Cell transmitter and traffic control system

[0001] [Technical field to which the invention belongs] The present invention relates to a cell transmission device and a traffic control system, and is suitable for application to, for example, traffic control using an ABR (Available Bit Rate) service in an ATM (Asynchronous Transfer Mode) network system. [0002] [Conventional technology] In the ATM network system, in order to support various services required for the data types (voice data, image data, other data, combinations of these data) to be handled, users can use the characteristics of the data they put on the ATM network. Select the most suitable service category. [0003] ABR service is one of the service categories provided by ATM network systems. [0004] The ABR service guarantees communication quality equal to or higher than the MCR (Minimum Cell Rate), which is the minimum rate of services declared and agreed upon at the time of call connection, and if network resources are available, the service declared and agreed upon at the time of call connection. PCR (Peak Cell), which is the maximum rate of Rate) A service that provides communication at speeds below. [0005] Depending on the status of network resources, in order to dynamically increase or decrease the transmission rate of the transmitting terminal up to the maximum rate PCR, a traffic control cell called a resource management cell (RM cell) is retaken between the transmitting terminal and the receiving terminal. Provide ABR service by doing. [0006] In the ABR service, a forward RM cell (FRM cell; hereinafter referred to as a forward control cell) is transmitted in the forward direction every time a fixed number of data cells (information cells) are transmitted from the transmitting terminal. When the receiving terminal receives the forward control cell, it transmits it as a backward RM cell (BRM cell; hereinafter referred to as a reverse control cell) to the transmitting terminal in the reverse direction. At this time, the receiving terminal adds the network congestion information obtained by receiving the forward data cell to the reverse control cell and transmits the information. Further, when the reverse control cell passes through a device such as an ATM switch in the middle, the device may explicitly write the rate that the device can tolerate in the reverse control cell. The transmitting terminal receives the reverse control cell, identifies the congestion state of the network, and controls the transmission rate. [0007] Here, the ATM switching device operates the transmission terminal and the reception terminal described above to divide the feedback loop (control loop) of the ABR service into a plurality of control loops to reduce one control loop and reduce the network. It enables traffic control that immediately reflects the status of. An ATM switch (ATM switch) that virtually acts as a transmitting terminal and a receiving terminal in such an ABR service is called a VD / VS (Virtual Destination / Virtual Source). [0008] The ABR service in an ATM network system can change the cell rate allowed for a terminal at any time by using an RM cell or a congestion indicator bit according to the traffic status in the ATM switch device in the network or in the network. [0009] Figure 2 is a simple conceptual diagram of the traffic control method in the ABR service. FIG. 2 shows an example in which one ATM switching device 3 intervenes in the communication from the transmitting terminal 1 to the receiving terminal 2. [0010] In FIG. 2, the transmission terminal 1 transmits one forward control cell FRM for every N transmissions of data cell DCs. The receiving terminal 2 receives the forward control cell FRM as well as the data cell DC. The receiving terminal 2 rewrites the data in the forward control cell FRM and returns the reverse control cell BRM to the transmitting terminal 1. [0011] Such management of RM cells is possible not only between the original transmission terminal 1 and the reception terminal 2, but also in VS (virtual transmission terminal) and VD (virtual reception terminal). .. For example, VS and VD are implemented in the ATM switching device 3, and the control loop of the ABR service is divided into a plurality of loops. The ATM exchange device 3 functions as a VD (virtual receiving terminal) when viewed from the transmitting terminal 1, and functions as a VS (virtual transmitting terminal) when viewed from the receiving terminal 2. [0012] When congestion occurs in its own exchange, the ATM switching device 3 sets the congestion display bit CI of the passing forward control cell FRM as congested and notifies the rear network of the congestion. Upon receiving this, the receiving terminal 2 rewrites the DIR bit indicating the directionality to the instruction (DIR = 1) related to the reverse direction control cell BRM and returns to the transmitting side. [0013] In addition, the ATM switching device 3 rewrites the permissible cell rate (explicit cell rate) ECR in the reverse control cell BRM to an explicit small value when congestion occurs. When the transmitting terminal 1 receives the reverse control cell BRM, the transmitting terminal 1 changes the transmitting cell rate (referred to as the execution cell rate in the embodiment) according to the congestion display bit CI. Here, when the congestion display bit CI indicates that there is congestion, the transmission cell rate is lowered, and when it indicates that there is no congestion, the transmission cell rate is increased within a range that does not exceed the declared maximum cell rate PCR. If the allowable cell rate ECR is smaller than the current cell rate, the transmission cell rate is set to be equal to or less than the allowable cell rate ECR. If the allowable cell rate ECR is smaller than the declared minimum cell rate MCR, the transmitted cell rate becomes the declared minimum cell rate MCR. [0014] The same processing is performed when the ATM switching device 3 operates as a virtual transmitting terminal. [0015] As described above, the transmitting side determines the next transmitting cell rate in consideration of various parameters such as the input information of the data cell and the information in the reverse control cell BRM. [0016] [Problems to be Solved by the Invention] In the conventional traffic control method, even when the data input rate is smaller than the declared minimum cell rate MCR, the data transmission cell rate does not fall below the declared minimum cell rate MCR, so the bandwidth for the declared minimum cell rate MCR is secured as the transmission cell rate. As a result, I continued to secure extra free bandwidth for (MCR-input rate), and I could not allocate free bandwidth to other connections belonging to the ABR connection group, so I could not perform efficient traffic control. [0017] Therefore, there is a demand for a cell transmission device and a traffic control system capable of performing efficient traffic control. [0018] [Means for solving problems] In order to solve such a problem, in the first invention, in the cell transmission device in which the minimum cell rate is declared for each connection and the data cell of each connection is transmitted according to the determined execution cell rate for each connection, ( 1) Input rate calculation means that obtains the input rate of each connection based on the input status of the data cell to the cell transmission device, and (2) For each connection, at least for cell rate update given by the opposite cell receiving device. The execution cell rate is updated according to the information and the input rate, and the minimum cell rate smaller than the minimum cell rate is updated under a predetermined condition where the input rate is smaller than the minimum cell rate. It is characterized by having an execution cell rate updating means. [0019] Further, in the second invention, the minimum cell rate is declared for each connection, and for each connection, the cell transmission device that transmits the data cell of each connection according to the determined execution cell rate, and the cell transmission device are directed to the cell transmission device. Further, in a traffic control system including a cell receiving device for transmitting rate update information required when updating the execution cell rate, the first cell transmitting device of the present invention is applied as the cell transmitting device. .. [0020] BEST MODE FOR CARRYING OUT THE INVENTION (A) First Embodiment Hereinafter, the first embodiment in which the cell transmission device and the traffic control system according to the present invention are applied to the ATM exchange device of the ATM network system will be described in detail with reference to the drawings. [0021] [0021] (A-1) Configuration of First Embodiment FIG. 1 is a block diagram showing a traffic control configuration based on the ABR service of the ATM switching device 10 according to the first embodiment. [0022]<u style="single">Figure 1</u>The ATM switching device 10 includes an incoming line unit 11, an ATM switch unit (SW unit) 13, and an outgoing line unit 12. In relation to traffic control, the incoming line unit 11 has a first ABR control unit 14 and a VCS (Virtual Channel Shaper) unit 15, and the outgoing line unit 12 has a VPS (Virtual Path Shaper) unit 16 and a VPS (Virtual Path Shaper) unit 16. It has a second ABR control unit 17. [0023] Here, the first ABR control unit 14 has an input rate calculation unit 18 and an ACR (Allowed Cell Rate) calculation unit 19, while the second ABR control unit 17 has an ECR (Explicit Cell Rate) calculation unit. Has 20. [0024] The input rate calculation unit 18 of the first ABR control unit 14 is used for each connection related to the ABR service (for example, defined by VCI and VPI; hereinafter, connection means only the connection related to the ABR service). The input rate IR (Input Rate) is calculated by counting the number of cell inputs. [0025] The ACR calculation unit 19 of the first ABR control unit 14 determines the execution cell rate ACR to be allowed for each connection, gives information on the execution cell rate ACR to the VCS unit 15, and sends the RM to the outgoing line unit 12 side. The value of the determined execution cell rate ACR is inserted into the octed of the cell's current cell rate CCR (Current Cell Rate) (the RM cell generation operation is also executed by, for example, VCS unit 15). The method of determining the execution cell rate ACR for each connection by the ACR calculation unit 19 will be clarified in the section of operation, but the ACR calculation unit 19 describes the above-mentioned input rate IR, maximum rate PCR declared at the time of connection setting, and minimum rate MCR. , Determined from the ECR information and congestion information (rate increase / decrease display bit NI, congestion display bit CI) in the RM cell returned from the outgoing line section 12 side. [0026] The VCS unit 15 prepares a queue for each connection of each ABR service, and data cells are sent from each queue to the ATM switch unit 13 according to the execution cell rate ACR given by the ACR calculation unit 19. The VCS unit 15 also has a function of generating and sending an RM cell for each connection. [0027] The ATM switch unit 13 determines the direction of the cell according to the header information of the arrived cell and performs the exchange process. [0028] The VPS unit 16 in the outgoing line unit 12 has a queue prepared for each service class, and sends out cells according to the rate given for each service. A queue for the ABR service (for example, a plurality of queues 16a may be provided for each VPI) is also provided in the VPS unit 16, and all cells of the ABR service are given to the connection group of the ABR service from this queue 16a. It is sent (shaped) according to the allocated bandwidth (cell rate) Bg. [0029] The second ABR control unit 17 incorporates predetermined information into the RM cell given by the incoming line unit 11 and returns it to the incoming line unit 11 (including changes). The second ABR control unit 17 has each unit for manipulating the information of the RM cell, but also has the ECR calculation unit 20 as described above. The ECR calculation unit 20 currently flows the connection based on the current cell rate CCR in the RM cell in the corresponding connection, the current cell rate CCR of the connection belonging to all other ABR services, and the bandwidth Bg allocated for the ABR service. The permissible rate may be calculated, written in the RM cell as an explicit cell rate ECR, and sent back to the first ABR control unit 14 side, which is the source. The specific calculation method of the explicit cell rate ECR by the ECR calculation unit 20 will be clarified in the section of operation. Further, the functional description of the information manipulation unit of the RM cell other than the ECR calculation unit 20 will be omitted. [0030] (A-2) Operation of the first embodiment Next, the traffic control operation related to the ABR service in the ATM switching device 10 having the above configuration will be described. [0031] In the incoming line unit 11, the incoming input data cell is given to the VCS unit 15 and queued for each connection, and then according to the execution cell rate ACR for each connection given by the ACR calculation unit 19, the ATM switch unit 13 Is sent to. Further, in the VCS unit 15, an RM cell in which the execution cell rate ACR is inserted as the current cell rate CCR is generated for each connection, and a predetermined rule (a predetermined cycle or a predetermined number of data cells is transmitted) is sent to the cell flow of the data cell. It is inserted according to (such as one for each) and sent to the ATM switch unit 13. [0032] Further, the input rate calculation unit 18 constantly calculates the input rate IR for each connection according to the arrival status of the input data cell for each connection. [0033] The ACR calculation unit 19 waits for the arrival of the RM cell returned from the outgoing line unit 12, and when the RM cell arrives, the ACR calculation unit 19 recalculates the execution cell rate ACR of the connection related to the RM cell. [0034] Here, the first embodiment is characterized by a method of calculating the execution cell rate ACR executed by the ACR calculation unit 19, and the calculation method will be described in detail below with reference to the flowchart of FIG. FIG. 3 is a flowchart showing a processing example of the ACR calculation unit 19. [0035] The ACR calculation unit 19 starts the process shown in FIG. 3 every predetermined cycle (for example, one cell time), and first determines whether or not the RM cell returned from the outgoing line unit 12 has arrived (step 100). ). If the RM cell has not arrived, the series of processes shown in Fig. 3 is terminated. [0036] On the other hand, when the RM cell arrives, it is determined whether or not the connection related to the RM cell is in communication by referring to the communication flag Connstt (step 101). In the communication flag Connstt, for example, "1" indicates that communication is in progress. For example, the input rate calculation unit 18 may have a function of setting the communication flag Connstt, which is set by the cell existence status of the queue for each connection of the VCS unit 15 and the input rate IR. [0037] When the communication flag Connstt indicates that communication is in progress (1), the ACR calculation unit 19 determines the execution cell rate from the congestion information (rate increase / decrease display bit NI, congestion display bit CI) in the RM cell that has arrived. Calculate the update candidate value ACR * (step 102). The calculation of the update candidate value ACR * of the execution cell rate is performed according to, for example, 5.10.4 Source Behavior of The ATM Forum Traffic Management Specification Version 4.0, which is a recommendation of the ATM Forum. [0038] The update candidate value ACR * of the execution cell rate obtained in this way exceeds the maximum cell rate PCR, is too fast when viewed from the input cell rate IR, or is an explicit rate that the second ABR control unit 17 can tolerate. Since it often does not match other parameters, such as exceeding the ECR or being lower than the minimum cell rate guaranteed to the user, the process of determining the suitability of the value ACR * shown in steps 103 and 104. I do. [0039] In the conformity determination process, first, the explicit rate ECR inserted in the incoming RM cell and calculated as the rate that the second ABR control unit 17 can tolerate, the maximum cell rate PCR declared at the time of connection setting, and the update candidate value. The minimum one is taken out from the ACR * and the input rate IR of the connection at that time (step 103), and then the large one of the minimum value MIN and the minimum cell rate MCR declared at the time of connection setting is selected. Determine the final execution cell rate ACR (step 104). Such a conformity determination process can be expressed as in Eq. (1). [0040] ACR = max (MCR, min (ECR, PCR, ACR *, IR)) ... (1) When the result of the communication communication determination in step 101 described above is obtained that communication is not in progress, the ACR calculation unit 19 sets the lowest cell rate LCR (Lowest Cell Rate) as the final execution cell rate ACR (step 105). [0041] In the case of this first embodiment, the minimum cell rate LCR is defined in common for all connections of the ABR service. It is preferable that the minimum cell rate LCR is smaller than the minimum value that can be declared as the minimum cell rate MCR. [0042] When the ACR calculation unit 19 determines the final execution cell rate ACR, whether or not the incoming RM cell connection is in communication, the determined execution cell rate ACR is given to the VCS unit 15 (step 106). , The series of processes shown in FIG. 3 is completed. [0043] The ACR calculation unit 19 that performs the above processing may be configured by either a hardware configuration or a software configuration. When the ACR calculation unit 19 is composed of software, the processes of steps 101 to 105 shown in FIG. 3 can be expressed programmatically as follows. If the processing represented by the following expressions can be executed, the processing flow is not limited to that shown in FIG. [0044] if (Connstt = 0) ACR = LCR; else else ACR = max (MCR, min (ECR, PCR, ACR *, IR)); The ATM cells (data cells and RM cells) related to the ABR service output from the VCS unit 15 are exchanged via the ATM switch unit 12 and reach the VPS unit 16 in the output line unit 12. [0045] When the ATM cell related to the ABR service arrives, the VPS unit 16 queues it in the queue 16a for the ABR service and then allocates the bandwidth (cell rate) given to the connection group of the ABR service. ) Send (shape) to the subsequent stage (not shown) according to Bg. On the other hand, when the ATM cell related to the arrived ABR service is an RM cell, the VPS unit 16 hands the RM cell to the second ABR control unit 17, whereby the second ABR control unit 17 causes the RM. Various information such as cell congestion information and explicit cell rate ECR are included and returned to the incoming line unit 11. [0046] RM cell return processing by the second ABR control unit 17<u style="single">The body is</u>, It is the same as the conventional one, but since it is related to the ACR calculation method shown in FIG. 3, the ECR calculation process executed by the ECR calculation unit 20 will be briefly described. FIG. 4 is a flowchart showing the ECR calculation process executed by the ECR calculation unit 20. [0047] The ECR calculation unit 20 starts the process shown in FIG. 4 every predetermined cycle (for example, one cell time), and first confirms whether or not the RM cell has arrived (step 150). When it arrives, the ECR calculation unit 20 retrieves the execution cell rate CCRi (i indicates a connection) contained in the RM cell (step 151). Then, the ECR calculation unit 20 calculates the explicit cell rate ECRi of the connection i according to the equation (2) (step 152). [0048] ECRi = CCRi + (Bg-ΣCCR) ... (2) In equation (2), Bg is the band (cell rate) allocated to the ABR connection group in the VPS section 16, and ΣCCR is the sum of the CCRs in the ABR connection groove. [0049] After that, the ECR calculation unit 20 determines whether or not the explicit cell rate ECRi obtained by the calculation is smaller than the minimum guaranteed explicit cell rate ECR0i for the connection i (step 153). If it is small, the ECR calculation unit 20 sets the minimum guaranteed explicit cell rate ECR0i as the explicit cell rate ECRi (step 154). [0050] Here, the explicit cell rate ECR0i of the minimum guarantee for the connection i can be expressed by Eq. (3). That is, the allocated bandwidth Bg of the ABR connection group can be expressed as being proportionally divided by the minimum cell rate MCR of each connection in the ABR connection groove. [0051] ECR0i = (MCRi / ΣMCR) * Bg ... (3) Finally, the ECR calculation unit 20 writes the obtained explicit cell rate ECRi in the RM cell (step 155), and ends the series of processes shown in FIG. [0052] As described above, this explicit cell rate ECR is used in the calculation of the execution cell rate ACR in the ACR calculation unit 19. [0053] (A-3) Effect of the first embodiment According to the first embodiment, when the cell sender of the ABR service calculates the execution cell rate ACR of a connection, if the connection is not in communication, the execution cell rate ACR is forced to be the lowest cell rate LCR. Therefore, the bandwidth (cell rate) for MCR-LCR can be allocated to other connections in the ABR connection group, and efficient traffic control can be performed. [0054] Hereinafter, the effects of the first embodiment will be described with reference to specific examples. In addition, the method of comparing with the first embodiment (hereinafter referred to as a comparative example method) is always the above-mentioned equation (1) regardless of whether or not the connection for which the calculation target of the execution cell rate ACR is calculated is in communication. The execution cell rate ACR shall be calculated according to. [0055] Here, there are four connections a, b, c, d of the ABR service with PCR = 8M (M stands for Mbps; the same applies hereinafter) and MCR = 2M, and this ABR service group has 8M as the group bandwidth Bg. Suppose it is given. Now, when data (data cell) is input to each connection a, b, c, d by 2.0M, each parameter value is as shown in FIG. In this state, the ABR service group is given 8M bandwidth Bg for the entire group, so the surplus bandwidth for traffic control is 8-8 (total CCR) = 0M. [0056] It is assumed that the communication of connection d is stopped in this state. That is, it is assumed that the input cell rate IR of the connection d becomes 0M. [0057] In the comparative example method, even if communication is stopped, the executed cell rate ACR drops only to the minimum cell rate MCR (ACR = MCR), so each parameter is shown in FIG. The surplus bandwidth for traffic control at this time is also 8-8 (total of CCR) = 0M, and even though there is actually 2M of free bandwidth (= total of 6M of group bandwidth 8M-IR), the group Even if other connections in the network try to send more data, the actual free bandwidth of 2M cannot be used, which means that efficient traffic control is not performed. [0058] [0058] On the other hand, in the first embodiment, in the state shown in FIG. 5, when the communication of the connection d is stopped (when the input cell rate IR of the connection d becomes 0M), the execution cell rate ACR of the connection d is forcibly forced. Since the lowest cell rate LCR is set, each parameter is shown in FIG. The surplus bandwidth for traffic control at this time is 8- (total of CCR) = (2.0-LCR) M, and when other connections in the group try to transmit more data, this surplus bandwidth (total of CCR) ( You will be able to send data using 2.0-LCR) M. As a result, the bandwidth for (MCR-LCR) can be used more effectively than in the comparative example method, and efficient traffic control can be performed. [0059] (A-4) Modified Embodiment of First Embodiment Examples of the modified embodiment of the first embodiment described above include the following. [0060] In the above explanation, the minimum cell rate LCR related to the execution cell rate ACR is shown to be a universal fixed value common to each connection, but it may be set to a predetermined ratio in consideration of the number of group connections with respect to the allocated bandwidth Bg of the ABR connection group. As such, it may be set to a fixed value according to the number of connections or the like. [0061] Further, a different minimum cell rate LCR may be set for each connection so that α (0 &lt;α &lt;1) times of the minimum cell rate MCR of each connection is set as the minimum cell rate LCR. [0062] Further, in the above description, the case where the execution cell rate ACR is forcibly set to the minimum cell rate LCR is the case where the communication of the connection is stopped, but other cases may be used. For example, when the input rate IR of the connection becomes less than β (0 &lt;β &lt;1) times the minimum cell rate MCR, the execution cell rate ACR may be forced to the minimum cell rate LCR. [0063] Furthermore, in the above description, the control loop of the ABR service to which the technical idea of forcibly setting the execution cell rate ACR to the minimum cell rate LCR when a predetermined condition is satisfied is the input side line portion 11 and the exit side of the ATM switching device. Although the control loop connecting the line units 12 is shown, the above technical idea can be applied to the control loop of other ABR services on the ATM network system. [0064] For example, a control loop between a virtual receiving terminal on a transmitting terminal and an ATM switching device, a control loop between a virtual transmitting terminal and a receiving terminal on an ATM switching device, or a virtual transmitting terminal on an ATM switching device. And the above technical idea can be applied to a control loop between virtual receiving terminals on another ATM switching device. [0065] (B) Second embodiment Next, a second embodiment in which the cell transmission device traffic control system according to the present invention is applied to an ATM switching device of an ATM network system will be described in detail with reference to the drawings. [0066] The ATM switching device of the second embodiment can also be represented by FIG. 1 according to the first embodiment when the functional block diagram is drawn from the traffic control aspect. [0067] However, the execution cell rate ACR calculation process executed by the ACR calculation unit 19 is different from that of the first embodiment. [0068] Therefore, in the following, the calculation process of the execution cell rate ACR executed by the ACR calculation unit 19 of the second embodiment will be described with reference to the flowchart of FIG. [0069] The ACR calculation unit 19 starts the process shown in FIG. 8 every predetermined cycle (for example, one cell time), and first determines whether or not the RM cell returned from the outgoing line unit 12 has arrived (step 200). ). If the RM cell has not arrived, the series of processes shown in FIG. 8 is terminated. [0070] On the other hand, when the RM cell arrives, the ACR calculation unit 19 calculates the update candidate value ACR * of the execution cell rate from the congestion information (rate increase / decrease display bit NI, congestion display bit CI) in the arrived RM cell. (Step 201). Again, regarding the calculation of the update candidate value ACR * of the execution cell rate, for example, 5.10.4 Source of The ATM Forum Traffic Management Specification Version 4.0, which is a recommendation of the ATM Forum. It is done according to Behavior. [0071] Also in this second embodiment, after the calculation of the update candidate value ACR * of the execution cell rate, the conformity determination process of this value ACR * is performed. [0072] In the conformity determination process, first, the explicit rate ECR inserted in the incoming RM cell and calculated as the rate that the second ABR control unit 17 can tolerate, the maximum cell rate PCR declared at the time of connection setting, and the update candidate value. The smallest ACR * and the input rate IR of the connection at that time are taken out (step 202), and then the larger one with the minimum value MIN and the lowest cell rate LCR is taken as the final execution cell rate ACR. (Step 203). Such conformity determination processing can be expressed as in Eq. (4). [0073] ACR = max (LCR, min (ECR, PCR, ACR *, IR)) ... (4) Also in this second embodiment, the minimum cell rate LCR is defined in common for all connections of the ABR service. In the second embodiment, the minimum cell rate LCR is less than the minimum value that can be declared as the minimum cell rate MCR. [0074] When the ACR calculation unit 19 determines the final execution cell rate ACR, the determined execution cell rate ACR is given to the VCS unit 15 (step 204), and the series of processes shown in FIG. 8 is completed. [0075] According to the second embodiment, when the cell sender of the ABR service calculates the execution cell rate ACR of a certain connection, the execution cell rate is such that the rate IR of the input data of the connection is lower than the minimum cell rate MCR. Since the lowest cell rate LCR and the larger input rate IR are selected as the ACR, more bandwidth (cell rate) can be allocated to other connections in the ABR connection group than before, and efficient traffic control can be achieved. It can be carried out. [0076] Hereinafter, the effects of such a second embodiment will be described with reference to specific examples. In the method of comparing with the second embodiment (hereinafter, referred to as a comparative example method), the execution cell rate ACR shall always be calculated according to the above-mentioned equation (1). [0077] Here, too, the initial state is the state shown in FIG. 5 described above. From this state, it is assumed that the input cell rate IR of the connection d becomes 1M, which is smaller than the minimum cell rate MCR (2M) and larger than the minimum cell rate LCR. [0078] In the comparative example method, even if this change occurs, the execution cell rate ACR decreases only to the minimum cell rate MCR (ACR = MCR), so that each parameter is shown in FIG. 9 (note that the same applies to the first embodiment). ). The surplus bandwidth for traffic control at this time is 8-7 (total of CCR) = 1M, and even though there is actually 1M of free bandwidth, other connections in the group are more data than they are now. Even if you try to send it, you cannot use the actual free bandwidth of 1M, and it can be said that efficient traffic control is not performed. [0079] On the other hand, in the case of the second embodiment, when the input rate IR of the connection d becomes 1M, which is smaller than the minimum cell rate MCR (2M), each parameter becomes as shown in FIG. That is, in the second embodiment, since the execution cell rate ACR is 1M (= 1M), the surplus bandwidth for connection management is 8-7 (total of CCR) = 1M, and the actual free bandwidth is 1M (= group). Bandwidth 8M-IR total 7M) can now be used effectively by other connections. In other words, even if the input rate IR is smaller than the minimum cell rate MCR, when it is larger than the minimum cell rate LCR, the execution cell rate ACR is continuously determined according to the input rate IR, which is more efficient and more data than before. Real-time traffic control can be executed according to the input rate of. [0080] [0080] Even if the input rate IR becomes less than the minimum cell rate LCR, the execution cell rate ACR at that time becomes the minimum cell rate LCR, and the bandwidth of the connection is continuously secured, and it responds immediately when the input rate increases. Be done. [0081] Incidentally, in the case of the second embodiment, the minimum cell rate MCR is not directly related to the determination of the execution cell rate ACR, but the user transmits data (data cell) exceeding the declared minimum cell rate during communication. In most cases, the effect of the second embodiment described above is rarely exerted, and there is no problem even if the minimum cell rate MCR is not directly reflected in the determination of the execution cell rate ACR. Rather, it is more problematic to set the execution cell rate ACR to the minimum cell rate MCR in a situation where the input rate IR is less than or equal to the minimum cell rate MCR. [0082] Examples of the modified embodiment of the second embodiment described above include the following. [0083] In the above explanation, the minimum cell rate LCR related to the execution cell rate ACR is shown to be a universal fixed value common to each connection, but it may be set to a predetermined ratio in consideration of the number of group connections with respect to the allocated bandwidth Bg of the ABR connection group. As such, it may be set to a fixed value according to the number of connections or the like. Further, a different minimum cell rate LCR may be set for each connection so that α (0 &lt;α &lt;1) times of the minimum cell rate MCR of each connection is set as the minimum cell rate LCR. [0084] Furthermore, the technical idea of the second embodiment can be described, for example, in a control loop between a transmitting terminal and a virtual receiving terminal on an ATM switching device, or control between a virtual transmitting terminal and a receiving terminal on an ATM switching device. It can be applied to a loop or a control loop between a virtual transmitting terminal on an ATM switching device and a virtual receiving terminal on another ATM switching device. [0085] (C) Other embodiments In each of the above embodiments, in the ATM switching device, the incoming line unit 11 and the output line unit 12 with respect to the ATM switch unit 13 are shown to be 1: 1. The same can be applied to multiple devices. The present invention can also be applied to an ATM switching device dedicated to the ABR service. [0086] Further, the technical idea of the first embodiment and the technical idea of the second embodiment may be combined. For example, the lowest cell rate according to the first embodiment is LCR1, the lowest cell rate according to the second embodiment is LCR2 (&gt; LCR1), and when the connection is not communicating, the execution cell rate ACR is set to the lowest cell rate LCR1 and the connection is established. When communicating with each other, the execution cell rate ACR may be determined according to the above-mentioned equation (4) in which the minimum cell rate is LCR2. [0087] The service to which the technical idea of the present invention is applied is not limited to the ABR service, and can be applied to a service in which the determination of the execution cell rate (lower limit method) is similar to the ABR service. Also, the network is not limited to the ATM network. [0088] [Effect of the invention] According to the present invention, when the input rate of the data cell of a certain connection is smaller than the minimum cell rate, the execution cell rate for sending out the data cell is set to the minimum cell rate smaller than the minimum cell rate under a predetermined condition. The rate distributed to connections can be increased, and efficient traffic control can be realized. [Simple explanation of drawings] FIG. 1 is a block diagram showing a traffic control configuration of the ATM switching device of the first embodiment. FIG. 2 is an explanatory diagram of a traffic control method related to a conventional ABR service. FIG. 3 is a flowchart showing an ACR calculation process of the first embodiment. FIG. 4 is a flowchart showing an ECR calculation process of the first embodiment. FIG. 5 is an explanatory diagram (1) of the effect of the first embodiment. FIG. 6 is an explanatory diagram (2) of the effect of the first embodiment. FIG. 7 is an explanatory diagram (3) of the effect of the first embodiment. FIG. 8 is a flowchart showing an ACR calculation process of the second embodiment. FIG. 9 is an explanatory diagram (1) of the effect of the second embodiment. FIG. 10 is an explanatory diagram (2) of the effect of the second embodiment. [Explanation of symbols] 10 ... ATM switching device, 11 ... Incoming line section, 12 ... Outer line section, 13 ... ATM switch section (SW section), 14 ... 1st ABR control section, 17 ... second ABR control unit, 18 ... input rate calculation unit, 19 ... ACR calculation unit, 20 ... ECR calculation unit.