JP2006324864A - Network switch and back pressure control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a network switch and a back pressure control method that can realize communication of high quality without increasing the buffer size of an output buffer even in a state of connection to a high-speed network. <P>SOLUTION: An output buffer part 2230a transmits back pressure in two stages according to the use state of the output buffer. When the consumption of the output buffer exceeds a normal threshold, the back pressure is transmitted to in-side switch blades 2100a to 2100n as usual. In addition, when the consumption of the output buffer exceeds an emergency threshold, the back pressure is transmitted to input control parts 2210a to 2210n in a main switch part 2200. The input control parts 2210a to 2210n are at short distances to the output buffer part 2230a and have short delay times of the back pressure, so the output buffer part 2230a can avoid a buffer overflow with a small buffer size. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an output buffer type network switch for controlling congestion of an output buffer by back pressure and a back pressure control method in the network switch, and more particularly to a buffer size of an output buffer even in a situation where it is connected to a high-speed network. The present invention relates to a network switch and a back pressure control method capable of realizing high-quality communication without increasing the number.

  With the progress of networking, the quality of network switches that relay packets (frames) in layer 2 and layer 3 is regarded as important. The quality of the network switch is expressed by, for example, the stability of the throughput, the low packet loss, the reliability of priority control, and the like.

  Network switches have architectures such as an input buffer type, a shared buffer type, and an output buffer type. Among these, the output buffer type is a method in which a buffer for priority control is provided on the output side, which is relatively simple. The configuration can be realized, and since the distance between the output interface and the output buffer is short, there is an advantage that a relatively small amount of memory is required.

  On the other hand, the output buffer type has a drawback that packet loss is likely to occur when packets are concentrated on a specific output destination. In order to eliminate this drawback, Patent Document 1 discloses a technique for avoiding packet loss due to overflow of the output buffer by changing the content of priority control according to the traffic volume.

JP 7-297840 A

  However, due to the recent increase in network speed and the generalization of network distribution of large-capacity data such as video and audio, the impact when packets are concentrated on a specific output destination is greater than before. The technique of Patent Document 1 effectively uses the capacity of the output buffer. Even if this technique is used, the capacity of the output buffer must be increased in order to maintain the quality when the load is concentrated. I need it.

  When the capacity of the output buffer is increased, the cost of the network switch increases, and the advantage of the output buffer method that the amount of memory is small is lost, and the superiority to other methods is lost.

  The present invention has been made to solve the above-mentioned problems caused by the prior art, and realizes high-quality communication without increasing the buffer size of the output buffer even in a situation where it is connected to a high-speed network. An object of the present invention is to provide a network switch and a back pressure control method that can be used.

  In order to solve the above-described problems and achieve the object, the present invention is an output buffer type network switch that performs output buffer congestion control by back pressure, and has a plurality of stages whose operation destinations differ depending on the congestion state. A back pressure output buffer for transmitting back pressure is provided.

  The present invention also relates to a back pressure control method for an output buffer type network switch, the step of transmitting a plurality of stages of back pressure according to the congestion state of the output buffer, and the back pressure according to the stage of the back pressure. And a step of changing the actuating destination.

  According to the present invention, since it is configured to be able to transmit back pressure with different destinations according to the congestion status of the output buffer, when the output buffer is congested, the position close to the output buffer The buffer size of the output buffer can be reduced by making a transmission stop request.

  Further, the present invention, in the above invention, further includes a degenerate class buffer common to all output destinations degenerated in the priority control class on the input side of the own device, and the back pressure that requests transmission stop of the specific priority control class is received. In this case, only the degenerate class buffer corresponding to the priority control class is set in a transmission stop state.

  According to the present invention, the packet (frame) in the process is held in the degenerate class buffer common to all output destinations degenerated in the priority control class, so that the packet due to the overflow of the output buffer by adding a small amount of memory Loss can be avoided.

  The present invention further includes a monitoring means for monitoring the amount of input traffic in the above invention, and when the monitoring means determines that the traffic volume is lower than a predetermined threshold value, the transmission stop request by the back pressure is ignored. It is characterized by doing.

  According to the present invention, when the input traffic is low, the transmission stop request due to the back pressure is ignored. Therefore, it is possible to avoid a decrease in the throughput due to erroneous back pressure.

  The present invention further includes an assembly buffer for reassembling the subdivided cells output from the output buffer for each priority control class in the above invention, and the usage amount of the assembly buffer exceeds a predetermined threshold value. In this case, a back pressure requesting to stop transmission of the priority control class is transmitted to the input unit.

  According to the present invention, since the congestion control is performed for each priority control class in the assembly buffer of the output unit, the congestion control is realized every minute, so that even if the buffer size of the output buffer is small, the buffer of the output buffer The possibility of packet loss due to overflow can be reduced.

  According to the present invention, since it is configured to be able to transmit back pressure with different operation destinations according to the congestion status of the output buffer, the position close to the output buffer when the congestion status of the output buffer is tight By making a transmission stop request at the same time, the buffer size of the output buffer can be reduced.

  In addition, according to the present invention, the packet (frame) in the process is held in the degenerate class buffer common to all output destinations in which the priority control class is degenerated, so that the buffer overflow of the output buffer can be achieved by adding a small amount of memory. The packet loss due to can be avoided.

  In addition, according to the present invention, when the input traffic is low, the transmission stop request due to the back pressure is ignored, so that it is possible to avoid a decrease in throughput due to an erroneous back pressure. Play.

  In addition, according to the present invention, since the congestion control is performed for each priority control class in the assembly buffer of the output unit, the congestion control is realized in a short time, so that even when the buffer size of the output buffer is small, the output buffer There is an effect that it is possible to reduce the possibility of packet loss due to buffer overflow.

  Exemplary embodiments of a network switch and a back pressure control method according to the present invention will be explained below in detail with reference to the accompanying drawings. In the following embodiments, first, a conventional output buffer type network switch will be described, and then a network switch and a back pressure control method according to the present invention will be described.

  Note that the network switch here is not limited to a specific communication method or network layer, and corresponds to, for example, a layer 2 switch, a layer 3 switch, a router device, an ATM switch, or the like.

  First, a conventional output buffer type network switch will be described. FIG. 12 is a functional block diagram showing a configuration of a conventional network switch 1000. As shown in FIG. Here, an example of a network switch having n input ports and n output ports is shown.

  As shown in the figure, the network switch 1000 includes input side switch blades 1100a to 1100n, a main switch unit 1200, and output side switch blades 1300a to 1300n.

  The ingress switch blades 1100a to 1100n are devices that exist for each input port. Since these have the same configuration, the details of the configuration will be described by taking the ingress switch blade 1100a as an example.

  The ingress switch blade 1100a includes an interface 1110a, a network processor 1120a, and a traffic manager 1130a. The interface 1110a is an interface for connecting to a network line.

  The network processor 1120a is a processing unit that analyzes a header portion of a packet input through the interface 1110a and determines a QoS (Quality of Service) class for priority control and an output destination port. In the present embodiment, it is assumed that QoS classes 1 to x exist.

  The traffic manager 1130a is a processing unit that divides a packet for which the QoS class is determined into fixed-length cells in order to simplify the processing in the main switch unit 1200. Packets divided into cells are temporarily stored in a buffer in a traffic manager 1130a provided for each QoS class and for each outgoing switch blade for congestion control.

  The main switch unit 1200 is a processing unit that performs cell allocation and priority control, and includes first in first out (FIFO) 1210a to 1210n, a switch 1220, output buffer units 1230a to 1230n, and a scheduler 1240. The FIFOs 1210a to 1210n exist one by one in correspondence with the ingress switch blades 1100a to 1100n, temporarily hold cells output from the corresponding ingress switch blades, and output to the switch 1220 in a first-in first-out manner.

  The switch 1220 is a processing unit that distributes the cells output from the FIFOs 1210a to 1210n toward the ports determined by the network processors 1120a to 1120n as output destinations.

  The output buffer units 1230a to 1230n exist one by one in correspondence with the output side switch blades 1300a to 1300n, and are processing units that output cells to the corresponding output side switch blades according to the priority of the QoS class. Each output buffer unit includes a buffer for each QoS class, and outputs the cells stored therein to the corresponding outgoing switch blade according to the schedule determined by the scheduler 1240.

  In order to avoid packet loss due to buffer overflow due to load concentration on a specific output port, the buffers provided in the output buffer units 1230a to 1230n have a relatively large capacity.

  The scheduler 1240 is a processing unit that performs priority control of packets, and determines a schedule for outputting the cells stored in the buffers in the output buffer units 1230a to 1230n to the outgoing switch blades 1300a to 1300n based on a predetermined rule. .

  The outgoing switch blades 1300a to 1300n are devices that exist for each output port. Since these have the same configuration, the details of the configuration will be described using the exit switch blade 1300a as an example.

  The outgoing switch blade 1300a includes a traffic manager 1310a, a network processor 1320a, and an interface 1330a. The traffic manager 1310a is a processing unit that assembles cells and reproduces packets.

  The network processor 1320a is a processing unit that rewrites the header portion so that the reproduced packet reaches the transfer destination, and sends the rewritten packet through the interface 1330a. The interface 1330a is an interface for connecting to a network line.

  Next, a conventional back pressure system will be described. Back pressure means that when the number of cells stored in the buffer exceeds a predetermined threshold so that packet loss due to buffer overflow does not occur, this is communicated to the previous process, and the transfer process is temporarily performed. It is to stop.

  FIG. 13 is an explanatory diagram for explaining a conventional back pressure system. As shown in the figure, in the conventional back pressure system, there are three types of back pressure.

  When the number of cells stored in the FIFOs 1210a to 1210n of the main switch unit 1200 exceeds a predetermined threshold, the back pressure 11 transmits the fact to the corresponding ingress switch blade.

  As described above, the traffic managers 1130a to 1130n of the ingress switch blades 1100a to 1100n have buffers 1131a to 1132x for each QoS class and for each egress switch blade. The cells stored in these buffers are read by the priority control unit 1133 in accordance with a predetermined priority order, temporarily stored in the FIFO 1134, and then sent to the main switch unit 1200.

  The back pressure 11 has an effect of completely stopping the cell sending from the corresponding ingress switch blade.

  When the number of cells stored in the packet assembly buffer in the outgoing switch blades 1300a to 1300n exceeds a predetermined threshold value, the back pressure 12 transmits the fact to the corresponding output buffer unit. .

  As already described, the output buffer units 1230a to 1230n have buffers 1231a to 1232x for each QoS class. The cells stored in these buffers are read by the priority control unit 1232 in accordance with a predetermined priority order, temporarily stored in the FIFO 1233, and then transmitted to the corresponding outgoing switch blade.

  The traffic managers 1310a to 1310n of the outgoing switch blades 1300a to 1300n have buffers 1311a to 1312x for each QoS class and for each incoming switch blade in order to reassemble the packets divided into cells. The cells stored in these buffers are assembled into packets by the frame assembling unit 1313 when cells that can be reassembled are prepared and sent to the next process.

  The back pressure 12 has the effect of completely stopping the cell output from the corresponding output buffer unit.

  When the number of cells stored in the priority control buffers 1231a to 1232x in the output buffer units 1230a to 1230n exceeds a predetermined threshold value, the back pressure 13 notifies the ingress switch blades 1100a to 1100n. To do.

  The back pressure 13 is transmitted in such a way that it can be distinguished which of the buffers 1231a to 1232x has exceeded the threshold, and has an effect of stopping only the cell transmission from the corresponding buffer of the ingress switch blades 1100a to 1100n.

  For example, in the output buffer unit 1230a corresponding to the outgoing switch blade 1300a, when the number of cells stored in the buffer 1231x corresponding to the QoS class x exceeds a predetermined threshold, the outgoing switch The sending of cells from the buffer 1131x corresponding to the blade 1300a and the QoS class x is stopped.

  Next, the buffer size required for the output buffer units 1230a to 1230n will be described. Here, the output buffer unit 1230a will be described as an example. FIG. 14 is an explanatory diagram for explaining a buffer size required for the output buffer unit 1230a in the conventional network switch.

  The output buffer unit 1230a generates a packet loss if a buffer of a size sufficient to store the cell that reaches the cell until the cell transmission is actually stopped is not secured for each QoS class after requesting the cell transmission stop. Resulting in.

The cell transmission stop request from the output buffer unit 1230a is made by the back pressure 13, and the delay time until the back pressure 13 reaches the ingress switch blades 1100a to 1100n from the output buffer unit 1230a is T1, and the back pressure is set. Assuming that the delay time until the cell sent just before reaching 13 reaches the output buffer unit 1230a is T2, and the maximum input speed of the cell is S, the output buffer unit 1230a has at least S × (T1 + T2) × n.
The buffer size must be provided.

  Next, the network switch according to the present embodiment will be described. FIG. 1 is a functional block diagram showing the configuration of the network switch 2000 according to the present embodiment. As shown in the figure, the network switch 2000 includes input side switch blades 2100a to 2100n, a main switch unit 2200, and output side switch blades 2300a to 2300n.

  The ingress switch blades 2100a to 2100n exist for each input port and have the same configuration as the conventional network switch 1000. For example, the ingress switch blade 2100a includes an interface 2110a, a network processor 2120a, and a traffic manager 2130a, which correspond to the interface 1110a, the network processor 1120a, and the traffic manager 1130a, respectively.

  The main switch unit 2200 is a processing unit that performs cell allocation and priority control, and includes input control units 2210a to 2210n, a switch 2220, output buffer units 2230a to 2230n, and a scheduler 2240. The switch 2220 and the scheduler 2240 are processing units similar to the switch 1220 and the scheduler 1240 in the conventional network switch 1000.

  The input control units 2210a to 2210n are processing units provided in place of the FIFOs 1210a to 1210n. The input control units 2210a to 2210n include a memory for avoiding buffer overflow of the output buffer units 2230a to 2230n, and a filtering unit that controls transmission of back pressure. Have. Detailed operations of the input control units 2210a to 2210n will be described later.

  The output buffer units 2230a to 2230n exist one by one in correspondence with the output side switch blades 2300a to 2300n, and are processing units that output cells to the corresponding output side switch blades according to the priority of the QoS class. In addition to the back pressure 24 corresponding to the conventional back pressure 13, the output buffer units 2230a to 2230n transmit the back pressure 25 having a higher degree of urgency.

  The outgoing switch blades 2300a to 2300n exist for each output port, and have substantially the same configuration as the conventional network switch 1000. For example, the outgoing switch blade 2300a includes a traffic manager 2310a, a network processor 2320a, and an interface 2330a, which correspond to the traffic manager 1310a, the network processor 1320a, and the interface 1330a, respectively.

  However, the traffic manager 2310a is different from the conventional one in that it transmits a back pressure 26 that is a back pressure of a QoS class unit in addition to the back pressure 23 corresponding to the conventional back pressure 12.

  Next, the back pressure system according to the present embodiment will be described. FIG. 2 is an explanatory diagram for explaining the back pressure system according to the present embodiment. As shown in the figure, in the back pressure system of this embodiment, there are eight types of back pressure.

  Of the eight types of back pressure, the back pressure other than the back pressure 23 corresponding to the conventional back pressure 12 is transmitted to or transmitted from the back pressure filter unit 2214 of the input control unit 2210a.

  FIG. 3 is a functional block diagram showing a configuration of the back pressure filter unit 2214 shown in FIG. As shown in the figure, the back pressure filter unit 2214 includes a congestion back pressure reception unit 2214a, an emergency back pressure reception unit 2214b, a DSWB back pressure reception unit 2214c, an input cell count unit 2214d, and an input amount threshold value excess determination. Unit 2214e, a back pressure control unit 2214f, a degenerate class buffer back pressure transmitting unit 2214g, a degenerate class buffer correspondence storage unit 2214h, a degenerate class buffer back pressure receiving unit 2214i, and an SSWB back pressure transmitting unit 2214j.

  The congestion back pressure receiving unit 2214a is a processing unit that receives the back pressure 24 corresponding to the conventional back pressure 13 from the output buffer units 2230a to 2230n and inputs this to the back pressure control unit 2214f.

  The data structure of the back pressure 24 is shown in FIG. As shown in the figure, when the number of ports on the outgoing side is n and the number of QoS classes is x, the back pressure 24 is composed of bits multiplied by n and x, and each bit is output buffer unit 2230a. Corresponds one-to-one with the buffers for each QoS class of ˜2230n. When the bit value is 0, it means that the number of cells stored in the corresponding buffer is equal to or less than a predetermined threshold value, and when the bit value is 1, the cell stored in the corresponding buffer. Means that the number exceeds the predetermined threshold.

  The emergency back pressure receiving unit 2214b is a processing unit that receives the back pressure 25 from the output buffer units 2230a to 2230n and inputs this to the back pressure control unit 2214f. The data structure of the back pressure 25 is the same as that of the back pressure 24, as shown in FIG.

  Similarly to the back pressure 24, the back pressure 25 has a bit corresponding to 1 when the number of cells stored in any of the buffers for each QoS class included in the output buffer units 2230a to 2230n exceeds a predetermined threshold. Set to The difference between the back pressure 25 and the back pressure 24 is that the back pressure 25 is set to have a higher threshold value for setting the bit to 1, and the input destination is not the input side switch blades 2100a to 2100n but the input control. Two points are that the buffers are provided in the portions 2210a to 2210n.

  Since the back pressure 25 is set to have a high threshold value, the effect of stopping the cell transmission acts later than the back pressure 24. This means that the buffer sizes of the output buffer units 2230a to 2230n depend not on the delay time of the back pressure 24 but on the delay time of the back pressure 25.

  The destination to which the back pressure 25 acts is a buffer provided in the input control units 2210a to 2210n, and the distance from the output buffer units 2230a to 2230n is shorter than the input side switch blades 2100a to 2100n. For this reason, the delay time of the back pressure 25 is shorter than that of the back pressure 24, and in the network device according to the present embodiment, the buffer sizes of the output buffer units 2230a to 2230n can be reduced accordingly.

  The DSWB back pressure receiving unit 2214c is a processing unit that receives the back pressure 26 from the output side switch blades 2300a to 2300n and inputs the back pressure 26 to the back pressure control unit 2214f.

  The data structure of the back pressure 26 is shown in FIG. As shown in the figure, when the number of ports on the input side is n, the number of ports on the output side is n, and the number of QoS classes is x, the back pressure 26 is calculated from the number of bits obtained by multiplying the square of n by x. Each bit has a one-to-one correspondence with a packet assembly buffer included in the outgoing switch blades 2300a to 2300n. When the bit value is 0, it means that the number of cells stored in the corresponding buffer is equal to or less than a predetermined threshold value, and when the bit value is 1, the cell stored in the corresponding buffer. Means that the number exceeds the predetermined threshold.

  Since the buffer for packet assembly exists in each outgoing switch blade for each QoS class and for each incoming switch blade, the back pressure 26 received by the DSWB back pressure receiving unit 2214c corresponds to the input control unit. Bits other than the incoming switch blade are also included.

  For this reason, the DSWB back pressure receiving unit 2214c deletes the bits other than the corresponding input side switch blade from the back pressure 26 to be received, and then inputs the bits to the back pressure control unit 2214f. As a result, the signal input from the DSWB back pressure receiving unit 2214c to the back pressure control unit 2214f has the same configuration as that in FIG.

  Since the packet assembly buffer is smaller in size than the buffer of the output buffer unit, it is considered that the bit threshold is exceeded earlier and more frequently in the back pressure 26 than in the back pressure 24. As a result, cell transmission stop / retransmission control according to the load concentration state on the output port is performed at an early stage and in small increments. Even if the buffer size of the output buffer units 2230a to 2230n is reduced, the buffer can be stored. The risk of overflow is reduced.

  When the value of any bit of the back pressure 24 that means a cell transmission stop request to the input control units 2210a to 2210n becomes 1, the input cell count unit 2214d and the output side switch blade corresponding to the bit and the QoS A processing unit that counts the number of input cells of a class.

  When the value of any bit of the back pressure 25 becomes 1, the input amount threshold value excess determination unit 2214e is configured to wait until the number of input cells counted by the input cell count unit 2214d becomes larger than a predetermined threshold value. In the meantime, the processing unit transmits a cancel signal instructing to ignore the back pressure 25 to the back pressure control unit 2214f. The predetermined threshold value is, for example, a value obtained by dividing the number of cells that can be stored in the buffer of the output buffer unit by the number of input ports.

  In this way, the cell input amount is monitored after the cell transmission stop request by the back pressure, and if this is smaller than the predetermined threshold, the cell transmission stop request is ignored, thereby causing the back pressure based on an erroneous determination. A decrease in throughput can be avoided.

  The back pressure control unit 2214f receives signals from the congestion back pressure receiving unit 2214a, the emergency back pressure receiving unit 2214b, the DSWB back pressure receiving unit 2214c, and the input amount threshold value excess determining unit 2214e, and according to the status of those signals This is a processing unit that transmits a signal to the degenerate class buffer back pressure transmission unit 2214g and the SSWB back pressure transmission unit 2214j. The signal transmitted by the back pressure control unit 2214f has the same configuration as that in FIG.

  The signal transmitted from the back pressure control unit 2214f to the degenerate class buffer back pressure transmission unit 2214g is the basis of the back pressure 28 which is a back pressure for the buffer inside the input control unit. The signal transmitted from the back pressure control unit 2214f to the SSWB back pressure transmission unit 2214j is the basis of the back pressure 27 that is the back pressure to the QoS class-specific buffer of the corresponding ingress switch blade.

  The processing logic of the back pressure control unit 2214f is shown in FIG. The back pressure control unit 2214f applies the corresponding bit of each input signal to this logic to determine the value of the bit of the signal to be output.

  As shown in FIG. 6, the bit transmitted to the SSWB back pressure transmission unit 2214j is ON if either of the bits of the signal input from the congestion back pressure reception unit 2214a and the DSWB back pressure reception unit 2214c is ON. It becomes. Further, the bit transmitted to the degenerate class buffer back pressure transmission unit 2214g is a cancellation signal input from the input amount threshold value excess determination unit 2214e when the bit of the signal input from the emergency back pressure reception unit 2214b is ON. It turns ON when the bit is OFF.

  Based on the signal transmitted from the back pressure control unit 2214f, the degenerate class buffer back pressure transmission unit 2214g is a processing unit that transmits a back pressure 28 that is a back pressure for the buffer inside the input control unit.

  As shown in FIG. 2, a buffer is provided in each of the input control units 2210a to 2210n, and a cell can be held when a request to stop cell transmission is made by back pressure. It is like that. Originally, it is preferable to provide a buffer for each QoS class, but this requires a large amount of memory.

  Therefore, in the back pressure system according to the present embodiment, a buffer is provided for each class in which the QoS class is degenerated. In this embodiment, two degenerate classes, High and Low, are set, and a buffer 2211a corresponding to the High class and a buffer 2211b corresponding to the Low class are provided.

  The data structure of the back pressure 28 is shown in FIG. As shown in the figure, the back pressure 28 is composed of two bits, and each bit has a one-to-one correspondence with a buffer 2211a which is a High class buffer and a buffer 2211b which is a Low class buffer. When the bit value is 1, it means that the cell transmission from the corresponding buffer should be stopped, and when the bit value is 0, it means that the cell can be transmitted from the corresponding buffer. To do.

  As described above, the degenerate class buffer back pressure transmission unit 2214g receives signals for each QoS class class and each outgoing switch blade as shown in FIG. 4 and converts them into signals as shown in FIG. This conversion is performed based on the degenerate class buffer correspondence data stored in the degenerate class buffer correspondence storage unit 2214h.

  The degenerate class buffer back pressure receiving unit 2214i is a processing unit that receives the back pressure 21 that is a back pressure from a buffer provided inside the input control unit, and inputs this to the SSWB back pressure transmitting unit 2214j. In the case of the present embodiment, there are two buffers, High and Low, in the input control unit, but the degenerate class buffer back pressure receiving unit 2214i is the result of logical product of the back pressures from these two buffers. Is input to the SSWB back pressure transmitter 2214j.

  The SSWB back pressure transmission unit 2214j is a processing unit that transmits back pressure to the corresponding ingress switch blade based on signals transmitted from the back pressure control unit 2214f and the degenerate class buffer back pressure reception unit 2214i.

  There are two types of back pressure transmitted by the SSWB back pressure transmission unit 2214j. One is the back pressure 22 transmitted based on the signal transmitted from the degenerate class buffer back pressure receiving unit 2214i. The back pressure 22 is composed of 1 bit as shown in FIG. 8, and when the value of the bit is 1, it means that cell transmission from the corresponding ingress switch blade should be completely stopped.

  Another back pressure is a back pressure 27 transmitted based on a signal transmitted from the back pressure control unit 2214f. As shown in FIG. 4, the back pressure 27 includes a bit for each QoS class and for each outgoing switch blade. When the value of these bits is 1, it means that cell transmission from the corresponding buffer should be stopped.

  Next, the buffer size required for the output buffer units 2230a to 2230n will be described. Here, the output buffer unit 2230a will be described as an example. FIG. 9 is an explanatory diagram for explaining a buffer size required for the output buffer unit 2230a in the network switch according to the present embodiment.

  The output buffer unit 2230a generates a packet loss unless a buffer of a size that can store the cells reached until the cell transmission is actually stopped is secured for each QoS class after the cell transmission is requested to stop. Resulting in.

The cell transmission stop request from the output buffer unit 2230a is made by the back pressure 25. The delay time until the back pressure 25 reaches the input control units 2210a to 2210n from the output buffer unit 2230a is T3, and the back pressure 25 When the delay time until the cell sent immediately before reaching the output buffer unit 2230a reaches T4 and the maximum input speed of the cell is S, the output buffer unit 2230a has at least S × (T3 + T4) × n.
The buffer size must be provided.

  Since T3 and T4 are shorter than T1 and T2, the buffer size required for the output buffer units 2230a to 2230n is smaller than that of the conventional one.

  Next, the processing content of the degenerate class buffer back pressure transmission unit 2214g will be described. FIG. 10 is an explanatory diagram for explaining the processing contents of the degenerate class buffer back pressure transmission unit 2214g. As shown in the figure, the degenerate class buffer back pressure transmission unit 2214g performs an OR operation between the back pressure signal transmitted from the back pressure control unit 2214f and the degenerate class buffer correspondence data acquired from the degeneration class buffer correspondence storage unit 2214h. The result of performing is transmitted as the back pressure 28.

  In the acquired degenerate class buffer correspondence data, it is set in which buffer in the input control unit the cell is stored for each QoS class and for each outgoing switch blade. In this embodiment, there are two types of buffers in the input controller, High and Low, but the degenerate class buffer compatible data has bits corresponding to High and Low for each QoS class and for each outgoing switch blade, and the cell The bit corresponding to the buffer to be stored is set to 1, and the bit corresponding to the buffer in which no cell is stored is set to 0.

  In the example of FIG. 10, for QoS class 1, all the bits corresponding to High are 1 and the bits corresponding to Low are 0. For all other than QoS class 1, the bit corresponding to High is 0, and the bit corresponding to Low is 1.

  The degenerate class buffer back pressure transmission unit 2214g calculates the logical sum of the bits of the back pressure signal and the acquired bits of the degenerated class buffer corresponding data for each class of the buffer in the input control unit, and the result of the back pressure of that class Value.

  Next, the processing content of the input amount threshold value excess determination unit 2214e will be described. FIG. 11 is an explanatory diagram for explaining the processing content of the input amount threshold value excess determination unit 2214e. As shown in the figure, the input cell count unit 2214d is a cell that belongs to the QoS class and has the output switch blade as the output destination when the back pressure 24 changes to ON. Start counting the number of. The counter value is reset to 0 when the back pressure 24 changes to OFF.

  The input amount threshold value excess determination unit 2214e monitors the value of this counter, and when the back pressure 25 is turned on, if the counter value is smaller than the predetermined threshold value, the cancellation signal is turned on and the threshold value is exceeded. If so, the cancel signal is turned OFF.

  As described above, in this embodiment, back pressure with different operation destinations is transmitted according to the congestion status of the output buffer, and transmission is stopped at a position close to the output buffer when the congestion status of the output buffer is tight. Since the request is made, the delay time of the back pressure is reduced, and the buffer size of the output buffer can be reduced.

(Appendix 1) An output buffer type network switch that performs congestion control of an output buffer by back pressure,
A network switch comprising a back pressure output buffer for transmitting back pressure at a plurality of stages whose operation destinations differ depending on a congestion state.

(Additional remark 2) When the back pressure which requests | requires the transmission stop of a specific priority control class is further provided in the input side of an own apparatus further, and the degeneration class buffer common to all the output destinations which reduced the priority control class is received, this priority is received. The network switch according to appendix 1, wherein only the degenerate class buffer corresponding to the control class is in a transmission stop state.

(Additional remark 3) It further has a monitoring means for monitoring the input traffic volume, and when the monitoring means determines that the traffic volume is lower than a predetermined threshold, the transmission stop request by the back pressure is ignored. 3. The network switch according to 1 or 2.

(Supplementary Note 4) An assembly buffer for reassembling the subdivided cells output from the output buffer is further provided for each priority control class, and the assembly buffer receives the priority control class when the usage amount exceeds a predetermined threshold value. The network switch according to any one of appendices 1 to 3, wherein a back pressure requesting to stop transmission is transmitted to the input unit.

(Supplementary Note 5) A back pressure control method in an output buffer type network switch,
Sending multiple stages of backpressure depending on the congestion status of the output buffer; and
And a step of changing a back pressure application destination in accordance with a stage of the back pressure.

(Additional remark 6) It further includes the monitoring process which monitors the amount of input traffic, and when the said monitoring process judges that the traffic volume is lower than a predetermined threshold value, the transmission stop request | requirement by a back pressure is disregarded. 5. The back pressure control method according to 5.

  As described above, the network switch and the back pressure control method according to the present invention are useful for realizing high-quality communication, and in particular, increase the buffer size of the output buffer even in a situation where it is connected to a high-speed network. It is suitable when it is necessary to realize high quality communication.

It is a functional block diagram which shows the structure of the network switch which concerns on a present Example. It is explanatory drawing for demonstrating the back pressure system which concerns on a present Example. FIG. 3 is a functional block diagram illustrating a configuration of a back pressure filter unit illustrated in FIG. 2. It is a block diagram which shows the data structure of the back pressure from an output buffer part. It is a block diagram which shows the data structure of the back pressure from the buffer classified by class of an outgoing side switch blade. It is explanatory drawing for demonstrating the filtering logic in a back pressure control part. It is a block diagram which shows the data structure of the back pressure to the degeneration class buffer of a main switch part. It is a block diagram which shows the data structure of the back pressure from the degeneration class buffer of a main switch part. It is explanatory drawing for demonstrating the buffer size required for an output buffer part in the network switch which concerns on a present Example. It is explanatory drawing for demonstrating the processing content of the degeneration class buffer back pressure transmission part. It is explanatory drawing for demonstrating the processing content of the input amount threshold value excess determination part. It is a functional block diagram which shows the structure of the conventional network switch. It is explanatory drawing for demonstrating the conventional back pressure system. It is explanatory drawing for demonstrating the buffer size required for the output buffer part in the conventional network switch.

Explanation of symbols

11, 12, 13 Back pressure 21, 22, 23, 24, 25, 26, 27, 28 Back pressure 1000 Network switch 1100a to 1100n Incoming switch blade 1110a to 1110n Interface 1120a to 1120n Network processor 1130a to 1130n Traffic manager 1131a to 1132x buffer 1133 priority control unit 1134 FIFO
1200 Main switch unit 1210a to 1210n FIFO
1220 switch 1230a-1230n output buffer unit 1231a-1231x buffer 1232 priority control unit 1233 FIFO
1240 Scheduler 1300a to 1300n Outgoing switch blade 1310a to 1310n Traffic manager 1311a to 1312x Buffer 1313 Frame assembly unit 1320a to 1320n Network processor 1330a to 1330n Interface 2000 Network switch 2100a to 2100n Incoming switch blade 2110a to 2110n Interface 2120a to 2120n Network processor 2130a to 2130n Traffic Manager 2131a to 1132x Buffer 2133 Priority Control Unit 2134 FIFO
2200 main switch units 2210a to 2210n input control units 2211a and 2211b buffer 2212 priority control unit 2213 FIFO
2214 Back pressure filter unit 2214a Congestion back pressure reception unit 2214b Emergency back pressure reception unit 2214c DSWB back pressure reception unit 2214d Input cell count unit 2214e Input amount threshold value excess determination unit 2214f Back pressure control unit 2214g Degeneration class buffer back pressure transmission unit 2214h Degeneration Class buffer correspondence storage unit 2214i Degenerate class buffer back pressure reception unit 2214j SSWB back pressure transmission unit 2220 Switch 2230a to 2230n Output buffer unit 2231a to 2231x Buffer 2232 Priority control unit 2233 FIFO
2240 scheduler 2300a to 2300n outgoing side switch blade 2310a to 3210n traffic manager 2311a to 2312x buffer 2313 frame assembly unit 2320a to 2320n network processor 2330a to 2330n interface

Claims (5)

An output buffer type network switch that controls congestion of the output buffer by back pressure,
A network switch comprising a back pressure output buffer for transmitting back pressure at a plurality of stages whose operation destinations differ depending on a congestion state.   A degeneration class buffer common to all output destinations with degenerated priority control class is further provided on the input side of its own device, and it corresponds to the priority control class when a back pressure requesting to stop transmission of a specific priority control class is received 2. The network switch according to claim 1, wherein only the degenerate class buffer to be transmitted is set in a transmission stop state.   3. A monitoring means for monitoring the amount of input traffic is further provided, and if the monitoring means determines that the traffic volume is lower than a predetermined threshold value, a transmission stop request by back pressure is ignored. The network switch described in 1.   An assembly buffer for reassembling the subdivided cells output from the output buffer is further provided for each priority control class, and the assembly buffer stops transmission of the priority control class when the usage amount exceeds a predetermined threshold. The network switch according to claim 1, wherein the requested back pressure is transmitted to the input unit. A back pressure control method in an output buffer type network switch,
Sending multiple stages of backpressure depending on the congestion status of the output buffer; and
And a step of changing a back pressure application destination in accordance with a stage of the back pressure.

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