ATM switch

An ATM switch includes a plurality of input line corresponding units, a plurality of output line corresponding units, and a wavelength shifting unit. The wavelength shifting unit is arranged between the input line corresponding units and the output line corresponding units to shift optical signals having different wavelengths in a plurality of wavelength-multiplexed optical signals arriving from the input line corresponding units and output the wavelength-multiplexed optical signals. Each input line corresponding unit includes an input-side basic switch for distributing N (N is a positive integer) cells respectively input to input ports to N lines, an electro-optic converter for converting the cells into optical signals having different wavelengths in units of N lines, and a multiplexer for multiplexing the optical signals into one wavelength-multiplexed optical signal. Each output line corresponding unit includes a demultiplexer for demultiplexing the wavelength-multiplexed optical signal in units of wavelengths, an opto-electric converter for converting outputs from the demultiplexer into electrical signals, respectively, and an output-side basic switch for distributing the cells converted into the electrical signals to a plurality of output ports.

BACKGROUND OF THE INVENTION 
The present invention is used for ATM (Asynchronous Transfer Mode) 
communication. The present invention relates to a technique of simplifying 
connection of the internal links of an ATM switch. The present invention 
also relates to a technique of constituting an ATM switch using an optical 
device. The present invention also relates to a technique of coping with 
traffic localization. 
FIGS. 16 to 18 explain a conventional ATM switch. FIG. 16 shows the 
arrangement of a 4.times.4 (m inputs and n outputs are represented by 
"m.times.n") basic switch. FIG. 17 shows the detailed arrangement of a 
cross point in the basic switch. FIG. 18 shows the arrangement of a 
16.times.16 ATM switch using eight 4.times.4 basic switches. The ATM 
switch is described in detail in reference "Illustrated standard ATM 
textbook, ASCII Shuppansha". 
The arrangement of the basic switch will be described with reference to 
FIGS. 16 and 17. An input buffer type basic switch will be described 
below. This basic switch comprises input buffers 51-1 to 51-4 for 
temporarily storing arriving cells, a controller 52 for controlling the 
congestion of cells, cross points 53 for transferring ATM cells output 
from the input buffers 51-1 to 51-4 to desired output ports, and output 
highways 54-1 to 54-4 to which ATM cells are transferred. The controller 
52 communicates with the respective input buffers 51-1 to 51-4 to permit 
cell transmission so as not to transfer the cells from the input buffers 
51-1 to 51-4 to the same one of the output highways 54-1 to 54-4. The 
cross point 53 has an address filter AF, as shown in FIG. 17, and 
transfers an input cell to the corresponding one of the output highways 
54-1 to 54-4 on the basis of the information in the header of the cell. 
The conventional ATM switch is constituted using a plurality of basic 
switches shown in FIGS. 16 and 17. FIG. 18 shows a 16.times.16 ATM switch 
constituted using eight 4.times.4 basic switches 71 to 78. The basic 
switches 71 to 74 are individually connected to the basic switches 75 to 
78 through links so that a cell from an arbitrary input line can be output 
to an arbitrary output line. 
When the ATM switch is to be constituted using a plurality of basic 
switches, a number of links are required to mutually connect the 
respective basic switches. In addition, wires for connection are 
intertwined with each other to result in a complex structure. In the 
example shown in FIG. 18, 16 links are necessary. An actual large-scale 
ATM switch uses several ten or several hundred basic switches, and the 
number of links therebetween is enormous. 
The links are constituted using optical fibers. The process of connecting 
the wires requires a long time. In addition, the check process for 
preventing erroneous interconnection increases the apparatus cost and the 
work time. Every time the number of basic switches is increased/decreased, 
interconnections between the wires must be changed for all the basic 
switches, so the degree of freedom in increasing/decreasing the number of 
basic switches is low. 
When the traffics localize in routes from the basic switch 71 to the basic 
switch 75 and from the basic switch 72 to the basic switch 76, the links 
connecting these switches congest. This situation is shown in FIG. 19. 
FIG. 19 shows the congestion situation of the 16.times.16 ATM switch. This 
largely degrades the throughput of the switch. 
SUMMARY OF THE INVENTION 
It is the principal object of the present invention to provide an ATM 
switch capable of flexibly coping with an increase/decrease in the number 
of input/output lines. 
It is another object of the present invention to provide an ATM switch 
capable of solving the conventional complex link connection to reduce the 
quantity of hardware. 
It is still another object of the present invention to provide an ATM 
switch capable of solving traffic localization generated in the respective 
lines. 
It is still another object of the present invention to provide an ATM 
switch applicable to a large-scale ATM switch structure. 
In order to achieve the above objects of the present invention, there is 
provided an ATM switch for distributing cells arriving from a plurality of 
input lines to a plurality of output lines, comprising a plurality of 
input line corresponding units each connected to the plurality of input 
lines, a plurality of output line corresponding units each connected to 
the plurality of output lines, and wavelength shifting means, arranged 
between the input line corresponding units and the output line 
corresponding units, for shifting optical signals having different 
wavelengths included in a plurality of wavelength-multiplexed optical 
signals arriving from the input line corresponding units and outputting 
the wavelength-multiplexed optical signals, wherein each of the input line 
corresponding units includes an input-side basic switch for distributing N 
(N is a positive integer) cells which are respectively input to a 
plurality of input ports to N lines, electro-optic conversion means for 
converting the cells distributed to the N lines into optical signals 
having different wavelengths in units of lines, and a multiplexer for 
multiplexing the optical signals converted in units of lines into one 
wavelength-multiplexed optical signal, and each of the output line 
corresponding units includes a demultiplexer for demultiplexing in units 
of wavelengths the wavelength-multiplexed optical signal obtained by 
wavelength-multiplexing the optical signals having N wavelengths, 
opto-electric conversion means for converting outputs from the 
demultiplexer into electrical signals, respectively, and an output-side 
basic switch for distributing the cells converted into the electrical 
signals to a plurality of output ports. 
The present invention is characterized in that basic switches are connected 
through wavelength multiplexing links such that the basic switches are 
connected through wavelength shifting means for distributing signals on 
the respective multiplexing links in units of wavelengths. The present 
invention is different from the prior art in that the number of links is 
reduced by wavelength multiplexing, the output-side basic switch is 
selected in units of wavelengths, and one output-side basic switch is 
connected to the respective input-side basic switches through links with 
different wavelengths. 
In addition, the present invention is characterized in that some output 
ports of the output line corresponding units are connected to the 
corresponding input ports of the input line corresponding units, 
respectively, or some output ports of a certain input line corresponding 
unit are connected to input ports of another input line corresponding unit 
such that bypass routes for avoiding congestion can be set. 
More specifically, the first gist of the present invention is an ATM switch 
for distributing cells arriving from a plurality of input lines to a 
plurality of output lines. 
According to the present invention, there is provided an ATM switch 
comprising a plurality of input line corresponding units each connected to 
the plurality of input lines, a plurality of output line corresponding 
units each connected to the plurality of output lines, each of the input 
line corresponding units including an input-side basic switch for 
distributing cells which are respectively input to a plurality of input 
ports to N lines, electro-optic conversion means for converting the cells 
distributed to the N lines into optical signals having different 
wavelengths in units of lines, and a multiplexer for multiplexing the 
optical signals converted in units of lines into one 
wavelength-multiplexed optical signal, and each of the output line 
corresponding units including a demultiplexer for demultiplexing in units 
of wavelengths the wavelength-multiplexed optical signal obtained by 
wavelength-multiplexing the optical signals having N wavelengths, 
opto-electric conversion means for converting outputs from the 
demultiplexer into electrical signals, respectively, and an output-side 
basic switch for distributing the cells converted into the electrical 
signals to a plurality of output ports, and wavelength shifting means, 
arranged between the input line corresponding units and the output line 
corresponding units, for shifting the optical signals having different 
wavelengths included in a plurality of wavelength-multiplexed optical 
signals arriving from the input line corresponding units and outputting 
the wavelength-multiplexed optical signals. 
Preferably, the wavelength shifting means includes a barrel shifter which 
distributes an optical signal having a pth (p=0, 1, 2, . . . , (N-1)) 
wavelength in an nth (n=0, 1, 2, . . . , (the number of input line 
corresponding units-1)) wavelength-multiplexed optical signal to the 
(n+p)th output and distributes the optical signal to the output of an 
ordinal number obtained by subtracting the number of output line 
corresponding units from (n+p) when n+p is equal to or larger than the 
number of output line corresponding units. 
With this arrangement, the cells arriving from the plurality of input lines 
can be distributed to the output lines determined in units of wavelengths. 
At this time, use of the wavelength shifting means such as a barrel 
shifter allows to omit complex interconnections and increases the degree 
of freedom in increasing/decreasing the number of lines. More 
specifically, one output-side basic switch is connected to the respective 
input-side basic switches through links with different wavelengths when 
viewed from this output-side basic switch. 
The number of input line corresponding units can be made equal to that of 
output line corresponding units. The numbers of input line corresponding 
units or output line corresponding units can be arbitrarily set. For this 
reason, an ATM switch having a high degree of freedom in design can be 
realized. 
Wavelength multiplexing links are preferably arranged between the output 
terminals of the multiplexers and the wavelength shifting means and 
between the wavelength shifting means and the input terminals of the 
demultiplexers. With this arrangement, the number of links input/output 
to/from the wavelength shifting means can be reduced, so that an ATM 
switch which can omit complex interconnections can be realized. The number 
of basic switches can be easily changed by increasing/decreasing the 
number of links input/output to/from the wavelength shifting means. More 
specifically, the number of basic switches can be easily changed by 
increasing/decreasing not the number of outputs of the basic switches but 
the number of links input/output to/from the wavelength shifting means in 
correspondence with the number of basic switches themselves. 
At least some input ports of the plurality of input line corresponding 
units may be connected to lines from any routes from other input line 
corresponding units to the plurality of output line corresponding units. 
With this arrangement, a plurality of routes via feedback routes can be 
selected as a route for transferring a cell from a certain input line to a 
certain output line. Therefore, in case of traffic localization, a bypass 
route can be formed to cope with the traffic localization. 
To obtain simple and regular interconnections, at least some output ports 
of each output-side basic switch are preferably connected to input ports 
of an input-side basic switch corresponding to the output-side basic 
switch. Alternatively, at least some output ports of each input-side basic 
switch may be connected to input ports of the input-side basic switch of 
another input line corresponding unit. 
Alternatively, for a combination of at least one input line corresponding 
unit and an output line corresponding unit corresponding to this input 
line corresponding unit, the output ports of the output line corresponding 
unit may be connected to the input ports of the input line corresponding 
unit. The combination of an input line corresponding unit and an output 
line corresponding unit corresponding to this input line corresponding 
unit is specialized to form bypass routes, and the remaining input line 
corresponding units and output line corresponding units can have the basic 
arrangement. With this arrangement, the degree of freedom in 
increasing/decreasing the number of input/output lines can be increased. 
Electro-optic conversion means for converting cells into optical signals 
having different wavelengths in units of inputs and a multiplexer for 
multiplexing the optical signals converted in units of inputs into one 
wavelength-multiplexed optical signal may be arranged. This multiplexer is 
connected to the input side of the wavelength shifting means. The 
plurality of output line corresponding units may include at least one 
output line corresponding unit whose output ports are connected to the 
input ports of the electro-optic converters. With this arrangement, in the 
above specialized arrangement, the arrangement corresponding to the input 
line corresponding units can be simplified. 
The second gist of the present invention is a large-scale ATM switch in 
which the above ATM switches are multiple-connected.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
(First Embodiment) 
The arrangement of the first embodiment of the present invention will be 
described below with reference to FIG. 1. FIG. 1 shows the arrangement of 
an ATM switch according to the first embodiment of the present invention. 
In the present invention, an ATM switch which distributes arriving cells 
from 64 input lines to 64 output lines will be described. 
The present invention has the following characteristic features. The ATM 
switch comprises input line corresponding units 2-1 to 2-8 (2-2 to 2-7 are 
not illustrated) each connected to eight lines of a total of 64 input 
lines, and output line corresponding units 4-1 to 4-8 (4-2 to 4-7 are not 
illustrated) each connected to eight lines of a total of 64 output lines. 
Each of the input line corresponding units 2-1 to 2-8 includes an 
8.times.8 input-side basic switch 6 for distributing cells input to eight 
input ports 1-11 to 1-18, . . . , or 1-81 to 1-88 to the eight lines, 
electro-optic converters 7-1 to 7-8 for converting the cells distributed 
to the eight lines into optical signals having different wavelengths in 
units of lines, and a multiplexer 8 for multiplexing the optical signals 
converted in units of lines into one wavelength-multiplexed optical 
signal. Each of the output line corresponding units 4-1 to 4-8 includes a 
demultiplexer 9 for demultiplexing the wavelength-multiplexed optical 
signal formed by wavelength-multiplexing eight optical signals into 
optical signals having wavelengths different from each other, 
opto-electric converters 10-1 to 10-8 for converting outputs from the 
demultiplexer 9 into electrical signals, respectively, and an 8.times.8 
output-side basic switch 11 for distributing the cells converted into the 
electrical signals to eight output ports 5-11 to 5-18, . . . , or 5-81 to 
5-88. A barrel shifter 3 serving as a wavelength shifting means for 
shifting the optical signals having different wavelengths included in a 
plurality of wavelength-multiplexed optical signals arriving from the 
input line corresponding units 2-1 to 2-8 and outputting the 
wavelength-multiplexed optical signals is arranged between the input line 
corresponding units 2-1 to 2-8 and the output line corresponding units 4-1 
to 4-8. 
The barrel shifter 3 distributes an optical signal having the pth (p=0, . . 
. , N-1) wavelength in the nth (n=0, 1, . . . , (the number of input line 
corresponding units-1)) wavelength-multiplexed optical signal to the 
(n+p)th output. When n+p is equal to or larger than the number of output 
line corresponding units, the optical signal is distributed to the output 
of an ordinal number obtained by subtracting (the number of output line 
corresponding units) from (n+p). 
In the first embodiment of the present invention, the number of the input 
line corresponding units 2-1 to 2-8 equals that of the output line 
corresponding units 4-1 to 4-8. 
Wavelength multiplexing links 15-1 to 15-8 and wavelength multiplexing 
links 16-1 to 16-8 are arranged between the output terminals of the 
multiplexers 8 and the barrel shifter 3 and between the barrel shifter 3 
and the input terminals of the demultiplexers 9, respectively. 
The electro-optic converters 7-1 to 7-8 output optical signals having 
wavelengths .lambda..sub.0 to .lambda..sub.7, respectively. Suffixes A to 
H are added to clarify the input line corresponding units 2-1 to 2-8 in 
which the optical signals are converted. More specifically, the 
wavelengths of optical signals in the input line corresponding unit 2-1 
are represented by .lambda..sub.0A to .lambda..sub.7A, and the wavelengths 
of optical signals in the input line corresponding unit 2-8 are 
represented by .lambda..sub.0H to .lambda..sub.7H. 
The barrel shifter will be described with reference to FIG. 2. FIG. 2 shows 
the situation of optical signal distribution by the barrel shifter. As 
shown in FIG. 2, a description will be made assuming two input lines #0 
and #1 and four output lines #0 to #3. Optical signals each having 
wavelengths .lambda..sub.0 to .lambda..sub.3 are transmitted to input 
lines #0 and #1, respectively. Output lines #0, #1, #2, and #3 are set as 
output lines of the optical signals having wavelengths .lambda..sub.0, 
.lambda..sub.1, .lambda..sub.2, and .lambda..sub.3 in input line #0, 
respectively. Output lines #1, #2, #3, and #0 are set as output lines of 
the optical signals having wavelengths .lambda..sub.0, .lambda..sub.1, 
.lambda..sub.2, and .lambda..sub.3 in input line #1, respectively. Output 
line #1 is used to output the wavelength .lambda..sub.1 of the optical 
signals transmitted through input line #0. Output line #1 is also used to 
output the wavelength .lambda..sub.0 of the optical signals transmitted 
through input line #1. In the ATM switch shown in FIG. 1, a cell to be 
output to the output line corresponding unit 4-1 may be input to the 
electro-optic converter 7-1 for converting the cell into an optical signal 
having the wavelength .lambda..sub.0A. The cell input to the electro-optic 
converter 7-1 is converted into the optical signal having the wavelength 
.lambda..sub.0A and input to the barrel shifter 3 through the wavelength 
multiplexing link 15-1. The cell is then output to the wavelength 
multiplexing link 16-1 and arrives at the output line corresponding unit 
4-1. 
The barrel shifter is a known technique. It is not directly associated with 
the present invention, and a detailed description thereof will be omitted. 
The barrel shifter will be briefly described below (reference: Hiroshi 
Takahashi et al., "Polarization-insensitive arranged waveguide grating 
wavelength multiplexer on silicon", OPTICS LETTERS, Vol. 17, No. 7, Apr. 1 
1992, pp. 499-501. 
The optical device used in the present invention, i.e., the optical device 
called a barrel shifter is one of optical devices generally called 
"arrayed-waveguide gratings". FIG. 3 shows the concept of the 
arrayed-waveguide grating. Normally, the arrayed-waveguide grating is 
integrated on a substrate together with input and output waveguides and 
two slab waveguides each functioning as a collimator/condenser lens, and 
manufactured as a multiplexer/demultiplexer. 
As shown in FIG. 3, the arrayed-waveguide grating is constituted by a 
plurality of waveguides arranged at an equal interval and having different 
lengths. The phase shift between the waveguides generates the same 
dispersion properties as those of a diffraction grating. Therefore, 
wavelength-multiplexed light from the input waveguide is demultiplexed and 
extracted from different output waveguides. This device is used as a 
multiplexer in a reverse direction. The slab waveguide has a sectorial 
shape whose center of curvature is at the end of the input or output 
waveguide. The slab waveguide also has a condenser function, like a 
concave mirror, because the axis of the waveguide of the arrayed-waveguide 
grating is directed to the center of curvature. To reduce the connection 
loss, a tapered waveguide is generally inserted between the channel 
waveguide and the slab waveguide, which constitute the arrayed-waveguide 
grating. 
A wavelength interval .DELTA..lambda. as one of the most important 
parameters of the multiplexer/demultiplexer using the arrayed-waveguide 
grating is represented as follows: 
EQU .DELTA..lambda.=.DELTA.x/(f.multidot.m/n.sub.x .multidot.d) . . . (1) 
EQU m=(n.sub.c .multidot..DELTA.L)/.lambda..sub.0 . . . (2) 
where .DELTA.L is the difference between a pitch d of the arrayed-waveguide 
grating and the length of the waveguides constituting the 
arrayed-waveguide grating, f is the focal length (=radius of curvature) of 
the slab waveguide, .DELTA.x is the interval of the input and output 
waveguides, and n.sub.x is the effective refractive index of the slab 
waveguide. The denominator (f.multidot.m/n.sub.x .multidot.d) on the 
right-hand side of equation (1) represents a linear dispersion and the 
proportional constant of the relationship between the wavelength and the 
condensing position, n.sub.c is the effective refractive index of the 
waveguide, .lambda..sub.0 is the center wavelength of the 
arrayed-waveguide grating, i.e., the wavelength obtained from the central 
output waveguide, and m is the degree of diffraction of the 
arrayed-waveguide grating, i.e., a numerical value representing the phase 
shift of light between adjacent waveguides. As the value m becomes large, 
the angular dispersion becomes large. For this reason, wavelengths having 
a small interval can be multiplexed/demultiplexed (the wavelength 
resolving power is high). For a conventional diffraction grating, the 
pitch must be reduced to increase the resolving power, though there is a 
process limitation. In the arrayed-waveguide grating, the waveguide can be 
elongated to increase the degree of diffraction, thereby easily realizing 
a high resolving power. This is the largest difference between the 
arrayed-waveguide grating and the conventional diffraction grating. 
As is represented by equation (2), since m is an arbitrary integer, a 
plurality of center wavelengths .lambda..sub.0 are present in one 
arrayed-waveguide grating. For example, when the optical path difference 
.DELTA.L=126 .mu.M, and n.sub.c =1.45, .lambda..sub.0 =1548.3 nm for 
m=118, and .lambda..sub.0 =1535.3 nm for m=119. That is, light components 
having a plurality of wavelengths .lambda..sub.0 including 1548.3 nm and 
1535.3 nm are output from the central output port. Therefore, a band 
usable without overlapping the wavelengths is 13 nm. For wavelength 
division multiplexing at a wavelength interval of 0.8 nm, the maximum 
number of wavelengths is "16". When the value m increases, the wavelength 
resolving power increases. However, the band usable without overlapping 
the wavelengths becomes narrow, so the value m must be carefully set. 
The barrel shifter used in the present invention is an arrayed-waveguide 
grating which positively utilizes its nature (circulation properties) that 
light components having the same wavelength are repeatedly output in units 
of bands usable without overlapping the wavelengths, as shown in Table 1. 
TABLE 1 
______________________________________ 
I/O O1 O2 O3 O4 O5 
______________________________________ 
i1 .lambda..sub.0 
.lambda..sub.1 
.lambda..sub.2 
.lambda..sub.3 
.lambda..sub.4 
i2 .lambda..sub.4 
.lambda..sub.0 
.lambda..sub.1 
.lambda..sub.2 
.lambda..sub.3 
i3 .lambda..sub.3 
.lambda..sub.4 
.lambda..sub.0 
.lambda..sub.1 
.lambda..sub.2 
i4 .lambda..sub.2 
.lambda..sub.3 
.lambda..sub.4 
.lambda..sub.0 
.lambda..sub.1 
i5 .lambda..sub.1 
.lambda..sub.2 
.lambda..sub.3 
.lambda..sub.4 
.lambda..sub.0 
______________________________________ 
FIG. 4 shows the situation of input/output of the barrel shifter 3 shown in 
FIG. 1. One output-side basic switch is connected to the respective 
input-side basic switches through links with different wavelengths when 
viewed from this output-side basic switch. 
The operation of the first embodiment of the present invention will be 
described next. Cells input to the input line corresponding units 2-1 to 
2-8 are switched by the input-side basic switches 6. The output line 
corresponding units 4-1 to 4-8 as destinations are determined in 
accordance with output lines switched by the input-side basic switches 6. 
For example, when one of cells input to the input line corresponding unit 
2-1 is to use the output line corresponding unit 4-1 as an output line, 
the cell may be input to the electro-optic converter 7-1 for converting 
the cell into an optical signal having the wavelength .DELTA..sub.0A. The 
cell input to the electro-optic converter 7-1 is converted into the 
optical signal having the wavelength .DELTA..sub.0A and input to the 
barrel shifter 3 through the wavelength multiplexing link 15-1 and arrives 
at the output line corresponding unit 4-1 through the wavelength 
multiplexing link 16-1. 
The operation of the input line corresponding unit 2-1 will be described in 
more detail. Cells output from the input-side basic switch 6 are converted 
into optical signals having the wavelengths .DELTA..sub.0A to 
.lambda..sub.7A by the electro-optic converters 7-1 to 7-8, respectively. 
These optical signals are multiplexed by the multiplexer 8 into one serial 
signal and output to the wavelength multiplexing link 15-1. The barrel 
shifter 3 selectively distributes the optical signals having the 
wavelengths .lambda..sub.0A to .lambda..sub.7A to the wavelength 
multiplexing links 16-1 to 16-8. On the other hand, when attention is paid 
to one wavelength multiplexing link, e.g., 16-1, optical signals from the 
input line corresponding units 2-1 to 2-8 are wavelength-multiplexed and 
transferred to the wavelength multiplexing link 16-1. 
The demultiplexer 9 demultiplexes the wavelength-multiplexed optical signal 
from the input line corresponding units 2-1 to 2-8. The opto-electric 
converters 10-1 to 10-8 convert the optical signals into cells of 
electrical signals. The cells are output to the output lines by the 
output-side basic switch 11 through the desired output ports 5-11 to 5-18, 
respectively. 
In connection between the input port 1-12 of the input-side basic switch 6 
of the input line corresponding unit 2-1 and the output port 5-14 of the 
output-side basic switch 11 of the output line corresponding unit 4-1, the 
electro-optic converter 7-1 at the uppermost stage is selected by the 
input-side basic switch 6. The optical signal having the 
wavelength.lambda..sub.0A is transferred to the output line corresponding 
unit 4-1 through the barrel shifter 3, demultiplexed by the demultiplexer 
9 to the output-side basic switch 11, and connected to the output port 
5-14 by the basic switch 11. 
As described above, cells arriving from the plurality of input lines can be 
distributed to the output lines which are determined in units of 
wavelengths. When the barrel shifter 3 is used, the internal links of the 
ATM switch can be simplified. 
When a plurality of ATM switches of the present invention are connected, a 
large-scale ATM switch having, e.g., three or five stages can be 
constituted. 
(Second Embodiment) 
The arrangement of the second embodiment of the present invention will be 
described with reference to FIGS. 5 and 6. FIG. 5 shows an ATM switch 
according to the second embodiment of the present invention. In the second 
embodiment, output ports 5-11 to 5-18, . . . , 5-81 to 5-88 of output-side 
basic switches 11 of output line corresponding units 4-1 to 4-8 are 
connected to input ports 1-11 to 1-18, . . . , 1-81 to 1-88 of input-side 
basic switches 6 of input line corresponding units 2-1 to 2-8 through 
lines 12-1 to 12-8. With this arrangement, when partial congestion occurs 
in the ATM switch, a bypass route for avoiding the congested route can be 
set. 
FIG. 6 explains an operation performed when traffic localization occurs in 
the ATM switch according to the second embodiment of the present invention 
and shows a case wherein the traffic of the input line corresponding unit 
2-1 concentrates to the output line corresponding unit 4-1. To transfer a 
cell from the input line corresponding unit 2-1 to the output line 
corresponding unit 4-1, a wavelength .lambda..sub.0A is selected, and the 
cell is automatically transferred by a barrel shifter 3. However, when the 
transfer rate of the input ports 1-11 to 1-18, . . . , 1-81 to 1-88 is 1 
Gb/s, traffics of 8 Gb/s may localize between the input line corresponding 
unit 2-1 and the output line corresponding unit 4-1 at maximum. Assume 
that the throughput at which a cell can be transferred via one wavelength 
of wavelength multiplexing links 15-1 to 15-8 or 16-1 to 16-8 is 1 Gb/s. 
When a cell is to be directly transferred from the input line 
corresponding unit 2-1 to the output line corresponding unit 4-1, only 
cells of 1 Gb/s of the cells of 8 Gb/s can be transferred. The remaining 
cells of 7 Gb/s are handled as a call loss. To avoid this, a feedback 
route is used. In the example shown in FIG. 6, in addition to a route A 
for directly transferring a cell from the input line corresponding unit 
2-1 to the output line corresponding unit 4-1, a route B is arranged to 
select .lambda..sub.1A for some cells to be transferred to the output line 
corresponding unit 4-1, and transfer the cells to the output line 
corresponding unit 4-2. The cell from the output line corresponding unit 
4-2 is fed back to the input line corresponding unit 2-2 via the feedback 
loop and transferred from the input line corresponding unit 2-2 to the 
output line corresponding unit 4-1. Therefore, congestion between the 
input line corresponding unit 2-1 and the output line corresponding unit 
4-1 can be avoided. 
Although one bypass route has been exemplified above, seven bypass routes 
can be additionally ensured between the input line corresponding unit 2-1 
and the output line corresponding unit 4-1. Consequently, a total of eight 
routes can be used. In addition, not one but a plurality of feedback 
routes can be set between the input line corresponding units 2-1 to 2-8 
and the output line corresponding units 4-1 to 4-8. 
(Third Embodiment) 
The third embodiment of the present invention will be described with 
reference to FIGS. 7 and 8. FIG. 7 shows an ATM switch according to the 
third embodiment of the present invention. The third embodiment of the 
present invention includes a circuit in which each of input line 
corresponding units 2-1 to 2-8 has a 9.times.9 input-side basic switch 13 
for distributing cells input to nine input ports 1-11 to 1-19, 1-21 to 
1-29, . . . , or 1-81 to 1-89, and one of the output ports of each 
input-side basic switch 13 is connected to the input port 1-19, 1-29, . . 
. , or 1-89 of the corresponding one of the input line corresponding units 
2-1 to 2-8 without interposing electro-optic converters 7-1 to 7-8. 
According to the third embodiment, no bypass route need be set for the 
subsequent paths. Only by increasing the number of input/output ports of 
the input-side basic switch 13 by one, an ATM switch having a 64.times.64 
arrangement can be constituted. 
More specifically, in the third embodiment of the present invention, eight 
input lines are connected to each of the input line corresponding units 
2-1 to 2-8, and eight output lines are connected to each of output line 
corresponding units 4-1 to 4-8. Instead of the 8.times.8 input-side basic 
switch 6 in the first and second embodiments of the present invention, 
each of the input line corresponding units 2-1 to 2-8 has the 9.times.9 
basic switch, i.e., the input-side basic switch 13 for distributing cells 
input to the nine input ports to the nine lines. Of these nine lines, 
eight lines are connected to the electro-optic converters 7-1 to 7-8, 
respectively, as in the first and second embodiments of the present 
invention. The remaining one line of each input-side basic switch 13 is 
connected such that the line of the input-side basic switch 13 of the 
input line corresponding unit 2-(8-k) (k=1, 2, . . . , 8) is connected to 
an input port of the input-side basic switch 13 of the input line 
corresponding unit 2-(8-(k+1)) (when k=8, the input line corresponding 
unit 2-1). The remaining arrangement in each of the input line 
corresponding units 2-1 to 2-8, and the arrangement of a barrel shifter 3 
and the output line corresponding units 4-1 to 4-8 are the same as those 
in the first embodiment of the present invention. 
FIG. 8 explains an operation performed when traffic localization occurs in 
the ATM switch according to the third embodiment of the present invention. 
Assume that the traffic localizes between the input line corresponding 
unit 2-1 and the output line corresponding unit 4-1, as in the description 
of FIG. 6. In this case, in addition to a route A for directly 
transferring a cell from the input line corresponding unit 2-1 to the 
output line corresponding unit 4-1, a route B is set. With this route B, 
some cells to be transferred to the output line corresponding unit 4-1 are 
transferred to the input line corresponding unit 2-2 by using the line 
14-1, and .lambda..sub.7B is selected to transfer the cells to the output 
line corresponding unit 4-1. When traffics also concentrate between the 
input line corresponding unit 2-2 and the output line corresponding unit 
4-1, some cells from the input line corresponding unit 2-1 can be further 
transferred to the input line corresponding unit 2-3. With this 
arrangement, a plurality of routes can be used to transfer cells from the 
input line corresponding unit 2-1 to the output line corresponding unit 
4-1. In addition, not only one but a plurality of routes can be set among 
the input line corresponding units 2-1 to 2-8. 
In the third embodiment of the present invention, an arrangement which 
includes a regular wire structure and can be easily practiced has been 
described. However, the present invention can be practiced even for 
another connection form. For example, outputs from some opto-electric 
converters 10-k of the output line corresponding units 4-1 to 4-8 can be 
connected to the input line corresponding units 2-1 to 2-8. Alternatively, 
some outputs from the input-side basic switch 13 can be connected to a 
common input line corresponding unit 2-k. 
(Fourth Embodiment) 
The fourth embodiment of the present invention will be described with 
reference to FIGS. 9 and 10. FIG. 9 shows an ATM switch according to the 
fourth embodiment of the present invention. In the fourth embodiment of 
the present invention, output ports 5-81 to 5-88 of an output-side basic 
switch 11 of an output line corresponding unit 4-8 are connected to input 
ports 1-81 to 1-88 of an input-side basic switch 6 of an input line 
corresponding unit 2-8 through lines 18-1 to 18-8 constituting a feedback 
circuit, respectively, thereby specializing the input line corresponding 
unit 2-8 and the output line corresponding unit 4-8 to set bypass routes. 
According to the fourth embodiment of the present invention, remaining 
input line corresponding units 2-1 to 2-7 and output line corresponding 
units 4-1 to 4-7 can have the basic arrangement shown in the first 
embodiment of the present invention. Therefore, the input line 
corresponding units and output line corresponding units can be easily 
increased/decreased. 
FIG. 10 explains an operation performed when traffic localization occurs in 
the ATM switch according to the fourth embodiment of the present 
invention. Assume that the traffics localize between the input line 
corresponding unit 2-1 and the output line corresponding unit 4-1, as in 
the description of FIG. 6. In this case, in addition to a route A for 
directly transferring cells from the input line corresponding unit 2-1 to 
the output line corresponding unit 4-1, a route B is set to transfer some 
cells to be transferred to the output line corresponding unit 4-1 to the 
output line corresponding unit 4-8. The cells are further transferred to 
the input line corresponding unit 2-8 and then transferred from the input 
line corresponding unit 2-8 to the output line corresponding unit 4-2. As 
described above, a plurality of routes can be used between the input line 
corresponding unit 2-1 and the output line corresponding unit 4-1. 
(Fifth Embodiment) 
The fifth embodiment of the present invention will be described with 
reference to FIGS. 11 and 12. FIG. 11 shows an ATM switch according to the 
fifth embodiment of the present invention. In the fifth embodiment of the 
present invention, a block without any input-side basic switch 6 is 
arranged as an input line corresponding unit 2-8', and output ports 5-81 
to 5-88 of an output-side basic switch 11 of an output line corresponding 
unit 4-8 are connected to the input terminals of electro-optic converters 
7-1 to 7-8 through lines 18-1 to 18-8 constituting a feedback circuit, 
respectively, thereby specializing the input line corresponding unit 2-8' 
and the output line corresponding unit 4-8 to set bypass routes. 
According to the fifth embodiment of the present invention, remaining input 
line corresponding units 2-1 to 2-7 and output line corresponding units 
4-1 to 4-7 can have the basic arrangement shown in the first embodiment of 
the present invention. Therefore, the input line corresponding units and 
output line corresponding units can be easily increased/decreased. 
In addition, according to the fifth embodiment of the present invention, 
the input line corresponding unit 2-8' can have a simpler arrangement than 
that of the fourth embodiment of the present invention. The input line 
corresponding unit 2-8' has no input-side basic switch 6. However, desired 
routes can be set on the side of the output-side basic switch 11 of the 
output line corresponding unit 4-8. 
FIG. 12 explains an operation performed when traffic localization occurs in 
the ATM switch according to the fifth embodiment of the present invention. 
Assume that the traffics localize between the input line corresponding 
unit 2-1 and the output line corresponding unit 4-1, as in the description 
of FIG. 6. In this case, in addition to a route A for directly 
transferring cells from the input line corresponding unit 2-1 to the 
output line corresponding unit 4-1, a route B is set to transfer some 
cells to be transferred to the output line corresponding unit 4-1 to the 
output line corresponding unit 4-8. The cells are further transferred to 
the input line corresponding unit 2-8' and then transferred from the input 
line corresponding unit 2-8' to the output line corresponding unit 4-2. As 
described above, a plurality of routes can be used between the input line 
corresponding unit 2-1 and the output line corresponding unit 4-1. 
(Sixth Embodiment) 
The sixth embodiment of the present invention will be described with 
reference to FIG. 13. FIG. 13 shows the sixth embodiment of the present 
invention. In the sixth embodiment of the present invention, the 
arrangement shown in the second embodiment of the present invention is 
combined with that shown in the third embodiment of the present invention. 
When traffic localization occurs in the ATM switch of the sixth embodiment 
of the present invention, not only the bypass route shown in FIG. 6 but 
also that shown in FIG. 8 can be set. With this arrangement, the degree of 
freedom in setting the bypass route can be increased. 
(Seventh Embodiment) 
The seventh embodiment of the present invention will be described with 
reference to FIG. 14. FIG. 14 shows the seventh embodiment of the present 
invention. In the seventh embodiment of the present invention, the 
arrangement shown in the third embodiment of the present invention is 
combined with that shown in the fourth embodiment of the present 
invention. 
When traffic localization occurs in the ATM switch of the seventh 
embodiment of the present invention, not only the bypass route shown in 
FIG. 6 but also that shown in FIG. 10 can be set. With this arrangement, 
the degree of freedom in setting the bypass route can be increased. 
The same description can apply to a combination of the arrangement shown in 
the third embodiment of the present invention and that shown in the fifth 
embodiment of the present invention. 
As has been described above, the present invention can solve the complex 
link connection and cope with traffic localization. In addition, a 
large-scale ATM switch with the minimum quantity of hardware can be 
realized. Furthermore, an ATM switch capable of flexibly coping with an 
increase/decrease in number of input/output lines can be realized. 
(Eighth Embodiment) 
The eighth embodiment of the present invention will be described with 
reference to FIG. 15. FIG. 15 shows the arrangement according to the 
eighth embodiment of the present invention. In the eighth embodiment, the 
present invention is applied to a large-scale ATM switch. 
In this embodiment, a first-stage ATM switch SW1 has the same arrangement 
as that shown in the block diagram of FIG. 1. In a second-stage ATM switch 
SW2, input-side basic switches 6 constituting input line corresponding 
units 2-1 to 2-8 are removed from the block diagram shown in FIG. 1, and 
the input terminals of electro-optic converters 7-1 to 7-8 are connected 
to the output terminals of output-side basic switches 11 constituting 
output line corresponding units 4-1 to 4-8 of the first-stage ATM switch 
SW1. When the third and subsequent stages must be connected, the same 
arrangement as that of the second-stage ATM switch SW2 is sequentially 
connected. The detailed structures, functions, and operations of the 
respective components have been described in detail in the embodiment 
shown in FIG. 1, and a detailed description thereof will be omitted. 
This arrangement can flexibly cope with a large-scale ATM switch, and the 
quantity of hardware can be largely reduced, as compared to the prior art. 
With such multiple arrangement, traffic localization can be solved without 
using any feedback circuit, unlike the above-described embodiments.