JP3695853B2 - Optical buffer device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical buffer device.
[0002]
[Prior art]
In recent years, optical technology has also been applied to the communication field, enabling high-speed and large-capacity communication. Along with this, research on optical exchange using optical technology has also been conducted in various fields in the field of switching equipment. In particular, in ATM (Asyncronus Transfer Mode) exchange, which is considered to be most effective in the future multimedia society, an optical buffer device is used to prevent fixed-length packets called cells from arriving at the same destination. Must be granted. In general, an optical buffer device uses an optical delay line composed of an optical fiber as an optical delay means (sometimes referred to as a delay memory or a delay element).
[0003]
FIG. 7 shows a conventional optical buffer device having four optical delay lines 14a to 14d (reference: “Optical Fiber Buffer for High-Perfomance Broadband Switching”, Eur Trans Telecommun Relat Technol, Vol. 4, No. 6, 1993, p.671-678 "(see Fig. 7) shows the situation when four cells A to D arrive at the same time. In general, since a plurality of cells cannot be output simultaneously from one output port 18, when four cells A to D arrive at the same time, the cell A switches the optical switch 12 so that it outputs with a delay of 0, The optical switch 12 is switched so that the cell B is output for one time slot, the cell C is output for two time slots, and the cell D is output for three time slots with a delay by the optical delay lines 14b to 14d. In this way, the four cells A to D are output without colliding.
[0004]
[Problems to be solved by the invention]
However, in the above-described conventional optical buffer device, when four cells A to D arrive at the same time and then two or more cells arrive at the same time, some cells are discarded. For example, as shown in FIG. 7, when four cells A to D arrive and subsequently two cells E and F arrive, the cell F cannot be processed and the cell is discarded. In order to prevent this, it is necessary to increase the size of the optical switch and further increase the number of optical delay lines. However, this method increases the amount of hardware dramatically. For example, in the case of ATM exchange, since the length of one cell is 53 bytes, if the transfer rate is 10 Gb / s, the length of the optical fiber necessary for delaying by one cell is 8 m. That's it.
[0005]
Therefore, the advent of an optical buffer device capable of avoiding cell discard without increasing the hardware amount has been desired.
[0006]
[Means for Solving the Problems]
Therefore, according to the optical buffer device of the present invention, a plurality of input ports, optical switch means, optical delay means, optical coupling means, and one output port are provided, and a cell input from the input port is optically connected. Light that is input to the switch means, the cell output from the optical switch means is input to the optical delay means, the cell output from the optical delay means is input to the optical coupling means, and the cell output from the optical coupling means is output from the output port In the buffer device, when a plurality of subsequent cells are simultaneously input from the input port following a plurality of preceding cells input simultaneously from the input port, the subsequent cells are timed one cell after the preceding cell output last from the optical delay means. A feedback means for shifting the output from the optical delay means non-simultaneously, and this feedback means is input from the output side of the optical switch means. Wherein the is provided connected to the side.
[0007]
According to such an optical buffer device, cells output from the optical switch means and input to the feedback means are delayed by a predetermined cell and input again to the optical switch means. As will be described in detail later, for example, when considering the case where two subsequent cells are simultaneously input from the input port following the four previous cells input simultaneously from the four input ports, all cells are discarded. In order to output from the output port without any input, one subsequent cell is delayed by one cell and input to the feedback means that can be input again to the optical switch means. By inputting one subsequent cell to the feedback means in this way, a delay time difference of one cell is generated between the two subsequent cells. Therefore, it is possible to output the subsequent cells from the optical delay means non-simultaneously by shifting the time by one cell after the preceding cell output last from the optical delay means. In this way, when the succeeding cells shift the time one cell at a time and output from the optical delay means non-simultaneously following the preceding cell output last from the optical delay means, the cells output without colliding with each other. Output from the port. Further, in order to output any cell from the output port without discarding the cell, the conventional optical buffer device is simply provided with a feedback means capable of delaying by one cell, so that the amount of hardware increases. Is suppressed.
[0008]
Preferably, the feedback means is composed of one or a plurality of optical fibers. Since the optical fiber can adjust the delay time of the cell that transmits the optical fiber by adjusting its length, it is suitable for use as a feedback means. In particular, when the feedback means is composed of a plurality of optical fibers and a difference in delay time of cells to be transmitted occurs between the individual optical fibers, it is possible to adapt to fluctuations in traffic.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In each drawing used for the following description, each component is merely schematically shown in shape, size, and arrangement relationship to the extent that the present invention can be understood. Moreover, in each figure used for description, the same number is attached | subjected and shown about the same structural component. Therefore, it should be understood that the present invention is not limited to the embodiments described below.
[0010]
FIG. 1 is a schematic configuration diagram showing an optical buffer device according to this embodiment. As shown in FIG. 1, in the optical buffer device 100 of this embodiment, there are cases where four input ports 10a to 10d (hereinafter, the four input ports 10a to 10d are referred to as first to fourth input ports, respectively). ), An optical switch 12 as an optical switching means, and four optical delay lines 14a to 14d (hereinafter referred to as four optical delay lines 14a to 14d) as optical delay means, respectively. And an optical coupler 16 as an optical coupling means, one output port 18, and a single optical feedback line 20 as an optical feedback means. Between the input ports 10a to 10d and the optical switch 12, four optical input lines 22a to 22d (hereinafter, the four optical input lines 22a to 22d are respectively connected to the first to fourth optical input lines). And a single optical output line 24 between the optical coupler 16 and the output port 18.
[0011]
In the optical buffer device 100 of this embodiment having such a configuration, since the cells input from the input ports 10a to 10d are input to the optical switch 12, one end of the first optical input line 22a is the first input port. The other end of the first optical input line 22a is connected to the first input end 26a of the optical switch 12. Similarly, one end of each of the second to fourth input lines 22b to 22d is connected to each of the second to fourth input ports 10b to 10d, and the other end of each of the second to fourth input lines 22b to 22d is light. The switch 12 is connected to the second to fourth input terminals 26b to 26d.
[0012]
In addition, since the cells output from the optical switch 12 are input to the optical delay lines 14a to 14d and the cells output from the optical delay lines 14a to 14d are input to the optical coupler 16, the first optical delay line 14a is used. One end of the optical switch 12 is connected to the first output end 28 a of the optical switch 12, and the other end of the first optical delay line 14 a is connected to the first input end 30 a of the optical coupler 16. Similarly, one ends of the second to fourth optical delay lines 14b to 14d are connected to the second to fourth output terminals 28b to 28d of the optical switch 12, respectively, and the second to fourth optical delay lines 14b to 14d are connected. Are connected to the second to fourth input terminals 30b to 30d of the optical coupler 16, respectively. Here, the cell input to the second optical delay line 14b arrives at the optical coupler 16 with a delay of one cell from the time when the cells simultaneously input to the first optical delay line 14a arrive at the optical coupler 16. To do. Similarly, the cell input to the third optical delay line 14c arrives at the optical coupler 16 with a delay of two cells from the time when the cells simultaneously input to the first optical delay line 14a arrive at the optical coupler 16. Then, the cell input to the fourth optical delay line 14d arrives at the optical coupler 16 with a delay of three cells from the time when the cells simultaneously input to the first optical delay line 14a arrive at the optical coupler 16. .
[0013]
In order to output the cell output from the optical coupler 16 from the output port 18, one end of the optical output line 24 is connected to the output end 32 of the optical coupler 16, and the other end of the optical output line 24 is connected to the output port 18. Connected.
[0014]
Further, in order to feed back the cell output from the output side of the optical switch 12 to the input side of the optical switch 12, one end of the optical feedback line 20 is connected to the fifth output end 28 e of the optical switch 12. The other end is connected to the fifth input end 26e of the optical switch 12. Here, the cell input to the optical feedback line 20 arrives at the fifth input terminal 26e of the optical switch 12 with a delay of one cell from the time of arrival at the fifth output terminal 28e of the optical switch 12. In general, since the time required for the cell to pass through the optical switch 12 is very short compared to the time required to pass through the optical feedback line 20, the cell input to the optical feedback line 20 is delayed by one cell and then the first to first It is possible to input to the four optical delay lines 14a to 14d.
[0015]
Such an optical buffer device 100 of this embodiment uses, for example, optical fibers as the optical delay lines 14a to 14d, the optical feedback line 20, the optical input lines 22a to 22d, and the optical output line 24, and 2 as the optical switch 12, for example. A 6-input 6-output (6 × 6) optical switch configured by combining unit switches of 2 inputs (2 × 2) is used. As the optical coupler 16, for example, an optical coupler, or 2 inputs and 2 outputs (2 × 2) 4 unit and 4 output (4 × 4) optical switches configured by combining the unit switches. In this case, the end of the optical fiber constituting the optical input line is used as each of the input ports 10a to 10d, and the end of the optical fiber constituting the optical output line is used as the output port 18. The delay time of the optical delay line and the optical feedback line is adjusted by changing the length of the optical fiber. Further, when a 2 × 2 directional coupler is used as a 2 × 2 unit switch, it can take two forms of a cross state and a bar state, and since the operation speed is as high as several ns, 2 × 2 The directional coupler is optimal as a 2 × 2 unit switch.
[0016]
Next, the operation of the optical buffer device 100 of this embodiment having such a configuration will be described. 2 and 3 are diagrams for explaining the operation of the optical buffer device 100 according to this embodiment. In FIG. 2 and FIG. 3, the cell A is the first input port 10a, and the cell B is the second. After the cell C arrives at the third input port 10c and the cell D arrives at the fourth input port 10d simultaneously at the input port 10b, the cell E arrives at the first input port 10a following the cell A, A case where the cell F arrives at the third input port 10c following the cell C is shown. That is, in FIG. 2 and FIG. 3, after the four cells A to D reach the first to fourth input ports 10a to 10d simultaneously, the two cells E and F are respectively delayed by one cell. The case where the first and third input ports 10a and 10c are simultaneously reached is shown. Hereinafter, the four cells A to D may be referred to as preceding cells, and the two cells E and F may be referred to as subsequent cells. 2 and 3, the cells A to F are indicated by squares represented by broken lines or solid lines.
[0017]
In order to output any cell of the six cells A to F from the output port 18 without discarding the cell, first, when the four preceding cells A to D input to the optical switch 12, the cell A receives the first light. The cell B is input to the second optical delay line 14b, the cell C is input to the third optical delay line 14c, and the cell D is input to the fourth optical delay line 14d. The optical switch 12 is switched. Next, when two subsequent cells E and F following the preceding cells A to D input to the optical switch 12, the cell E inputs to the fourth optical delay line 14d, and the cell F inputs to the optical feedback line 20 Thus, the optical switch 12 is switched (see FIG. 2). Finally, when the cell F is input to the optical switch 12 again after being delayed by one cell, the optical switch 12 is switched so that the cell F is input to the fourth optical delay line 14d (see FIG. 3). Such switching of the optical switch 12 is performed based on data recorded in the headers of the cells A to F. That is, before inputting to each of the input ports 10a to 10d, the data recorded in the headers of the cells A to F are detected in advance, and the optical switch 12 is switched based on the data.
[0018]
By switching the optical switch 12 in this manner, the cell B transmits the second optical delay line 14b, and therefore is delayed from the cell A by one cell and output from the output port 18. In addition, since the cell C is transmitted through the third optical delay line 14c, the cell C is delayed from the cell A by two cells and output from the output port 18. In addition, since the cell D transmits the fourth optical delay line 14d, the cell D is delayed from the cell A by 3 cells and output from the output port 18. The cell E arrives at the first input port 10a after being delayed by one cell from the cell A, and then is delayed by four cells from the cell A and transmitted from the output port 18 to be transmitted through the fourth optical delay line 14d. Output. The cell F arrives at the third input port 10c with a delay of one cell from the cell A, and then transmits the optical feedback line 20 and then transmits the fourth optical delay line 14d. The output is output from the output port 18 with a delay of the cell.
[0019]
In this way, the cells A to F can output from the output port 18 without colliding with each other.
[0020]
The present invention is not limited to the above-described embodiment, and it is obvious that the number of optical feedback lines or the number of optical delay lines may be increased in accordance with traffic fluctuations. For example, in the case of the optical buffer device 100 having the above-described configuration, if four subsequent cells arrive at the same time after four previous cells arrive at the same time, some subsequent cells are discarded, so that In this case, as shown in a modification 110 of the optical buffer device shown in FIG. 4, three optical feedback lines 20a to 20c (hereinafter, the three optical feedback lines 20a to 20c are respectively connected to the first to third light beams. May be referred to as a feedback line) from the output side of the optical switch 12 to the input side. More specifically, one end of the first optical feedback line 20a that can be delayed by one cell is connected to the fifth output end 28e of the optical switch 12, and the other end is connected to the fifth input end 26e of the optical switch 12. One end of the second optical feedback line 20b that can be connected and delayed by two cells is connected to the sixth output end 28f of the optical switch 12, and the other end is connected to the sixth input end 26f of the optical switch 12. One end of the third optical feedback line 20c that can be delayed by three cells may be connected to the seventh output terminal 28g of the optical switch 12 and the other end to the seventh input terminal 26g of the optical switch 12. When three optical feedback lines 20a to 20c are provided in this way, as shown in FIG. 5 and FIG. 6, four subsequent cells E to H follow the optical switch 12 following the four preceding cells A to D. Cell E is input to the fourth optical delay line 14d, cell F is input to the first optical feedback line 20a, cell G is input to the second optical feedback line 20b, and cell H is The optical switch 12 is switched so as to input to the third optical feedback line 20c (see FIG. 5). Then, when the cell F is input to the optical switch 12 again after being delayed by one cell, the optical switch 12 is switched so that the cell F is input to the fourth optical delay line 14d, and the cell G is delayed by two cells. When the signal is again input to the optical switch 12, the optical switch 12 is switched so that the cell G is input to the fourth optical delay line 14d, and when the cell H is input to the optical switch 12 again after being delayed by three cells, the cell H Switches the optical switch 12 so as to be input to the fourth optical delay line 14d (see FIG. 6). By switching the optical switch 12 in this way, the cells A to H can output from the output port 18 without colliding with each other. In order to provide the three optical feedback lines 20a to 20c from the output side to the input side of the optical switch 12 as described above, it is necessary to change the configuration of the optical switch 12. In FIGS. 5 and 6, the cells A to F are indicated by squares represented by broken lines or solid lines.
[0021]
【The invention's effect】
As is apparent from the above description, according to the optical buffer device of the present invention, an optical buffer comprising a plurality of input ports, optical switch means, optical delay means, optical coupling means, and one output port. In the apparatus, when a plurality of subsequent cells are simultaneously input from the input port following a plurality of preceding cells input simultaneously from the input port, the subsequent cells are timed one cell after the preceding cell output last from the optical delay means. Feedback means for shifting the output from the optical delay means non-simultaneously is connected from the output side of the optical switch means to the input side.
[0022]
According to such an optical buffer device, it is possible to cause the subsequent cells to be output from the optical delay means non-simultaneously by shifting the time by one cell following the preceding cell last output from the optical delay means. Each cell can be output from the output port without colliding with each other. Further, it is possible to suppress an increase in the amount of hardware for outputting any cell from the output port without discarding the cell.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an optical buffer device according to an embodiment;
FIG. 2 is a diagram (part 1) for explaining an operation of the optical buffer device according to the embodiment;
FIG. 3 is a diagram (part 2) for explaining the operation of the optical buffer device according to the embodiment;
FIG. 4 is a schematic configuration diagram showing a modification of the optical buffer device according to the embodiment.
FIG. 5 is a diagram (part 1) for explaining an operation of a modification of the optical buffer device according to the embodiment;
6 is a diagram (No. 2) for explaining the operation of the modification of the optical buffer device according to the embodiment; FIG.
FIG. 7 is a diagram for explaining the configuration and operation of a conventional optical buffer device;
[Explanation of symbols]
10a to 10d: First to fourth input ports 12: Optical switches 14a to 14d: First to fourth optical delay lines 16: Optical coupler 18: Output port 20: Optical feedback lines 20a to 20c: First to fourth Third optical feedback lines 22a to 22d: First to fourth optical input lines 24: Optical output lines 26a to 26g: First to seventh input terminals 28a to 28g: First to seventh output terminals 30a to 30d: 1st to 4th input terminal 32: Output terminal

Claims (1)

A plurality of input ports, optical switch means, optical delay means, optical coupling means, and one output port are provided. A cell input from the input port is input to the optical switch means, and the optical switch means In the optical buffer device for inputting the output cell to the optical delay unit, causing the cell output from the optical delay unit to be input to the optical coupling unit, and outputting the cell output from the optical coupling unit from the output port.
When a plurality of subsequent cells are simultaneously input from the input port following a plurality of preceding cells input simultaneously from the input port, the subsequent cells are placed one cell after the preceding cell output last from the optical delay means. Comprising feedback means for causing the optical delay means to output non-simultaneously at different times,
The feedback means is composed of a plurality of optical fibers connected from the output side to the input side of the optical switch means, and a delay time difference between cells transmitted between the individual optical fibers of the plurality of optical fibers. An optical buffer device characterized in that

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