JP3044521B2 - Cell flow rate limiter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cell flow rate limiting device for adjusting the flow rate of cells input to an outgoing line queue in a cell exchange according to a system for transferring and exchanging various information in the form of cells.

[0002]

2. Description of the Related Art A conventional cell flow rate limiting device will be described below with reference to the drawings.

First, FIG. 4 is a diagram showing a configuration of a cell transferred / exchanged by a cell exchange, wherein 1 is a cell, 2 is a header, 3 is an information section, 4 is a channel identifier, 5 is a discardable cell or a discarded cell. This is a discard permit identifier indicating whether the cell is a non-permissible cell.

Next, FIG. 5 shows a configuration of a cell exchange, and FIG.
Is a cell exchange that transfers and exchanges various information in the form of cells.
Is a communication line incoming line in which discarded cells and non-discarded cells are multiplexed and input, 13 is a cell switch for exchanging cells for each destination, and 14 is a discarded cell according to the congestion status of each output line queue described later. A cell flow limiting device that selectively discards
15 is an outgoing line queue provided as an outgoing line buffer, 16 is a communication line outgoing line for outputting cells for each destination, and 17 is an outgoing line queue 15.
A cell input notification signal notifying that a cell has been input to the
Reference numeral 18 denotes a cell output notification signal for notifying that a cell has been output from the output line queue 15 to the output line. In FIG. 5, the communication line input line 12, the cell flow rate limiting device 14, the output line queue
15, the communication line outgoing line 16 shows three systems a to b,
Here, description will be made using one of the series.

The communication line input line 12 of the cell exchange 11 has
The discarded cells and the discarded non-permitted cells arrive in a multiplexed state, and the cell switch 11 exchanges the cells 1 according to the destination by the cell switch 13 and passes through the cell flow limiting device 14 to the outgoing line queue 15. After inputting, FI
They are sent out in the order of FO (output first arrived first).

FIG. 6 shows the structure of a conventional cell flow rate limiting device. Here, components having the same functions and effects as those in FIGS. 4 and 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. In FIG. 6, reference numeral 21 denotes a cell input notification signal 17 and a cell output notification signal 18 notified from the outgoing line queue 15, and adds 1 each time the cell input notification signal 17 is received. A queue length counter section 22 for obtaining and outputting the number of cells waiting to be transmitted to the output line in the output line queue 15 (hereinafter, referred to as queue length) by subtracting 1 every time the signal 18 is received, 22 is preset. A threshold holding unit that holds and outputs a threshold (congestion determination threshold) used for determining the congestion state of the output line queue 15;
Reference numeral 3 denotes a queue length signal from the queue length counter 21 and a threshold signal from the threshold holding unit 22. If the queue length is larger than the threshold (queue length> threshold), the output queue indicates the congestion of the output queue 15. The comparison unit 24 that outputs the status notification signal,
A discard permitting identifier extracting unit that refers to the discarding permit identifier 5 in the header 2 of the cell 1 for each input cell 1 and generates a discard permitting notification signal when the content indicates the discard permitting cell of the corresponding cell 1; The discard judging unit outputs a cell discard instruction signal for instructing discard of the corresponding cell 1 when receiving the discard enable notification signal from the discard allowable identifier extracting unit 24 and receiving the outgoing queue state notification signal from the comparing unit 23. , 26 receive the cell 1 from the cell switch 13 and output the cell 1 to the outgoing line queue 15 when the cell discard instruction signal is not received from the discard determination unit 25, and when the cell discard instruction signal is received. Is a cell discarding unit for discarding the cell 1 without outputting it to the output line queue 15.

In the conventional cell flow rate limiting device configured as described above, the queue length counter 21
Cell input notification signal 17 and cell output notification signal received from 15
The queue length is counted by 18 and output to the comparing unit 23. Further, the threshold holding unit 22 outputs the held threshold to the comparing unit 23. The comparison unit 23 receives the queue length signal from the queue length counter unit 21 and the threshold signal from the threshold value holding unit 22, compares the queue length with the threshold value, and when the queue length is larger than the threshold value, the outgoing line queue 15 is congested. And outputs an outgoing line queue state notification signal to the discard determination unit 25.

On the other hand, the discard-permissible identifier extracting unit 24 refers to the discard-permissible identifier 5 in the header 2 of the cell 1 received from the cell switch 13 and generates a discard-possible notification signal when the corresponding cell 1 is a discard-permissible cell. Output to the discard determination unit 25.

The discard judging unit 25 outputs a cell discard instruction signal to the cell discarding unit 26 when receiving the discard enable notification signal from the discard allowable identifier extracting unit 24 and receiving the outgoing line queue status notifying signal from the comparing unit 23. Then, it instructs the received corresponding cell 1 to be discarded without being input to the outgoing line queue 15.

When the cell discard unit 26 receives the cell discard instruction signal from the discard determination unit 25, it discards the corresponding cell 1.

As described above, even in the conventional cell flow rate limiting device 14, when it is determined that the outgoing line queue 15 is congested due to an increase in the queue length, the continuously arriving discardable cells are selectively discarded. By doing so, it is possible to prevent a further increase in the queue length, and to reduce the possibility that a discarded non-permissible cell arriving afterwards will be lost due to overflow of the output line queue.

[0012]

However, in the cell flow rate limiting device having such a configuration, the discarding of the discardable cells input to the output line queue is determined only by the congestion state of the output line queue. Cells belonging to a channel may be discarded multiple times in a short period of time, and such repeated cell discards within a short period of time may result in services that are relatively tolerant of cell discards such as voice communications. There was also a risk that the quality would be significantly reduced.

The present invention solves the above-mentioned problem of the prior art. In the present invention, when a discardable cell is discarded by a discarding history holding unit having holding information of a discarding history for each channel identifier in a cell header. It is another object of the present invention to provide a cell flow rate limiting device that suppresses a decrease in transmission quality without continuously discarding cells belonging to the same channel identifier using a discard history.

[0014]

In order to achieve this object, the present invention relates to a cell flow rate limiter for controlling the flow rate of cells input from a cell switch in a cell exchange by connecting to an output line queue of the cell exchange. In the apparatus, a queue length counter means for obtaining the number of cells staying waiting for output to an outgoing line in an outgoing line queue, a threshold value holding means for holding a threshold value regarding the number of output waiting cells in the outgoing line queue, A comparison unit that compares the number of output waiting cells in the output line queue counted by the queue length counter unit with a threshold value held by the threshold value holding unit and notifies a congestion state of the output line queue; and Channel identifier extracting means for referring to and outputting the channel identifier contained in the header of the input cell, and being included in the header of the cell input from the cell switch Referencing the discard tolerable identifier, discard tolerable identifier extracting means for notifying that discarding is possible, notifying the congestion of the outgoing line queue, notifying that the received cell can be discarded, and discarding history indicating that the received cell has not been discarded. When indicating, a discard determination means for instructing the discard of the received cell,
When the discard instruction is notified from the discard determination unit, the cell discard is held as a discard history in combination with the channel identifier notified from the channel identifier extraction unit, and the channel identifier is input by inputting the channel identifier. The discard history holding means for outputting the discard history held in accordance with the above, and deleting all the discard history held by input of the reset notification, and outputting the cell received by the cell discard instruction to the outgoing line queue. It is characterized by comprising a cell discarding means for discarding cells by not performing the operation and a timer means for outputting a reset notification at regular time intervals.

A threshold value a holding means for holding a threshold value a relating to the number of output waiting cells in the output line queue, and a threshold value b for retaining a threshold value b relating to the number of output waiting cells in the output line queue
Holding means, comparing the number of output waiting cells in the outgoing line queue counted by the queue length counter means with the threshold value a held by the threshold value a holding means and the threshold value b held by the threshold value b holding means, If the number of output waiting cells in the outgoing line queue is equal to or greater than threshold value b and less than threshold value a, the status of the outgoing line queue is notified that the state is semi-congested, and the number of output waiting cells in the outgoing line queue is equal to the threshold value. a is greater than or equal to a, the comparing means for notifying that the state of the outgoing line queue is congestion, the quasi-congestion of the outgoing line queue is notified, the received cell is discardable, and the discarding history is received. When indicating that the cell has not been discarded, or when congestion of the outgoing line queue is notified, and when notified that the reception cell can be discarded, the discard determination means for instructing discard of the reception cell is provided. Make up It is intended.

[0016]

According to the above construction, in addition to the outgoing line queue status information notified by the comparing means and the information indicating that the cell input to the outgoing line queue notified by the discard allowable identifier extracting means is a discard allowable cell, The discard history holding means searches based on the channel identifier of the corresponding cell, which is referred to and notified by the channel identifier extracting means, and determines whether to discard the corresponding cell based on the discard history of the cell belonging to the same channel identifier as the presented cell. Therefore, it is possible to prevent cells belonging to the same channel identifier from being discarded a plurality of times in a short time.

If the comparing means determines that the state of the outgoing line queue is semi-congested, the discard-permissible identifier extracting means notifies the discriminable-permitted cell of the channel identifier extracting means. Can be determined based on the discard history of the cell presented by the discard history holding means based on the channel identifier notified by the cell identifier, and the cell belonging to the same channel identifier can be prevented from being discarded multiple times in a short time. If the comparison means determines that the state of the outgoing line queue is congested, the arriving discardable cells are discarded to prevent the queue length from increasing, and thereafter, the arriving discard non-permissible cells are output. The probability of cell loss due to line queue overflow can be reduced.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the structure of a cell flow rate limiting device according to a first embodiment of the present invention, in which the same reference numerals are given to those having the same functions and effects as described in FIG. 6 of the conventional example, and detailed description thereof will be omitted. . In FIG. 1, reference numeral 30 denotes a discard history signal indicating that the cell 1 having the same channel identifier 4 as the corresponding cell 1 has not been discarded from the discard history holding unit to be described later, When a discard enable notification signal is received from 24 and an outgoing queue status notification signal is received from the comparison unit 23, a discard determination unit that outputs a cell discard instruction signal for discarding cell 1 is provided. The channel identifier extraction unit 32, which refers to the channel identifier 4 in the header 2 of the cell 1 received for each cell reception notification signal (not shown) from 13 and outputs its value, 32
Every time a channel identifier signal is received from the channel identifier extractor 31, a discard history indicating whether or not the corresponding cell 1 stored up to that point and stored in combination with the value of the channel identifier 4 of the cell 1 is discarded is output. When a cell discard instruction signal is received from the discard judging unit 30, the discard history indicating that the cell 1 has been discarded after outputting the discard history is stored in combination with the value of the channel identifier 4, and a timer unit to be described later is used. If a reset notification signal is received from
A discard history holding unit that deletes the discard history held in combination with all the values of the channel identifier 4 is a timer unit that outputs a reset notification signal at regular time intervals.

Next, the operation of the cell flow rate limiting device of the first embodiment will be described. First, the queue length counter unit 21
The queue length is determined from the received cell input notification signal 17 and cell output notification signal 18 and output to the comparison unit 23. Threshold storage unit 22
Outputs the threshold (congestion determination threshold) of the outgoing line queue 15 held in advance to the comparing unit 23.

The comparing section 23 receives the threshold signal from the threshold holding section 22 and the queue length signal from the queue length counter section 21 and compares the threshold with the queue length. Is determined to be congested, and outputs an outgoing line queue state notification signal to the discard determination unit 30.

On the other hand, the cell flow rate limiting device is a cell switch.
When cell 1 is received from 13, the channel identifier extracting unit 31
Extracts the channel identifier 4 from the header 2 of the received cell 1 and outputs it to the discard history holding unit 32.

When the discard-permissible identifier 5 in the header 2 of the received cell 1 indicates a discard-permissible cell, the discard-permissible identifier extractor 24 outputs a discard-permissible notification signal to the discard determiner 30.

Upon receiving the channel identifier signal from the channel identifier extracting unit 31, the discard history holding unit 32
The discarding history relating to the channel identifier 4 of the discarding unit 30
Output to

Upon receiving the discard history signal from the discard history holding unit 32, the discard judging unit 30 receives the discard enable notification signal from the discard allowable identifier extracting unit 24, and stores the corresponding cell 1 in the received discard history.
Only when the cell 1 having the same channel identifier 4 has not been discarded by that time, and when the outgoing line queue status notification signal is received from the comparing unit 23, the corresponding cell 1 inputted from the cell switch 13 is received. To the cell discarding unit 26.

When receiving the cell 1, the cell discard unit 26 receives the cell discard instruction signal from the discard judging unit 30.
Discard.

At the same time, upon receiving the cell discard instruction signal from the discard judging unit 30, the discard history holding unit 32 notified of the discard of the corresponding cell 1 is used. Keep as history.
As a result, when the cell 1 having the same channel identifier 4 value is subsequently inputted from the cell switch 13 and the discard history is referred to, the cell 1 belonging to the channel identifier 4 of the corresponding cell 1 has already been discarded. Can be presented.

The timer 33 outputs a reset notification signal to the discard history holding unit 32 at regular time intervals, and upon receiving the reset notification signal, the discard history holding unit 32 stores the discard history holding information of all the channel identifiers 4. To delete.

Next, FIG. 2 shows the structure of a cell flow rate limiting device according to a second embodiment of the present invention. Description is omitted.

In FIG. 2, reference numeral 34 denotes a threshold value a (congestion judgment threshold value) used for judging the congestion state of the outgoing line queue 15 scheduled in advance.
Is a threshold a holding unit that holds and outputs a threshold b (quasi-congestion determination threshold) used to determine a congestion state of the outgoing line queue 15 scheduled in advance, and a threshold b holding unit that holds and outputs a queue length When the queue length signal is input from the counter unit 21, the threshold a signal is input from the threshold a holding unit 34, and the threshold b signal is input from the threshold b holding unit 35, and the queue length is equal to or larger than the threshold b and smaller than the threshold a.
(Threshold value a> queue length ≧ threshold value b) outputs an outgoing line queue status notification signal indicating quasi-congestion of the outgoing line queue 15, and if the queue length is equal to or more than the threshold value a (threshold value a ≦ queue length), the outgoing line queue 15 is output. 37, which outputs an outgoing line queue status notification signal indicating the congestion of
Receives the output queue status notification signal indicating the quasi-congestion of the output queue from the comparison unit 36, and receives the discard possible notification signal from the discard allowable identifier extraction unit 24, and from the discard history holding unit 32 to that point in time. When a discard history signal indicating that the cell 1 having the same channel identifier 4 as the corresponding cell 1 has not been discarded is received, or an output line status notification signal indicating the congestion of the output queue is received from the comparing unit 36, And a discard judging unit that outputs a cell discard instruction signal for instructing discard of the cell 1 when receiving a discard enable notification signal from the discard allowable identifier extracting unit 24.

FIG. 3 shows the relationship between the queue length of the outgoing line queue and the congestion state in the second embodiment. The queue length indicates the number of output waiting cells in the output line queue 15, and the thresholds a and b are thresholds related to the queue length. When the queue length is smaller than the threshold b (threshold value b> queue length), the output line queue is not congested. When the queue length is smaller than the threshold a and equal to or larger than the threshold b (threshold a> queue length ≧ threshold b), it is quasi-congestion of relatively light congestion, and when the queue length is equal to or larger than the threshold a (threshold a ≦ Queue length) is congested.

Next, the threshold value a holding unit 34 and the threshold value b holding unit 35 of the second embodiment
The 15 thresholds a (congestion determination threshold) and 15 thresholds (quasi-congestion determination threshold) are output to the comparison unit 36.

The comparing unit 36 receives the threshold a signal from the threshold a holding unit 34, the threshold b signal from the threshold b holding unit 35, and the queue length signal from the queue length counter unit 21. When the queue length is equal to or more than the threshold b and smaller than the threshold a, it is determined that the outgoing queue is semi-congested, and the outgoing queue status notification signal indicating the semi-congestion of the outgoing queue is discarded. Output to the determination unit 37.

The cell flow rate limiting device receives the cell 1 from the cell switch 13, and the channel identifier extracting unit 31 extracts the channel identifier 4 from the header 2 of the received cell 1, and outputs a channel identifier signal to the discard history holding unit 32. . When the discard-permissible identifier 5 in the header 2 of the received cell 1 indicates a discard-permissible cell, the discard-permissible identifier extracting unit 24 outputs a discard-possible notification signal to the discard-determining unit 37. Channel identifier extractor
Discard history holding unit that received the channel identifier signal from 31
32 outputs the discard history signal relating to the channel identifier 4 of the corresponding cell 1 to the discard judging unit 37.

The discard judging unit 37 that has received the discard history signal from the discard history holding unit 32 receives the discard enable notification signal from the discard allowable identifier extracting unit 24, and stores the corresponding cell 1 in the received discard history.
If the cell 1 having the same channel identifier 4 as that of the cell switch 13 has not been discarded by that time and has received the output queue status notification signal indicating the quasi-congestion of the output queue from the comparator 36, the cell switch 13 And outputs to the cell discarding unit 26 a cell discard instruction signal for instructing discarding of the corresponding cell 1 input from.

The comparing unit 36 compares the threshold value a with the queue length,
When the queue length is equal to or greater than the threshold a, the output queue is determined to be congested, and an output queue status notification signal indicating congestion of the output queue is output to the discard determination unit 37.

When the discard judging unit 37 receives the output queue status notification signal indicating the congestion of the output queue from the comparing unit 36, and receives the discard enable notification signal from the discard allowable identifier extracting unit 24, the discard history holding unit 32 Outputs a cell discard instruction signal to the cell discarding unit 26 irrespective of the discard history signal output by.

The subsequent operation is the same as in the first embodiment, and a description thereof will be omitted. Also, the same effect can be obtained by holding two thresholds as described in the second embodiment as the threshold for determining the congestion state of the outgoing line queue in the threshold holding unit in the configuration of the first embodiment. Needless to say.

[0039]

As described above, according to the present invention,
By adding the cell flow limiting device to determine the cell discard based on the past discard history, it is possible to guarantee the average cell discard quality regardless of the congestion state of the output line queue, and In the lightly congested state of the queue, it is possible to guarantee the quality of continuous discarding within a short time.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a cell flow rate limiting device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a cell flow rate limiting device according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a relationship between a queue length of an outgoing line queue and a congestion state according to the second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a cell transferred and exchanged by a cell exchange.

FIG. 5 is a block diagram showing a configuration of a cell exchange.

FIG. 6 is a block diagram showing a configuration of a conventional cell flow rate limiting device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cell, 2 ... Header, 3 ... Information part, 4 ... Channel identifier, 5 ... Discard allowable identifier, 11 ... Cell exchange, 12 ... Communication line incoming line, 13 ... Cell switch, 14 ... Cell flow rate limiter, 15 ... Out Line queue, 16 ... Communication line outgoing line, 17 ... Cell input notification signal, 18 ... Cell output notification signal, 21 ... Queue length counter unit, 22 ... Threshold holding unit,
23, 36 ... Comparator, 24 ... Discardable identifier extractor, 25,
30, 37: Discard determination unit, 26: Cell discard unit, 31: Channel identifier extraction unit, 32: Discard history holding unit, 33: Timer unit, 34: Threshold a holding unit, 35: Threshold b holding unit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-362283 (JP, A) JP-A-2-1433753 (JP, A) JP-A-4-252535 (JP, A) JP-A-6- 169290 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04L 12/28

Claims (2)

(57) [Claims] In a cell flow rate limiting device which is connected to an output line queue of a cell exchange and controls a flow rate of cells input from a cell switch in the cell exchange, an output to an output line is waited in an output line queue. Queue length counter means for determining the number of staying cells; threshold value holding means for holding a threshold value relating to the number of output waiting cells in the output line queue; output waiting cells in the output line queue counted by the queue length counter means Comparing means for comparing the number with the threshold value held by the threshold value holding means to notify the congestion state of the outgoing line queue, and referring to and outputting the channel identifier contained in the header of the cell input from the cell switch A channel identifier extracting means, and a discard permit identifier for notifying that discard is possible by referring to a discard permit identifier included in the header of the cell input from the cell switch. Extracting means for notifying the congestion of the output line queue, notifying that the received cell can be discarded, and discarding the received cell when the discard history indicates that the received cell has not been discarded. Means, when a discard instruction is notified from the discard determination means, the fact that the cell has been discarded is combined with a channel identifier notified from the channel identifier extraction means and held as a discard history. A discard history holding means for outputting the discard history held corresponding to the channel identifier, and erasing all the discard histories held by input of the reset notification; It consists of cell discarding means for discarding cells by not outputting to the queue, and timer means for outputting reset notifications at regular time intervals. Cell flow limiting device according to claim. 2. A cell flow rate limiting device which is connected to an output line queue of a cell exchange and controls the flow rate of cells input from a cell switch in the cell exchange, waits for output to an output line in the output line queue. Queue length counter means for calculating the number of staying cells, threshold value a holding means for holding a threshold value a relating to the number of output waiting cells in the output line queue, and threshold value b relating to the number of output waiting cells in the output line queue. A threshold b holding unit compares the number of output waiting cells in the outgoing line queue counted by the queue length counter unit with a threshold a held by the threshold a holding unit and a threshold b held by the threshold b holding unit. When the number of output waiting cells in the output line queue is equal to or greater than the threshold value b and smaller than the threshold value a, the state of the output line queue is notified that the state is semi-congested, and the number of output waiting cells in the output line queue is If is greater than or equal to the threshold a, comparing means for notifying that the state of the outgoing line queue is congestion,
Channel identifier extracting means for referring to and outputting a channel identifier included in the header of the cell input from the cell switch, and discardable identifier by referring to the discard allowable identifier included in the header of the cell input from the cell switch Disposal allowed identifier extracting means for notifying, the quasi-congestion of the outgoing line queue is notified, it is notified that the received cell can be discarded,
And when the discarding history indicates that the received cell has not been discarded, or when the congestion of the outgoing line queue is notified and the discarding of the received cell is notified, a discard determination instructing discarding of the received cell. Means, when a discard instruction is notified from the discard determination means, the fact that the cell has been discarded is combined with a channel identifier notified from the channel identifier extraction means and held as a discard history. A discard history holding means for outputting the discard history held corresponding to the channel identifier, and erasing all the discard histories held by input of the reset notification; It consists of cell discarding means for discarding cells by not outputting to the queue, and timer means for outputting reset notifications at regular time intervals. Cell flow restrictor, characterized in that.