Title: Optical one-to-one protection switching apparatus
Abstract: An optical one-to-one protection switching apparatus exchanges signals between a transmit node and a receive node. If a fault is detected in the first transmission line (down-stream), a controller in the node controls a drive circuit so as to shut off a gate. Then, the controller in the transmit node upon receiving a switching request from the receive node, controls the drive circuit so as to shut off the gate. Thereby, the optical switch is switched. The transmitter of the client terminal is thus connected to the second transmission line (down-stream). Upon receiving the switching request from the transmit node, the optical switch in the receive node is switched. Thereby the receiver in the client terminal is connected to the second transmission line (down-stream).
Patent Number: 6,975,811 Issued on 12/13/2005 to Kakizaki, et al.
| Inventors:
|
Kakizaki; Sunao (Kawasaki, JP);
Tsushima; Hideaki (Komae, JP);
Mori; Takashi (Yokohama, JP);
Takatori; Masahiro (Yokohama, JP);
Hayashi; Yukio (Fujisawa, JP);
Kuwano; Shinichi (Yokohama, JP)
|
| Assignee:
|
Hitachi, Ltd. (Tokyo, JP)
|
| Appl. No.:
|
650506 |
| Filed:
|
August 29, 2000 |
Foreign Application Priority Data
| May 29, 2000[JP] | P2000-158554 |
| Current U.S. Class: |
398/2; 398/5 |
| Intern'l Class: |
H04B 010/00 |
| Field of Search: |
398/1,2,5,145
385/16
|
References Cited [Referenced By]
U.S. Patent Documents
Other References
ITU-T G.841, "Types and Characteristics of SDH Network Protection Architectures",
Oct. 1998, pp. 11 and 17.
Rajiv Ramaswami and Kumar N. Sivarajan, "Optical Networks: A Practical Perspective",
Morgan Kaufman Publishers pp. 430-434.
|
Primary Examiner: Chan; Jason
Assistant Examiner: Li; Shi K.
Attorney, Agent or Firm: Knoble Yoshida & Dunleavy
Claims
1. A method of switching optical transmission lines among terminals, a first
terminal and a third terminal being initially communicating via a first optical
transmission line, a second terminal and a fourth terminal being initially communicating
via a second optical transmission line, a first node being located between the
first terminal and the first optical transmission line as well as the second terminal
and the second optical transmission line, a second node being located between the
third terminal and the first optical transmission line as well as the fourth terminal
and the second optical transmission line, comprising the steps of;
detecting a predetermined fault condition on the first optical transmission at
the second node;
blocking an output to the fourth terminal from the second node;
transmitting a first switch request from the second node to the first node;
blocking an input from the second terminal to the first node in response to the
first switch request;
switching the first terminal to connect to the second optical transmission line
from the first optical line transmission after the input is blocked from the second
terminal;
transmitting a second switch request from the first node to the second node;
and
switching the third terminal to connect to the second optical transmission from
the first optical transmission in response to the second switch request.
2. The method of switching optical transmission lines according to claim 1 wherein
said blocking steps are accomplished by gating of the optical signals.
3. The method of switching optical transmission lines according to claim 1 wherein
said blocking steps are accomplished by failing to perform electronic to optical
conversion of the optical signals.
4. The method of switching optical transmission lines according to claim 1 wherein
said blocking steps are accomplished by processing of electrical signals representing
the optical signals.
5. The method of switching optical transmission lines according to claim 1 further comprising:
storing correspondence data on the first terminal, a second terminal a third
terminal and a fourth terminal for ascertaining original connections subsequent
to said switching steps.
6. A system for switching optical transmission lines among terminals, a first
terminal and a second terminal being initially communicating via a first optical
transmission line, a third terminal and a fourth terminal being initially communicating
via a second optical transmission line, comprising:
a second node being located between the second terminal and the first optical
transmission line as well as the fourth terminal and the second optical transmission
line, further comprising:
a fault detection unit detecting a predetermined fault condition on the first
optical transmission;
a second blocking unit connected to the fourth terminal blocking an output to
the fourth terminal from the second node;
a second switch request unit for transmitting a first switch request from the
second node to the first node; and
a second switch connected to the second terminal, the fourth terminal, the first
optical transmission line and the second optical transmission line; and
a first node being located between the first terminal and the first optical transmission
line as well as the third terminal and the second optical transmission line, further
comprising:
a first blocking unit connected to the third terminal for blocking an input from
the third terminal to the first node in response to the first switch request;
a first switch connected to the first terminal, the third terminal, the first
optical transmission line and the second optical transmission line for switching
the first terminal to connect to the second optical transmission line from the
first optical transmission line after the input is blocked from the third terminal;
and
a first switch request unit for transmitting a second switch request from the
first node to the second node, wherein said second switch unit switching the second
terminal to connect to the second optical transmission line from the first optical
transmission line in response to the second switch request.
7. The system for switching optical transmission lines according to claim 6 wherein
said first blocking unit and said second blocking unit further comprise an optical gate.
8. The system for switching optical transmission lines according to claim 6 wherein
said first blocking unit and said second blocking unit further comprise an electronic-to-optical converter.
9. The system for switching optical transmission lines according to claim 6 wherein
said first blocking unit and said second blocking unit further comprise an optical-to-electronic
converter for converting an optical signal to an electrical signal and a processing
unit connected to said optical-to-electronic converter for processing the electrical signal.
10. The system for switching optical transmission lines according to claim 6
further comprising:
a storage unit connected to said first switch and second switch for storing correspondence
data on said first terminal, a second terminal a third terminal and a fourth terminal
for ascertaining original connections subsequent to switching.
11. An optical protection switching apparatus, a first terminal being initially
connected to another one of the optical protection switching apparatus via a first
optical transmission line, a second terminal being initially connected to said
another one of the optical protection switching apparatus via a second optical
transmission line, comprising:
a switch for switching connections of the first terminal and the second terminal
with respect to the first optical transmission line and the second transmission
line in response to a switch activation signal;
a switch request unit connected to the first optical transmission line for transmitting
to said another one of the optical protection switching apparatus a switch request
message indicative of a switch between the first optical transmission line and
the second optical transmission line in response to a switch request signal;
a blocking unit connected between the second terminal and said switch for blocking
an optical signal between the second terminal and said switch in response to a
blocking signal and generating a block completion signal upon completing the block;
a monitor unit connected to the first optical transmission line for detecting
a predetermined fault condition in the first optical transmission line and generating
a fault condition signal; and
a controller connected to said monitor unit, said switch request unit and said
blocking unit for generating the blocking signal in response to the fault condition
signal and the switch request signal in response to the block completion signal.
12. The optical protection switching apparatus according to claim 11 wherein
said switch is a four-in-four-out optical switch.
13. The optical protection switching apparatus according to claim 11 wherein
said switch is a set of two two-in-two-out optical switches.
14. The optical protection switching apparatus according to claim 11 wherein
said switch further comprises one one-in-two-out optical switch, two two-in-one-out
switch and an optical splitter.
15. The optical protection switching apparatus according to claim 11 wherein
said switch further comprises two two-in-two-out optical switches.
16. The optical protection switching apparatus according to claim 11 wherein
said line isolator is an optical gate.
17. The optical protection switching apparatus according to claim 11 wherein
said line isolator is an electronic-to-optical converter.
18. The optical protection switching apparatus according to claim 11 wherein
said line isolator further comprises an optical-to-electronic converter for converting
an optical signal to an electrical signal and a processing unit connected to said
optical-to-electronic converter for processing the electrical signal.
19. The optical protection switching apparatus according to claim 11 further comprising:
a storage unit connected to said switch for storing correspondence data on the
transmitters and the receivers subsequent to switching.
20. An optical protection switching apparatus according to claim 11 wherein said
controller generates the switch activation signal upon receiving another one of
the switch request message from said another one of the optical protection switching
apparatus after said switch request unit has transmitted to said another one of
the optical protection switching apparatus an original one of the switch request message.
21. An optical protection switching apparatus, a first terminal being initially
connected to another one of the optical protection switching apparatus via a first
optical transmission line, a second terminal being initially connected to said
another one of the optical protection switching apparatus via a second optical
transmission line, comprising:
a switch for switching connections of the first terminal and the second terminal
with respect to the first optical transmission line and the second transmission
line in response to a switch activation signal;
a switch request unit connected to the first optical transmission line for transmitting
to said another one of the optical protection switching apparatus a switch request
message indicative of a switch between the first optical transmission line and
the second optical transmission line in response to a switch request signal;
a blocking unit connected between the second terminal and said switch for blocking
an optical signal between the second terminal and said switch in response to a
blocking signal and generating a block completion signal upon completing the block;
and
a controller connected to said switch request unit and said blocking unit for
generating the blocking signal upon receiving another one of the switch request
message from said another one of the optical protection switching apparatus and
for further generating the switch request signal in response to the block completion
signal.
Description
RELATED APPLICATIONS
JP application numbers 2000-157922(May 29, 2000) and 2000-155267(May 25, 2000)
are related to the present invention and they are to be applied for patents in
the United States of America, hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an optical one-to-one protection switching apparatus,
more particularly to an optical one-to-one protection switching apparatus employed
to prevent miss-connection that might occur between a transmitter and a receiver
while a working line and a protection line are switched.
Optical Networks (Ramaswami et al. Morgan Kaufman publishers pp430-434) is
a known example in this field.
FIG. 12A shows a block diagram of an optical one-to-one protection switching
apparatus in the related art. In the case of this related art, extra traffic can
be included. According to this optical one-to-one protection switching apparatus,
client terminals 200 and 210 at different points communicate with
each other through first transmission lines 180 and 185. At this
time, the optical switches 145 and 165 select the first transmission
line 180 for down-stream communications. For up-stream communications, the
optical switches 175 and 155 select the first transmission line 185.
The client terminals 205 and 215 communicate with each other through
the second transmission lines 190 and 195. At this time, the optical
switches 145 and 165 select the second transmission line 190
for down-stream communications and the optical switches 175 and 155
select the second transmission line 195 for up-stream communications. The
arrows in each optical switch denote a transmission direction of signals. Solid
lines arrow denote "the normal state", and broken lines denote "a state after switching".
The same notations are used in the subsequent embodiments.
Referring to FIG. 12B, if a fault is detected in the first transmission
line 180 or 185 in down-stream or up-stream communications, the optical
switches are changed between 145 and 155, as well as between 165
and 175. Thereby, the client terminals 200 and 210 communicate
with each other through the second transmission lines 190 and 195.
The client terminal 205 or 215 that transmits low priority extra
traffics communicates with each other through the first transmission line 180
or 185.
Unlike the configuration of the optical one plus one protection switching,
the configuration of the optical one-to-one protection switching requires communications
of control signals between nodes. The optical one-to-one protection switching configuration
is characterized by the inclusion of extra traffic. However, because the optical
switch changes the corresponding transmission lines in the configuration, the following
problem (A) arises. Problem (A): If any extra traffic is included in a transmission
line, when the switching block uses only optical switches as shown in FIG. 12A,
the configuration might experience a miss-connection between client terminals in
the switching process.
FIG. 12B shows a miss-connection between client terminals in the switching process
after a switching request is issued. In FIG. 12B, the miss-connection occurs during
a switching operation when a fault is detected in the first transmission line 180
in the down-stream communications. Still also referring to FIG. 12A, in the normal
state, the transmitter 200
a of the client terminal 200 and
the receiver 210
b of the client terminal 210 are connected
to each other through the first down-stream transmission line 180. The transmitter
205
a of the client terminal 205 and the receiver 215
b
of the client terminal 215 are connected to each other through the down-stream
second transmission line 190.
In the case of a fault/maintenance, the optical switches 145 and 155
are switched in the transmit node 120. During this switching in the transmit
node 120, their connection states are changed, and a miss-connection might
arise. Concretely, the transmitter 200
a of the client terminal 200
and the receiver 215
b of the client terminal 215 are connected
to each other through the down-stream transmission line 190 as partially
indicated by dotted-lines. The transmitter 205
a of the client terminal
205 and the receiver 210
b of the client terminal 210
are connected to each other through the first down-stream transmission line 180
as partially indicated by dotted-lines. After the switching is ended, the connection
is normalized after both transmit node 120 and receive node 130 are
changed over.
SUMMARY OF THE INVENTION
Under the circumstances, the present invention aims at providing an optical
one-to-one protection switching apparatus that prevents the miss-connection between
a transmitter and a receiver in the switching process in response to a switching
request while a working line is changed to a protection line due to a fault, maintenance,
or the like.
According to the solving means of the present invention, a plurality of
client terminals is connected to each other in an optical one-to-one switching
protection apparatus for enabling optical signals to be exchanged among nodes through
the first down-stream and up-stream transmission lines and the second down-stream
and up-stream transmission lines. Each of the nodes comprises an optical switch
for switching the first and second client terminals to the first or second down-stream
transmission line so as to connect them to each other, as well as for switching
the first and second client terminals to the first or second up-stream transmission
line so as to connect them to each other; up-stream and down-stream gates provided
between the second client terminal node and the optical switch; and a controller
for controlling the optical switch and the up-stream and down-stream gates. If
the second node detects a fault in the first down-stream transmission line while
a signal is transmitted through the first down-stream transmission line between
the first and second nodes, the controller controls the up-stream and down-stream
gates, thereby shutting off or attenuating the object line signal in the second
node so as to prevent a miss-connection. The second node transmits a switching
request to the first node via the first or second up-stream transmission line.
Receiving the switching request, the first node enables the controller to change
the optical switch connection so as to connect the first client terminal to the
second down-stream transmission line. After that, the first node transmits a switching
request to the second node via the second down-stream transmission line. Receiving
the switching request, the second node enables the controller to change the optical
switch connection so as to connect the first client terminal to the second down-stream
transmission line. The present invention provides the optical one-to-one protection
switching apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the present invention will now be described in
conjunction with the accompanying drawings, in which:
FIG. 1 is a block diagram illustrating the optical one-to-one protection switching
apparatus in an embodiment of the present invention;
FIG. 2 is a flow chart illustrating a switching sequence for preventing a miss-connection
during a transmission line switch;
FIG. 3 is a block diagram illustrating the optical one-to-one protection switching
apparatus provided with a line input device and a line output device in another
embodiment of the present invention;
FIG. 4 shows the relationship between a line and each line I/O device for switching
control communications in the configuration as shown in FIG. 3;
FIG. 5 shows the relationship between a line and each line I/O device for monitoring
the performance of the object transmission line in the configuration as shown in
FIG. 3;
FIG. 6 is a block diagram illustrating the optical one-to-one protection switching
apparatus, which is expanded from the optical one plus one protection switching
apparatus, in still another embodiment of the present invention;
FIG. 7 shows the relationship between a line and each line I/O device for switching
control communications in the configuration as shown in FIG. 6;
FIG. 8 shows the relationship between a line and each line I/O device for monitoring
the performance of the object transmission line in the configuration as shown in FIG.6;
FIG. 9 is a block diagram illustrating the optical one-to-one protection switching
apparatus, which is expanded from an optical one plus one protection switching
apparatus, in another embodiment of the present invention.
FIG. 10 shows the relationship between a line and each line I/O device for monitoring
the performance of the object transmission line in the configuration as shown in
FIG. 7;
FIG. 11 is a block diagram illustrating the optical one-to-one protection switching
apparatus in another embodiment of the present invention;
FIG. 12A is a block diagram illustrating an optical one-to-one protection switching
apparatus of a related art;
FIG. 12B is a block diagram illustrating the optical one-to-one protection switching
apparatus after switching in a fault condition; and
FIG. 13 shows a miss-connection between client terminals in the switching process
in response to a switching request.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a block diagram illustrating a first embodiment of the optical
one-to-one protection switching apparatus according to the present invention. In
the first embodiment, in addition to the components shown in FIG. 12, the nodes
220 and
225 in the apparatus is respectively provided with controllers
230,
235; drive circuits
240,
245, and pairs of gates
260a,
260b and
265a,
265b.
In the node
220, the controller
230 controls the drive circuit
240.
The drive circuit
240 drives the gates
260a and
260b
under the control of the controller
230. The gates
260a and
260b driven by the drive circuit
240 turn on or off a signal.
The similar operations are also performed in the node
225 by a corresponding
set of the components
235,
245,
265a and
265b.
In this embodiment, gates
260a,
260b,
265a,
and
265b are provided on transmission lines so as to solve the above
described problem (A), and signals to and from the client terminals
205
and
215 are shut off as needed so as to prevent a miss-connection.
In the first embodiment, it is assumed that clients
1 carries high priority
data while clients
2 exchange low priority data.
FIG. 2 shows a flow chart illustrating steps involved in a switching sequence
for preventing a miss-connection during a transmission line switch according to
the current invention. In this case, a description is provided for a switching
procedure in shutting off a gate when a fault occurs in the first transmission
line
180 during down-stream communications. However, the switching is also
performed in another transmission line, such as the up-stream transmission line,
the second transmission line, or the like during a switching operation required
due to maintenance, etc. other than a fault. The process is described with respect
to steps performed by components as shown in FIG.
1.
At first, signals are exchanged between the transmit node
220 and the
receive
node
225. The receive node
225 monitors the performance of the first
transmission line or down-stream
180 through a performance monitor
232
and
233 in Act
274. At this time, if a fault is detected in the first
transmission line
180 in Act
276, a miss-connection preventive processing
is executed in Act
278. In the above described processing, the controller
235 controls the drive circuit
245 in the node
225 so as to
open the optical gates
265b to block the transmission of optical
signals to the receiver
215b. Then, a switching request controller
or unit
237 and
238 of the receive node
225 transmits a switching
request
282 to the transmit node
220 in Act
280. The switching
request
282 transmitted to the transmit node
220 from the receive
node
225 is transmitted through the first transmission line or up-stream
185 or the second transmission line or up-stream
195.
On the other hand, the transmit node
220, upon receiving a switching request
in Act
284, executes a miss-connection preventive processing in Act
286.
In Act
286, the controller
230 controls the drive circuit
240
in the transmit node
220 so as to open the optical gates
260a
to block the transmission of optical signals from the transmitter
205a.
After that, the switch setting of the optical switch
250 is changed in Act
288, thereby the transmitter
200a of the client terminal
200
is connected to the second transmission line or down-stream
190. At this
time, the receiver
200b is connected to the second transmission line
or up-stream
195 in the client terminal
200, and the receiver
205b
is connected to the first transmission line or up-stream
185. The transmitter
205a is connected to the first transmission line or down-stream
180
respectively in the client terminal
205.
A switching request controller of the transmit node
220 sends a switching
request
292 to the receive node
225 in Act
290. The switching
request
292 is sent from the transmit node
220 to the receive node
225 via the second transmission line or down-stream
190. When the
receive node
225 receives the switching request
292 in Act
294,
the switching setting of the optical switch
255 is changed in Act
296.
Thereby, the receiver
210b of the client terminal
210 is connected
to the second transmission line
190. At this time, the transmitter
210a
in the client terminal
210 is connected to the second transmission line
195, and the receiver
215b is shut off by the gate
265b
in the client terminal
215. Thereby, the transmitter
215a
is connected to the first transmission line (up-stream)
185. In the
node
225, a performance monitor
23 monitors the performance of the
second transmission line (down-stream)
190 in Act
298. The gates
260b and
265a are also simultaneously as the gates
260a and
265b open in the miss connection preventive
processings in Acts
278 and
286. When the gates
260b and
265a are subsequently open after the gates
260a and
265b, the above described process is repeated for transmitters and
receivers associated with the transmission lines
185 and
195.
FIG. 3 shows a block diagram of the optical one-to-one protection switching
apparatus provided with a line input device and a line output device in a second
embodiment of the present invention. In this embodiment, in addition to the components
shown in FIG. 12, each of the node
220 and the node
225 is respectively
provided with a controller
230,
235 and a drive circuit
240,
245, line input devices
340,
345,
360 and
365
as well as line output devices
350,
355 and
370,
375.
The optical switches
300,
310,
305, and
315 are provided
physically closer to transmission lines than those line input/output devices.
Each of the line input devices
340,
345,
360, and
365
is provided with an O/E converter
340a,
345a,
360a,
365a for converting optical signals from the client terminals
200,
210 and the client terminals
205 and
215 to electric signals;
processors
340b,
345b,
360b,
365b
for performance monitoring, sending/receiving of control signals, and multiplexing
of data signals; and electronic-to-optical (E/O) converters
340c,
345c,
360c,
365c for converting electric
signals to optical signals appropriate to the object transmission line. These line
input devices thus enter the signals to their object transmission lines. At this
time, the signal speed, the transmission rate, and the signal format may differ
between the client terminal and the transmission line. However, the transmission
rate and the signal format are unified between the transmission lines.
Each of the line output devices
350,
355,
370, and
375
is respectively provided with optical-to-electronic (O/E) converters
350a,
355a,
370a,
375a for converting optical
signals from transmission lines; processors
350b,
355b,
370b,
375b for performance monitoring, sending/receiving
of control signals, and demultiplexing of data signals; and E/O converters
350c,
355c,
370c,
375c for converting electric
signals to optical signals. These line output devices thus output signals to object
client terminals.
In the embodiment as shown in FIG. 3, the above described gate function as shown
in FIG. 1 is implemented by use of the line input devices
340,
345,
360, and
365, as well as the line output devices
350,
355,
370, and
375 so as to solve the above described problem (A). Shutting
off a signal is performed by the following two exemplary methods.
(1) The E/O converters 360c, 365c, 370c,
375c stop the output of optical signals therefore.
(2) The processors 360b, 365b, 370b,
375b shut off transmission signals in which a control signal such
as an AIS (Alarm Indication Signal) is respectively inserted.
At this time, the line output device
375 monitors the performance of each
input signal even when the signal is shut off.
In the above described related art of the optical one-to-one protection switching
apparatus that includes only optical switches, miss-connections occur during a
line change-over. To avoid the miss-connection, therefore, each of the processors
360b,
365b,
370b, and
375b
in this embodiment is provided with a line input device
360,
365
and a line output device
370,
375, thereby shutting off transmit
signals or attenuate those signals enough so as to prevent the miss-connection.
Although two 2-input-2-output optical switches are used for each node in this embodiment,
it is also possible to use only one 4-input-4-output optical switch as shown in
FIG.
1.
Although the starting point and the terminating point of a switching control
signal differ during switching in the related art, the correspondence table is
stored in the controllers
230,
235 or in another memory in advance
for communications between the nodes.
In the configuration of the switching block in this embodiment expanded from
the
optical one plus one switching apparatus by a splitter at the transmitter, miss-connections
as described in the following problems (B) and (C) might occur during and after
switching. Problem (B): If the optical switch is located closer to the object line
than both starting and terminating points of a switching control communication,
the correspondence between the transmitter and the receiver is changed with respect
to the communication signal in the switching process after a switching request
is issued or after the switching of both nodes. Problem (C): If the optical switch
is positioned closer to the object line than the performance monitoring point,
the correspondence between the signal to be monitored and the receiver for monitoring
the signal is changed in the switching process after switching request or after
the switching of both nodes.
FIG. 4 shows the correspondence between a line and each of the line input/output
devices for switching control communications in the switching configuration as
shown in FIG.
3.
In the chart of the switching sequence shown in FIG. 2, the operation of the
embodiment
as shown in FIG. 3 is considered. The switching request
282 issued from
the receive node
225 to the transmit node
220 is given a first priority
for transmission to the line output device
370 from the line input device
365 via the second transmission line or up-stream
195. The switching
request
282 is given a second priority for transmission to the line output
device
360 from the line input device
345 via the first transmission
line or up-stream
185. Consequently, if a fault is detected in the first
transmission line or down-stream
180, the second transmission line or up-stream
195 that is considered to be normally functioning in comparison to the first
transmission line or up-stream
185 can be used. On the other hand, the switching
request
292 issued from the transmit node
220 to the receive node
225 is given the first priority for transmission to the line output device
340 from the line input device
375 via the second transmission line
or down-stream
190. The switching request
292 is given the second
priority for transmission to the line output device
360 from the line input
device
355 via the second transmission line or down-stream
180. Also
in this case, the line that is considered to be normally functioning is used to
transfer the request more surely.
Furthermore, in the second embodiment as shown in FIG. 3, in order to
solve the above (B) problem, the correspondence between a transmission line and
each of the line input/output devices during switching in each node is stored in
a memory provided in the controllers
230 and
235 or in another memory
in advance. Thereby, each node sends/receives a control communication signal according
to the above correspondence. If the processor of each line input/output device
adds or drops a control communication signal in the second embodiment, the correspondence
between an object transmission line and the line input/output device during switching
in a node is stored in a memory in the controllers
230,
235 in advance,
so that each node sends or receives a control communication signal according to
the correspondence.
Furthermore, in the second embodiment, in order to solve the above problem
(C), the correspondence between an object transmission line and a line input/output
during switching of each node is stored in the memory in the controllers
230,
235 or another memory in advance. Thereby each node can monitor the performance
of the object transmission line according to the correspondence. In the second
embodiment, if the processor of each line input/output device is provided with
a function for monitoring the performance of an optical signal, the correspondence
between an object transmission line and each line input/output device during switching
of a node is stored in the memory provided in the controllers
230,
235
or in another memory in advance, thereby each node can monitor the performance
of the object transmission line according to the correspondence.
Concretely, for example, the correspondence between an object transmission
line to be monitored and each line input/output device is different from that before
and after switching. However, the following correspondence table is stored in the
memory in the controllers
230,
235 or in another memory in advance
so that each node monitors the performance of the object transmission line.
FIG. 5 shows the correspondence between an object transmission line to be monitored
and a line input/output device in the configuration of the switching apparatus
shown in FIG.
3. In the normal state before switching, the line input device
340 sends a signal via the first transmission line down-stream
180,
and the line output device
355 decides the characteristics of the received
signal. In the same way, the line input device
345 sends a signal via the
first transmission line (up-stream)
185, and the line output device
350
decides the characteristics of the received signal. The line input device
360
sends a signal via the second transmission line (down-stream)
190, and the
line output device
375 decides the characteristics of the received signal.
The line input device
365 sends a signal via the second transmission line
(up-stream)
195, and the line output device
370 decides the characteristics
of the received signal.
On the other hand, the line input device
340 sends a signal via the second
transmission line (down-stream)
190, and the line output device
355
decides the characteristics of the received signal. In the same way, the line input
device
345 sends a signal via the second transmission line (up-stream)
195,
and the line output device
350 decides the characteristics of the received
signal. The line input device
360 sends a signal via the first transmission
line (down-stream)
180, and the line output device
375 decides the
characteristics of the received signal. The line input device
365 sends
a signal via the first transmission line (up-stream)
185, and the line output
device
370 decides the characteristics of the received signal.
The above signal shuts off the line input devices
360,
365 that
have a gate function, as well as a line output device
370,
375 to
prevent a miss-connection in the second embodiment. In addition, the correspondence
between an object transmission line to be monitored and a line input/output device
as shown in FIG.4 is stored in the controllers
230,
235 in advance
for communications between the nodes. In addition, the correspondence between an
object transmission line to be monitored and a line input/output device for monitoring
the transmission line as shown in FIG. 5 is stored in the controllers
230,
235 in advance so that each node monitors the performance of the object
transmission line.
FIG. 6 shows a block diagram illustrating the optical one-to-one protection
switching apparatus in a third embodiment of the present invention. The apparatus
is expanded from the optical one plus one switching apparatus. In the third embodiment,
the switching block includes splitters
400 and
405 for splitting
a signal from the first client terminal so that the optical one plus one protection
switching apparatus performs the optical one-to-one protection switching method.
The third embodiment is an optical one-to-one protection switching apparatus
expanded from an optical one plus one protection switching apparatus disclosed
in a known document with addition of client terminals
205 and
215,
as well as second transmission lines
190 and
195. This is why the
node
220 is provided with optical switches
410,
420, and
430,
and the node
225 is provided with optical switches
415,
425,
and
435. Each of the nodes
220 and
225 is further provided
with a controller
230 or
235 and a drive circuit
240 or
245.
In addition, the input lines to each node are connected to line input devices
340,
345,
360, and
365 and the output lines from each node are
provided with line output devices
350,
355,
370, and
375.
The splitter
400 of the node
1 splits an optical signal entered from
the line input device
340 to the first transmission line
180 and
the optical switch
420. The optical one-to-one protection switching apparatus
includes the optical switch
420 that selects the signal from the client
terminal
2 in the normal state,
In the third embodiment, the line output devices
375,
370 are not
connected to the first transmission line
180,
185 via the optical
switches
430,
435 after switching. Consequently, a client terminal
miss-connection might occur only during switching. In the third embodiment of the
optical one-to-one protection switching apparatus, a signal is shut off so as to
prevent such a miss-connection with, for example, line output devices
370,
375 that have a gate function. In the switching sequence flow chart shown
in FIG. 2, the line output device
375 shuts off a signal in the miss-connection
preventive process
278 executed in the node
225.
In this optical one plus one protection switching apparatus, the following correspondence
between an object line and a line input/output device is stored in the controllers
230,
235 for enabling communications between the nodes.
FIG. 7 shows the correspondence between a line used for switching control communications
and a line input/output device in the configuration of the switching apparatus
as shown in FIG.
6. In the flow chart of a switching sequence shown in FIG.
2, the switching request signal
282 issued from the receive node
225
to the transmit node
220 is given a first priority for transmission to the
line output device
370 from the line input device
365 via the second
transmission line (up-stream)
195. The switching request
282 is given
a second priority for transmission to the line output device
350 from the
line input device
345 via the first transmission line (up-stream)
185.
On the other hand, the switching request signal
292 issued from the receive
node
225 to the transmit node
220 is given a first priority for transmission
to the line output device
375 from the line input device
340 via
the second transmission line (down-stream)
190. The switching request signal
292 is given a second priority for transmission to the line output device
355 from the line input device
340 via the first transmission line
(down-stream)
180. In the above described manner, if a fault occurs in the
first transmission line (down-stream)
180, the second transmission line
190 or
195 that is considered to be in normal operation with higher
possibility in comparison to the first transmission line (up-stream)
185,
and the second transmission line
190 or
195 is used to transmit the
switching request.
Furthermore, in FIG. 7, the following correspondence between an object
transmission line to be monitored and a line input/output device for monitoring
the transmission line is stored in the controllers
230,
235 so that
each node monitors the performance of the transmission line.
FIG. 8 shows the correspondence between an object transmission line to be monitored
and a line input/output device for monitoring the transmission line in the switching
apparatus as shown in FIG.
6.
The following operation will be described with respect to FIG.
6. In the
normal state before switching, the line input device
340 sends a signal
via the first transmission line (down-stream)
180, and the line output device
355 decides the characteristics of the received signal. In the same way,
the line input device
345 sends a signal via the first transmission line
(up-stream)
185, and the line output device
350 decides the characteristics
of the received signal. The line input device
360 sends a signal via the
second transmission line (down-stream)
190, and the line output device
375
decides the characteristics of the received signal. The line input device
365
sends a signal via the second transmission line (up-stream)
195, and the
line output device
370 decides the characteristics of the received signal.
On the other hand, after switching, the line input device
340 sends a
signal
via the second transmission line (down-stream)
190, and the line output
device
355 decides the characteristics of the received signal. In the same
way, the line input device
345 sends a signal via the second transmission
line (up-stream)
195, and the line output device
350 decides the
characteristics of the received signal. The first transmission line (down-stream)
180 and the first transmission line (up-stream)
185 are respectively
disconnected from the line output devices by the optical switches
415 and
410.
FIG. 9 shows a block diagram illustrating a fourth embodiment of the optical
one-to-one protection switching apparatus according to the present invention. The
apparatus is expanded from the optical one plus one protection switching method.
In this embodiment, the switching block includes splitters
400 and
405
for splitting the signal from the client terminal
200 so that the optical
one-to-one protection switching apparatus is expanded from the optical one plus
one protection switching apparatus.
In the forth embodiment, in addition to the components of the optical one plus
one protection switching apparatus disclosed in a known document, the optical one-to-one
protection switching apparatus is further provided with client terminals
205
and
215, as well as the second transmission lines
190 and
195.
Consequently, the node
220 is provided with optical switches
440
and
420, and the node
225 is provided with optical switches
445
and
425. Each of the nodes
220 and
225 is provided with controllers
230,
235 and drive circuits
240,
245. In addition,
input lines to each node are provided with line input devices
340,
345,
360, and
365, and output lines from each node are respectively provided
with line output devices
350,
355,
370, and
375. In
the third embodiment as shown in FIG. 6, each node is provided with one 2-input-1-output
optical switch and one 1-input-2-output optical switch, but each node in the fourth
embodiment is provided with one 2-input-1-output optical switch and one-2-input
2-output optical switch.
In the fourth embodiment, after switching, the line output devices
375
and
370 are connected to the first transmission lines
180 and
185
via the optical switches
445 and
440 so as to monitor the characteristics
of the signals in those transmission lines. Consequently, a miss-connection might
occur in a client terminal during and after switching.
In this optical one-to-one protection switching apparatus, a signal is shut off
by an optical switch
420,
425 and line output devices
370,
375 with a gate function to prevent a miss-connection.
In the switching sequence shown in FIG. 2, the line output device
375
shuts
off an object signal in the miss-connection preventive processing
278 executed
in the node
225.
Furthermore, in the fourth embodiment of the optical one-to-one protection
switching apparatus, as described with reference to FIG. 7, the correspondence
between an object line and each line input/output device is stored in the controllers
230,
235 for enabling communications between nodes. Details of the
correspondence and the miss-connection preventive processing are the same as those
in the third embodiment shown in FIG.
6.
In the configuration in the fourth embodiment of the optical one-to-one protection
switching apparatus shown in FIG. 9, the following correspondence between an object
transmission line to be monitored and a line input/output device for monitoring
the line is stored in the controller
230,
235 so as to enable each
node to monitor the performance of the transmission line.
FIG. 10 shows the correspondence between an object transmission line to be monitored
and a line input/output device for monitoring the transmission line in the configuration
of the switching apparatus as shown in FIG.
9.
In the normal state before switching, the line input device
340 sends a
signal via the first transmission line (down-stream)
180, and the line output
device
355 decides the characteristics of the received signal. In the same
way, the line input device
345 sends a signal via the first transmission
line (up-stream)
185, and the line output device
350 decides the
characteristics of the received signal. The line input device
360 sends
a signal via the second transmission line (down-stream)
190, and the line
output device
375 decides the characteristics of the received signal. The
line input device
365 sends a signal via the second transmission line (up-stream)
195, and the line output device
370 decides the characteristics of
the received signal.
On the other hand, after switching, the line input device
340 sends a
signal
via the second transmission line (down-stream)
190, and the line output
device
355 decides the characteristics of the received signal. In the same
way, the line input device
345 sends a signal via the second transmission
line (up-stream)
195, and the line output device
350 decides the
characteristics of the received signal. The line input device
340 sends
a signal via the first transmission line (down-stream)
180, and the line
output device
375 decides the characteristics of the received signal. The
line input device
345 sends a signal via the first transmission line (up-stream)
185, and the line output device
370 decides the characteristics of
the received signal.
FIG. 11 shows a block diagram illustrating a fifth embodiment of the optical
one-to-one protection switching apparatus according to the present invention. In
the fifth embodiment, both starting and terminating points of a control communication
signal are positioned closer to the transmission line than the optical switch so
as to solve the problem in the above described embodiment. An optical supervised
channel of a wavelength division multiplexing (WDM) transmission line is used for
switching control communications.
In the fifth embodiment of the optical one-to-one protection switching apparatus,
in addition to the components in the configuration shown in FIG. 12, each of the
node
220 and the node
225 is provided with a controller
230,
235 and a drive circuit
240,
245. In addition, each transmission
line is provided with WDM transmission equipments
500,
505,
510,
515,
520,
525,
530, and
535. Input lines from
each node are provided with line input devices
340,
345,
360,
and
365 while output lines to each node are provided with line output devices
350,
355,
370, and
375.
Each of the WDM transmission equipments
500,
505,
510,
515,
520,
525,
530, and
535 is provided with
multiplexers
500a,
515a,
520a,
535a;
splitters DMUX
505c,
510c,
525c,
530c;
optical supervised channel transmitters (Tx)(OSC-Tx)
500b,
515b,
520b,
535b; OSC receivers (OSC-Rx)
505d,
510d,
525d,
530d.
For example, if the first transmission line (down-stream)
180 is disconnected,
the signal break is detected through the performance monitor of the line output
device
355, then the E/O
375c of the line output device
375
is masked, thereby preventing a miss-connection. After that, the line output device
375 stops its alarm detection and the OSC transmitter
535b of
the WDM transmission equipment
535 of the second transmission line (up-stream)
195 outputs a switching request signal via the controller
235. The
switching request signal is received by the OSC receiver
530d of
the WDM transmission equipment
530 of the node
1 and the E/O of the
line input device
360 is masked via the controller
230, thereby changing
over the optical switches
300,
310. The controller
230 adds
a switching request signal to the monitoring signal from the OSC transmitter
520b.
The switching request signal is multiplexed in the signal output from the line
input device
340. The multiplexed signal is then output to the second transmission
line (down-stream)
190. In response to the switching request signal received
by the OSC receiver
525d of the WDM transmission equipment
525,
the controller
235 changes the setting of the optical switches
305,
315, thereby terminating the switching process.
In the optical one-to-one protection switching apparatus composed as described
above, the controllers
230,
235 have an interface
233,
238
for exchanging information with WDM transmission equipment
500,
505,
510,
515,
520,
525,
530,
535. The controllers
230,
235 enable switching control communications between nodes through
an optical supervised channel by the OSC transmitters
500b,
515b,
520b,
535b and the OSC receivers
505d,
510d,
525d,
530d provided in the WDM
transmission equipment, thereby keeping the sending/receiving relationship of the
switching control communications constant during after switching.
Because both starting and terminating points of a control switching signal
in the communication are located closer to the line than the optical switch, the
correspondence between the transmitter and the receiver is maintained constant
with respect to communication signals. Thereby the switching algorithm is implemented
more easily by the controller.
According to the present invention, therefore, it is possible to provide
an optical one-to-one switching apparatus that prevents a miss-connection between
the transmitter and the receiver in the switching process in response to a switching
request for switching from a working line to a protection line due to a fault,
maintenance, etc. as described above.
Although the invention has been described in its preferred embodiments with
a certain degree of particularity, it is understood that the present disclosure
of the preferred embodiments has been changed in the details of construction and
the combination and arrangement of parts may be resorted without departing from
the spirit and the scope of the invention as hereinafter claimed.
*
