JP5821705B2 - Network relay device and packet transfer control method - Google Patents

Description

  The present invention relates to a network relay device such as a router or a switch and a packet transfer control method.

  When congestion occurs, ECN (Explicit Coordination Notification) is standardized (see RFC 3168) as a mechanism for recognizing the occurrence of congestion between terminals such as servers and storages (end to end) and suppressing the transmission rate. .

  In this ECN, when a network relay device such as a router or a switch arranged on a path where TCP / IP (Transmission Control Protocol / Internet Protocol) communication is performed detects congestion, the network relay device detects a congested port or queue. Congestion notification is made to the receiving terminal in the IP layer for the packet. The receiving terminal that has received the congestion notification notifies the transmitting terminal of the congestion at the TCP layer. Thereby, congestion is recognized between the transmitting and receiving terminals.

  The basic operation of ECN will be specifically described with reference to FIG.

  As shown in FIG. 4A, in the network relay device 41 in which three servers 42a to 42c and one storage 43 are connected to different ports, the amount of data transmitted from the server 42a to the storage 43 increases and congestion occurs. Suppose that occurs. It is assumed that the server 42a is a device that supports ECN.

  Since the server 42a is a device that supports ECN, the ECT (ECN Capable Transport) defined in the 6th bit of the ToS (Type of Service) field in the IP header is set to 1, and the packet is sent. Send.

  When detecting the congestion, the network relay device 41 sets CE (Congestion Experience) defined in the seventh bit of the ToS field in the IP header of the packet transmitted from the server 42a to the storage 43 to 1. Thereby, congestion detection information is added to the IP header.

  When receiving the packet with CE set to 1, the storage 43 on the receiving side recognizes that congestion has occurred in the network relay device 41 in the middle of the communication path, and as shown in FIG. At the time of ACK response, ECE (ECN Echo) in the TCP header is set to 1, and congestion is notified to the server 42a on the transmission side.

  When the server 42a receives an ACK in which 1 is set in the ECE, the server 42a recognizes that the congestion has occurred, and suppresses the TCP window size (suppresses the transmission rate), thereby avoiding the congestion. The server 42a transmits a packet with a TCP header CWR (Congestion Window Reduce) of 1 to the storage 43 on the receiving side, notifying that the window size has been reduced.

  By the way, in the network relay device 41, when congestion is detected, the CE of all packets is not set to 1, but the ratio of setting CE to 1 according to the degree of congestion (that is, the buffer amount of the port or queue in which congestion is detected). Generally, the mark ratio is changed. As a method for determining the mark rate, a method using a CE bit marking curve as shown in FIG. 5 is known.

  As shown in FIG. 5, the CE bit marking curve (hereinafter simply referred to as a marking curve) is represented by a graph with the vertical axis representing the mark rate and the horizontal axis representing the buffer amount, and the mark start amount, maximum mark amount, and maximum mark rate. These are characterized by the three set values.

Specifically, the marking curve is
(1) When the buffer amount is equal to or less than the mark start amount, the mark rate is 0%,
(2) When the buffer amount is greater than or equal to the maximum mark amount, the mark rate is 100%,
(3) When the buffer amount is larger than the mark start amount and smaller than the maximum mark amount, the mark rate is set to increase in proportion to the buffer amount from 0% to a preset maximum mark rate. In the case of (3), that is, when the mark start amount <buffer amount <maximum mark amount, the mark rate is: Mark rate = maximum mark rate × (buffer amount−mark start amount) / (maximum mark amount−mark Starting amount)
It is represented by When the buffer amount is equal to or greater than the maximum buffer amount (the maximum buffer amount allocated to the port or queue), a packet drop (packet loss) occurs because the buffer is not possible.

  In the conventional network relay device 41, the mark start amount, the maximum mark amount, and the maximum mark rate are set as predetermined values.

  In addition, there exists patent documents 1-4 as prior art document information relevant to the invention of this application.

JP 2011-15288 A International Publication No. 2008/149434 JP 2004-104417 A JP 2004-357177 A

  However, if the mark start amount, the maximum mark amount, and the maximum mark rate are set to constant values, there is a possibility that a problem may occur in the shared buffer type network relay device.

  In the shared buffer method, generally, the buffer amount that can be used per port or queue is determined according to the free capacity, and the maximum buffer amount of each port or queue is variable.

  As a network relay device of the shared buffer method, for example, there is a device that makes it possible to use a predetermined ratio of the free capacity of the shared buffer by one port or one queue. In this method, as shown in FIG. If the used amount of the shared buffer is small, the maximum buffer amount that can be used in each port or queue increases. As shown in FIG. 6B, if the used amount of the shared buffer is large, each port Alternatively, the maximum amount of buffer that can be used in the queue is reduced.

  Even if the maximum buffer amount of each port or queue changes, for example, if the mark start amount, maximum mark amount, and maximum mark rate are set to constant values, for example, the maximum buffer amount is large and the buffer has a margin. There may be a problem that congestion notification is performed, or that congestion notification is hardly performed even though the maximum buffer amount is small and the buffer has no room.

  If congestion notification is frequently made even though there is room in the buffer, packet loss is less likely to occur, but the operation to reduce the window size works frequently, increasing the number of times transmission is interrupted, resulting in a decrease in throughput. End up. On the other hand, if there is almost no congestion notification even though there is no room in the buffer, the operation to suppress the window size becomes difficult to work, but packet loss is likely to occur due to continuously transmitted packets, and this packet loss causes throughput. Will fall.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a network relay device and a packet transfer control method capable of suppressing a decrease in throughput when congestion is detected in a shared buffer network relay device. And

The present invention was created to achieve the above object, and is arranged in a communication path performed by a terminal corresponding to ECN (Explicit Congestion Notification). When congestion is detected, the seventh ToS field in the IP header is detected. A network relay device that sets CE (Congestion Experience) defined in the bit as 1 as congestion detection information, and uses a common shared buffer for each port or queue, and can be used for each port or queue. In a network relay device of the shared buffer method in which the buffer amount changes depending on the usage amount of the shared buffer, a congestion detection unit that detects congestion, and when the congestion detection unit detects congestion, from the port or queue that detected the congestion In the header of the packet to be transferred, It is configured to add congestion detection information at a mark rate corresponding to the buffer amount of the port or queue, and when the buffer amount of the port or queue detecting the congestion is equal to or less than a preset mark start amount When the rate is 0% or more than the preset maximum mark amount, the mark rate is 100%. When the rate is greater than the mark start amount and less than the maximum mark amount, the mark rate is from 0% to a preset maximum mark rate. Using the marking curve that is set to increase in proportion to the buffer amount, the congestion notification unit that determines the mark rate, and the maximum buffer amount that can be used for each port or queue changes. A mark rate adjustment unit that changes any one or more of the mark start amount, the maximum mark amount, and the maximum mark rate according to the change amount of the buffer amount A network relay apparatus having a.

  The mark ratio adjustment unit is configured to change the mark start amount and the maximum mark amount while keeping a difference between the mark start amount and the maximum mark amount constant according to a change amount of the maximum buffer amount. May be.

  The mark rate adjustment unit may be configured to increase the mark start amount at a rate equal to the increase rate of the maximum buffer amount.

  The mark rate adjustment unit may be configured to increase the mark start amount by an amount equal to the increase amount of the maximum buffer amount.

In addition, the present invention is arranged in a communication path performed by a terminal corresponding to ECN (Explicit Connection Notification), and when congestion is detected, a CE (Congestion Experience) defined in the seventh bit of the ToS field in the IP header is detected. Is a packet transfer control method performed by a network relay device that sets 1 as congestion detection information, and uses a common shared buffer for each port or queue, and the maximum buffer amount that can be used for each port or queue is Applied to shared buffer type network relay devices that change according to the usage of the shared buffer. When congestion is detected, the header of the packet transferred from the port or queue where congestion is detected corresponds to the buffer amount of the port or queue. Congestion detection by mark rate When the information rate is given and the buffer amount of the port or queue in which the congestion is detected is less than or equal to the preset mark start amount, the mark rate is 0% or more than the preset maximum mark amount When the mark rate is 100%, larger than the mark start amount and smaller than the maximum mark amount, the mark rate is set to increase in proportion to the buffer amount from 0% to a preset maximum mark rate. In the packet transfer control method for determining the mark rate using a curve, when the maximum buffer amount that can be used for each port or queue changes, the mark start amount according to the change amount of the maximum buffer amount, The packet transfer control method changes one or more of the maximum mark amount and the maximum mark rate.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of the throughput at the time of congestion detection can be suppressed in the network relay apparatus of a shared buffer system.

1 is a schematic configuration diagram of a network relay device according to an embodiment of the present invention. It is a figure explaining the change of the marking curve used with the network relay apparatus of FIG. It is a flowchart which shows the control flow in the mark rate adjustment part of the network relay apparatus of FIG. (A), (b) is a figure explaining the basic operation | movement of ECN. It is a figure which shows a general marking curve. (A), (b) is a figure explaining that the maximum buffer amount which can be used for every port or queue changes in the network relay apparatus of a shared buffer system.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  The network relay device of the present invention is, for example, a router or a switch (including an L2 switch). Here, a case where the network relay device is a switch will be described as an example.

  FIG. 1 is a schematic configuration diagram of a network relay device according to the present embodiment.

  As shown in FIG. 1, the network relay device 1 includes a packet receiver 12 and a packet transmitter 13 provided for each port 11, and a packet buffer 14 that temporarily stores packets received by the packet receiver 12. A packet buffer 14, a buffer control unit 15 provided between the packet receiving unit 12 and the packet transmitting unit 13, and a path control unit 16 for determining an output destination port 11 according to the packet contents. Yes.

  The buffer control unit 15 is configured to temporarily store the packet received from the packet receiving unit 12 in the packet buffer 14 when the packet buffer 14 is empty, and from the packet buffer 14 in response to an instruction from the path control unit 16. The packet is read out and output to the output destination port 11 (packet transmission unit 13). The path control unit 16 is configured to determine an output destination port 11 by referring to an unillustrated FDB (forwarding database) with the destination address of the packet and to instruct the buffer control unit 15 to output.

  The network relay device 1 includes a congestion detection unit 2 and a congestion notification unit 3.

  The network relay device 1 uses a shared buffer common to each port or queue, and is a shared buffer type network relay device in which the maximum buffer amount that can be used for each port or queue varies depending on the usage amount of the shared buffer. .

  The congestion detection unit 2 detects congestion. In the present embodiment, the congestion detection unit 2 is configured to determine that congestion has occurred in the port or queue when the buffer amount of any port or queue is greater than zero.

  The congestion notification unit 3 notifies the receiving device of the occurrence of congestion when congestion occurs. When the congestion detection unit 2 detects congestion, the congestion notification unit 3 adds congestion detection information to the header of the packet transferred from the port or queue where the congestion is detected with a mark rate corresponding to the buffer amount of the port or queue. Configured to do. The congestion notification unit 3 is configured to give congestion detection information by setting the CE of the IP header of the packet to 1. The “packet” in the present embodiment includes a layer 2 “frame” and means a unit of data chunk. When the packet is output from the packet buffer 14 to the buffer control unit 15, the congestion notification unit 3 adds congestion detection information in response to an instruction from the congestion detection unit 2 (if there is no congestion, the packet is passed without doing anything. ).

  In the present embodiment, the congestion notification unit 3 is configured to determine the mark rate using the marking curve 3a in accordance with the buffer amount of the port or queue in which congestion is detected. As described with reference to FIG. 5, the marking curve 3a is characterized by three set values of the mark start amount, the maximum mark amount, and the maximum mark rate.

More specifically, the marking curve 3a indicates that the mark rate is 0% when the buffer amount of the port or queue in which congestion is detected is equal to or less than the mark start amount, and the mark rate when it is equal to or greater than the preset maximum mark amount. but 100%, is smaller than the maximum mark amount larger than the mark starting amount is set so that the mark ratio is increased in proportion to the buffer volume to the maximum mark ratio set in advance 0%. Mark rate when mark start amount <buffer amount <maximum mark amount is: Mark rate = maximum mark rate x (buffer amount-mark start amount) / (maximum mark amount-mark start amount)
It is represented by

  Now, when the maximum buffer amount that can be used for each port or queue changes, the network relay device 1 according to the present embodiment changes the mark start amount, the maximum mark amount, A mark rate adjustment unit 4 that changes (increases or decreases) any one or more of the maximum mark rates is further provided.

  In the present embodiment, the mark rate adjustment unit 4 is configured to change the mark start amount and the maximum mark amount while keeping the difference between the mark start amount and the maximum mark amount constant according to the change amount of the maximum buffer amount. did. More specifically, in the present embodiment, the maximum mark amount is set to a value obtained by adding a predetermined offset value to the mark start amount so that the mark start amount and the maximum mark amount are simultaneously decreased or increased. I made it. In the present embodiment, the maximum mark rate is set to a constant value.

  Furthermore, in the present embodiment, the mark rate adjustment unit 4 is configured to increase the mark start amount by a rate equal to the increase rate of the maximum buffer amount.

  With this configuration, for example, when the maximum buffer amount increases (1 + α) times as shown in FIG. 2, the mark start amount is also increased by (1 + α), and the maximum mark amount increases with the mark start amount. Minutes (mark start amount × α). At this time, the marking curve 3a moves left and right while maintaining its shape (maintaining the relative relationship of the bent portions), and the marking curve 3a is a straight line in the range of mark start amount <buffer amount <maximum mark amount. The slope remains constant.

  In this embodiment, the mark start amount is increased by a rate equal to the increase rate of the maximum buffer amount. However, the present invention is not limited to this, and the mark start amount is increased by an amount equal to the increase amount of the maximum buffer amount. You may do it. In this case, when the maximum buffer amount increases by (1 + α) times, both the mark start amount and the maximum mark amount are increased by the increase in the maximum buffer amount (maximum buffer amount × α).

  Note that the mark start amount and the maximum mark amount may be increased in proportion to the increase in the maximum buffer amount. In this case, when the maximum buffer amount increases (1 + α) times, both the mark start amount and the maximum mark amount are values obtained by multiplying the increase in the maximum buffer amount by a proportional constant C (maximum buffer amount × α × C ) Will be increased.

  In the present embodiment, the case has been described in which the mark start amount and the maximum mark amount are changed while keeping the difference between the mark start amount and the maximum mark amount constant according to the change amount of the maximum buffer amount. Not only, but only the mark start amount or only the maximum mark amount may be changed, or the difference between the mark start amount and the maximum mark amount is changed by changing the mark start amount and the maximum mark amount change amount. It is also possible to make it.

  In this embodiment, the maximum mark rate is constant, but the maximum mark rate may be variable. In this case, for example, when the maximum buffer amount is reduced, packet loss is likely to occur, and it is necessary to increase the mark rate. Therefore, when the maximum mark rate is increased and the maximum buffer amount is increased, the mark rate is increased. In order to suppress the window size from being lowered, the maximum mark rate may be lowered.

  Next, a packet transfer control method according to this embodiment will be described.

  The packet transfer control method according to the present embodiment is applied to a shared buffer network relay device, and when congestion is detected, the port or queue buffer is transferred to the header of the packet transferred from the port or queue where the congestion is detected. In the method of adding congestion detection information at the mark rate determined using the marking curve 3a according to the amount, when the maximum buffer amount that can be used for each port or queue changes, the change amount of the maximum buffer amount In accordance with this, one or more of the mark start amount, the maximum mark amount, and the maximum mark rate is changed.

  Here, the control by the mark rate adjusting unit 4 will be described with reference to FIG. FIG. 3 shows a case where the maximum mark rate is a constant value. Further, it is assumed that initial values are set in advance for the mark start amount, the maximum mark amount, and the maximum mark rate.

  As shown in FIG. 3, first, the mark rate adjustment unit 4 determines whether the maximum buffer amount has changed in step S1. For example, it may be determined that the maximum buffer amount has changed when the change amount of the maximum buffer amount exceeds a predetermined threshold. If NO is determined in step S1, that is, if there is no change in the maximum buffer amount, it is not necessary to change the mark start amount and the maximum mark amount, and the process returns to step S1.

  If YES is determined in step S1, in step S2, the mark rate adjustment unit 4 changes (increases or decreases) the mark start amount and the maximum mark amount according to the change amount of the maximum buffer amount. In the present embodiment, as described with reference to FIG. 2, the mark start amount is increased by a rate equal to the increase rate of the maximum buffer amount, and the maximum mark amount is increased by the increase of the mark start amount. . Then, it returns to step S1.

  As described above, in the network relay device 1 according to the present embodiment, when the maximum buffer amount that can be used for each port or queue changes, the mark start amount, A mark rate adjustment unit 4 is provided to change one or more of the maximum mark amount and the maximum mark rate.

  By providing the mark rate adjustment unit 4, it is possible to change the mark start amount, the maximum mark amount, and the maximum mark rate by following the maximum buffer amount. It is possible to suppress problems such as notifications being made, and congestion notifications being hardly made even though there is no room in the buffer. As a result, it is possible to suppress a decrease in throughput when congestion is detected.

  The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Network relay apparatus 2 Congestion detection part 3 Congestion notification part 4 Mark rate adjustment part

Claims (2)

When congestion is detected when placed in a communication path performed by a terminal that supports ECN (Explicit Congestion Notification), the CE (Congestion Experience) defined in the seventh bit of the ToS field in the IP header is set as 1 as congestion detection information. A network relay device,
In a shared buffer type network relay device that uses a shared buffer common to each port or queue, and the maximum buffer amount that can be used for each port or queue varies depending on the usage amount of the shared buffer,
A congestion detector for detecting congestion;
When the congestion detection unit detects the congestion in the header of the packet to be transferred from the port or queue detects congestion, it is configured to impart the congestion detection information in the mark ratio corresponding to the buffer amount of the port or queue And when the buffer amount of the port or queue in which the congestion is detected is less than or equal to a preset mark start amount, the mark rate is 0%, and when it is greater than or equal to the preset maximum mark amount, the mark rate is 100%, When the mark rate is larger than the mark start amount and smaller than the maximum mark amount, the mark rate is set by using a marking curve set so as to increase in proportion to the buffer amount from 0% to a preset maximum mark rate. A congestion notification unit to be determined;
When the maximum buffer amount that can be used for each port or queue changes, the mark start amount is maintained while keeping the difference between the mark start amount and the maximum mark amount constant according to the change amount of the maximum buffer amount. And a mark rate adjustment unit for changing the maximum mark amount ,
Equipped with a,
The mark rate adjustment unit increases the mark start amount by a rate equal to the increase rate of the maximum buffer amount, or increases the mark start amount by an amount equal to the increase amount of the maximum buffer amount. Configured network relay equipment. When congestion is detected when placed in a communication path performed by a terminal that supports ECN (Explicit Congestion Notification), the CE (Congestion Experience) defined in the seventh bit of the ToS field in the IP header is set as 1 as congestion detection information. A packet transfer control method performed by a network relay device,
A common buffer is used in each port or queue, and the maximum buffer amount that can be used for each port or queue is applied to a network relay device of a shared buffer method that changes according to the usage amount of the shared buffer.
When detecting congestion in the header of the packet to be transferred from the port or queue detects congestion, the mark ratio corresponding to the buffer amount of the port or queues to impart the congestion detection information, and the congestion When the detected port or queue buffer amount is less than or equal to the preset mark start amount, the mark rate is 0%, and when it is greater than or equal to the preset maximum mark amount, the mark rate is 100%, which is greater than the mark start amount. A packet transfer control method for determining the mark rate by using a marking curve set so that the mark rate increases in proportion to the buffer amount from 0% to a preset maximum mark rate when the mark rate is smaller than the maximum mark amount In
When the maximum buffer amount that can be used for each port or queue changes, the mark start amount is maintained while keeping the difference between the mark start amount and the maximum mark amount constant according to the change amount of the maximum buffer amount. And change the maximum mark amount,
A packet transfer control method in which the mark start amount is increased by a rate equal to the increase rate of the maximum buffer amount, or the mark start amount is increased by an amount equal to the increase amount of the maximum buffer amount .