JP3414349B2 - Switching system - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art As an example of a conventional method for controlling the quality of an ATM switching network for wideband ISDN, Japanese Patent Laid-Open No. Hei 2 (1999) -2000 is known.
No. 25045 discloses a "bandwidth allocation method in a packet communication network". In this method, two types of priority are provided for each call, a band is secured for a call of the first priority at the time of call setup, and a band is reserved for a call of the second priority. The call is set without being secured, and the packet generated from the call of the first priority is processed with priority over the packet generated from the call of the second priority. According to this method, quality is ensured for calls of the first priority, but quality is not always ensured for calls of the second priority.

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 be concentrated on a specific output line. Therefore, in the ATM switching system,
A buffer for cell queuing is required. Even in this case, when the waiting cell exceeds the buffer capacity, cells are discarded by the amount overflowing from the buffer.

When the bandwidth is secured by the call setting, the cell amount coming from the call source per unit time is constant, and the cell amount arriving at one output line of the switch within a certain fixed period is It will never exceed the band set for this output. Therefore, the cell discard rate can be suppressed to a sufficiently low level by securing buffers for cells concentrated in one output in a certain fixed period. Further, the cell delay amount in the buffer is determined by the cell amount concentrated on one output line for a certain fixed period. Therefore, if the band set for each output line is made somewhat small, the cell amount is reduced. The delay amount can be kept small.

When a system for securing a band for a call is used,
For fixed-rate voice and moving images with a constant transmission rate, the cell loss rate and delay amount can be suppressed to a low level, and the quality can be secured. Therefore, as in the conventional example, if the band is secured for the call of the first priority and the call is set so that the call of the second priority is always treated, 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 its quality can be secured.

[0006]

The maximum bandwidth of data generated from a LAN terminal or the like can be defined, but the average bandwidth itself is difficult to set in advance because the data generation is not constant. Therefore, in the above-mentioned conventional example, the call must be classified into the second priority call. For these calls,
The delay amount may be slower than that of voice and moving images, but only the cell loss rate needs to be sufficiently low. Generally, LAN
In the data of terminals and the like, when a cell discard occurs during transmission, data retransmission control is performed between the terminals. When the data is retransmitted, the delay amount of cell transfer increases and the throughput between terminals decreases.

On the other hand, when a file transfer of several megabytes or more transfers cells, about 10 ⁵ cells are transferred. However, in order to make the cell loss rate negligible in one file transfer, 10 ^-5 It should be a few orders of magnitude lower. In the case of burst transfer of 10 ⁵ cells 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 10 ⁵ by several digits is prepared. This is not possible and requires a huge amount of buffers to achieve this. Therefore, in the conventional method, it is extremely difficult to suppress the cell discard rate to a sufficiently low level for calls of the second priority whose band cannot be accurately set like LAN data.

An object of the present invention is to sufficiently reduce the cell delay amount and the cell discard rate for data such as voice and moving images, and further, for data such as LAN terminals, the cell discard rate. It is to provide a switching system capable of keeping the voltage sufficiently low.

[0009]

In order to achieve the above object, according to the present invention, a first subscriber who sets (reports) a used band and a second subscriber who does not set (report) a used 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 that the cell quality of the first subscriber is not affected, a congestion control signal is generated before the cell cannot be stored in the buffer of the second subscriber, and the switching system or terminal at the preceding stage is It is characterized in that the cell output from the second subscriber is suppressed or stopped.

[0010]

According to the present invention, the cells from the first subscriber whose bandwidth has been set are preferentially controlled in the switching system so as not to be affected by the cells generated from the second subscriber. The cell delay amount and the cell discard rate can be kept extremely low. For cells generated by the second subscriber, a congestion control signal is generated before the buffer overflows in the switching system to suppress or stop the output from the switching system or the terminal in the preceding stage, thereby performing switching. Cell discard within the system is prevented.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 the input lines 3-1 to 3-n.
It is stored in the buffer memory 22 or 23 from -n.
The cells coming from the band-set call are stored in the buffer memory 22, and the cells coming from the band-unset call are stored in the buffer memory 23. One of the buffer memories 22 and 23 is selected by the selector 24, and the output cells are the lines L6-1 to L6- on the output lines 4-1 to 4-n.
is assigned to n.

The selector 24 outputs the cells of the buffer memory 22 preferentially, and outputs the cells of the buffer memory 23 only when there are no cells to be output to the buffer memory 22, for example. Are output to the output line without being disturbed by the cells of the buffer memory 23. Buffer memory 22
Cells are generated from a call source for which a band is set, and the amount of cells generated per unit time is constant. Therefore, the capacity of cells that are concentrated on one output line within a certain period is If the buffer is secured, the cell discard rate can be suppressed to a sufficiently low level without causing any practical problems.
In addition, the cell delay time in the buffer is determined by the amount of cells concentrated on one output line within a certain unit period. The amount can be limited, and the cell delay amount can be suppressed small. That is, the cell discard rate and the delay time of the cell generated from the call source for which the band is set can be suppressed sufficiently small.

In the above configuration, the selector 24
However, the cells from the buffer memory 23 may be stored in the buffer memory 22 within, for example, an empty band of each output line (a margin band obtained by removing the set band from the band capacity) or a band slightly smaller than that. The output may be performed in the same manner as the cell or in priority to this, and a certain band may be guaranteed even for calls for which no band is set.

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

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

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

FIGS. 2A to 2E show the traffic volume and
It is a figure for explaining the relation between the amount of buffer memory and the occurrence 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 number of cells generated from the terminal is a predetermined amount, and thus the traffic amount becomes constant with time. FIG. 2B shows the traffic volume from a call for which no band is set. The traffic volume of cells to be input to the exchange occurs in bursts, but since the exchange gives priority to the cells of the call for which bandwidth has been set, the cells for which no bandwidth has been set are limited to the remaining bandwidth on the output line. No output.

FIG. 2 (c) shows the change in the amount of memory used in the buffer memory 23 in FIG. 1, and FIG. 2 (d) shows the traffic amount of the call whose band has not been set and which is actually input to the exchange. FIG. 2E shows the generation of the 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 actually required input cell, the usage amount of the buffer memory gradually increases, but When the amount of cells exceeds a certain threshold, a congestion control signal is generated before cell discard occurs, and flow control is performed so as to stop the input traffic. As a result, the buffer memory usage decreases, and when it becomes smaller than a certain threshold value, 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 as described above. It is also possible to release the unused band not occupied by the band setting call to some extent to the traffic of the band non-setting call and then perform flow control so as to avoid the cell discard.

FIG. 3 shows another embodiment of the present invention. The input cell reaching the exchange passes through lines L1-1 to L1-n on the input lines 3-1 to 3-n, and the line corresponding units 1-1 to 1-
n, and further 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 so that the lines L4-1 to L4-
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 input to the input lines 3-1 to 3-1.
Line corresponding part 1 from lines L5-1 to L5-n on 3-n
-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 cell output from the band-unset call. In addition, 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 storing the cells from the band-unset call is full.
By generating a congestion control signal at n, it is prohibited to input a cell from a band-unset call from the line corresponding units 1-1 to 1-n.

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

FIG. 4 shows the structure of the line interface shown in FIG. The line interface 1 stores in the buffer memory 11 only the cells that have come from the band-unset call, out of the cells that have been input from the line L1, and transfers the cells from the band-set call directly to the selector 12. The selector 12 preferentially outputs the cell from the band setting call, and outputs the cell of the buffer memory 11 when the cell output from the band setting call has a free time. The congestion control signal on the line L5 coming from each input line is directly output on the line L7 and input to the switch unit. Further, when the 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 an empty timing. The buffer memory 11 stores the cells before the cells are discarded.
The congestion control signal is output to the line L6 to stop the cell of the band unset call to the input line. The cell output from the switch unit onto the line L4 is output onto the line L2 and goes out to the output line.

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

In 24-1 to 24-n, the cells of the buffer memories 22-1 to 22-n are buffer memories 23-1.
It is a selector that controls so as to output without being disturbed by the cells of 23 to 23-n. Each selector 24-1 to 24
-N preferentially outputs the cells of the buffer memories 22-1 to 22-n, and if the buffer memories 22-1 to 22-
If there is no cell to be output in n, the buffer memory 23
It operates so as to output cells of -1 to 23-n. The number of cells of the buffer memories 23-1 to 23-n is set to the buffer memory 22 within 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.
You may make it output similarly to the cells of -1 to 22-n. In this way, cells can be transmitted in a form in which a certain band is guaranteed even in a call in which no band has been set. Selector 24-
The cells output from 1 to 24-n are lines L4-1 to L4-1.
It is output to L4-n and output to the output line via the line interface.

When the congestion control signal generated in the lines L7-1 to L7-n is received from the input line through the line corresponding part, cell output from the buffer memories 23-1 to 23-n is prohibited. Further, the buffer memories 23-1 to 23-
If the cell overflows at n, the congestion control signal is output to the lines L8-1 to L8-n before that, and the cell output from the call whose band is not set is prohibited from the line interface.

In FIG. 5, a plurality of divided buffer memories should be commonly processed by the method disclosed in the specification of the "switching system" proposed by the present applicant in Japanese Patent Application No. 62-174674. Is also possible. In particular,
If the buffer memories 22-1 to 22-n are made common, the cell loss rate of the call for which the call is set can be suppressed to be lower than that in the case where the calls are not made common. For calls with bandwidth settings,
The congestion control can suppress the cell discard rate to a sufficiently low level.

FIG. 6 is a diagram for explaining congestion control between exchanges in the configuration shown in FIG. In this figure,
The cells are transferred from the exchange 0 in the front stage to the exchange 0'in the rear stage, and the distance between the exchanges is L (km). The latter-stage exchange generates a congestion control signal before the buffer memory 11 'provided in the line-corresponding part overflows, and prohibits cell output from the buffer memory 23 provided in the switch part of the former-stage exchange. The amount of data (cells that arrive from the time when the congestion control signal generated by the buffer memory 11 'is received by the buffer memory 23 of the preceding-stage exchange until the output cell from the buffer memory 23 does not reach the buffer memory 11' (cell The number is approximately proportional to the distance L between the exchanges, ignoring the processing delay in the exchange. Therefore, if the 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 discard in the buffer memory 11' can be prevented.

FIG. 7 shows the relationship between the transmission distance L between the exchanges and the capacity of the buffer memory required for each line interface. Assuming that the transmission rate between exchanges is 150 Mbps, approximately 200k when the distance between exchanges is 100km.
It can be seen that a buffer memory of about 1 Mbit should be prepared when the distance is 500 km and the distance is 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 sufficiently reduce the delay amount, but these can be handled as a call 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 above-described embodiment of the present invention, these requirements can be satisfied, and the unused band of the band-set first call can be used for the cell transmission of the band-unset second call. By using it, the band can be effectively utilized.

[0031]

According to the present invention, the generated call is divided into a first call in which a use band is designated and a second call in which the band is not set, and the first call used by the first call in the exchange. 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 cells of the first call, and the second buffer is also provided. The congestion control signal is generated before the memory is full, and the transmission of cells from the second call to the exchange or the terminal device at the preceding stage is stopped or suppressed. Both calls can reduce cell loss.

Further, according to the present invention, the first band setting
Call is controlled in the switching system so as not to be affected by the cell generated from the second call for which band setting is not performed, so that not only the cell discard rate but also the cell delay amount can be suppressed to be low. .

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining the relationship between traffic volume, buffer memory volume, and congestion control signal generation 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.

4 is a configuration diagram showing details of a line interface 1 in FIG.

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

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

FIG. 7 is a diagram for explaining a relationship between a transmission distance between exchanges and a buffer memory amount required for a line interface.

[Explanation of symbols]

0, 0 '... switch, 1-1 to 1-n ... line interface,
2 ... Switch part 3-1 to 3-n ... Input line, 4-1 to 4-n ... Output line 11, 11 ', 22, 23, 222-1 to 22-n, 23
-1 to 23-n ... Buffer memory, 12, 12 ', 2
4, 24-1 to 24-n ... Selector 21 ... Multiplexer.

Claims (7)

(57) [Claims] 1. A switching system for accumulating and switching ATM cells received by a plurality of input lines to any one of a plurality of output lines, each accommodating the input line and the output line and receiving from the input line. A first buffer memory for accumulating ATM cells not reporting the used bandwidth, an ATM cell for reporting the used bandwidth received from the input line, and a first selecting means for selecting an output of the first buffer memory. A plurality of line-corresponding units provided, and the ATM cells connected to the plurality of line-corresponding units and received by the plurality of line-corresponding units are transferred to the line-corresponding unit having an output line as a destination of the ATM cells. ATM that declares the used band in correspondence with the plurality of output lines in the switch unit
A second buffer memory for accumulating cells, a third buffer memory for accumulating ATM cells that do not declare a band to be used, and a second selecting means for selecting the output of the second buffer memory or the third buffer memory. And a first buffer memory or a third buffer when a free capacity of the first buffer memory or the third buffer memory becomes equal to or less than a predetermined capacity. A switching system comprising means for suppressing or stopping the input of an ATM cell which does not declare the used band to the memory. 2. A switching system for accumulating and switching ATM cells received by a plurality of input lines to any of a plurality of output lines, each accommodating the input line and the output line and receiving from the input line. A first buffer memory for accumulating ATM cells not reporting the used bandwidth, an ATM cell for reporting the used bandwidth received from the input line, and a first selecting means for selecting an output of the first buffer memory. A plurality of line-corresponding units provided, and the ATM cells connected to the plurality of line-corresponding units and received by the plurality of line-corresponding units are transferred to the line-corresponding unit having an output line as a destination of the ATM cells. ATM that declares the used band in correspondence with the plurality of output lines in the switch unit
A second buffer memory for accumulating cells, a third buffer memory for accumulating ATM cells that do not declare a band to be used, and a second selecting means for selecting the output of the second buffer memory or the third buffer memory. And a switch unit provided with, when the free capacity of the first buffer memory or the third buffer memory becomes less than a predetermined capacity, the first buffer memory or the third buffer memory to the third buffer memory. A switching system characterized by suppressing or stopping the input of ATM cells that do not declare the used band. 3. The switching system outputs an ATM cell from the second buffer memory to the output line which is the destination in the declared band, and when the output line has a free band, the output band is below the free band. 3. The switching system according to claim 1 or 2, wherein the ATM cells stored in the third buffer memory with the capacity of 5 are also output to the output line. 4. The switching system, when it receives congestion information from another switching system, stops the output of the third buffer memory corresponding to the output line addressed to the other switching system. Item 1
4. The switching system according to any one of 3 to 3. 5. The switching system of the first buffer memory, wherein when the free capacity of the third buffer memory becomes equal to or smaller than a predetermined capacity, an ATM cell that does not declare a band is output to the third buffer memory. AT for each
The switching system according to claim 1, wherein the switching system operates so as to suppress or stop the output of the M cell. 6. The switching system according to claim 1, wherein said switching system outputs an ATM cell whose band is not declared to said first buffer memory when the free capacity of said first buffer becomes less than a predetermined capacity. The switching system according to any one of claims 1 to 5, wherein input control or stoppage of an ATM cell input to the buffer memory is requested. 7. The switching system according to claim 1, wherein the second buffer memory is a buffer memory common to the output lines.