JP2000156695A - Switching system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease both cell delay value and cell disuse rate against the data of voices and moving images by controlling with priority the cell that is received from a 1st subscriber whose band is set in a switching system so as to receive no influence of cells caused by a 2nd subscriber. SOLUTION: The cell received from a 1st subscriber whose band is set is controlled with priority in a switching system so as to receive no influence of a cell caused by a 2nd subscriber. In an exchange 0, for example, the cell received from a call whose band is set is stored in a buffer memory 22 and the cell received from a call whose band is not set is stored in a buffer memory 23 respectively. A selector 24 outputs the cell of the memory 22 with priority and then outputs the cell of the memory 23 only when no cell to be outputted is stored in the memory 22, for example. Thus, the control is performed to output the cell of the memory 22 to an output line with no disturbance caused by the cell of the memory 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ATM (Asynchronous Machine) used for a channel device of a broadband ISDN exchange.
More particularly, the present invention relates to an ATM switching system suitable for performing quality control suited to the characteristics of each medium when performing multimedia communication such as voice, moving image, and data.

[0002]

2. Description of the Related Art An example of a conventional system for controlling the quality of an ATM switching network for a broadband ISDN is disclosed in Japanese Unexamined Patent Publication No.
-25045 proposes a "bandwidth allocation method in a packet communication network". In this method, two types of priorities are provided for each call, a band is reserved for a call of the first priority at the time of call setting, and a band is reserved for a call of the second priority. The call is set without securing the packet, and the packet generated from the first priority call is processed with higher priority than the packet generated from the second priority call. According to this method, quality is ensured for a first priority call, but quality is not necessarily ensured for a second priority call.

In the ATM system, information is transmitted in fixed-length packets called cells. In an ATM switch that switches cells from a plurality of input lines to any of a plurality of output lines, input cells may concentrate on a specific output line. Therefore, in an ATM switching system,
A buffer for cell queuing is required. Even in this case, when the number of waiting cells exceeds the buffer capacity, cells are discarded by an amount that overflows from the buffer.

[0004] When a band is secured by call setting, the amount of cells coming from a call source per unit time is constant, and the amount of cells arriving at one output line of a switch within a certain fixed period is: There will be no more than the bandwidth set for this output. Therefore, if a buffer is reserved for cells that concentrate on one output during a certain period, the cell discard rate can be suppressed sufficiently low. In addition, the amount of cell delay in the buffer is determined by the amount of cells concentrated on one output line during a certain period of time. Therefore, if the bandwidth set for each output line is reduced to some extent, the amount of cells decreases. Thus, the amount of delay can be kept small.

[0005] If a method of securing a band for a call is adopted,
For a fixed transmission rate, such as fixed-rate audio and video, the cell discard rate and the delay amount can be kept low, and the quality can be ensured. Therefore, as in the conventional example, if a band is reserved for a call of the first priority and call setting is performed, and these are always treated with higher priority than the call of the second priority, the call of the first priority can be obtained. The cell generated by the call can be transmitted without being disturbed by the cell generated by the call of the second priority, and the quality can be ensured.

[0006]

The data generated from a LAN terminal or the like can define the maximum bandwidth, but it is difficult to set the average bandwidth itself because the data generation is not constant. In the above-described conventional example, the call must be classified as the second priority call. For these calls,
Although the delay amount may be made slower than the sound and the moving image, it is necessary to keep only the cell discard rate sufficiently low. Generally, LAN
When data is discarded during transmission of a terminal or the like, data retransmission is controlled between the terminals. When this data retransmission is performed, the amount of delay in cell transfer increases, and the throughput between terminals decreases.

On the other hand, when a file of several Mbytes or more is transferred by file transfer, about 10 ⁵ cells are transferred. However, in order to make the cell loss rate negligible in one file transfer, 10 ^-5 cells are transferred. Must be several orders of magnitude lower. If 10 ⁵ cells are to be transferred in a burst manner in this file transfer, the cell discard rate is set to a sufficiently low value unless a buffer capable of storing a cell amount exceeding several 10 ⁵ digits is prepared. This requires a huge amount of buffers to achieve this. Therefore, in the conventional system, it is extremely difficult to suppress the cell discard rate sufficiently low for the second-priority call in which the band cannot be set accurately, such as LAN data.

An object of the present invention is to reduce the cell delay amount and the cell discard rate for data such as voice and moving images to a sufficiently low level. Is to provide a switching system capable of keeping the switching power sufficiently low.

[0009]

In order to achieve the above object, according to the present invention, a first subscriber who sets (declares) a use band of a subscriber and a second subscriber who does not set (declares) a use band. In the switching system, the cell buffer is divided into those for the first subscriber and those for the second subscriber, and the cell output from the buffer for the second subscriber is While controlling so as not to affect the cell quality of the first subscriber, a congestion control signal is generated before cells can no longer be stored in the buffer of the second subscriber, and the preceding switching system or terminal The cell output from the second subscriber is suppressed or stopped.

[0010]

According to the present invention, the cells from the first subscriber whose band is set are preferentially controlled in the switching system so as not to be affected by the cells generated from the second subscriber. In addition, the cell delay amount and the cell loss rate can be kept extremely low. In addition, for cells generated from the second subscriber, a congestion control signal is generated before buffer overflow occurs in the switching system, and output from the preceding switching system or terminal is suppressed or stopped, so that switching is performed. Cell discard in the system is prevented.

[0011]

An embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, cells input to the exchange 0 are lines L1-1 to L1 on input lines 3-1 to 3-n.
-N is stored in the buffer memory 22 or 23.
Cells coming from a call whose bandwidth has been set are stored in the buffer memory 22, and cells coming from a call whose bandwidth has not been set are stored in the buffer memory 23. Either of the buffer memories 22 and 23 is selected by the selector 24, and the output cells are output from the lines L6-1 to L6- on the output lines 4-1 to 4-n.
n.

The selector 24 outputs the cells of the buffer memory 22 preferentially, for example, by outputting the cells of the buffer memory 23 only when there are no cells to be output to the buffer memory 22. Is output to the output line without being disturbed by the cells of the buffer memory 23. Buffer memory 22
Are generated from a call source whose bandwidth is set, and since the amount of cells generated per unit time is constant, a cell having a capacity corresponding to the amount of cells concentrated on one output line within a certain period of time. If a buffer is secured, the cell discard rate can be sufficiently reduced to a level that does not hinder practical use.
Further, the cell delay time in the buffer is determined by the amount of cells concentrated on one output line in a certain unit period. The amount can be limited, and the cell delay amount can be kept small. That is, for a cell generated from a call source for which a band has been set, the cell discard rate and the delay time can be kept sufficiently small.

In the above configuration, the selector 24
The cells from the buffer memory 23 are stored in the buffer memory 22 within, for example, a free band of each output line (a surplus band obtained by removing the set band from the band capacity) or a band slightly smaller than that. The output may be equal to or higher than that of the cell, and a certain degree of band may be guaranteed even for a call for which no band is set.

The line L5- on the input lines 3-1 to 3-n
When the congestion control signal is input from 1 to L5-n, the cell output of the unset-band call from the buffer memory 23 is suppressed.

If the amount of cells in the buffer exceeds a certain threshold before the buffer memory 23 becomes full and cell discarding is performed, a congestion control signal is output to the line L2-L on the output lines 4-1 to 4-n. 1 to L2-n. As a result, another switch or terminal currently transmitting a cell to the exchange 0 is requested to prohibit or suppress the output of cells from a call whose bandwidth has not been set. It is designed to avoid occurrence.

As a method of transmitting a congestion control signal on the input lines 3-1 to 3-n and the output lines 4-1 to 4-n, for example, a bit for congestion control is added to a header portion of each cell. A method of providing congestion control bits in a frame signal on a transmission frame, a method of transmitting congestion control information by a control cell, and the like can be adopted.

2 (a) to 2 (e) show the traffic volume and
FIG. 4 is a diagram for explaining a relationship between a buffer memory amount and generation of a congestion control signal. FIG. 2A shows the traffic volume from a call for which a band has been set. When the band is set, the terminal generates cells in a predetermined amount, so that the traffic amount is constant with time. FIG. 2B shows the traffic volume from a call for which no band is set. Although the traffic volume of the cells to be input to the exchange occurs in a burst manner, the exchange outputs the cells of the call for which the bandwidth has been set in priority, so that the cells for which the bandwidth has not been set are limited to the remaining bandwidth on the output line. No output.

FIG. 2 (c) shows a change in the amount of memory used by the buffer memory 23 in FIG. 1, and FIG. 2 (d) shows a traffic volume of an unset-band call actually input to the exchange. FIG. 2E shows generation of a congestion control signal. As shown in FIG. 2B, since the traffic volume of the output cell from the switch is smaller than the traffic volume of the input cell actually required, the usage amount of the buffer memory gradually increases. When the cell amount exceeds a certain threshold, a congestion control signal is generated before the cell is discarded, and flow control is performed so as to stop the input traffic. As a result, when the usage of the buffer memory decreases and becomes smaller than a certain threshold, the congestion control signal stops and the input traffic resumes. The present invention is characterized in that the flow control is performed so that the buffer overflow does not occur in the buffer memory 23. It is also possible to release a certain amount of unused bandwidth that is not occupied by the bandwidth setting call to the traffic of the bandwidth unset call, and then perform flow control so as to avoid occurrence of cell discard.

FIG. 3 shows another embodiment of the present invention. The input cells that have reached the exchange are passed through lines L1-1 to L1-n on the input lines 3-1 to 3-n, respectively.
n, and arrives at the switch unit 2 via the lines L3-1 to L3-n. The input cells from each line are exchanged by the switch unit 2 and the lines L4-1 to L4-
n to the lines L2-1 to L2-n on the output lines 4-1 to 4-n via the line corresponding units 1-1 to 1-n.

On the other hand, the congestion control signal is transmitted from the input lines 3-1 to 3-1.
From line L5-1 to L5-n on 3-n to line corresponding unit 1
-1 to 1-n, and arrives at the switch unit 2 through the lines L7-1 to L7-n. When the congestion control signal is input, the switch unit 2 stops the output of the cell from the unset-band call. Further, the switch unit 2 sets the lines L8-1 to L8- at the time when the cell amount reaches a predetermined value before the buffer for storing cells from the unset-band call becomes full.
By generating a congestion control signal at n, the cells from the unset-band call are prevented from being input from the line corresponding units 1-1 to 1-n.

The line corresponding units 1-1 to 1-n send the congestion control signals to the lines L6-1 to L6-1 on the output lines 4-1 to 4-n.
Outputting to L6-n prevents cell discard.

FIG. 4 shows the configuration of the line corresponding unit shown in FIG. The line handling unit 1 stores only the cells that have come from the unset-band call out of the cells input from the line L1 in the buffer memory 11, and transfers the cells from the band-set call directly to the selector 12. The selector 12 outputs the cell from the band setting call preferentially, and outputs the cell in the buffer memory 11 when the cell output from the band setting call has an idle time. The congestion control signal on line L5 coming from each input line is output as is on line L7 and input to the switch unit. Further, when a congestion control signal is received from the switch unit via the line L8, the cell output operation of the buffer memory 11 is not performed even if there is a vacant timing. Before the cell discard is performed, the buffer memory 11
A congestion control signal is output to the line L6 to stop the generation of a cell for which the bandwidth is not set on the input line. The cell output from the switch unit on the line L4 is output on the line L2 and goes to the output line.

FIG. 5 shows an example of the detailed configuration of the switch section 2 in FIG. Cells input from each of the lines L3-1 to L3-n are multiplexed in the multiplexer 21, and buffer memories 22-1 to 22- corresponding to the lines to be output are provided.
n, or one of 23-1 to 23-n. The buffer memory is provided with a pair of buffer memories 22-i and 23-i corresponding to the output lines. Of the cells to be output to the i-th output line, the cells coming from the band setting call are stored in the buffer memory 22. -I also
Cells coming from the unset-band call are respectively stored in the buffer memories 23-i.

The cells 24-1 to 24-n have buffer cells 22-1 to 22-n.
To 23-n so as to be output without being disturbed. Each selector 24-1 to 24
-N preferentially outputs the cells of the buffer memories 22-1 to 22-n.
If there is no cell to be output at n, the buffer memory 23
It operates to output cells -1 to 23-n. The cells of the buffer memories 23-1 to 23-n are stored in the buffer memory 22 in an amount corresponding to the remaining band of the band occupied by the band setting call, or within a band slightly smaller than the remaining band.
The output may be equivalent to that of cells -1 to 22-n. In this manner, cells can be transmitted in a form in which a certain band is guaranteed even for a call whose band is not set. Selector 24-
Cells output from 1 to 24-n are connected to lines L4-1 to L4-1.
The signal is output to L4-n, and output to an output line via a line corresponding unit.

When a congestion control signal generated on the lines L7-1 to L7-n is received from the input line through the line corresponding unit, cell output from the buffer memories 23-1 to 23-n is prohibited. The buffer memories 23-1 to 23-
If the cell overflows with n, before that, the congestion control signal is output to the lines L8-1 to L8-n, and the output of the cell from the call whose bandwidth is not set from the line corresponding unit is prohibited.

In FIG. 5, the buffer memory divided into a plurality is processed in common by the method disclosed in the specification of "switching system" proposed by the present applicant in Japanese Patent Application No. 62-174677. Is also possible. In particular,
If the buffer memories 22-1 to 22-n are shared, the cell discard rate of the call that has been set can be further reduced as compared with the case where the calls are not shared. In addition, for calls with bandwidth settings,
The cell discard rate can be kept sufficiently low by the congestion control.

FIG. 6 is a diagram for explaining congestion control between exchanges in the configuration shown in FIG. In this figure,
A cell is transferred from the upstream exchange 0 to the downstream exchange 0 ', and the distance between the exchanges is set to L (km). The downstream switch generates a congestion control signal before the buffer memory 11 'provided in the line corresponding section overflows, and inhibits the cell output from the buffer memory 23 provided in the switch section of the upstream switch. The amount of data (cells) arriving between the time when the buffer memory 23 of the upstream switch receives the congestion control signal generated by the buffer memory 11 'and the time when there are no more output cells from the buffer memory 23 in the buffer memory 11'. ) Is almost proportional to the distance L between the switches, ignoring the processing delay in the switches. Therefore, if a congestion control signal is generated when the remaining capacity of the buffer memory 11 'reaches a predetermined value substantially proportional to the distance L, cell discarding in the buffer memory 11' can be prevented.

FIG. 7 shows the relationship between the transmission distance L between exchanges and the capacity of the buffer memory required for each line corresponding unit. Assuming that the transmission rate between the exchanges is 150 Mbps, when the distance between the exchanges is 100 km, about 200 km
It can be seen that a buffer memory of about 1 Mbit should be prepared for a bit and a distance of 500 km.

In general, for media such as voice and moving images, it is necessary to suppress the cell discard rate to some extent and to reduce the amount of delay sufficiently, but these can be handled as calls whose bandwidth can be set. On the other hand, it is difficult to set a band for a cell generated from a LAN terminal or the like because it is difficult to predict when the cell will occur, but it is necessary to keep the cell discard rate sufficiently low. According to the embodiment of the present invention described above, these requirements can be satisfied, and the unused band of the band-set first call is used for cell transmission of the second call without the band set. By using it, the band can be used effectively.

[0031]

According to the present invention, the generated call is divided into a first call for which a use band is designated and a second call for which no band is set, and the first call used by the first call in the exchange is provided. A buffer memory and a second buffer memory used by the second call are provided, and the cell output from the second buffer memory is controlled so as not to affect the communication quality of the cell of the first call. Since the congestion control signal is generated before the memory becomes full, the transmission of cells from the second call to the preceding exchange or terminal device is stopped or suppressed. Both calls can reduce cell discard.

Further, according to the present invention, the first set band can be set.
Is subjected to flow control in the switching system so as not to be affected by cells generated from the second call for which the band is not set, so that not only the cell loss rate but also the cell delay amount can be reduced. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an exchange according to the present invention.

FIG. 2 is a diagram for explaining a relationship between a traffic amount, a buffer memory amount, and generation of a congestion control signal in the exchange according to the present invention.

FIG. 3 is a configuration diagram showing another embodiment of the exchange according to the present invention.

FIG. 4 is a configuration diagram showing details of a line corresponding unit 1 in FIG. 3;

FIG. 5 is a configuration diagram showing details of a switch unit 2 in FIG. 3;

FIG. 6 is a diagram for explaining congestion control between exchanges.

FIG. 7 is a diagram for explaining the relationship between the transmission distance between exchanges and the amount of buffer memory required for a line corresponding unit.

[Explanation of symbols]

0, 0 '... exchange, 1-1-1-n ... line corresponding unit,
2. Switch section 3-1 to 3-n ... input line, 4-1 to 4-n ... output line 11, 11 ', 22, 23, 22-1 to 22-n, 23
-1 to 23-n ... buffer memory, 12, 12 ', 2
4, 241-1 to 24-n... Selector 21... Multiplexer.

Claims (7)

[Claims] 1. A switching system for storing and switching ATM cells received on a plurality of input lines to one of a plurality of output lines, each of which accommodates the input line and the output line and receives the ATM cells from the input line. A first buffer memory for storing the ATM cells that do not declare the used bandwidth, and an ATM cell for declaring the used bandwidth received from the input line and first selection means for selecting the output of the first buffer memory. A plurality of line-corresponding units, and an ATM cell connected to the plurality of line-corresponding units and received by the plurality of line-corresponding units is transferred to a line corresponding unit having an output line serving as a destination of the ATM cell. ATM for declaring the used band corresponding to the plurality of output lines in a switch unit
A second buffer memory for storing cells, a third buffer memory for storing ATM cells whose use bandwidth is not declared, and a second selecting means for selecting the output of the second buffer memory or the third buffer memory A congestion control signal when a free space of the first buffer memory or the third buffer memory becomes equal to or less than a predetermined capacity, and the first buffer memory or the third buffer Means for suppressing or stopping the input of an ATM cell for which the use bandwidth is not declared to a memory. 2. A switching system for storing and switching ATM cells received on a plurality of input lines to one of a plurality of output lines, each of which accommodates the input line and the output line and receives from the input line. A first buffer memory for storing the ATM cells that do not declare the used bandwidth, and an ATM cell for declaring the used bandwidth received from the input line and first selection means for selecting the output of the first buffer memory. A plurality of line-corresponding units, and an ATM cell connected to the plurality of line-corresponding units and received by the plurality of line-corresponding units is transferred to a line corresponding unit having an output line serving as a destination of the ATM cell. ATM for declaring the used band corresponding to the plurality of output lines in a switch unit
A second buffer memory for storing cells, a third buffer memory for storing ATM cells whose use bandwidth is not declared, and a second selecting means for selecting the output of the second buffer memory or the third buffer memory And a switch unit having the following configuration: when the free space of the first buffer memory or the third buffer memory becomes equal to or smaller than a predetermined capacity, the switch to the first buffer memory or the third buffer memory is performed. A switching system characterized by suppressing or stopping the input of an ATM cell whose use band is not declared. 3. The switching system outputs an ATM cell from the second buffer memory to the destination output line in a declared band, and, if the output line has a free band, the ATM cell is below the free band. 3. The switching system according to claim 1, wherein the ATM cells stored in the third buffer memory with the capacity of (i) are also output to the output line. 4. The switching system according to claim 1, wherein when the congestion information is received from another switching system, the output of the third buffer memory corresponding to the output line addressed to the other switching system is stopped. Item 1
4. The switching system according to any one of claims 1 to 3. 5. The switching system according to claim 1, wherein when the free space of said third buffer memory becomes equal to or less than a predetermined capacity, said first buffer memory outputs an ATM cell whose bandwidth is not declared to said third buffer memory. AT for each
5. The switching system according to claim 1, wherein the switching system operates to suppress or stop the output of the M cell. 6. The switching system according to claim 1, wherein the first buffer memory outputs an ATM cell whose bandwidth is not declared to the first buffer memory when an available capacity of the first buffer becomes equal to or less than a predetermined capacity. 6. The switching system according to claim 1, wherein a request is made to suppress or stop input of ATM cells to the buffer memory. 7. The switching system according to claim 1, wherein said second buffer memory is constituted by a buffer memory common to an output line.