JP2006074484A - Network switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a network switch in which such a defect as to drop high-priority frames at the time of congestion is prevented. <P>SOLUTION: A frame determining section 11 determines a priority of received frames to store the frames in queues Q0 to Q3 by priority depending on the results of the determination. A memory monitor 22 determines a free space of a buffer memory 21 from total capacity of the frames stored in the queues Q0 to Q3. When the free space reaches a threshold value, low-priority frames are not stored in the buffer memory 21 to give instructions of discarding the low-priority frames to a memory manager 12. Consequently, prevented is such a defect that the low-priority frames are excessively stored in the buffer at the time of congestion to thus drop the high-priority frames. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a network switch such as a router or a bridge, and more particularly to a network switch that efficiently performs discard processing according to packet priority during congestion.

  In recent years, the Internet has become widespread, and users can access various information on sites operated in various parts of the world and obtain the information. Along with this, the demand for broadband access such as ADSL (Asymmetric Digital Subscriber Line) and FTTH (Fiber To The Home) is also increasing rapidly.

  In such communication, network switches such as routers and bridges are used to relay packets. In general, such a network switch is provided with a function of discarding a low-priority packet at the time of congestion, which is disclosed in Japanese Patent Laid-Open No. 2002-26965 and Japanese Patent Laid-Open No. 7-135512. There are other inventions.

  In the transmission queue management system disclosed in Japanese Patent Laid-Open No. 2002-26965, the packet header information identifying unit compares the header of the received packet with the packet header pattern of the lookup table in the discard priority information holding unit, and In this case, discard priority information corresponding to the packet header pattern is output. The discard priority information adding unit adds discard priority information to the packet based on the discard priority information. Packets to which the discard priority information is added are accumulated in the transmission queue, but when the accumulation number reaches the threshold value, the packet having the highest discard priority is collectively discarded by the batch discard process.

In the router device disclosed in Japanese Patent Laid-Open No. 7-135512, the priority control unit determines the processing priority and the discard tolerance from the received packet priority information and protocol information, and stores them in the priority queue. Add a packet. The packet management unit monitors the state of the free buffer area, and when the capacity of the free buffer area is insufficient and becomes congested, the discard control unit discards the packet selected based on the processing priority and the discard tolerance.
JP 2002-26965 A JP-A-7-135512

  In recent years, the specifications required for network switches have changed, and instead of managing queues so as not to drop frames as much as possible, the direction is toward managing queues so that necessary frames are never dropped. .

  However, in the above-mentioned patent document, a function of discarding a low priority packet at the time of congestion is provided. However, the frame is received on the input side regardless of the free capacity of the buffer. This is because the network switch is designed in such a manner that the frames once input are stored in the buffer as much as possible, and “discard processing” of each queue is performed by the traffic manager on the output side.

  As described above, since the frame arrived at the input side is designed to be stored in the buffer for the time being, there is a problem that a frame having a high priority may be dropped at the time of congestion.

  The present invention has been made to solve the above-mentioned problems, and its purpose is to prevent a problem that a frame having a low priority is accumulated in a buffer at the time of congestion and a frame having a high priority is dropped. It is to provide a network switch that can do this.

  According to an aspect of the present invention, a network switch that relays a received frame, a storage unit for storing the received frame, a determination unit for determining the priority of the received frame, and a determination unit According to the determination result, the free space of the storage means is obtained from the multiple queues that accumulate frames by priority and the total capacity of the frames that are accumulated in the multiple queues, and the free space has reached the threshold value. And a discarding unit for discarding the low priority frame without storing the frame in the storage unit.

  Preferably, the discriminating unit discriminates the priority of the frame with reference to a predetermined area of the received frame.

  According to an aspect of the present invention, the discarding unit obtains the free space of the storage unit from the total capacity of the frames accumulated in the plurality of queues, and when the free space has reached the threshold, the priority is Since the frame is discarded without storing the low frame in the storage means, it is possible to prevent a problem that the frame with low priority is accumulated in the buffer at the time of congestion and the frame with high priority is dropped. It became.

  In addition, since the discriminating unit discriminates the priority of the frame with reference to a predetermined area of the received frame, it becomes possible to easily discriminate the priority of the frame.

  FIG. 1 is a block diagram showing a schematic configuration of a network switch according to an embodiment of the present invention. The network switch includes a queue management unit 10-1 to 10-N that manages the queues of the ports # 1 to #N, and a shared buffer memory (hereinafter, referred to as a shared buffer memory that stores frames corresponding to the ports # 1 to #N 21) and a memory monitoring unit that monitors the capacity of the frames stored in the buffer memory 21 and outputs frame discard information when the free capacity of the buffer memory 21 has reached a threshold value. 22 and a frame output unit 23 for outputting a frame to the upper network.

  Each of the queue managers 10-1 to 10-N includes a frame discriminating unit 11 that discriminates the priority of a frame input from a lower network, and a queue for each priority according to the discrimination result by the frame discriminating unit 11. Queues Q0 to Q3, and a memory manager 12 that manages frames stored in the queues Q0 to Q3 and discards frames according to discard information output from the memory monitoring unit 22. The frame itself is stored in the buffer memory 21, and information such as pointers pointing to the frames stored in the buffer memory 21 is queued in the queues Q0 to Q3. Further, Q0 to Q3 correspond to the highest, high, medium and low priority levels, respectively, and are discarded in order from the frames queued in the low priority queue.

  The frame discriminating unit 11 discriminates attributes of a VLAN (Virtual Local Area Network) frame, an IP (Internet Protocol) frame, and other frames with reference to the header of the frame. If the frame is a VLAN frame, the priority is determined with reference to the priority field of the VLAN ID in the header. If the frame is an IPv4 frame, the priority is determined with reference to the TOS (Type Of Service) field of the header.

  The memory manager 12 manages frames input to the queues Q0 to Q3 and frames output from the queues Q0 to Q3, and manages the frame capacity of the queues Q0 to Q3. Also, the memory manager 12 sends the frame capacity according to priority to the memory monitoring unit 22 as statistical information.

  The memory manager 12 discards the frames input to the queues Q <b> 0 to Q <b> 3 according to the discard information output from the memory monitoring unit 22 and does not store the frames in the buffer memory 21. For example, if the discard information indicates discard of a frame in queue Q3 (low priority), the frame input to queue Q3 is discarded and the frame is not stored in buffer memory 21.

  The memory monitoring unit 22 sequentially extracts frames from each queue according to a preset calculation formula and causes the frame output unit 24 to output the corresponding frames. At this time, the memory monitoring unit 22 refers to the statistical information output from the queue management units 10-1 to 10-N, and if the free capacity of the buffer memory 21 has reached the threshold value, the low priority frame. Is generated and output to the memory manager 12.

  For example, if the sum of the frame capacities stored in the buffer memory 21 is 1/2 of the total capacity of the buffer memory 21 (the free capacity is 1/2), an instruction to discard the frame in the queue Q3 (low priority) is given. Output discard information.

  If the sum of the frame capacities stored in the buffer memory 21 is 3/4 of the total capacity of the buffer memory 21 (the free capacity is 1/4), the queue Q2 (priority is medium) and the queue Q3 (priority) Output discard information instructing the discard of a frame of (low).

  Also, if the sum of the frame capacities stored in the buffer memory 21 is 7/8 of the total capacity of the buffer memory 21 (the free capacity is 1/8), the queue Q3 (high priority) and the queue Q2 (priority) ) And discard information instructing discard of frames in queue Q3 (low priority).

  Here, the capacity of the Ethernet (registered trademark) frame is managed not by the number of bytes but by the number of frames. The Ethernet® frame does not exceed 1522 bytes even in a VLAN frame. Therefore, if 1536 bytes are set as one frame unit, 2048 buffers for each frame can be secured if the capacity of the buffer memory 21 is 3 Mbytes. it can. As a result, the threshold of the free space can be defined as 1024 (free space is 1/2), 512 (free space is 1/4), and 256 (free space is 1/8).

  FIG. 2 is a flowchart for explaining the processing procedure of the network switch in the embodiment of the present invention. First, the frame determination unit 11 determines whether or not there is a priority tag in the frame (S11). If the frame has a priority tag (S11, Yes), it is determined that the frame is a VLAN frame, the priority tag is converted into a queue number, and the frame is queued in the corresponding queue (S12). The process proceeds. The conversion of the queue number is performed by determining the priority according to the priority tag and obtaining the queue number corresponding to the priority.

  If there is no priority tag in the frame (S11, No), it is determined by referring to the header of the frame whether it is an IP frame (S13). If the frame is an IP frame (S13, Yes), the TOS field is converted into a queue number and the frame is queued in the corresponding queue (S14), and the process proceeds to step S16. The conversion of the queue number is performed by determining the priority according to the TOS field and obtaining the queue number corresponding to the priority.

  If the frame is not an IP frame (S13, No), a prescribed value is set as the queue number and the frame is queued in the corresponding queue (S15), and the process proceeds to step S16.

  In step S16, the memory monitoring unit 22 determines whether or not the free capacity of the buffer memory 21 has reached a threshold value (S16). If the free capacity of the buffer memory 21 has not reached the threshold value (S16, No), the memory manager 12 stores the frame in the buffer memory 21 according to the frame input to the queues Q0 to Q3 (S19). ), The process is terminated.

  If the free capacity of the buffer memory 21 has reached the threshold value (S16, Yes), the memory monitoring unit 22 generates discard information corresponding to the threshold value and outputs it to the memory manager 12. The memory manager 12 determines whether or not the frame input to the queues Q0 to Q3 is a frame corresponding to the threshold value according to the discard information (S17).

  If the frame input to the queues Q0 to Q3 is not a frame corresponding to the threshold value (S17, No), the memory manager 12 stores the frame in the buffer memory 21 according to the frame input to the queues Q0 to Q3. Accumulate (S19), and the process ends. If the frame input to the queues Q0 to Q3 is a frame corresponding to the threshold value (S17, Yes), the memory manager 12 discards the frame and does not store it in the buffer memory 21 (S18). ), The process is terminated.

  In the above description, the threshold value is described as a fixed value. However, the threshold value may be dynamically changed based on the occupation ratio of each queue. Also, different thresholds may be set for each port, and priority may be assigned between ports.

  As described above, in the network switch according to the present embodiment, when the free capacity of the buffer memory 21 reaches the threshold value, the frame having the lower priority is discarded and is not stored in the buffer memory 21. At this time, it is possible to prevent such a problem that a frame having a low priority is stored in the buffer and a frame having a high priority is dropped.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a block diagram which shows schematic structure of the network switch in embodiment of this invention. It is a flowchart for demonstrating the process sequence of the network switch in embodiment of this invention.

Explanation of symbols

  10-1 to 10-N Queue management unit, 11 frame discrimination unit, 12 memory manager, 21 shared buffer memory, 22 memory monitoring unit, 23 frame output unit, Q0 to Q3 queue.

Claims (2)

A network switch that relays received frames,
Storage means for storing received frames;
A discriminating means for discriminating the priority of the received frame;
A plurality of queues for accumulating frames according to priority according to a determination result by the determination unit;
The free capacity of the storage means is obtained from the total capacity of the frames accumulated in the plurality of queues, and when the free capacity has reached the threshold value, the low priority frame is not stored in the storage means. And a discarding means for discarding the frame.   The network switch according to claim 1, wherein the determination unit determines the priority of the frame with reference to a predetermined area of the received frame.

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