= 180 seconds), the route destination router determines that a call is in progress with a router on another LAN, and prevents the node from selecting the metric value MA [infinite]. Large]. Further, the limit allowable time T
If the update is not performed for more than ₃ (= 270 seconds), the router or the ISDN line 8 and the dedicated line 9 corresponding to the corresponding route information 19a have any abnormality or the corresponding ISD
It is determined that the N line 8 or the dedicated line 9 has been removed, and the corresponding path information 19a is deleted from the internal table 19.

Each node 3a of each LAN 1a to 1d
3 to 3d are configured to execute communication processing in accordance with a flowchart shown in FIG. 11 when a new communication request is issued to a node belonging to another LAN.

The flow chart is started, and the communication destination LAN is
Then, when a communication request specifying a node is generated, an Ethernet packet 21a for normal communication shown in FIG. 4 is created.
Then, each route information 19a in the table transmitted from each router of the LAN to which it belongs is searched, and the route information 19a having the same destination network address NTA is searched.
a is read (Q7).

Route information 19 whose communication route condition matches
When there are a plurality of a's (Q8), the route of the route information 19a having the minimum metric value MA is selected (Q9). If the selected route is the dedicated line 9 which is always in the line connection state, or the ISDN line 8 whose corresponding route is already in the line connection state (Q10), the process immediately proceeds to Q14 to execute communication. If the ISDN line 8 of the corresponding route is in the line cutoff state, Q11
Then, the Ethernet packet 21a created earlier is transmitted to the selected ISDN IFs 15a to 15d, and line connection to the corresponding ISDN line 8 is attempted.

If the line connection fails (Q12), it is determined that the route destination router is communicating with, for example, a router of another LAN, and the metric value MA of the corresponding route information 19a is changed to [infinity]. (Q13) Return to Q9. In this state, the route information 19a of the minimum metric value MA
Moves from the previously selected route information 19a to the route information 19a with the next smaller metric value MA.

As described above, until the line connection is successful, the paths for which the line connection is attempted are sequentially moved to the one having the larger metric value MA. If the line connection is successful in Q12, the process proceeds to Q14, and actual communication with the communication destination node is executed. When the necessary communication is completed, the connection state of the corresponding ISDN line 8 is cut off after a certain delay time (Q15).

If only one piece of route information 19a that matches the communication route condition is found in Q8, an attempt is made to connect a line to the corresponding route (Q16). If the line connection is successful (Q17), the process proceeds to Q14. If the route is the dedicated line 9, Q14
Proceed to.

If the line connection is not successful in Q17, since the destination router is communicating, the metric value MA of the route information 19a of the corresponding route is set to [infinity].
And Then, the Ethernet packet 2 created earlier
1a is discarded and communication is stopped (Q19).

In Q20, line connection is attempted to all the routes having the same communication route condition, but if the connection fails in all the routes, the communication is also stopped (Q19).

After the average required time T ₂ (allowable time) of one communication has elapsed since the communication was stopped (Q 21), each metric value MA previously set to [infinity] is stored in the internal table 19.
(Q22).

As described above, when a node newly starts communication with a node on another LAN, it selects an ISDN line 8 or a dedicated line 9 connected to the partner LAN.
First, the route information 19a of the network address NTA of the partner LAN is searched, and a line connection is attempted to the route of the route information 19a. If there is a plurality of pieces of route information 19a satisfying the communication route conditions, first, the ISDN line 8 or the dedicated line 9 of the route information 19a having the smallest metric value MA is selected from the plurality of pieces of route information 19, and the line connection is attempted. If it fails, the metric value MA of the corresponding route is set to [infinity], and the route information 19a having the smallest metric value MA is selected again.

Metric value MA set to [infinity]
Return to the original after the required time T ₂ has elapsed. Therefore, when the next communication request occurs, the route of the metric value MA returned to the original one is also selected.

Once the line is connected, the metric value MA of the other path information 19a of the same communication path condition is set to [infinity] by the processing in S12 of FIG. Control is performed so that the communication path does not change to another communication path during a period in which a series of communication is performed. When the communication with the corresponding node is completed, the line is cut off, and each metric value MA of each piece of route information 19a set to [infinity] returns to the original value.

Further, as shown by Q13 and Q18 in FIG. 11, when all the routes are busy, each metric value MA becomes [infinity] even if there is no route connected to the line. because, even in the required time T ₂ has the same communication request occurs, not from the beginning of the line connection attempt is executed.

[0087] Further, although a detailed description is omitted, as described above, the router 6a1 is that by changing the metric values from the line connection, come within the route information is not not span go correctly throughout the communication system Maintain reachability of communication data
Evidencing Therefore, Ru configurable der the desired delay time before transmitting the communication data from the line connection.

Further, the route information 19a corresponding to the ISDN line 8 in the internal table 19 is stored in the emulation table 20 every specified period T ₀ , regardless of whether each ISDN line 8 is connected or disconnected. Is updated with the route information 20a stored in the. As a result, each route information 19a corresponding to the ISDN line 8 in the internal table 19 is obtained.
Is always updated at the specified period T ₀ , so that it is not deleted from the internal table 19 even when the line is disconnected, and the node always accurately grasps the route information of each route to another LAN. it can. Then, when performing communication with a node of another LAN based on the accurate route information, a route selection setting can be performed.

As described above, since the line can be cut off except during communication, the use of the ISDN line 8 in place of the dedicated line 9 can greatly reduce the line installation cost,
As compared with the communication system shown in FIG. 12 in which it is necessary to maintain the line connection state at all times, the maintenance cost can be significantly reduced.

Further, since the ISDN line 8, which is a kind of public line, is used, it is possible to easily add or remove a line.

[0091]

As described above, in the communication system according to the present invention, a metric value that changes according to the use status of the corresponding route is added to the route information of each route stored in the internal table. Therefore, when there are a plurality of routes that satisfy the communication route conditions, even if a route in a communication state with another network already exists, another unused route that is not being communicated is automatically searched for communication. I can do it. As a result, each route can be used effectively,
In addition, the line other than the communication state can be cut off, and the maintenance cost of the entire system can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a network connection device incorporated in a communication system according to an embodiment of the present invention.

FIG. 2 is a view showing the storage contents of an internal table formed in the network connection device.

FIG. 3 is a view showing the storage contents of an emulation table formed in the network connection device.

FIG. 4 is a frame configuration diagram of an Ethernet packet transmitted between networks.

FIG. 5 is a diagram showing a schematic configuration of the communication system according to the embodiment.

FIG. 6 is a flowchart showing the operation of the network connection apparatus of the embodiment.

FIG. 7 is a flowchart showing the operation of the apparatus of the embodiment.

FIG. 8 is a flowchart showing the operation of the apparatus of the embodiment.

FIG. 9 is a flowchart showing the operation of the apparatus of the embodiment.

FIG. 10 is a flowchart showing the operation of the apparatus of the embodiment.

FIG. 11 is a flowchart showing the operation of the apparatus of the embodiment.

FIG. 12 is a diagram showing a general communication system.

[Explanation of symbols]

1a-1d: LAN, 2a-2d: Transmission line, 3a-3d
... Nodes, 6a1-6d ... Routers, 8 ... ISDN lines, 9
... Dedicated line, 11 ... CPU, 13 ... Dedicated line IF, 14 ...
Ethernet IF, 15a to 15d ... ISDN IF
19: internal table, 19a, 20a: route information, 20
... Emulation table.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Yoshikazu Kobayashi Inventor 5-7-1 Shiba, Minato-ku, Tokyo Within NEC Corporation (56) References JP-A-6-334687 (JP, A) JP-A Heihei 7-74772 (JP, A) JP-A-7-74773 (JP, A) JP-A-5-56080 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04L 12/46 H04L 12/56 H04L 12/66

Claims (1)

(57) [Claims] A plurality of paths (8) which are connected only when communicating between a plurality of computer networks (1a-1d) each comprising a plurality of nodes (3a-3d) connected via transmission paths. Via multiple network connection devices (6a1-6
In the communication system connected in d), each of the network connection devices, for each of the routes, an internal table (19) storing connection destination information and route information including a metric value indicating the degree of optimality of the route, Route information updating means (S17, S19, S21) for updating each piece of route information of the internal table with route information transmitted at a specified period via the corresponding route during the line connection of each route; and Metric value lowering means (S11) for lowering the metric value of the route information corresponding to the route being connected to the line during the line connection period, and wherein each of the nodes In response to a communication request to a node, a communication destination computer network in an internal table of a network connection device of a computer network to which the node belongs. A route information search means (Q7) for searching for route information including the connection destination information to be specified, and sequentially for each of the routes specified by each of the searched route information until the line connection succeeds in the order of the smallest metric value. Line connection attempt means (Q9 to Q12) for attempting line connection, and metric value increasing means (Q13, Q18) for increasing the metric value of the path in the internal table for which the line connection was not successful for a predetermined time. A communication system characterized by the above-mentioned.