JPH10276208A - Communication system and its path selection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow each communication station to quickly select an optimum path in response to a state change of a network by reducing a control traffic for a type of service(TOS) routing. SOLUTION: Each of communication stations 101 interconnected in a data communication network ranks communication quality detected depending on the state of its own communication station 101 changing timewise and on the state of link 102 with an adjacent communication station 101, informs link state notice information to each communication station 101 for every change in the ranking of the communication quality of its own communication station 101 to allow each communication station 101 to change contents of its path selection table. Furthermore, each communication station 101 limits a notice range of link state notice information attended with a change in the ranking depending on a degree of the ranking change and limits the notice range when the rank change is small so as to suppress useless control packets from being increased.

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 communication network in which a plurality of communication stations are interconnected performs communication by selecting an optimum communication path according to service quality such as delay time, throughput, and error rate. The present invention relates to a system and a route selection method thereof.

[0002]

2. Description of the Related Art With the development of the information-oriented society, communication networks have been developed by companies, and so-called LANs have become widespread. In addition, the demand for performing communication between geographically dispersed LANs has increased, and accordingly, as the LAN has been interconnected via an interconnecting device such as a router or a gateway, and the configuration has become widespread, the scale of the network has become larger. Is progressing.

Further, in recent years, with the use of multimedia communication data, a user or an application may specify that communication quality such as delay time, throughput, error rate, and billing should be optimized.
Various methods for providing a service corresponding to the designation have been studied.

As one of them, TOS (Type of Type)
A method of selecting an optimal communication path according to the above-described service quality (hereinafter abbreviated as TOS) called service (Service) routing is known. Was accompanied.

Here, for the sake of simplicity, the problems will be sequentially arranged by taking an example of a network configuration in which communication stations 101 having a route selection function as shown in FIG. 1 are interconnected. To The communication station 101 in this network is an existing router or ATM.
(Asynchronous Transfer Mode) Refers to a server having a route selection function for providing a connectionless service in a network. Each communication station 101 is assigned an address, and an identifier is also defined for a link 102 between adjacent communication stations 101. In particular, the link 102 between adjacent communication stations will be referred to as an adjacent link. The link 102 may be a physical link or a logical link.

[0006] The route selection method in each communication station 101 is as follows.
When data (NP packet) as shown in FIG. 5 is transmitted to an arbitrary destination communication station, a route selection table 400 as shown in FIG. In this case, a method of deciding which link of the adjacent links 403 should transmit a packet is applied.

As a first problem in performing the TOS routing, there is a problem of an increase in traffic due to a control packet for updating the optimum route information. Delay time,
Communication quality such as throughput and error rate frequently changes with time due to traffic conditions in the network, as compared to changes such as addition and deletion of terminals related to the network configuration and line disconnection. Therefore, each communication station 101 detects information related to communication quality at regular intervals, and recognizes the change in the other communication station 101.
, The route selection table 400 of the other communication station 101 needs to be updated. Therefore, every time the status of each communication station 101 or each link 102 changes, a packet for notifying the information change fluctuates in the network.

For example, in FIG. 1, communication station A (101
-A) transmits data to the communication station H (101-H) such that the delay time is minimized. In this case, at some point, the optimal communication path is the communication station A (101-A)
To communication station C (101-C), communication station E (101-E)
It is assumed that the route is to the communication station H (101-H) via. However, after that, the load status of the network changes and the communication station C (101-C) and the communication station E (101-C).
If the delay time of the link CE (102-CE) between E) increases, the other paths may become optimal. Therefore, in order to change the optimum route in response to the change in the network situation, that is, to change the route selection table 400, the communication station E (10
1-E) notifies the other communication station 101 of the status change. Then, each communication station 101 that has received the change information changes the route selection table 400 based on the information and changes the optimal communication route. Thereby, for example, the communication station C (101-
C), the optimal route via the communication station E (101-E) may change to via the communication station B (101-B) and the communication station E (101-E).

When the route is selected according to the dynamically changing communication quality as described above, each communication station 101 exchanges control packets for notifying change information at each communication quality detection cycle.
Therefore, the traffic load due to the control packet in the network increases.

[0010] The second and third problems in performing the TOS routing are as follows.
01, which is a procedure for correcting the routing information between R.01, ie, RIP (Routing Info).
rmation Protocol), a protocol based on a distance-vector algorithm, and OSPF (Operations
This is a problem that arises depending on which protocol is selected by a link-state type algorithm, such as hortest path first.

First, the distance-vector type algorithm will be described. According to a typical protocol based on this algorithm, each communication station 101 has an adjacent link information table 50 shown in FIG. 7 in addition to the route selection table 400 shown in FIG.
0 and all communication stations EE (end-end) shown in FIG.
It holds a cost information table 600.

Of these, the adjacent link information table 500
Is a table for managing the communication quality of the adjacent link, and the address 501 of the adjacent communication station, the TOS 502, and the cost 503 are associated with each other. Here, the cost is a value obtained by quantifying communication quality such as a delay time and an error rate. Also, all communication stations EE cost information table 600
Is a table for managing end-to-end costs from the own communication station to all destination communication stations, and addresses 601 of all the destination communication stations, TOS 602, and cost 604 are associated with each other.

Each communication station 1 related to the present algorithm
01 is a control packet for exchanging path information, the adjacent link state notification packet 700 shown in FIG.
There is an EE path information notification packet 800 shown in FIG. The adjacent link state notification packet 700 is a packet for notifying the cost of the adjacent link between the adjacent communication stations at a constant period. Each communication station 101 detects the cost of the adjacent link and, when there is a change in the cost, notifies the change information. In order to confirm the continuity of the adjacent link even when there is no change, this packet is used. Send.
The EE route information notification packet 800 is a packet for notifying the adjacent communication station 101 of the change information when the optimum route is changed (change of the route selection table 400) and the cost of the optimum route is changed. The changed destination communication station 803, TOS 804, and cost 806 are associated with each other.

The case where the change of the route selection table 400 and the change of the cost of the optimum route are performed is as follows.
No. 01 adjacent link status notification packet 700
Is received, the cost to the destination communication station notified from the current all communication stations EE cost information table 600 is recalculated, and the adjacent link for transmission with the minimum cost changes. When the link has not changed but the cost has changed. E transmitted from the adjacent communication station 101 due to the above change
-When the optimum route has changed after receiving the E route information notification packet 800:-The cost of the optimum route has changed.

Using the tables 500 and 600 and the control packets 700 and 800, the communication station 101 in the network
Is optimized, and the route selection table 400 is changed. Hereinafter, in this algorithm, a certain link 10
The flow of processing when the route selection table 400 of each communication station 101 is updated when the cost of No. 2 changes will be described.

Each communication station 101 exchanges an adjacent link state notification packet 700 between adjacent communication stations for confirming the continuity of the link 102 and monitoring the cost of the adjacent link.
Communication station 1 that has received adjacent link state notification packet 700
In step 01, the entry in the all-stations EE cost information table 600 transmitted from the corresponding adjacent link 102 is updated from the notified change information. A variety of cost update algorithms are conceivable. For example, a delay time may be a sum of delay times of the links 102, and an error rate may be a product of the error rates of the links 102. When the optimum route is changed by updating the EE cost information table 600 for all communication stations (when the adjacent link to be transmitted to a certain destination communication station and the TOS is changed), the route selection table 400 is updated, and The communication station is notified of the change information by the EE route information notification packet 800. If the optimal route does not change but the cost of the optimal route changes, the route selection table 400 is not changed, but the E-
The notification is performed by the E route information notification packet 800. Otherwise, no notification is required.

The adjacent communication station 101 notified by the EE path information notification packet 800 transmits the received cost change information of the destination communication station and the EE path information notification packet 800 in the adjacent link information table 500. The cost from the own communication station 101 to the destination communication station 101 is calculated from the information of the entry corresponding to the adjacent communication station that is the transmission source, and the destination communication station 1 in the total communication station EE cost information table 600 is calculated.
The cost of the entry corresponding to 01 is updated by the algorithm described above.

All communication stations EE cost information table 600
In the case where the optimum route changes or the cost of the optimum route changes due to the update of the
The same process as when 00 is received is performed. In these procedures, every time the EE path information notification packet 800 is notified, the cost is recalculated.
The communication station 101 repeats this in the form of transmitting an -E path information notification packet 800, and a change in the state of the link 102 is notified to the network. Then, the communication station 101 in which the change of the optimum route and the change of the cost of the optimum route do not occur.
To optimize the routing of the entire network.

As described above, in the distance-vector type routing protocol, each communication station 101 calculates the end-to-end cost from the own communication station 101 to the destination communication station 101 from the notified change information. Then, since the information is sent to the adjacent communication station 101, the propagation speed of the information on the network state change (change in cost) is low. Therefore, even if the cost of a certain link 102 changes, a second problem occurs that it takes time for the information to propagate to all the communication stations 101 concerned.

Next, the link-state type algorithm will be described. In a typical protocol based on this algorithm, each communication station 101 uses the route selection table 4 shown in FIG.
00 and a network configuration information table 900 shown in FIG. 9 in addition to the adjacent link information table 500 shown in FIG.

The adjacency link information table 500 has a distan
This is a table for managing the communication quality of the adjacent link 102 similarly to the ce-vector type protocol, and the address 501, the TOS 502, and the cost 503 of the adjacent communication station 101.
Is associated with.

The network configuration information table 900 includes:
This is a table for managing an adjacent link 102 between arbitrary communication stations 101, and includes addresses (901, 902), TOS 903, and cost 90 of two adjacent communication stations 101.
4 is correlated. This table 900 is common to all communication stations, whereby each communication station 101 can check the configuration of the entire network.

Since each communication station 101 can recognize the configuration of the entire network and the cost of each link 102 from this table 900, the cost according to any destination communication station 101 and TOS can be determined using the Dijkstra's algorithm using these information. The optimal route can be calculated by performing the above calculation.

Each communication station 1 related to the present algorithm
The packets for exchanging the route information at 01 include an adjacent link status notification packet 700 shown in FIG. 8 and a link status notification packet 1200 shown in FIG.

The adjacent link status notification packet 700
Adjacent link 10 as well as stance-vector type protocol
2 is a packet for notifying the cost of 2 between adjacent communication stations 101 at a constant period. Each communication station 101 detects the cost of the adjacent link 102 and notifies the change information when the cost has changed. In order to confirm the continuity of the adjacent link even if there is no change, the packet Send

The link state notification packet 1200 notifies the state change of the link 102 to the other adjacent communication stations 101 excluding the adjacent communication station 101 notified by the adjacent link state notification packet 700 by the communication station 101 detecting the state change. And an adjacent link status notification packet 700 and a link status notification packet 1200.
This is a packet for the communication station 101 notified of the state change by this to notify other adjacent communication stations 101 of the change information.
The content describes the link 102 whose status has changed, its TOS, and its cost.

As a method of broadcasting the packet 1200 to all the communication stations 101, a broadcast address is defined in advance, and the communication station 101 which has received the packet 1200 sends it to an adjacent link 102 other than the reception link 102. I just need. When the communication path loops, the life control is performed to delete the expired packet or delete the packet having the same information as the previously received packet, that is, the packet that does not update the network configuration information table 900. do it. Therefore, the communication station 101 that has received the packet 1200 checks whether the packet is a looped packet, and if it is not a loop, only relays the contents as it is. The updating of each table may be performed thereafter.

Based on these tables 500 and 900 and the control packets 700 and 1200, the communication station 101 in the network
Is optimized, and the route selection table 400 is updated. Hereinafter, in this algorithm, a certain link 10
The flow of processing when the route selection table 400 of each communication station 101 is updated when the cost of No. 2 changes will be described.

Each communication station 101 exchanges an adjacent link status notification packet 700 between the adjacent communication stations 101 to confirm the existence and monitor the cost of the adjacent link 102. The communication station 101 that has received the adjacent link status notification packet 700 transmits the notified change information to the link status notification packet 12.
In step S00, the broadcast address is transmitted to the adjacent communication station 101, and the network configuration information table 900 of the corresponding link 102 is updated. When the network configuration information table 900 is updated, each destination communication station 101 and TOS
Re-calculates the optimal communication route with the lowest cost for, and updates the route selection table 400 if there is a change in the adjacent link 102 to be transmitted in the optimal route. Upon receiving the link status notification packet 1200, the adjacent communication station 101 compares the notified information with the network configuration information table 900 held by the own communication station 101. If there is no difference, the link status notification packet 1200 loops. And erase the packet. If there is a difference, the received information is relayed as it is, and the network configuration information table 900 of the corresponding link 102 is updated. If necessary, the route selection table 400 is also updated.

These procedures are repeated in each communication station 101 each time the link state notification packet 1200 is notified as the link state changes, and information changes are notified in the network. In this case, unlike the above-described distance-vector type algorithm, since each communication station 101 does not perform a process of recalculating the cost and rewriting the packet from the reception of the packet to the transmission of the packet, the change information is not stored in the network. At a high speed.

However, the communication station 101 that has detected a change in the state of the link 102 needs to broadcast to all the communication stations 101 even though the route selection table 400 of all the communication stations 101 does not need to be updated. , Distance-vec
The notification range of the link state information is larger than that of the tor type algorithm, and as a result, there is a third problem that the traffic by the control packet increases.

[0032]

As described above, the communication quality such as the delay time, the error rate, the throughput, and the like, are not as good as changes such as addition and deletion of terminals related to the network configuration and changes in the line disconnection. In order to cope with this, in the conventional TOS routing, each communication station detects information related to the communication quality at regular intervals and transmits the change to other communication stations. Since the route selection table of the other communication station was updated by notifying, the packet for notifying the change information every time the state of each communication station or each link changed was disturbed in the network. There is a problem that the increase in traffic due to the control packet for updating the optimum route information cannot be avoided.

Further, as one of the conventional TOS routing protocols, there is a distance-vector type routing protocol. In the case of this protocol, the destination information is transmitted from the own communication station each time based on the change information notified at each communication station. Recalculate the end-to-end cost to the communication station,
Since the information is sent to the adjacent communication station, the propagation speed of the network state change (cost change) information is slow, and the change in the cost of a certain link cannot be immediately notified to all the communication stations concerned. there were.

Further, a link-state type routing protocol has also been proposed as a useful one for improving the response of the optimum route information updating process. However, in the case of this protocol, all communication stations that have detected a change in the link state have been proposed. Although the route selection table of the communication station does not need to be updated, it is necessary to broadcast the link state information to all the communication stations, and as a result, the notification range of the link state information increases,
There has been a problem that the control packet causes an increase in traffic.

A first object of the present invention is to provide a communication system capable of suppressing an increase in traffic due to a control packet for updating the optimum route information in TOS routing, and a route selection method therefor.

A second object of the present invention is to improve the response during the update of the route selection table of each communication station after detecting a change in the state of the network in the TOS routing and to quickly select the optimum route. An object of the present invention is to provide a feasible communication system and a route selection method thereof.

[0037] A third object of the present invention is that, in TOS routing, the broadcast notification range of link state information is not substantially limited, and a control packet for broadcasting the link state information is transmitted between all communication stations. It is an object of the present invention to provide a communication system capable of avoiding an increase in traffic due to distribution and a route selection method thereof.

[0038]

According to a first aspect of the present invention, a plurality of communication stations are physically or logically connected to each other in a data communication network, and each of the communication stations corresponds to a destination communication station address. Then, by searching the route selection table holding the optimum link for each communication quality, the optimum route to the destination communication station is determined and data is transmitted, and according to the change in the link state between the adjacent communication station and By notifying the adjacent communication station and all the communication stations except the destination communication station of the adjacent link state notification information and the link state notification information, respectively, the route selection table of the receiving communication station of the respective notification information is notified. In a path selection method of a communication system for updating contents and changing an optimum communication path, the communication station detects a communication path that is detected based on a time-varying state of its own communication station and a link state with an adjacent communication station. And a control information notification range control unit that controls a notification range of the link state notification information according to the rank of the communication quality. Each time the rank unit changes, the content of the route selection table of the communication station existing within the range corresponding to the rank of the communication quality is updated.

Preferably, the ranking means divides the continuous value of the detected communication quality by a plurality of thresholds, and ranks the communication quality within each of the adjacent thresholds as the same rank.

The control information notification range restricting means includes means for adding a specified value defining the number of communication stations that can pass through an arbitrary communication path to the communication data and transmitting the communication data to an adjacent communication station. Means for updating the value so that the number of traversable communication stations is reduced and transmitting the updated value to the adjacent communication station until the prescribed value in the data reaches a value that does not need to be relayed to the adjacent communication station. And

According to a second aspect of the present invention, there is provided a communication system in which a plurality of communication stations are physically or logically connected to each other in a data communication network, wherein the communication station has an address of a destination communication station. A path selection table in which the communication quality of an optimal communication path to the destination communication station and a link to an adjacent communication station which is the starting point of the optimal communication path are described in association with each other, and vary with time. Communication quality detection means for detecting communication quality from the state of the own communication station, and the state of the link between the communication station and the adjacent communication station; and ranking means for ranking the communication quality detected by the communication quality detection means. In the case where the rank ranked by the ranking means has changed, a notification method for notifying other communication stations of change information representing the details of the change in the rank after limiting the range of notification according to the change in the rank. Route selection table updating means for updating the route selection table according to the change information received from the other communication station; and when transmitting data, the destination communication station address and the communication quality of the communication quality of the route selection table. And a link selecting means for selecting a link to an adjacent communication station which is a starting point of the optimum communication path with reference to the communication station.

Preferably, the ranking means divides the communication quality having continuous values by a plurality of thresholds, and sets the discontinuous ranks indicating the communication quality included between adjacent thresholds by the same rank. It is characterized by attaching.

Also, the notifying means adds via-station number data defining the number of communication stations that may pass through the communication path in the transmitting communication station to the communication data and transmits the communication data to an adjacent communication station. In the via communication station that has received the data, the via-station number data is updated so as to decrease unless the via-station number data is a value indicating that there is no need to relay to the adjacent communication station, and the updated via-station number data is updated. The attached communication data is transmitted to an adjacent communication station.

[0044]

According to the present invention, the communication quality taking a continuous value is divided by several thresholds, and if it is within a certain threshold, it is treated as the same rank. Only the state change is notified to other communication stations. Since the communication quality such as the delay time and the error rate takes a continuous value, it is too many control packets to notify the status change for each continuous change. The communication traffic is ranked (discretized), and control traffic is reduced by making notification unnecessary in the case of a small state change. The rank according to the present invention corresponds to the cost handled by the above-described control.

In the present invention, since all communication stations have configuration information and operate basically using the same table update algorithm as the link-state type, each communication station transmits the received link state notification packet. It is only necessary to relay as it is, and the change information in the network can be propagated quickly and the response can be kept good.

Further, with respect to the problem of an increase in the number of broadcast packets when the link-state type algorithm is used, the notification range of the link state notification packet according to the above-mentioned rank change is appropriately limited. We are dealing with it.

That is, according to the present invention, even if the state of the cost of a certain link changes, it is necessary to update the route selection table at a communication station distant from the change point (via many relay communication stations). And that the range in which the route selection table is updated also changes depending on the degree of rank. Even if the rank changes, all communication stations (in the case of hierarchization, the same Instead of notifying all communication stations, the range of information notification is limited according to the degree of the change.

For example, when a large change occurs,
The communication station that detects this will report far away, and if there is a slight change in the level slightly changed, the communication station that detects this will notify only the nearby communication station By limiting the range in which meaningless link state notification packets flow, control traffic can be reduced. As a method of limiting the state notification range according to the degree of the state change, a method of adjusting the number of reachable HOPs and broadcasting the same can be applied.

[0049]

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows a network configuration of a communication system to which a TOS routing method according to the present invention is applied. In FIG. 1, each communication station 101 is connected to another single or a plurality of communication stations 101 via a link 102 capable of bidirectional data communication. This link 102 can be realized by, for example, an ATM connection. In this case, each communication station 101
The link 102 between them is not a physical link but a logical one corresponding to a virtual channel identifier (VPI / VCI).

A link 102 is defined between the communication stations 101 according to the direction in which data flows.
Different link identifiers (link *
*) Is given. Since the link 102 is logical, a single or a plurality of exchanges may be interposed in the link 102.
There is no problem as long as the link identifier and the adjacent communication station are associated on a one-to-one basis. The communication quality of each link 102 changes over time due to traffic conditions, occurrence of a failure, and the like.

An address (STN **) is assigned to the communication station 101, and the route selection at the communication station 101 is performed by selecting the destination communication station address stored in the transmission data and the specified service quality (TOS **). ) To determine the adjacent link 102 to which data should be sent (TOS routing method).

FIG. 2 is a block diagram showing a functional configuration of each communication station 101 of the communication system according to the present invention.
3 is a block diagram showing a detailed configuration of a main part of each communication station 101. As shown in FIG. 2, each communication station 101 includes an interface unit 11, a switch unit 12, a packet
It comprises an assembling unit 13, a CPU 14, a memory 15, and a timer 16. Of these, the CPU 14
As shown in FIG. 3, a communication quality detection unit 141, a ranking unit 142, a change detection unit 143, a link state notification range restriction unit 144, a control packet notification unit 145, a table update processing unit 146, a timer monitoring unit 147, a route Selector 148
It comprises. Further, the memory 15 is provided with a route selection table 400, an adjacent link information table 500, a network configuration information table 900, a communication station table 1000 via the optimum route, and a notification range setting table 1100.

FIG. 4 shows the T of the communication system according to the present invention.
3 shows an example of a protocol stack used in OS routing. The exchange of control packets between the communication stations 101 for performing the TOS routing is performed by this protocol stack. In this protocol stack, an RP (routing protocol) 200-
Reference numeral 1 denotes a protocol for exchanging the communication quality of the link 102 between the communication stations 101 in performing the TOS routing and updating the optimum route according to the TOS. The packets include an adjacent link status notification packet 700 shown in FIG. 8 and a link status notification packet 1200 shown in FIG.
Is defined.

NP (Network Protocol) 200-
Reference numeral 2 denotes a network layer protocol represented by IP (Internet Protocol) for determining an adjacent link to be transmitted according to a destination communication station address. In the present embodiment, the packet format of the NP 200-2 is defined as shown in FIG. This NP
The RP packet 201 is stored in the information section 202-B of the packet 300 in order to exchange path information.
Each communication station 101 is assigned an NP address.

AAL (ATM adaptation layer)
Reference numeral 200-3 denotes a sublayer for ATM adaptation. The header 203-A and the trailer 203-C describe a data length, a CRC, and the like.

The ATM 200-4 has the AAL packet 20
3 into 53-byte fixed-length packets called cells, and conversely, AAL packets 20
3 for assembling. Cell header 20
4-A, VPI / VC between the communication station 101 and the exchange
I or VPI / VCI between exchanges. In FIG. 1, the link identifier (link **) is the identifier of the link 102 between the communication stations 101, but the communication station 1
If a connection is set between 01 and 01, the VPI / VCI corresponding to the adjacent communication station 101 corresponds to the link identifier. In this embodiment, the ATM is assumed as the physical layer, but it is needless to say that it is not necessary to limit the ATM to only the ATM.

FIG. 5 shows an example of the format of the NP packet 300 used in the communication system according to the present invention. The NP packet 300 has a header part 2 including a destination communication station address field 301, a source communication station address field 302, a TOS field 303, a protocol field 304, and a data length field 305.
02-A and an information section 202-B. Each communication station 1
In 01, a route is selected based on the information in the header section 202-A of the NP packet 300.

In the destination communication station address field 301, the NP address of the communication station 101 to which data is finally sent is written. Therefore, the relay communication station 101 does not rewrite this address. Communication station 101 transmitting NP packet 300 or received NP packet 3
The communication station 101 relaying 00 determines which adjacent communication station 101 to transmit from this NP address. In the originating communication station address field 302, the NP address of the origin of the data is written. This address is not rewritten when relaying.

In the TOS field 303, parameters for designating the service quality of the NP packet 300 are written. That is, service qualities such as delay, error rate, throughput, and billing are specified. In the communication station 101 that transmits or relays the NP packet 300, when the TOS parameter is specified, the path to the destination communication station 101 for the specified TOS is optimized (minimum delay time, minimum error rate, etc.). Next, the adjacent communication station 101 is determined.

In the protocol field 304, a parameter for designating an upper layer protocol is written.
This value is a value corresponding to the upper layer protocol on a one-to-one basis. In particular, in a protocol stack as shown in FIG. 4 used for exchanging route information, for example,
The value corresponding to RP200-1 is written. The data length field 305 includes a header section 202-A and an information section 2
The octet length of the NP packet 300 including 02-B is written. The information part 202-B stores the data of the protocol of the upper layer.

FIG. 6, FIG. 7, and FIG. 9 to FIG.
Reference numeral 01 denotes a configuration example of each table necessary for route selection and updating of route information according to TOS. 8 and 12 show RPs for exchanging route information.
2 shows an example of the format of a control packet 200-1. Using these tables and packets, the communication path of the entire network is optimized.

Hereinafter, details of these tables and packets will be sequentially described. First, the route selection table 400 shown in FIG. 6 indicates that the communication station 101 transmitting the NP packet 300 has the destination communication station address specified in the NP packet header and the optimum link 102 for the TOS.
7 is a table for determining (corresponding to an ATM layer link identifier VPI / VCI).

In the table 400, the destination communication station address 401 is the NP address of the destination communication station. TOS4
02 is service quality such as delay, error rate, throughput, and payment.

The link identifier 403 is an ATM corresponding to the destination communication station address 401 and the TOS 402 and transmitted to the optimal adjacent communication station 101 to be received or relayed.
It shows VPI / VCI in the cell header. A
The VPI / VCI in the TM cell header is the transmitting communication station 101
Is a link identifier to be added, and when an exchange is interposed between the links 102, the VPI / VCI may be changed in the adjacent communication station 101 on the receiving side.

FIG. 7 shows an adjacent link information table 500. The adjacent link information table 500 is a table for managing the cost of the link 102 from the adjacent communication station 101 to the own communication station.
01 is associated with a TOS 502, a cost 503, and a monitoring counter 504. Each communication station 101 detects the communication quality of the adjacent link 102 directed to its own communication station at a fixed period, and if there is a change in the information of the adjacent link information table 500 up to that time, updates the table contents and updates the change. Notify the other communication station 101.

The adjacent communication station address 501 is the NP address of the adjacent communication station corresponding to the adjacent link to be managed.
The TOS 502 is a type of service quality to be managed, and has the same delay (delay) and error rate (e) as the route selection table 400.
rror rate), throughput (throughput), billing (pay)
ment).

The cost 503 is a value obtained by ranking the communication quality for the TOS 502. Here, the communication qualities such as delay and error rate are continuous values, and these values are also ranked and represented by being separated by a specific number (for example, 8) of thresholds. The cost 503 indicates this rank. Therefore, even if the communication quality changes, the table is not changed if it is within the threshold range.

The monitoring counter 504 indicates that the adjacent link 102
Is a counter for checking the continuity of the data. The adjacent link state shown in FIG. 8 is used between the adjacent communication stations 101 for the purpose of notifying the communication quality of the link 102 directed to the own communication station and for checking the continuity of the link 102 regardless of whether or not the communication quality has changed. The notification packet 700 is exchanged at regular intervals. Each communication station 101 has an adjacent link monitoring timer (timer 16 in FIG. 2), and when the adjacent link state notification packet 700 is not received within a certain period,
Update this counter. If the counter value becomes equal to or more than a specified value (for example, 3), it is determined that the line is disconnected.

FIG. 9 shows a network configuration information table 9.
00 is shown. Network configuration information table 90
0 is a table for managing all link information of the network, and the TOS 903 and the cost 904 are associated with the originating communication station address 901 and the destination communication station address 902. Each communication station 101 uses this table 9
00, the configuration of the entire network is ascertained, and from this information the optimum route to the destination communication station 101 and TOS is calculated.

The originating communication station address 901 and the destination communication station address 902 are the respective NP addresses, and correspond to the link from the originating communication station to the destination communication station. The TOS 903 and the cost 904 are the service quality type and the communication quality rank, as in the adjacent link information table 500.

FIG. 10 shows a communication station table 1 via the optimum route.
000. Communication station table 10 via optimal route
Reference numeral 00 denotes a table that indicates a relay station through which a certain TOS 1002 communicates with the destination communication station before reaching the destination communication station.
2, the relay communication station 1003 is associated. Each communication station 101 determines a communication path for each destination communication station address 1001 from the network configuration information table 900.
By calculating with Dijkstra's algorithm or the like, the relay communication station (that is, the link 102 to be routed) on the optimum route can be obtained. However, in that case, link 102
FIG. 12 transmitted by each communication station 101 detecting the state change of
It is necessary to recalculate the optimum route according to the link status notification packet 1200 shown in FIG. In this case, based on the notified change information and the table 1000, it is determined which destination address should be recalculated for the route. The criterion for the determination is performed by various table update routines shown in FIG. 15, but the details will be described later.

The destination communication station address 1001 is the NP address of the destination communication station. TOS1002 is a service quality type. Relay communication station 1003 is the destination communication station 1
01 is the NP address of the relay station through which the optimal route passes when transmitting with the TOS designated as 01.

FIG. 11 shows a notification range setting table 1100.
Is shown. The notification range setting table 1100 is a table for determining a range to which change information is notified in response to a state change (cost change 1101) of the adjacent link 102, that is, a range to which the link state notification packet 1200 is transmitted. 1101, TOS 1102, and notification range 1103 are associated with each other.

Communication station 101 that has detected a change in an adjacent link
Is transmitted by the adjacent link state notification packet 700 to the adjacent communication station 101 corresponding to the link 102 whose change is detected.
, And the detection result is also notified to other adjacent communication stations 101 by the link state notification packet 1200. Further, the communication station 101 notified of the link state change by the adjacent link state notification packet 700 also notifies other adjacent communication stations 101 by the link state notification packet 1200. At this time, a parameter of the number of HOPs of the link state notification packet 1200 is set for the purpose of limiting the notification range. Link status notification packet 120
The communication station 101 that receives and relays 0 checks the number of HOPs. If the number is a positive value, the value is decremented and relayed. If 0, the link state notification packet 1200 is discarded without relaying. By this processing, the communication station 101 that has detected the link state can limit the notification range according to the degree of cost change.

In the table 1100, the cost change 110
1 is the absolute value of the difference cost between the cost of the link 102 up to then and the cost notified by the link status notification packet 1200. TOS 1102 is the service quality corresponding to the changed cost. The notification range 1103 is a value corresponding to the number of HOPs of the link status notification packet 1200 obtained from the cost change 1101 and the TOS 1102 by the communication station 101 that has detected the status change of the adjacent link.

Next, the control packet will be described. FIG. 8 shows an example of the format of the adjacent link status notification packet 700. Adjacent link status notification packet 7
00 is a PR packet for notifying the cost of the adjacent link 102 directed to the own communication station from the adjacent communication station 101, and includes a packet type field 701, a packet length field 702, an address type field 703, and a HOP number field 704. It comprises a header section 201-A, an information section 201-B including an originating communication station address field 705, a TOS number field 706, a TOS field 707, and a cost field 708.

Each communication station 101 detects the communication quality of the adjacent link 102 directed to its own communication station at a fixed cycle, and if there is a change from the information of the adjacent link information table 500 up to that time, the packet 700 Notify the other communication station 101. Even if there is no change, a packet having no field equal to or less than the TOS number field 706 is transmitted to confirm the continuity of the adjacent link 102.

In the adjacent link status notification packet 700, the packet type field 701 includes the packet 700 or the link status notification packet 120 shown in FIG.
The RP packet type is written in order to distinguish 0. The packet length field 702 includes a common header 2
The octet length of the packet including 01-A and the information part 201-B is written.

In the address type field 703, I
The type of address used in NP, such as P, OSI, and IPX, is written. The HOP number field 704 describes the number of relay communication stations through which the packet 700 can pass. Each communication station 101 decrements this value every time the RP packet is relayed, and discards the value when this value becomes 0. In the originating communication station address field 705, the address of the NP originating station corresponding to the address type is written. In the TOS number field 706, the number of TOS changed in the adjacent link notified by this packet is written. This number corresponds to the number of TOS and cost entries below. TOS field 707, cost field 7
08 indicates the changed TOS and the changed link cost value.

FIG. 12 shows a link status notification packet 120.
It shows an example of a format of 0. The link state notification packet 1200 is transmitted from the communication station 101 which has detected the change of the adjacent link 102 to the adjacent link state notification packet 70.
0 and the communication station 101 notified of the change in the link state by the adjacent link state notification packet 700.
Is used when the communication station 101 notified of the change in the link state by the link state notification packet 1200 notifies the adjacent communication station 101.

The field of this packet 1200 is R
A common header portion 201-A common to P packets, a link number field 1201, an originating communication station address field 1202 and a destination communication station address field 1203 for identifying a link, a TOS number field 1204, TOS
The information section 201-B includes a field 1205 and a cost field 1206.

The common header 201-A is the same as the common header 201-A of the adjacent link status notification packet 700.

The number of links for notifying the change is written in the number of links field 1201 and corresponds to the number of entries of a series of link change information from the address of the originating communication station to the cost. The originating communication station address field 1202 and the destination communication station address field 1203 include an adjacent communication station 10.
The address 10 is written in the link 10 from the calling side to the receiving side.
Corresponds to 2. This address is an NP address indicated by the address type in the common header.

In the TOS number field 1204, the number of TOS which has changed in the link 102 specified by the source communication station address field 1202 and the destination communication station address field 1203 is written. TOS field 120
5. The cost field 1206 is the same as that of the adjacent link state notification packet 700.

Hereinafter, a routine for transmitting the NP packet 300 using the above-described NP, and each communication station 101
Will be described in detail with reference to flowcharts shown in FIGS. 13 to 18.

FIG. 13 shows a flowchart of the transmission request routine 1300. Transmission request routine 13
00 is a routine for transmitting the NP packet 300 using the NP.

When a request to transmit the NP packet 300 is issued (step 1301), in the originating communication station 101, first, the control packet issuing unit 145 causes the NP packet 300 including information such as a destination communication station address and TOS to be transmitted.
(See FIG. 5) is generated (step 1302). next,
The route selection unit 148 searches the route selection table 400 from the destination communication station address 301 of the NP packet 300, and finds an adjacent communication station to be transmitted, that is, the link identifier 4
03 is determined (step 1303).

When the link identifier 403 can be determined, the control packet issuing unit 145 decomposes the ATM cell into ATM cells based on the protocol stack shown in FIG. 4, attaches the link identifier 403 to the cell header, and transmits the ATM cell (step 130).
4). After transmitting the NP packet 300, the transmission request routine 1
300 ends (step 1305).

FIG. 14 shows a communication quality detection routine 1400.
Is shown. The communication quality detection routine 1400 is a routine for each communication station 101 to detect the communication quality of an adjacent link at a fixed period, and to notify another communication station if there is a change.

When a certain period of time has passed since the previous detection time,
Each communication station 101 starts the routine 1400 (step 1401), and checks statistical information such as the delay time and error rate of the adjacent link collected by the communication quality detection unit 141 from the previous detection time (step 1402). The statistical information is converted into a cost (step 1403). The cost is indicated by a value obtained by dividing the detected value of the communication quality by the ranking unit 142 stepwise by a specific number of thresholds and ranking the number of ranks, for example, eight ranks. There are various methods for converting the cost, such as an average value, a maximum value, and a minimum value of the statistical information.

After obtaining the cost, the change detecting section 143 checks the previous cost of the corresponding adjacent link from the adjacent link information table 500, and compares it with the detected and converted cost (step 1404).

If the detected cost is different from the previous cost, the control packet issuing unit 145 writes predetermined information in the header of the adjacent link status notification packet 700 and writes its own communication station address in the information. Then, after writing the changed TOS number and all the changed costs, the adjacent link state notification packet 700 is completed (step 1405), and the adjacent link station corresponding to the detected adjacent link is notified of the adjacent link state notification. The packet 700 is transmitted (Step 1406).

Next, change information is notified to the adjacent communication stations other than the notified adjacent communication station by the link state notification packet 1200. First, the link status notification range limiting unit 144
Indicates the absolute value of the difference between the detected cost and the previous cost (cost change 1101) and the notification range 1103 from the TOS to the hop destination communication station from the own communication station using the notification range determination table 1100. It is determined (step 1407). Notification range 1 obtained here
103 is the header part 2 of the link status notification packet 1200
Write to the HOP number field of 01-A.

Further, in the information section 201-B, the number of changed links, the link identification based on the source communication station address and the destination communication station address, and the number of TOS, TOS, and cost are written as in the adjacent link status notification packet 700. Thus, after generating the link status notification packet 1200 (step 1408), the link status notification packet 1200 is generated.
Is transmitted by the control packet issuing unit 145 to all the adjacent communication stations not notified by the adjacent link state notification packet 700 (step 1409). Further, the link status notification packet 1200 also transmits the information of the link information notification packet received from another communication station up to that time.

After transmitting the link state notification packet 1200, the originating communication station 100 sets the table update processing unit 146
Accordingly, the various tables of the own communication station are updated with respect to the above-mentioned cost change (step 1410), and thereafter, the communication quality detection routine 1400 ends (step 1412). A specific processing method for updating the table will be described later.

On the other hand, as a result of the cost comparison (step 1404), if the detected cost is the same as the previous cost, the adjacent link state notification packet 70
The predetermined information is written in the header portion of 0, and only the address of the own communication station is written in the information portion, and transmitted to the adjacent communication station corresponding to the detected adjacent link (step 1411).
This series of communication quality detection routine 1400 ends (step 1412).

FIG. 15 shows various table update routines 15.
00 shows the flowchart of FIG. The various table update routine 1500 is used when the link cost changes, and the communication quality detection routine 140 shown in FIG.
0, the adjacent link status notification packet reception routine 1600 shown in FIG. 16, the link status notification packet reception routine 1700 shown in FIG. 17, and the adjacent link monitoring timer expire routine 1800 shown in FIG. Information table 500,
This is a subroutine for updating the network configuration information table 900 and the optimal route communication station table 1000. Note that these table update processes are performed by the table update processing unit 146.

After the start of the various table update routine 1500 (step 1501), first, the link 102 whose cost has changed and the network configuration information table 90 of the TOS are changed.
0 is updated (step 1502). Then, it is determined whether the cost has increased since before the table update (step 1503). If the cost has increased, a destination communication station address including the cost change link is searched from the optimal route communication station table 1000 (step 1504). ). If the cost is reduced, the optimal route communication station table 100
A destination communication station address not including the cost change link is searched from 0 (step 1505).

Next, an optimal route that minimizes the cost for the destination address and TOS detected by the Dijkstra algorithm or the like from the network configuration table 900 is recalculated (step 1506). As a result of recalculation,
It is checked whether the optimum route has changed from the previous optimum route (step 1507). If there has been a change, the communication station table 1000 via the optimum route is updated (step 1508). It is determined whether or not the adjacent link changes (step 1509).
When the adjacent link changes, the route selection table 400
Is also updated (step 1510). If there is no change in the optimum route, the table is not updated. After these recalculations are repeated for the number of searched destination communication stations (step 1511), the various table update routines are terminated (step 1512).

FIG. 16 shows a flowchart of the adjacent link state notification packet reception routine 1600. Adjacent link status notification packet reception routine 1600
Is a routine for notifying another communication station according to the information notified when the adjacent link state notification packet 700 is received, and updating various tables of the own communication station.

When the adjacent link status notification packet 700 is received (step 1601), first, the adjacent link is recognized from the source communication station address in the packet, and the monitoring counter of the corresponding adjacent communication station entry in the adjacent link information table 500 is checked. Is returned to 0 (step 1602). Regarding the handling of the monitoring counter, the neighbor link monitoring timer expire
Described in routine 1800.

Next, it is checked whether link cost change information is written in the information section of the packet (step 160).
3) If the link cost change information is written, the link state notification packet 1200 is used to notify an adjacent communication station other than the adjacent communication station that has been notified based on the change information. Further, various tables of the own communication station are updated. The method of notification by the link state notification packet 1200 and the method of updating various tables are the same as those in steps 7 to 10 of the communication quality detection routine 1400. (Steps 1604-
1607) After updating the various tables, if no change information is written in the packet, the adjacent link state notification packet reception routine 1600 ends (step 1608).
Since the adjacent link state notification packet 700 is a packet exchanged only between adjacent communication stations and does not need to be relayed, the number of HOPs is not checked at the time of reception.

FIG. 17 shows a flowchart of the link status notification packet reception routine 1700. The link state notification packet receiving routine 1700 is a routine for relaying to another communication station according to the information notified when the link state notification packet 1200 is received, and marching through various tables of the own communication station.

When the link status notification packet 1200 is received (step 1701), first, the link cost change information in the packet information section is compared with the network configuration information table 900 held by its own communication station (step 1).
702), it is determined whether the received information is the same as the previously received information (step 1703). That is, since the link state notification packet 1200 is transmitted to all adjacent communication stations other than the adjacent communication station corresponding to the received adjacent link, FIG.
A link state notification packet 1200 having the same information circulates between the communication stations 101 (for example, between the communication stations A, B, and C, and between the communication stations B, D, and E) forming a loop in the network configuration shown in FIG. May be. In order to reduce the traffic caused by such meaningless packets, the communication station 101 that has received the link state notification packet 1200 needs to identify whether the circulated packet is for notifying new change information. If the link status notification packet 1200 has been received before, the network configuration information table 900 should have been updated, and is compared with this table information.

Link status notification packet 1200 received
If is a new one, the number of HOPs in the common header part of the received packet is checked (step 1704). HOP
If the number is valid, the HOP number is updated by decrementing it (step 1705), and the link status notification packet 1200 is relayed and transmitted to an adjacent communication station other than the received link (step 1706). If the number of HOPs is invalid (0), relaying is not performed since the range of notification from the communication station transmitting the link status notification packet 1200 is up to the own communication station. Thereafter, in order to update the various tables according to the change information, the various table updating routine 15 shown in FIG.
00 is performed (step 1707).

After updating the various tables, if the received packet has been circulating, the link state notification packet receiving routine 1700 ends (step 170).
8).

FIG. 18 shows a flowchart of the adjacent link monitoring timer expire routine 1800. Each communication station 101 transmits the adjacent link status notification packet 7 regardless of the presence or absence of the link cost change information with the adjacent communication station.
00 are exchanged at regular intervals, so that the link 10
The continuity check of 2 is performed.

The fixed period is managed by an adjacent link monitoring timer (monitored by the timer monitoring unit 147 based on the time measured by the timer 16) of each communication station 101 for each adjacent link. Routine 1
800 is a routine for processing when the adjacent link state notification packet 700 is not received within the expiration of the timer, that is, within a certain period.

When the adjacent link monitoring timer expires (step 1801), first, the adjacent link information table 500 is used.
To find out how many times the corresponding adjacent link has expired continuously. How many times in a row timer expi
Whether it has been re-executed can be determined by checking the monitoring timer value in the adjacent link information table 500 (step 1802).

When the monitoring timer reaches a specified value (for example, 3), it is determined that the adjacent link is disconnected, and the link status notification packet 1200 notifies other communication stations and updates various tables of the own communication station. . However, since the notification of the link state is a line disconnection, the notification range is set to the maximum value that can be notified. Process of generating and transmitting link state notification packet 1200 (steps 1803 and 180
4) and the process of updating the various tables after transmission (step 1805) are the same as steps 1408 to 1410 described in the communication quality detection routine 1400. If the value of the monitoring counter is equal to or smaller than the specified value, the monitoring counter is incremented and updated (step 1806).
This counter is cleared to 0 when the adjacent link state notification packet 700 is received. Neighbor link monitoring timer after updating various tables or monitoring timer
The expire routine 1800 ends (step 180)
7).

[0111]

As described above, according to the present invention,
The communication station ranks the communication qualities detected by the continuously changing state of its own communication station and the link state with the adjacent communication station, and ranks the link state for each change in the rank unit of the communication quality. In addition to notifying the notification information, the notification range of the link state notification information is also limited according to the rank, so that the communication status changes with a continuous value in accordance with the continuous change. As compared with the case of notifying the change, the number of control packets for TOS routing can be greatly reduced, and the notification of the change in the state of the network is provided by the synergistic effect of the reduction in the number of control packets and the limitation of the notification range of the control packet. And high-speed updating of the route selection table can be expected. As a result, optimal route selection according to changes in network conditions at each communication station is enabled. It has an advantage of being able to achieve effective data communications.

[Brief description of the drawings]

FIG. 1 is a diagram showing a network configuration of a communication system according to the present invention.

FIG. 2 is a block diagram showing a functional configuration of a communication station in the system of the present invention.

FIG. 3 is a block diagram showing a detailed configuration of a main part of a communication station in the system of the present invention.

FIG. 4 is a diagram showing an example of a protocol stack used in the system of the present invention.

FIG. 5 is a diagram showing a format of an NP packet used in the system of the present invention.

FIG. 6 is a configuration diagram of a route selection table used in the system of the present invention.

FIG. 7 is a configuration diagram of an adjacent link information table used in the system of the present invention.

FIG. 8 is a diagram showing a format of an adjacent link state notification packet used in the system of the present invention.

FIG. 9 is a configuration diagram of a network configuration information table used in the system of the present invention.

FIG. 10 is a configuration diagram of a communication station table via an optimum route used in the system of the present invention.

FIG. 11 is a configuration diagram of a notification range setting table used in the system of the present invention.

FIG. 12 is a configuration diagram of a link status notification packet format used in the system of the present invention.

FIG. 13 is a flowchart showing a transmission request routine in the system of the present invention.

FIG. 14 is a flowchart showing a communication quality detection routine in the system of the present invention.

FIG. 15 is a flowchart showing various table update routines in the system of the present invention.

FIG. 16 is a flowchart showing an adjacent link state notification packet reception routine in the system of the present invention.

FIG. 17 is a flowchart showing a link state notification packet reception routine in the system of the present invention.

FIG. 18 shows an adjacent link monitoring timer e in the system of the present invention.
9 is a flowchart illustrating an xwire routine.

FIG. 19 is a configuration diagram of an all communication station EE cost information table used in the conventional system.

FIG. 20 is a diagram showing a format of an EE path information notification packet used in a conventional system.

[Explanation of symbols]

 101 Communication Station 11 Interface Unit 12 Switch Unit 13 Packet Disassembly / Assembling Unit 14 CPU 141 Communication Quality Detecting Unit 142 Ranking Unit 143 Change Detection Unit 144 Link Status Notification Range Limiting Unit 145 Control Packet Issuing Unit 146 Table Update Processing Unit 147 Timer Monitoring Unit 148 Route selection unit 15 Memory 400 Route selection table 500 Neighboring link information table 900 Network configuration information table 1000 Communication station table via optimum route 1100 Notification range setting table 16 Timer 102 Link 200-1 Routing protocol 200-2 Network protocol 200- 3 AAL 200-4 ATM 300 NP packet 600 All communication stations EE cost information table 700 Adjacent link status notification packet 800 EE path information Intellectual packet 1200 link state notification packet

Claims (6)

[Claims] A plurality of communication stations are physically or logically connected to each other in a data communication network, and each of the communication stations has an optimal link for each communication quality corresponding to a destination communication station address. A route selection table is searched to determine an optimal route to the destination communication station, and data transmission is performed. In addition, according to a change in a link state between the adjacent communication station, all except the adjacent communication station and the destination communication station are performed. Communication system that notifies the communication station of the adjacent link state notification information and the link state notification information, thereby updating the contents of the path selection table of the receiving communication station of the notification information and changing the optimum communication path. In the route selection method, the communication station ranks communication quality detected based on a time-varying state of its own communication station and a link state with an adjacent communication station. And a control information notification range control unit that controls a notification range of the link status notification information according to the rank of the communication quality. A route selection method for a communication system, wherein the contents of a route selection table of a communication station existing within a range corresponding to a rank of communication quality are updated. 2. The method according to claim 1, wherein the ranking unit divides the continuous value of the detected communication quality by a plurality of thresholds, and ranks the communication quality within each of adjacent thresholds as the same rank. 2. The route selection method of the communication system according to 1. 3. The control information notification range restricting means includes means for adding a specified value defining the number of communication stations that can be routed on an arbitrary communication path to communication data and transmitting the communication data to an adjacent communication station; Means for updating the value so that the number of traversable communication stations is reduced and transmitting the updated value to the adjacent communication station until the prescribed value in the data reaches a value that does not need to be relayed to the adjacent communication station. 3. The route selection method for a communication system according to claim 1, wherein: 4. A communication system in which a plurality of communication stations are physically or logically connected to each other in a data communication network, the communication stations comprising: an address of a destination communication station; A path selection table in which the communication quality of a communication path and a link to an adjacent communication station which is the starting point of the optimum communication path are described in association with each other; Communication quality detection means for detecting communication quality from the state of the link between the own communication station and the adjacent communication station; ranking means for ranking the communication quality detected by the communication quality detection means; ranking by the ranking means When the rank is changed, a notification unit that notifies another communication station of change information indicating the content of the change in the rank after limiting a range to be notified according to the rank change, from the other communication station. Route selection table updating means for updating the route selection table in accordance with the received change information; and at the time of data transmission, referring to the contents of the destination communication station address and the communication quality of the route selection table for the optimum communication. A communication system comprising: link selection means for selecting a link to an adjacent communication station that is a starting point of a route. 5. The ranking means divides communication quality having continuous values by a plurality of thresholds, and discontinuous ranking indicating communication quality in which communication quality values are included between adjacent thresholds with the same rank. The communication system according to claim 4, wherein the communication is performed. 6. The notifying means adds, to the communication data, via-station number data defining the number of communication stations that may pass through a communication path in the transmitting communication station, and transmits the communication data to an adjacent communication station. In the via communication station that has received the data, the number of via station data is updated so as to decrease unless the number of via station data is a value indicating that there is no need to relay to an adjacent communication station, and the updated via station number data is updated. The communication system according to claim 4, wherein the attached communication data is transmitted to an adjacent communication station.