JPH088929A - Optical atm switch - Google Patents

Abstract

PURPOSE:To obtain the optical ATM switch easily formed by providing a prescribed wavelength conversion means, a path changeover means, a waveguide means and an optical signal delay means in an optical ATM device to make the scale of the path changeover means equal to the scale of the optical ATM switch. CONSTITUTION:An optical signal generated by wavelength conversion means 31-1, 31-2 is given respectively to a path changeover means 32, in which the signal is switched to a prescribed path. One of the two optical signals switched by the means 32 enters a waveguide means 33-2 and the other enters a waveguide means 33-1. The optical signals given to the means 33-1, 33-2 are outputted to prescribed delay lines 34-12, 34-21 of an optical signal delay means. Then the signal passes through relevant synthesis means 35-1, 35-2 respectively and outputted to object output terminals 36-1, 36-2. Thus, the scale of the path changeover means is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to ATM (Asyncronus
Transfer Mode) The present invention relates to an optical ATM switch which constitutes a switching part of an exchange.

[0002]

2. Description of the Related Art A method has been considered in which an optical circuit network is used to configure a part of an ATM switch, which is a type of packet switch, for switching. This optical network portion is called an optical ATM switch. As a conventional example of such an optical ATM switch, for example, Document I (ECOC) '93 september 12-16, 1993 Proceeding, Volume
3 pages 77-80). The configuration and operation of this conventional ATM switch will be described below with reference to FIGS.

In this conventional optical ATM switch, the optical cell signals input from the input fibers 10-1 to 10-L are exchanged with the output fibers 16-1 to 16-N and output. Therefore, this optical ATM switch uses the input optical fibers 10-1 ...
Wavelength conversion means 11-1 to 11-, which are respectively provided at the subsequent stages of 10-L and convert the optical cell signals input from the corresponding input fibers into optical signals of a certain wavelength among wavelengths λ ₁ to λ _N L
And an optical switch 12-0 having a scale of L input and M output provided at a stage subsequent to these L wavelength converting means 11-1 to 11-L (where M is a value corresponding to the number of required buffers). ), M optical delay elements 13-1 to 13-1 to 1-3 connected to the M outputs of the optical switch in a one-to-one correspondence and having a delay time extended by one cell.
13-M, a star coupler 14-0 that multiplexes the light from these optical delay elements 13-1 to 13-M and distributes it to N, and one-to-one correspondence with the N outputs of this star coupler 14-0. Connected by λ ₁ ~ λ
It was provided with optical filters 15-1 to 15-N to which any transmission wavelength of _N wavelengths was assigned.

In this optical ATM switch, an input optical cell is converted into an optical signal having the same wavelength as the transmission wavelength assigned to the optical filter in the preceding stage of the fiber to be output, so that this optical cell can be used as a target. It was possible to output by exchanging with the output fiber. Hereinafter, a specific description will be given. FIG. 3 shows an example of exchanging optical signal cells from the input fiber 10-1 to the output fiber 16-2 and from the input fiber 10-2 to the output fiber 16-1. here,
The transmission wavelength assigned to the optical filter in the preceding stage of the output fiber 16-1 is λ ₁ , and the same wavelength of the output fiber 16-2 is λ ₂ . Therefore, the optical cell input from the input fiber 10-1 is converted into an optical signal of wavelength λ ₂ , and
The optical cell input from the input fiber 10-2 is converted into an optical signal of wavelength λ ₁ . As a result, the predetermined exchange can be performed. By the way, in ATM exchange, there are cases where optical cells that have arrived at a plurality of input fibers at the same time are output to the same output fiber. In that case, it is necessary to prevent the optical cells from competing with each other in the output fiber. this is,
This conventional optical ATM switch operates as follows. Figure 4 shows an example of this, and the input fiber 10
1 is a diagram showing an example in which optical cells respectively input to -1 and 10-2 are output together to an output fiber 16-2. FIG. Each of the two input cells is converted into an optical signal of wavelength λ ₂ . The optical switch 12-0 is an optical delay element 13-1 for receiving one of two optical signals.
Then, the other is output to the optical delay element 13-2. Since the two optical signals are time-shifted by one cell in both delay elements 13-1 and 13-2, they do not conflict with each other. Next, these optical signals are multiplexed by the star coupler 14-0, and this multiplexed optical signal is distributed to the N optical filters 15-1 to 15-N. Even if distributed, since the wavelength of this multiplexed optical signal is λ ₂ , the multiplexed optical signal is transmitted only through the optical filter 15-2. Therefore, the optical cells respectively input to the input fibers 10-1 and 10-2 can be output to the output fiber 16-2 while avoiding competition.

[0005]

However, in the conventional optical ATM switch, in order to reduce the cell discard when a high load is applied to this (that is, when a large number of cells are input within a certain time). By increasing the number of buffers,
Since it is composed of M, it was necessary to increase the scale of the optical switch 12-0 accordingly. For example, an optical ATM switch having a conventional configuration, which is an 8 × 8-scale optical AT and which satisfies a cell discard rate of 10 ⁻¹⁰ at a load of 95%.
If an M switch is to be constructed, the number of buffers will be 64 according to the simulation. Therefore, in this case, it is necessary to manufacture the optical switch 12-0 having a scale of 8 × 64, but it is quite difficult at present to manufacture an optical switch having such a scale.

[0006]

Therefore, in the present invention, L
An optical ATM switch having N input terminals and N output terminals is characterized by including the following means (a) to (e).

(A) The electric or optical cell signals, which are respectively provided at the subsequent stages of the L input terminals and are input from the corresponding input terminals, are converted into optical signals of a predetermined wavelength among predetermined m kinds of wavelengths. Wavelength conversion means.

(B) Route switching means of L input and N output scale to which the optical signals from the L wavelength converting means are input.

(C) Each of the above-mentioned route switching means is provided in a stage subsequent to the N outputs, has a maximum of m outputs, and
Waveguide means for guiding the converted optical signal to one of the outputs according to its wavelength when the converted optical signal is input.

(D) Optical signal delay means provided at the subsequent stage of the above N waveguide means, each comprising a maximum of m delay lines, and these delay lines have a delay time of one cell. Optical signal delaying means, the delay amounts of which are adjusted respectively.

(E) Multiplexing means for multiplexing the optical signals output from the delay lines belonging to the corresponding optical signal delaying means, which are respectively provided in the subsequent stages of the N optical signal delaying means, and output the same. Is a multiplexing means connected to the output end of the optical ATM switch.

However, L and N are positive integer values, and L =
It may be N. In addition, m is a positive integer value that is predetermined in consideration of the degree of competition of optical signals.

In the above description of the waveguide means and the optical signal delay means, the maximum number of outputs and the maximum number of delay lines are m.
The reason that the number of input cells is m or m is that there may be a system in which the competition of signal cells does not occur so much in the N input systems. In such a system, the waveguide means and the optical signal delay means are used. This is because the purpose can be achieved even if the scale is smaller than m.

[0014]

According to the structure of the present invention, the scale of the route switching means (for example, the optical switch) can be the same as the scale of the optical ATM switch, L × N. In the above conventional technique, the number of buffers M
The present invention is significantly different from the prior art in comparison with the necessity of the route switching means of L × M (M >> N) in consideration of the above. Further, in the present invention, the wavelength becomes a parameter for specifying the delay line for the competition control of the optical cell. Compared with the above-mentioned conventional technique in which the wavelength was a parameter for specifying the output fiber, the present invention is significantly different from the conventional technique. Here, in the present invention, the number of different wavelengths m, which is equal to the number of buffers, is required. However, for example, reference II (I
EICE TRANS. COMMUN., Vol.E75-B, No.4 APRIL 1992) mainly uses a large number of semiconductor lasers and a star coupler of a certain size, for example, an optical frequency (Optical Frequency) of 100 channels. It is possible to obtain multiple wavelengths since a system capable of obtaining is obtained.

[0015]

Embodiments of the optical ATM switch of the present invention will be described below with reference to the drawings. However, in all of the drawings, the dimensions, shapes, and arrangement relationships of the respective constituent components are schematically shown so that the present invention can be understood. Further, in each of the drawings used for description, the same components are denoted by the same reference numerals.

1. Description of Configuration First, the configuration of the optical ATM switch of the embodiment will be described. FIG. 1 is a diagram used for the explanation, and shows the light A of the embodiment.
It is a figure showing composition of a TM switch.

The optical ATM switch, which will be described in detail later, has L input terminals 30-1 to 30-N and L wavelength converting means 31.
-1 to 31-L, and a route switching means 32 of L input and N output scale,
N waveguide means 33-1 to 33-N and N optical signal delay means 34
-1 to 34-N, N multiplexing means 35-1 to 35-N, and N output terminals 36-1 to 36-N. However, L and N are optical ATM
It is a value determined according to the scale of the switch, and is a value that may be L = N. The individual components will be described below in order.

First, the L input terminals 30-1 to 30-N are for inputting electric or optical cells to the optical ATM switch, and are of various types according to the form of the input signal.
If the input signal is an optical cell, the L input terminals 30-1 ...
Each of 30-N can be composed of, for example, an optical fiber.

Each of the wavelength converting means 31-1 to 31-L has a predetermined m kinds of electric or optical cell signals (hereinafter also referred to as "input signals") input from the corresponding input terminals. Is converted into an optical signal of a predetermined wavelength within the wavelength (λ _{1 to} λ _m ). These L wavelength converting means 31-1 to
The 31-L is provided in a one-to-one correspondence after the input terminals 30-1 to 30-N. That is, the wavelength conversion means 31 is provided after the input terminal 30-1.
-1, is connected, the wavelength conversion means 31-2 is connected after the input end 30-2, ..., The wavelength conversion means 31-L is connected after the input end 30-L. These wavelength changing means 31-1 to 31N can be constituted by modulators, for example. For example, the system disclosed in the above-mentioned Document II can be used as the wavelength converting means 31-1 to 31-L mentioned here. The wavelength conversion control can be performed, for example, by reading information stored in the header portion of the input signal by a control device (not shown) and controlling the wavelength conversion means based on the read information (details will be described later. See description section).

In the present invention, the reason why the wavelength converting means is used to properly use the wavelengths of λ ₁ to λ _m m is to avoid that input signals input from a plurality of input terminals compete with one output terminal. Therefore, which wavelength of λ ₁ to λ _m the input signal is converted into is determined by the timing at which the competing input signal is output from the output end. This will also be described in the section of operation description below.

The route switching means 32 operates using the optical signals from the L wavelength converting means as an input signal and has N outputs. That is, it is a route switching means of L × N scale. The route switching means 32 determines to which of the N output terminals the input signal is to be output. The route switching means 32 can be composed of, for example, an optical matrix switch. The control of the route switching can be performed, for example, by the control device (not shown) reading the information stored in the header portion of the input signal, and the control device controlling the route switching means based on the information.

The waveguide means 33-1 to 33-N are respectively
When the optical signal having a maximum of m outputs and converted by the wavelength conversion means is input, it is converted into one of the outputs (maximum m outputs) according to the wavelength. It is a guide. However, in the case of the example of FIGS. 1 and 2, each of the waveguiding means 33-1 to 33-N is an example having m outputs. The waveguide means 33-1 to 33-N are provided in a one-to-one correspondence with the N outputs of the route switching means 32. Each of the wave guiding means 33-1 to 33-N receives the optical signal of wavelength λ ₁ and receives the first delay line (34-11, 34-21 of m outputs). , --34-N1) outputs an optical signal to the output, and ..., When an optical signal of wavelength λ _m is input, the m-th delay line (34 -1m, 34-2m,
・ ・ ・ 34-Nm) and outputs an optical signal to the output. Such waveguide means can be configured by an optical circuit in which, for example, m optical filters and a required number of demultiplexers are combined.

Further, the optical signal delay means 34-1 to 34-N are connected in a one-to-one correspondence with the latter stage of the above-mentioned waveguide means 33-1 to 33-N, and delays of a maximum of m lines are provided. The delay amount is adjusted so that the delay time of each cell is increased by one cell. However, in the example of FIGS. 1 and 2, each of the optical signal delay units 34-1 to 34-N is composed of m delay lines. Therefore, m output lines of the optical signal delay means 34-1 to m output lines of the wave guide means 33-1.
34-1m are connected without duplication. Also, m delay lines 34
-11 to 34-1m can obtain a delay time of 0 delay, 1 delay cell, ..., Delay m cells in this order. Other optical signal delay means 34-2 to 34-m,
The configuration is similar to that of the optical signal delay means 34-1. It should be noted that these optical signal delay means can be configured by any suitable means such as using optical fibers having different lengths.

The multiplexers 35-1 to 35-N combine the optical signals output from the delay lines belonging to the corresponding optical signal delay means, and output the optical signals at the corresponding output terminals (36- Any one of 1 ~ 36-N). These multiplexers 35-1 to 35-N
Can be constituted by a conventionally known optical multiplexer.

2. Description of Operation Next, in order to deepen the understanding of the optical ATM switch of the present invention, the operation of the optical ATM switch will be described with reference to FIGS.

2-1. Operation When There Is No Output Contention First, the operation when there is no output contention will be described with reference to FIG. In addition, this explanation, the input signal input from the input end 30-1 is exchanged with the output end 36-2 and output, and
This is performed by an example in which the input signal input from the input end 30-2 is exchanged with the output end 36-1 and output.

The input signals respectively input to the input terminals 30-1 and 30-2 are supplied to the corresponding wavelength converting means 31-1 and 31-2.
It is converted into an optical signal having a predetermined wavelength of the wavelengths λ _{1 to} λ _m . Since this example is an example in which there is no output competition, there is no problem whether the two input signals are converted into optical signals of the same wavelength or light of different wavelengths. However, since it is preferable that there is no unnecessary delay in the optical signal delay means, both are converted into an optical signal of wavelength λ _{1 in} order to send the input signal to the delay line having the delay amount of 0. The wavelength to be converted is controlled by a control device (not shown) that reads the wavelength information stored in advance in the header portion of the input signal and controls the wavelength conversion means.
It can be determined by any suitable method.

The optical signals generated by the wavelength converting means 31-1 and 31-2 are input to the route switching means 32 and switched to a predetermined route. That is, here, the wavelength conversion means
The optical signal sent from 31-1 is output to the output connected to the waveguide means 33-2 out of the N outputs of the route switching means 32, while the wavelength conversion means 31-2 outputs the optical signal. The transmitted optical signal is guided by the waveguide means 33 out of the N outputs of the route switching means 32.
It is output to the output connected to -1. Note that the route can be determined by any suitable method, such as pre-stored in the header portion of the input signal and reading the route information by a control device (not shown) to control the route switching means 32. .

One of the two optical signals switched by the route switching means 32 (one coming from the input end 30-1) is directed to the waveguide means 33-2, and the other (coming from the input end 30-2). thing)
Enter the waveguide means 33-1 respectively. Waveguide means 33-1 or 33
Since these optical signals entering -2 are guided in the waveguide means by the wavelength selectivity of the waveguide means and the wavelengths of the optical signals themselves, a predetermined delay line of the optical signal delay means is used here. It is output to 34-11 and 34-21. Then, these optical signals are output to the target output end 36-1 or 36-2 after passing through the corresponding multiplexing means 35-1 or 35-2, respectively.

2-2. Operation when there is output conflict Next, regarding the operation when trying to output each input signal input from multiple input terminals to one output terminal,
This will be described with reference to FIG. Note that this explanation
-1 and two input signals respectively input from the input end 30-2 are exchanged with the output end 36-2 and output.

The input signals input to the input ends 30-1 and 30-2 are converted into optical signals of a predetermined wavelength of wavelengths λ _{1 to} λ _{m in} the corresponding wavelength converting means 31-1 and 31-2. To be converted. At this time, in order to prevent these two signals from being output to the output end 36-1 at the same time (in order not to compete with each other), both are converted into optical signals of different wavelengths. Here, the input signal input from the input end 30-1 is converted into an optical signal of wavelength λ ₁ , and the input signal input from the input end 30-2 is converted into an optical signal of wavelength λ ₂ . Of course, the reverse is also possible, or different wavelengths may be used respectively.

The optical signals generated by the wavelength converting means 31-1 and 31-2 are input to the route switching means 32 and switched to a predetermined route. That is, here, the wavelength conversion means
The two optical signals sent from 31-1 are route switching means 32.
Is output to the output connected to the waveguide means 33-1.

These optical signals entering the waveguide means 33-1 are guided in the waveguide means by the wavelength selectivity of the waveguide means and the wavelengths of these optical signals, so that the optical signal delay means It is output to a predetermined delay line 34-1. That is, the optical signal related to the input signal input from the input end 30-1 is
Since it is an optical signal of wavelength λ ₁ , it is output to the delay line 34-11, while the optical signal related to the input signal input from the input end 30-2 is an optical signal of wavelength λ _2. Because there is
Output to delay line 34-12. Each delay line 34-11,
The two optical signals have the same timing at the time of entering 34-12, but the delay line 34-11 has a delay amount of 0 (considered to be 0), and the delay line 34-12 is different from the delay line 34-12. Since the delay amount for one cell is large, a time difference for one cell is generated between both optical signals when leaving each delay line.

These two optical signals having the time difference pass through the combining means 35-1 with the time difference, and then the output end.
Output to 36-1 with this time difference. Therefore, it is possible to prevent the two optical signals from competing at the output end 36-1.

If the signal input to the input terminal at the timing subsequent to the above-mentioned two input signals is in the same competitive state as the above-mentioned two signals, the same operation as described above is performed. In that case, the delay line 34 Delay lines other than -11 and 34-12, such as delay line
34-13, 34-14 are used, one of the two input signals is an optical signal of wavelength λ ₃ and the other is an optical signal of wavelength λ ₃ , for example.
_It is better to convert each to ₄ optical signals. In this way, even if there is a risk of continuous race conditions, it can be avoided.

In the optical ATM switch of the present invention, L = N
= 8, that is, when considering an example of an optical ATM switch of 8 × 8 scale, the route switching means 32 may be of 8 × 8 scale. In the prior art, a scale of 8 × 64 was required, whereas in the present invention, the route switching means can be easily manufactured. However, if an optical ATM switch of 8 × 8 scale and a cell discard rate of 10 ⁻¹⁰ at a load of 95% is to be constructed, the number of buffers is 6 according to the simulation.
Since the number is 4, the number of wavelengths m convertible by the wavelength converting means is 6
4 will be needed. However, it is considered that such wavelength conversion can be easily realized by, for example, the technique disclosed in the above-mentioned Document II. From these points, the superiority of the optical ATM switch of the present invention over the prior art can be understood.

Although the embodiment of the optical ATM switch according to the present invention has been described above, the present invention is not limited to the above embodiment. For example, in the above, the waveguide means 33
Each of -1 to 33-N has the same number of outputs m, and each of the optical signal delay means 34-1 to 34-N has m delay lines. However, the number of delay lines of each signal delay means may be different in whole or in part depending on the case. For example, in the case where there is one in which there is little danger of outputting a signal in a competition state (less traffic) among the output terminals 36-1 to 36-N, even if the number of delay lines of the corresponding optical signal delay means is reduced. Because it is good. Of course, in this case, the wave guiding means in the preceding stage of the optical signal delaying means in which the number of delay lines is reduced can be correspondingly small in the number of outputs (small in the number of wavelength selections).

[0038]

As is apparent from the above description, according to the optical ATM switch of the present invention, the predetermined wavelength conversion means, the predetermined route switching means, the predetermined waveguide means, and the predetermined optical signal delay means. Further, since the predetermined multiplexing means is provided, the scale of the route switching means (for example, the optical switch) can be set to the same L × N scale as the scale of the optical ATM switch. The present invention can reduce the scale of the route switching means as compared with the case where the conventional technique requires the route switching means of L × M (M >> N) in consideration of the number M of buffers. Therefore, it is considered that an optical ATM switch that can be easily manufactured can be realized.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a configuration of an optical ATM switch of an embodiment and an operation when there is no competition.

FIG. 2 is a diagram for explaining the operation of the optical ATM switch of the embodiment when there is contention.

FIG. 3 is an explanatory diagram of a conventional technique and its problems.

FIG. 4 is an explanatory diagram of a conventional technique and its problems.

[Explanation of symbols]

 30-1 to 31-N: Input end 31-1 to 31-L: Wavelength conversion means 32: Path switching means 33-1 to 33-N: Waveguide means 34-1 to 34-N: Optical signal delay means 34-11 to 34-1m, 34-21 ..., 34-N1 to 34-Nm: Delay line 35-1 to 35-N: Combiner 36-1 to 36-N: Output end

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04Q 3/52 B 9566-5G

Claims (1)

[Claims] 1. An optical ATM switch having L input terminals and N output terminals, wherein an electrical or optical cell signal input from a corresponding input terminal is provided after each of the L input terminals. , Wavelength conversion means for converting the light signal into a light signal of a predetermined wavelength among predetermined m kinds of wavelengths, and light signals from the L wavelength conversion means are input.
A route switching means of L input and N output scale, and N outputs of the route switching means are respectively provided at the subsequent stages, have a maximum of m outputs, and receive the converted optical signal. Then, a waveguide means for guiding it to one of the outputs according to its wavelength, and an optical signal composed of a maximum of m delay lines respectively provided at the subsequent stages of these N waveguide means. These delay lines are provided as optical delay units for adjusting delay amounts such that the delay time is increased by one cell, and the delay lines are provided at the subsequent stages of the N optical signal delay units, respectively. The optical signal output from the delay line belonging to the optical signal delaying means, the output having the output of the optical ATM switch. Characteristic optical ATM switch (however, L, N It is a positive integer value, if the L = N there may be. Moreover, m is a positive integer value determined in advance considering the conflict condition of the optical signal.).