JP3592586B2 - Contention control device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is used for communication using packets. The present invention is suitable for use in a large-scale and high-speed packet switch.
[0002]
[Prior art]
In a packet switch, a plurality of buffers are provided for temporarily storing packets. When reading packets from this buffer, contention control between buffers is required so that a plurality of packets destined for the same output line do not collide with each other.
[0003]
FIG. 7 shows the configuration of a conventional contention control device. FIG. 8 shows the operation of the conventional contention control device. The input packet is input to each buffer as shown in FIG. In FIG. 7, there are buffers # 1 to #N. For example, these buffers may be provided for each input line, or may be provided for each class. The packet is generally a variable length packet. In FIG. 7, packets are divided into fixed length units for simplification of the description. The read control unit 10 selects one buffer from the N buffers and reads the first packet.
[0004]
The operation of the conventional conflict control will be described with reference to FIG. After the contention control is started and the time T has elapsed, the contention control ends, and a buffer to be read next is selected. Ring arbitration, for example, is a method of contention control. Here, if there is no packet in any of the buffers, the buffer to be read next is not selected. If the packet has been read even after the conflict control ends, the process waits until the packet reading ends. If the reading of the packet has been completed and there is a read packet, the packet is read from the previously selected selection buffer and the conflict control is started again at the same time. These operations are repeated.
[0005]
[Problems to be solved by the invention]
However, when the packet length L is short and the read time L / C (C is the read line speed) is shorter than the contention control required time T, even if the packet is read, the buffer to be selected next cannot be found. The line becomes idle. Therefore, the throughput is reduced.
[0006]
In the conventional method, in order to prevent a decrease in throughput, it is necessary to make T smaller than the read time L _min / C of the minimum packet length L _min , but in a high-speed processing switch, there are restrictions on implementation, It is difficult to realize economically.
[0007]
As described above, the conventional contention control device has a problem in that when a packet satisfying L / C <T arrives, the throughput is reduced. In particular, in a large-scale and high-speed packet switch, such a decrease in throughput becomes a serious problem.
[0008]
The present invention has been made in such a background, and an object of the present invention is to provide a contention control device which does not cause a decrease in throughput even when a packet satisfying L / C <T arrives. It is in. An object of the present invention is to provide a contention control device suitable for a large-scale and high-speed packet switch.
[0009]
[Means for Solving the Problems]
The most important feature of the present invention is to simulate contention control using a model based on the packet accumulation status of the actual buffer, separately from the packet reading from the actual buffer.
[0010]
In this model, virtual queues corresponding to the actual buffers are assumed, and the identification information of the packets stored in the actual buffers is stored in the virtual queues and the queues are stored in the virtual queues. A competition control simulation is executed on the identification information stored in the.
[0011]
Therefore, the competition control in the simulation is executed at a constant cycle. On the other hand, when reading packets from an actual buffer, packets of various packet lengths are read out. Therefore, while reading out a packet having a relatively long packet length, the transmission permission is given to the next buffer to be read out. Waiting time occurs a lot. Even during this waiting time, the competition control in the simulation is executed at a constant cycle.
[0012]
Therefore, in the competition control in the simulation, the transmission permission given to the actual buffer can be generated prior to the actual packet reading. The transmission permission generated in this way is recorded and accumulated in chronological order. As a result, it is possible to give transmission permission for packet reading in the actual buffer without any gap.
[0013]
As a result, even if a situation where L / C <T occurs, read permission can be given promptly because packet contention control has been completed in advance. Therefore, it is possible to realize a contention control device that does not cause a decrease in throughput even when a packet satisfying L / C <T arrives.
[0014]
That is, the present invention includes a plurality of buffers for temporarily storing incoming packets, and a read control unit for controlling the reading of packets from the plurality of buffers. The read control unit does not cause packets to collide with each other. A contention control device including means for performing contention control so as to be read from the plurality of buffers.
[0015]
Here, the feature of the present invention is characterized in that the means for controlling contention includes means for simulating contention control in accordance with the packet accumulation status of the plurality of buffers, and means for simulating contention control in accordance with a simulation result of the simulating means. And means for giving packet read permission to the
[0016]
At this time, the simulating means includes a plurality of virtual queues corresponding to the plurality of buffers, and stores identification information of packets stored in the plurality of buffers in the plurality of virtual queues. It is desirable to include means for executing a conflict control simulation on the identification information stored in the plurality of queues.
[0017]
It is preferable that the apparatus further comprises means for recording the order of buffers to which packet read permission is given by the permission means in time series.
[0018]
Further, it is preferable that a means is provided for temporarily stopping the simulation by the simulating means when the number of records of the recording means exceeds a threshold value.
[0019]
For example, if there is a buffer a in which packets frequently arrive and a buffer b in which it does not, the buffer a in which packets frequently arrive will be transmitted by the simulating means during a period in which no packets arrive in buffer b. Permissions will be generated one after another.
[0020]
At this time, if a packet arrives at the buffer b where the packet does not frequently arrive, the transmission permission given to the buffer a one after the other end of the reading of most of the packets from the buffer a and finally the transmission permission to the buffer b Which results in an increase in the waiting time of the buffer b. In order to correct such unfairness of the throughput, the simulation is temporarily stopped when the transmission permission for the buffer a is accumulated to some extent. If a packet arrives at the buffer b during this pause period, when the simulation is restarted, the transmission permission for the buffer b is given on an equal basis to the buffer a, and the unfairness of the throughput is corrected.
[0021]
The means for simulating may include, for example, means for simulating competitive control by ring arbitration.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
( Reference example )
A configuration of a conflict control device according to a reference example of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a configuration of a contention control device according to a reference example of the present invention.
[0023]
In this embodiment , as shown in FIG. 1, a plurality of buffers # 1 to #N for temporarily storing incoming packets, and a read control unit 10 for controlling the reading of packets from the plurality of buffers # 1 to #N. The read control unit 10 is a contention control device that performs contention control so that packets are read from a plurality of buffers # 1 to #N without colliding with each other.
[0024]
Here, the feature of the present reference example is that the virtual queue unit 20 is provided as means for simulating contention control according to the packet accumulation status of the plurality of buffers # 1 to #N. According to the result, a packet read permission is given to the buffers # 1 to #N.
[0025]
The virtual queue unit 20 includes a plurality of virtual queues # 1 to #N corresponding to the plurality of buffers # 1 to #N, and serves as identification information of packets stored in the plurality of buffers # 1 to #N. The request information is stored in the plurality of virtual queues # 1 to #N, respectively, and a contention control simulation is performed on the request information stored in the plurality of virtual queues # 1 to #N.
[0026]
Further, the read control unit 10 includes a read information queue 22 which is a means for recording in chronological order the order of buffers to which packet read permission is given by the read control unit 10.
[0027]
The virtual queue unit 20 simulates contention control by ring arbitration.
[0028]
Next, the operation of the reference example of the present invention will be described with reference to FIGS. FIG. 2 is a flowchart showing the operation of the virtual queue unit according to the reference example of the present invention. FIG. 3 is a flowchart showing the operation of the buffer unit according to the reference example of the present invention.
[0029]
FIG. 1 shows a configuration in which packets transferred to a plurality of input lines are input to buffers # 1 to #N for each line. The reason why the packet is divided into fixed length units is to simplify the description. When a packet is input to a certain buffer #i (i is any one of 1 to N), request information for a request request is input to a corresponding virtual queue #i. The virtual queue #i has a counter (not shown) for counting the number of requests.
[0030]
As shown in FIG. 2, the virtual queue scheduler 21 performs a contention control simulation on the virtual queues # 1 to #N. The required time T of the competitive control simulation is set close to L _min / C. When a read buffer is selected by the contention control simulation, the transmission permission is input to a read information queue (FIFO) 22. Here, ring arbitration is used for the competition control simulation.
[0031]
That is, the counters provided in the virtual queues # 1 to #N indicate the number of packets stored in the buffers # 1 to #N, respectively. As the ring arbiter circulates through the virtual queues # 1 to #N, transmission permission is sequentially given to the virtual queues whose counters are not "0".
[0032]
The operation of the virtual queue unit 20 is performed independently of the packet reading timing in the buffers # 1 to #N of the buffer unit 30. Therefore, when a packet that satisfies L / C> T is read, the contention control ends earlier than the packet read, and the next read buffer is searched.
[0033]
As shown in FIG. 3, when the reading of the packet is completed, the read control unit 10 of the buffer unit 30 determines, if there is information in the read information queue 22 of the virtual queue unit 20, the head information of the read information queue (to be selected). Buffer), and reads the first packet of the buffer from the buffer unit 30.
[0034]
This operation, even if it is L _{min / C <T,} can be performed prior to contention control in the case of L _{min / C <T} becomes packets, it is possible to prevent a decrease in throughput.
[0035]
(Real施例)
This onset AkiraMinoru施例be described with reference to FIG. Figure 4 is a diagram showing a configuration of a contention control apparatus of the present onset AkiraMinoru施例.
[0036]
Contention control apparatus of the present onset AkiraMinoru施例, in addition to the contention control device of the reference example of the present invention shown in FIG. 1, as shown in FIG. 4, a simulation by the virtual queue scheduler 21 according to the queue length of the read information queue 22 Is different in that a queue length threshold value for temporarily suspending is provided.
[0037]
Next, the operation of the contention control apparatus of the present onset AkiraMinoru施例with reference to FIGS. Figure 5 is a flowchart showing the operation of the virtual queuing unit 20 of the present onset AkiraMinoru施例. The operation of the buffer unit 30 is the same as that of the reference example of the present invention.
[0038]
When the onset AkiraMinoru施例is different from the reference example of the present invention is to setting the threshold value Q to the read information queue 22 of the virtual queue section 20. As shown in FIG. 5, if the queue length of the read information queue 22 is equal to or less than Q, the operation is the same as that of the first embodiment of the present invention. The signal is transferred, and the start of the conflict control simulation is stopped. If the queue length is equal to or less than Q, the contention control simulation is started.
[0039]
If Q is set small by this operation, the unfairness of the throughput of each of the buffers # 1 to #N can be improved. The principle is that, as described above, if there is a buffer a where packets frequently arrive and a buffer b where it does not, for the buffer a where packets frequently arrive, the buffer a during which packets do not arrive at the buffer b The transmission permission is generated one after another by the virtual queue scheduler 21.
[0040]
At this time, if a packet arrives at the buffer b where the packet does not frequently arrive, the transmission permission given to the buffer a one after the other end of the reading of most of the packets from the buffer a and finally the transmission permission to the buffer b Which results in an increase in the waiting time of the buffer b. In order to correct such unfairness of the throughput, the simulation is temporarily stopped when the transmission permission for the buffer a is accumulated to some extent. If a packet arrives at the buffer b during this pause period, when the simulation is restarted, the transmission permission for the buffer b is given equally to the buffer a, and the unfairness of the throughput is corrected. However, if it is too small, it approaches the conventional method, so it is necessary to select an appropriate Q.
[0041]
(Example summary)
FIG. 6 compares the throughputs of the conventional contention control device and the contention control device of the present invention. FIG. 6 shows the average packet length on the horizontal axis and the throughput on the vertical axis. The packet length is assumed to follow an exponential distribution, and the average packet length L is a value standardized for the contention control time. Q was assumed to be infinity. According to the present invention, even if the contention control time is relaxed, since the packets are selected in advance using the virtual queue, a decrease in throughput can be prevented.
[0042]
【The invention's effect】
As described above, according to the present invention, it is possible to realize a contention control device that does not cause a decrease in throughput even when a packet satisfying L / C <T arrives. According to the present invention, it is possible to realize a contention control device suitable for a large-scale and high-speed packet switch.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a contention control device according to a reference example of the present invention.
FIG. 2 is a flowchart illustrating an operation of a virtual queue unit according to the reference example of the present invention.
FIG. 3 is a flowchart illustrating an operation of a buffer unit according to the reference example of the present invention.
4 is a diagram showing a configuration of a contention control apparatus of the present onset AkiraMinoru施例.
5 is a flowchart showing the operation of the virtual queue portion of the onset AkiraMinoru施例.
FIG. 6 is a diagram comparing throughputs of a conventional contention control device and the contention control device of the present invention.
FIG. 7 is a diagram for explaining a conventional conflict control device.
FIG. 8 is a flowchart showing the operation of a conventional conflict control device.
[Explanation of symbols]
10 read control unit 20 virtual queue unit 21 virtual queue scheduler 22 read information queue 30 buffer unit

Claims (1)

A plurality of buffers for temporarily storing incoming packets, and a read control unit for controlling reading of packets from the plurality of buffers,
The read control unit is a contention control device including means for performing contention control such that packets are read from the plurality of buffers without colliding with each other,
The contention control means includes means for simulating contention control according to the packet accumulation status of the plurality of buffers, and means for giving packet read permission to the buffer according to a simulation result of the simulation means.
The means for simulating comprises a plurality of virtual queues corresponding to the plurality of buffers, and a plurality of counters provided for each of the queues,
The plurality of counters hold the number of packets stored in the corresponding buffer,
Look including means for simulating the competition control according to the number of packets held by the plurality of counters,
A means for recording the order of buffers to which packet read permission is given by the means for giving permission in chronological order,
Means for temporarily stopping simulation by the simulating means when the number of records of the recording means exceeds a threshold,
The contention control device, wherein the threshold is set according to throughput and fairness .

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