JP3589260B2 - Traffic shaping device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a traffic shaping device, and more particularly, to a traffic shaping device suitable for use in controlling a cell flow in digital communication in an asynchronous transfer mode (ATM).
[0002]
[Prior art]
Generally, the ATM communication network has a property that when a large number of cells temporarily arrive at one relay point in a concentrated manner, it becomes difficult to smoothly operate the communication network. For this reason, the ATM communication network has a Usage Parameter Control (UPC) function on the network side that monitors the cell flow from the terminal and extracts and discards the offending cell. On the other hand, on the terminal side, even if the subscriber keeps the value of the contract bandwidth declared at the time of contract, the transmission path has burstiness due to disturbance of the cell flow generated while passing through the transmission path. There is a shaping technique for controlling the generation interval of cells generated in a burst.
[0003]
As a conventional technique related to this shaping method, for example, a technique described in Japanese Patent Application Laid-Open No. 06-315034 is known. This prior art is composed of a transmission time control unit that calculates the transmission time of a cell, a memory that stores the cell, and a read control unit that reads out the cell from this memory to a transmission line, and temporarily stores the cell in the memory. This makes it possible to control cell transmission time intervals at equal intervals, thereby absorbing fluctuations in cell arrival time intervals.
[0004]
[Problems to be solved by the invention]
In the ATM wide area network, in order to effectively utilize limited intra-network resources such as a transmission band, a usable band is contracted for each subscriber, and the network side device uses the UPC function to protect the contract band. Monitor for discard and discard the offending cell. On the other hand, a private network such as an ATM LAN is designed to have a margin in bandwidth, does not have a UPC function as a network, and does not require a shaping function in a terminal device, thereby reducing the device price. It is common.
[0005]
When an ATM switch or an ATM multiplexer applied to such a private network is connected to an ATM wide area network, if the cell stream having a high burstiness of the private network is transmitted to the wide area network as it is, cell discard is caused by the UPC function of the wide area network. This causes a problem that communication cannot be practically performed.
[0006]
In order to solve such a problem, the prior art described in the above-mentioned publication is used. However, in this prior art, since a cell is written in a memory address corresponding to a scheduled transmission time, a possible transmission time is determined in advance. It is necessary to prepare a memory capacity equivalent to all of them, but when shaping a low-speed connection on a high-speed transmission path, the cell interval becomes extremely long, and the amount of memory to be prepared becomes enormous. have. For example, when shaping a connection of 64 kbps on a 155 Mbps transmission line, the cell transmission interval becomes 2400 cells or more. In order to withstand burst arrival of N cells, the cell transmission scheduled time of 2400 × N or more is required. A corresponding memory address was required.
[0007]
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art, and to efficiently shape a cell stream having a high burstiness in a private network, which is suitable for an ATM switch or an ATM multiplexer. It is to provide a device.
[0008]
[Means for Solving the Problems]
According to the present invention, there is provided a traffic control system comprising: a cell buffer unit for temporarily storing arriving cells; a scheduled cell transmission time calculating unit for calculating a scheduled cell transmission time; and a transmission control unit for transmitting cells. The shaping device includes a sorting unit that performs a sorting process using the estimated cell transmission time obtained by the estimated cell transmission time calculation unit and determines a cell having the earliest estimated transmission time among the cells in the cell buffer unit. This is achieved by:
[0009]
Also, the object is to provide a means for managing the scheduled cell transmission time in a binary tree structure in the sorting unit, to perform processing using the past sorting result, and to provide a connection together with the estimated cell transmission time. This is achieved by providing a function of comparing the priority of the cell with the highest priority and selecting the cell having the earliest scheduled transmission time and the highest priority as the cell to be transmitted next.
[0010]
Further, the above object is achieved by providing a leaky bucket counter in the cell transmission scheduled time calculation unit and calculating an optimum cell transmission scheduled time at which cells are not discarded by the leaky bucket UPC of the opposing device.
[0011]
Further, the above object is achieved by further comprising means for receiving a cell transmission suppression signal from a next-stage device, and transmitting cells only during a period in which the cell transmission suppression signal is not input.
[0012]
A first feature of the present invention is to provide a sorting unit for selecting a cell to be transmitted earliest among cells that have already arrived. As a result, it is only necessary to sort the first cell in the cell buffer for each connection to be shaped, and it is sufficient to prepare only the memory necessary for sorting for the number of connections, thereby reducing the memory capacity. Can be.
[0013]
A second feature of the present invention resides in that the sorting unit manages the scheduled cell transmission time in a binary tree structure and utilizes the information at the time of the previous sorting. As a result, the processing time and the amount of memory required for sorting can be further reduced. Also, the sorting section needs to determine the next cell to be transmitted next within one cell time on the transmitting side, but if the band to be transmitted is large, an extremely high-speed operation is required. According to the second feature of the present invention, even in such a case, the required memory amount and processing time can be suppressed.
[0014]
A third feature of the present invention is that a priority is set for each connection, and a function of the sorting unit selecting an optimal cell as the next transmission cell in consideration of both the scheduled transmission time of the cell and the priority. It has a point. The ATM switch generally performs priority control in order to prevent traffic having a high burstiness such as LAN data and a certain amount of delay, such as voice data, from adversely affecting traffic not allowing a delay such as voice data. It is. However, even if priority control is performed by a switch, priority control must be performed even when the scheduled transmission time of LAN data and the scheduled transmission time of voice data become the same as a result of shaping during transmission to a line. For example, a problem that the delay of the audio data increases may occur. According to the third feature of the present invention, it is possible to prioritize so that audio data is preferentially transmitted even when the scheduled transmission times are the same.
[0015]
A fourth feature of the present invention resides in that a function is provided for calculating an optimal scheduled cell transmission time at which cells are not discarded by the leaky bucket method UPC. In the prior art, it is common to perform shaping to ensure that the transmission time interval of a cell is equal to or greater than a certain time interval. At this time, if the input cell flow in which the maximum value of the fluctuation of the cell interval is τ is shaped, the output cell flow after the shaping is delayed by τ with respect to the input cell flow. According to the fourth feature of the present invention, the delay time of the output cell flow after shaping can be reduced by leaving the fluctuation of the input cell flow within the range allowed by the UPC on the network side.
[0016]
A fifth feature of the present invention resides in that there is provided means for receiving a cell transmission suppression signal from the next-stage device. For example, when shaping cells to be transmitted to a plurality of low-speed lines, a configuration may be considered in which after shaping is performed by a traffic shaping device, a separating device is placed in the next stage and output to a plurality of low-speed lines. In this case, it is necessary to perform control so that the cell flow is correctly shaped with respect to the output cell flow of the separation device, but there is a possibility that the cell interval may fluctuate before being output from the separation device to the line. When the output speed is different for each output line, it is difficult to control. According to the fifth aspect of the present invention, by performing control such that the cell transmission suppression signal is released in accordance with the timing at which the demultiplexer transmits a cell, it is possible to correctly shape even in such a case.
[0017]
According to the present invention, the scheduled transmission time of an arriving cell is determined at the arrival of the cell if the cell immediately before the connection has already been transmitted, and is determined at the time of transmission if the immediately preceding cell has not been transmitted yet. . That is, the memory for managing the scheduled transmission time of the cell may be prepared for the maximum number of connections.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a traffic shaping device according to the present invention will be described in detail with reference to the drawings.
[0019]
FIG. 1 is a block diagram showing a configuration of a traffic shaping device according to an embodiment of the present invention, FIGS. 2 and 3 are diagrams illustrating an application example of the traffic shaping device according to an embodiment of the present invention, and FIG. It is a figure explaining the example of updating of the binary tree for sorting which manages time in a binary tree structure. 1 to 3, reference numeral 10 denotes a traffic shaping device, 11 denotes a cell buffer unit, 12 denotes a scheduled transmission time calculation unit, 13 denotes a sorting unit, 14 denotes a transmission control unit, 100 to 102 denote terminal devices, 103 to 105 and 107. Is a line interface unit, 106 is an ATM switch unit, 108 is an ATM wide area network, 109 is an ATM switch, 110 is a separation device, and 111 to 113 are line termination units.
[0020]
As shown in FIG. 1, a traffic shaping device 10 according to an embodiment of the present invention includes a cell buffer unit 11, a scheduled transmission time calculation unit 12, a sorting unit 13, and a transmission control unit 14.
[0021]
The cells arriving at the illustrated traffic shaping device 10 are temporarily stored in the cell buffer unit 11 and managed in a queue for each connection (VP connection, VC connection, or a set thereof) to be shaped.
[0022]
Either when a cell arrives in an empty queue (no cells in the queue) or when one cell is transmitted from the transmission control unit 14, the cell that arrives or is transmitted For the shaping target connection to which the cell belongs, the scheduled transmission time of the first cell in the queue of the connection in the cell buffer unit 11 is calculated by the scheduled transmission time calculation unit 12 according to a predetermined calculation formula. The sorting unit 13 performs a sorting process using the scheduled transmission time obtained as a result of the calculation, and determines the earliest cell to be transmitted among the cells in the cell buffer unit 11 and the scheduled transmission time.
[0023]
The transmission control unit 14 constantly monitors and compares the scheduled transmission time of the scheduled transmission cell determined by the sorting unit 13 with the current time, and if the current time has reached the scheduled transmission time and the cell transmission suppression signal has not been received. For example, the corresponding cell is taken out from the cell buffer unit 11 and transmitted, and at the same time, the scheduled transmission time calculating unit 12 is notified to calculate the scheduled transmission time of the next cell.
[0024]
When the priority control function is added, the traffic shaping device according to an embodiment of the present invention may include a sorting unit 13 which can assign a high priority cell such as an emergency cell or voice data at the time when the sorting result is obtained. It is determined whether or not there is. Then, if there is a cell with a high priority, sorting section 13 instructs transmission control section 14 to transmit a cell with a high priority before a cell obtained as a result of sorting. If there is no corresponding cell, the sorting unit 13 sends the connection No. to the transmission control unit 14. Is sent.
[0025]
Further, when the circuit for receiving the cell transmission signal is added, the traffic shaping apparatus according to the embodiment of the present invention suppresses the cell transmission to the transmission control unit 14 until the cell transmission suppression signal is received. And the transmission control unit 14 stops transmitting cells.
[0026]
In FIG. 2 showing an application example of the traffic shaping device 10 having the above-described configuration, the ATM switch 109 includes line interface units 103 to 105 for terminal devices 100 to 102, an ATM switch unit 106, an ATM switch unit 106, and an ATM wide area. A line interface 107 located between the network 108 and the network 108.
[0027]
The traffic shaping device 10 described above is applied to the transmission unit to the ATM wide area network of the line interface unit 107, and controls the cell transmission interval so that the UPC function of the ATM wide area network 108 does not discard cells.
[0028]
FIG. 3 shows another application example of the traffic shaping apparatus 10 having the above-described configuration.
[0029]
The example shown in FIG. 3 is an example in the case of shaping cells to be transmitted to a plurality of low-speed lines. After shaping the multiplexed cells by the traffic shaping device 10, the cells are separated to the next stage. The device 110 is placed so that cells are output to line terminations 111 to 113 of a plurality of low-speed lines.
[0030]
In this case, it is necessary to control the output cell flow of the separator 110 so that the cell flow is correctly shaped, but there is a possibility that the cell interval fluctuates until the cell flow is output from the separator to the low-speed line. In the case or when the speed is different for each output line, the control becomes difficult. However, by performing control such that the cell transmission suppression signal to the traffic shaping device 10 is released according to the timing at which the demultiplexer 110 transmits the cell, In the above case, the shaping can be performed correctly.
[0031]
Next, an example of updating a binary tree for sorting that manages the scheduled cell transmission time in a binary tree structure will be described with reference to FIG.
[0032]
In order to manage the scheduled cell transmission time in a binary tree structure, when a new cell transmission scheduled time is determined as a result of cell transmission or arrival, the binary tree of the previous sorting result is used as the root starting from the corresponding connection. By repeating the comparison according to the scheduled transmission time and the priority order while following the direction, the next earliest cell to be transmitted and the scheduled transmission time can be obtained. That is, in the example shown in FIG. 4, for example, when the scheduled transmission time of the connection 3 is updated, only the shaded information in the figure needs to be updated by comparing the information of the transmission time of the adjacent connection.
[0033]
Most of the processing time for the above-described processing is the access time to the memory storing the binary tree, and the processing can be performed in the order of log2 (the number of connections). The amount of memory required for this processing is a memory for storing a binary tree, which is on the order of twice the number of connections, and can be greatly reduced as compared with the case of the existing technology.
[0034]
Further, by comparing the priority information of the connection with the scheduled cell transmission time, when there are a plurality of connections to be output at the same time by the sorting unit 13, selection is made such that the higher priority one is output earlier. can do.
[0035]
In the leaky bucket UPC, the current counter value is C, the counter value at the last cell arrival is c, the increment due to cell arrival is i, the subtraction value at the elapse of unit time is d, the threshold is N, Assuming that the elapsed time from the arrival of the cell is t,
C + i> N
Is determined as a violation cell. Since C = max {0, c-dt}, the above equation becomes:
max ｛0, c-dt + i｝> N.
[0036]
In other words,
t ≧ max {0, c + i−N} / d (1)
In this case, the cell is not determined to be a violation cell. Thus, the scheduled cell transmission time calculation unit 12 determines the minimum cell interval t that satisfies the expression (1), thereby obtaining the optimal cell transmission scheduled time at which cells are not discarded by the leaky bucket UPC. it can.
[0037]
Further, assuming that the next scheduled cell transmission time determined by the sorting unit 13 is T, the transmission control unit 14
The condition that {(current time) ≧ T} and (the cell transmission suppression signal is not received from the next stage) is constantly monitored, and cells are transmitted only when the condition is satisfied. Can be realized.
[0038]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a traffic shaping device capable of reducing the number of external devices such as memories and selecting a cell having the earliest transmission time as a cell to be transmitted next.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a traffic shaping device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating an application example of a traffic shaping device according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating another application example of the traffic shaping device according to the embodiment of the present invention.
FIG. 4 is a diagram illustrating an example of updating a binary tree for sorting that manages scheduled cell transmission times in a binary tree structure.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Traffic shaping apparatus 11 Cell buffer unit 12 Scheduled transmission time operation unit 13 Sorting unit 14 Transmission control unit 100-102 Terminal devices 103-105, 107 Line interface unit 106 ATM switch unit 108 ATM wide area network 109 ATM exchange 110 Separation device 111- 113 Line termination

Claims (5)

In a traffic shaping device including a cell buffer unit that temporarily accumulates arriving cells, a scheduled cell transmission time operation unit that calculates a scheduled cell transmission time, and a transmission control unit that transmits cells,
A sorting unit that performs a sorting process using the scheduled cell transmission time calculated by the scheduled cell transmission time calculation unit, and determines a cell having the earliest scheduled transmission time among the cells in the cell buffer unit. Traffic shaping device. 2. The traffic shaping device according to claim 1, wherein the sorting unit includes means for managing a scheduled cell transmission time in a binary tree structure, and performs processing using a past sorting result. The sorting unit has a function of comparing the priority of the connection with the scheduled transmission time of the cell and selecting a cell having the earliest scheduled transmission time and the highest priority as the cell to be transmitted next. The traffic shaping device according to claim 1 or 2, wherein: 4. The cell transmission scheduled time calculation unit includes a leaky bucket counter, and calculates an optimal cell transmission scheduled time at which cells are not discarded by a leaky bucket type UPC of the opposite device. A traffic shaping device as described. 5. The method according to claim 1, further comprising: means for receiving a cell transmission suppression signal from a next-stage apparatus, and having a function of transmitting cells only during a period in which the cell transmission suppression signal is not input. 2. The traffic shaping device according to 1.

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