JP2967767B2 - Scheduling method in ATM switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scheduling control method in an ATM switch, and more particularly, to a buffer unit provided at a preceding stage or a subsequent stage of a switch in order to cope with various traffics. AT that separates and controls traffic
The present invention relates to a scheduling control method for guaranteeing a bandwidth of each traffic class in an M switch.

[0002]

2. Description of the Related Art Conventional WRR (Weighted Round Rob)
An example of the scheduling control method by the in) method will be described below with reference to FIGS.

FIG. 4 shows a case where three traffic classes (class 1 to class 3) are accommodated in independent queues.
FIG. 9 is an explanatory diagram schematically showing an example of a WRR scheduling method in an input buffer unit or an output buffer unit provided in a stage before or after a TM switch. In FIG.
21 to 23 are queues for each traffic class, 24 is W
An RR scheduler. The queues 21 to 23 accumulate cells of the corresponding traffic class among the cells input to the buffer unit.

A WRR scheduler 24 has a counter for setting a weight for each queue, and an RR for selecting an output cell by selecting a traffic class from a plurality of traffic classes with priority given to rotation.
(Round robin: rotation priority) circuit.

The operation of the WRR scheduler 24 will be described with reference to the flowchart shown in FIG.

After the start, in step S1, a wait setting counter provided for each queue is reset, and the counter is loaded with an initial value. This initial value can be changed by the software interface. Here, the value of each counter is Wi, and the number of cells stored in each queue is Qi. Also, f (i) = Wi · Qi.

Next, in step S2, Δf (i)
It is determined whether or not ≠ 0. That is, the number of stored cells Qi in each queue is 0, or the value of the counter corresponding to each queue is 0
Monitor for In the determination processing in step S2, if f (i) = 0 for all traffic classes, the process returns to step S1. On the other hand, if f (i) ≠ 0 in any of the classes, the process proceeds to step S3.

In step S3, a class whose output is permitted is selected from the classes of f (i) ≠ 0. Even if cells are accumulated in the queue (Qi ≠ 0), the value of the counter is 0
Classes with (Wi = 0) are excluded from class selection in this step. As a selection method, a rotation priority method is used so that all classes have the same priority.
Then, the cell is output from the queue of the selected class.

Next, in step S4, the value Wi of the weight counter of the class selected in step S3 is set to 1
cut back. Thereafter, returning to step S2, the steps S3 to S4 are repeated according to the determination of Σf (i) ≠ 0. When Σf (i) = 0, the process returns to step S1 to reset the weight counter.

Each time one cell is output from the queue of each class, the value of the weight counter is reduced by one, and when the value of the weight counter becomes 0, the output of cells from that class is stopped. In all classes, when the number of accumulated cells in the wait counter or queue becomes 0, all the wait counters are reset to their initial values. Therefore, when sufficient input cells are given to all classes, cells are output according to the weight ratio given from each class.

The relation between the weight and the band is equivalent to the band of weight 1 = C / 10, where the total of all the weights is 10, and the entire band of the cell output is C.

As a result of following the above processing flow, in the example shown in FIG. 4, cells are output in the order shown.

In this method, it is possible to allocate weights to a plurality of traffic classes and guarantee the bandwidth of each class according to the ratio.

[0014]

However, in such a conventional scheduling control method based on the WRR system, when a large number of traffic classes are accommodated, after outputting a certain class of cells, all the worst classes are output once. Only after output, can cells of this class be output again.

FIG. 6 shows an operation example of the conventional scheduling control method. FIG. 6 shows an example in which the number of classes is 6, and the weight of each class is 1, and it is shown that a cell of class 6 has to wait for 5 cells at worst from arrival to output.

As described above, in the conventional scheduling control method based on the WRR system, when handling traffic that requires a real-time property because the delay characteristic is important, the delay characteristic of the traffic may be deteriorated. In particular, CBR (C
CDV (Cel) like onstant Bit Rate traffic
l Delay Variation (cell delay variation) has a significant effect on traffic for which a guarantee of characteristics is required.

Accordingly, the present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to reduce the bandwidth without deteriorating the delay characteristics of a traffic class requiring real-time performance. It is another object of the present invention to provide a scheduling control method that guarantees the above.

[0018]

In order to achieve the above object, the scheduling control method according to the present invention is set in advance in an output cell selection unit for selecting an output cell from the weight of each class and the number of stored queues. The priority of each class is referred to, and a class having a higher priority is preferentially selected.

The present invention preferably provides a switch body,
An ATM switch provided at each of a plurality of input ports and output ports of the switch and including an input buffer unit and an output buffer unit for accumulating cells;
In the scheduling method in the input buffer unit and the output buffer unit, in the input buffer unit and the output buffer unit, for each outgoing path, for each type of cell traffic, a queue logically divided buffers, A corresponding weight counter, and when there are a plurality of queues of a class in which the weight counter is not 0, a queue whose output is permitted is determined by a rotation priority method from among the queues of the class having a higher priority, and the weight counter is determined. If there is no high-priority class queue among the non-zero classes, a queue for which output is permitted is determined from the low-priority class queues by a rotation priority method, and cells are read out. Features.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. In a preferred embodiment of the present invention, a queue for storing input cells for each traffic class, a weight counter for setting an output ratio for each queue, a cell storage status of the queue, a value of the weight counter, and a priority of each class are set. And a reset control unit that monitors the cell accumulation state of the queue and the value of the wait counter, and outputs a reset instruction to each wait counter when a reset condition occurs. The unit gives priority to the class whose priority is set to high priority among the classes whose queue length is not 0 and the value of the weight counter is not 0, and the queue length of the high priority class is 0, or after the wait counter reaches 0, allow output from the class with the lower priority. Obtain.

According to the embodiment of the present invention configured as described above, the ATM section which divides the buffer section provided before or after the switch for each traffic class and for each outgoing path and performs traffic control. In the switch, among the cells input to the buffer unit, for the traffic class that requires real-time performance, the priority is set to high priority, so that the output is immediately performed without waiting for the output of another class Is possible, and deterioration of the delay characteristic can be prevented.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to explain the above-mentioned embodiment of the present invention in more detail, an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a configuration of an input or output buffer unit of an ATM switch in which a WRR scheduling control method according to an embodiment of the present invention is performed.

Referring to FIG. 1, in one embodiment of the present invention, an ATM cell and an identifier indicating a traffic class of the cell or an outgoing route are added to the head of the cell and input to the cell input section 1. You.

When receiving a cell from the cell input unit 1, the queue selecting unit 2 identifies the traffic class or the outgoing route information added to the head of the cell, and classifies the traffic class or outgoing route into a plurality of traffic classes or outgoing routes. Select which queue to write from among a plurality of deployed queues 31 to 3n,
Cells are stored in the selected queue. FIG. 1 shows an example in which the number of traffic classes is n and the number of outgoing routes is 1, for simplicity of explanation.

Upon receiving the output permission signal 9 from the output cell selection unit 5, the queue in which the cells are stored is replaced by one of the cells stored in the queue that has been written first.
Read out.

The cell read from the queue reaches the cell output unit 7 and is output to a switch unit (not shown) or a circuit corresponding unit.

Next, in one embodiment of the present invention, WRR
The configuration of the scheduling control method will be further described.

The weight counters 41 to 4n are provided corresponding to the respective queues, and the weight corresponding to the band required for each traffic class is set in advance. The setting of the weight is performed by a software interface and can be changed. Also, weight counters 41 to 4
When n receives the reset instruction signal 12 from the reset control unit 6, n loads a value preset by the software interface into the counter as an initial value.

The reset control unit 6 monitors the queue length notification signal 10 indicating the number of cells stored in each queue and the counter value notification signal 8 indicating the value of each weight counter, and determines the queue length Qi for all traffic classes. Counter value Wi
Is zero, that is, when Qi · Wi = 0, the reset instruction signal 1 is sent to all the weight counters 41 to 4n.
Send out 2.

The output cell selector 5 monitors a queue length notification signal 10 indicating the number of cells stored in each queue, a counter value notification signal 8 indicating the value of each weight counter, and priority information of each traffic class. By the priority control, the output queue is selected once per one cell time, and the output permission signal 9 is transmitted to the selected queue.

The output cell selection method of the output cell selection section 5 will be described in detail below.

If the product of the queue length Qi and the counter value Wi is not 0, that is, if there is a class of Qi · Wi ≠ 0, if there is a class of which priority is set to high priority, the class is A queue for which output is permitted is selected from the classes by the rotation priority control.

If there is no class in which the priority is set to high priority among the classes of Qi · Wi ≠ 0, a queue for which output is permitted is selected from the classes having low priority by rotation priority control. .

If no class of Qi · Wi ≠ 0 exists, output is not permitted to any queue.

Next, a series of W in one embodiment of the present invention will be described.
The RR scheduling operation will be described with reference to the flowchart in FIG.

After the start, in step S1, a counter for setting a weight provided for each queue is reset, and an initial value is loaded into the counter.

Next, in step S2, it is determined whether or not Σf (i) ≠ 0. That is, the queue length Qi of each queue is 0,
Alternatively, it monitors whether the value of the counter corresponding to each queue is not zero. In step S2, if f (i) = 0 for all traffic classes, the process returns to step S1.
On the other hand, if f (i) ≠ 0 in any of the classes, the process proceeds to step S3.

In step S3, it is determined whether Pi = 1, that is, a class having a high priority is present in the classes of f (i) ≠ 0. If there is a class of Pi = 1, the process proceeds to step S4, and if not, the process proceeds to step S5.

In step S4, f (i) ≠ 0, Pi =
A queue for which output is permitted is determined by rotation priority control from one class.

In step S5, f (i) ≠ 0, Pi =
0, that is, a queue whose output is permitted is determined by the rotation priority control from among the classes of low priority.

From the queue determined in steps S4 and S5, one cell can be read.

Next, in step S6, the value Wi of the weight counter corresponding to the queue determined in the flow of step S4 or step S5 is decremented by one.

Thereafter, the flow returns to step S2, where Δf (i)
Steps S3 to S6 are repeated according to the determination of ≠ 0, and Σ
When f (i) = 0, the process returns to step S1 to reset the weight counter.

In this manner, cells are output from each queue in accordance with the weight ratio set in the weight counter, and the priority is set to high priority for a traffic class requiring delay characteristics. As a result, cells can be output without waiting for cell output of another class.

FIG. 3 is a diagram schematically showing an example of the operation of the WRR scheduling control system according to one embodiment of the present invention, and is a diagram for comparison with FIG. 6 showing an example of the operation of the conventional system. .

FIG. 3 shows an example in which the number of classes is 6, the weight 1 of each class, and the priority of only class 6 is given high priority. When a cell of class 6 arrives, a cell of class 6 is output immediately. It is shown that.

[0047]

As described above, according to the WRR scheduling control method of the present invention, when a priority is given to a traffic class requiring delay characteristics, and an output queue is selected by rotation priority control, By preferentially selecting from the higher priority classes, it is possible to output cells without waiting for cells of other lower priority classes to be output. Therefore, according to the present invention, even if the number of traffic classes to be accommodated increases, it is possible to reduce the deterioration of the delay characteristic of the traffic class requiring real-time performance, and to prevent the influence on the CDV characteristic. It has the effect of being able to.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a scheduling control method according to the present invention.

FIG. 2 is a flowchart showing a processing flow of an embodiment of the scheduling control method of the present invention.

FIG. 3 is a diagram schematically illustrating a cell output operation according to an embodiment of the scheduling control method of the present invention.

FIG. 4 is an explanatory diagram schematically showing a conventional scheduling control method.

FIG. 5 is a flowchart showing a processing flow of a conventional scheduling control method.

FIG. 6 is a diagram schematically illustrating a cell output operation according to a conventional scheduling control method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cell input part 2 Queue selection part 3 1-3n Queue 4 1-4n Weight counter 5 Output cell selection part 6 Reset control circuit 7 Cell output part 8 Counter value notification signal 9 Output enable signal 10 Empty signal 12 Reset instruction signal 21 22, 23 queue 24 WRR scheduler

Claims (4)

(57) [Claims] 1. An ATM switch, comprising: a switch main body; and an input buffer unit and an output buffer unit provided in each of a plurality of input ports and output ports of the switch and accumulating cells. In the scheduling method in the buffer unit, the input buffer unit and the output buffer unit, for each output path, for each type of traffic of the cell, a queue that logically divided the buffer, a weight counter corresponding to each queue, Based on the weight counter value and buffer amount of each class.
WRR (Weighted Round Robi) for selecting output cells
n; weighted round robin) control,
Priority (priority) is set between target classes.
In the case where there are a plurality of queues of a class whose weight counter is not 0, a queue for which output is permitted is determined by a rotation priority method from among the queues of the class with a higher priority, and the queue whose weight counter is not 0 is selected. If there is no high-priority class queue, an ATM switch that determines a queue for which output is permitted from among low-priority class queues by a rotation priority method and reads out cells is characterized by scheduling. method. 2. An ATM switch including a switch body, and an input buffer unit and an output buffer unit provided at each of a plurality of input ports and output ports of the switch and accumulating cells, wherein input cells are classified by traffic class. Or a plurality of queues to be accumulated for each departure route, and a weight counter for setting a ratio of the output to each of the queues , based on the value of the weight counter of each class and the buffer amount.
WRR (Weighted Round Robi) for selecting output cells
n; weighted round robin) control,
Priority (priority) is set between target classes.
The output cell selection unit that selects an output cell based on the weight of each class and the number of accumulated queues refers to a preset priority (priority) of each class and preferentially selects a class with a higher priority. AT characterized by the following
Scheduling method in M switch. 3. An ATM switch comprising: a switch body; and an input buffer unit and an output buffer unit provided at each of a plurality of input ports and output ports of the switch and accumulating cells. Alternatively, it comprises a plurality of queues provided for each output route, and a weight counter for setting an output ratio for each of the queues. Each traffic class is set with a low-priority or high-priority priority, and For traffic classes that require time, give high priority
If the product of the weight counter value of each class and the queue length of the queue is not 0 and there is a class whose priority is set to high priority, the output cell selection unit selects the rotation priority from among those classes. Determines the queue for which output is permitted by the method, and if there is no class with high priority, the queue for which output is permitted in the rotation priority method from among the classes with low priority WR in the ATM switch
ATM characterized by performing R scheduling control
Scheduling method in the switch. 4. A cell input unit for inputting an ATM cell; a plurality of queues provided for each of a plurality of traffic classes or for each outgoing route; a weight counter corresponding to each of the queues; a queue selection unit; And a cell selector , based on the value of the weight counter and the buffer amount of each class.
WRR (Weighted Round Robi) for selecting output cells
n; weighted round robin) control,
Priority (priority) is set between target classes.
Only, the queue selection section receives the cell from the cell input part, the added traffic class to the cell or to identify the output path information, are deployed by the plurality of traffic classes, or by outgoing line The cell is stored in the selected queue, and the output cell selection unit includes a queue length notification signal indicating the number of cells stored in each queue, The counter value notification signal indicating the value of the counter and the priority information of each traffic class are monitored.
A scheduling method in an ATM switch, comprising selecting an output queue, transmitting an output permission signal to the selected queue, and reading cells from the queue receiving the output permission signal from the output cell selection unit.