WO2002037727A1

WO2002037727A1 - Optical routers and redundancy

Info

Publication number: WO2002037727A1
Application number: PCT/US2001/047397
Authority: WO
Inventors: Vibha Goel
Original assignee: Vitesse Semiconductor Corporation
Priority date: 2000-11-03
Filing date: 2001-11-05
Publication date: 2002-05-10
Also published as: US20020186700A1; AU2002228910A1; WO2002037727A9; US7149426B2

Abstract

An all optical switching system (125) which is optically switched from the signal channel (100) all the way to a router (130). Errors in the routers (130) are detected, and indications (142) of those errors are sent back to the optical switch. The optical switch (125) uses a system which picks off a piece of the signal to use the control signal to control the switching.

Description

OPTICAL ROUTERS AND REDUNDANCY

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority from provisional application no. 60/245,818 filed November 3, 2000 and provisional application no. 60/246, 683 filed November 7, 2000.

BACKGROUND [0002] This application relates to routing of optical signals in communication systems.

[0003] Routing of signals, and specifically optical signals, allows the signals to be properly sent from an origin to a destination. Because of the importance of reliability during such communication, many such systems include multiple levels of backup. This may be especially true in high-end routers, which may require double layers of redundancy. This redundancy, may, in turn, increase significantly the cost of such a router.

SUMMARY [0004] The present application teaches a traffic restoration and management system which may provide redundancy in the system, in a less expensive way.

BRIEF DESCRIPTION OF THE DRAWINGS [0005] These and other aspects will now be described in detail with reference to the accompanying drawings, wherein: [0006] Figure 1 shows a block diagram of the basic electronic system;

[0007] Figure 2 shows how a similar system can be carried out using an optical system with an optical tone, and that may return information about the router; [0008] Figure 3 shows further details on the optical switch and how it processes the optical tones; and [0009] Figure 4 shows a 100 percent redundant optical system.

DETAILED DESCRIPTION [0010] A first embodiment is shown in figure 1. The figure 1 embodiment may represent a building block of the basic system. A number of signals, here 12 optical signals, are input as 100. The optical signals are each input to optical receivers, such as the receiver shown as 102. These receivers receive the -optical signal, and convert the optical signal into the electrical domain. Since there are twelve such signals, there may be twelve such receivers shown as 102... 110. The output signal 115 is an electrical signal corresponding to the respective optical input signal. The twelve electrical signals 115... 120 are connected to a switching matrix 125 which may be a multiplexer, for example. The switching matrix 125 receives twelve inputs on its left side, and has 16 outputs on its right side. Notably, the switching matrix 125 has the capability of switching any of the input signals to any output signal location. Each of the 16 outputs is connected to a router. Conventional routers may handle four inputs, as shown. Therefore, each router 130... 135 is shown receiving four inputs. There may be four basic routers to carry out the operations for switching for all of the 16 inputs. Each of the lines 140 between the switching matrix 125 and the router 130 carries signals to the router, but also carries control information from the router. The control information shown as 142 may include various kinds of information including the so-called Kl, K2 bits .

[0011] The Kl, K2 bits may inform the multiplexer switch 125 that there is a failure in the router 130, e.g. in a specified channel of the router. However, since there are four extra channels on the right side of the multiplexer 125, the multiplexer 125 may then switch the incoming channels to one or more of the redundancy channels. So long as not more than four channels are indicated as failed by the Kl, K2 bits, the redundancy will fully handle this problem. [0012] The system shown in figure 1 may be highly advantageous, since it may reroute any input signal to the other outputs. Moreover, because of the high-speed operation, this rerouting may occur within a short time, e.g., 50 milliseconds or so, to achieve a high speed operation.

[0013] However, a disadvantage of this system is that this requires complex switching units within the optical switch 125. For example, any input such as 115 may be required to switch to any of the different outputs. This may require a very complex electrical switching network. Moreover, individual transceivers may be required which may also increase the cost of the system. The present system recognizes that this solution may be an extremely expensive solution.

[0014] A second embodiment is shown in figure 2. This setting embodiment carries out a similar functionality using an all optical network.

[0015] Optical input signals 200 are connected to an optical switch 205 which may be an optical switch of the type capable of connecting any input signal to any output signal. Since the system is all optical, it can operate without the transceivers that are necessary in the first embodiment. The output signals 210 are connected to the routers shown as 215, with again blocks of four signals being connected to each router. An existing 16 by 16 switch is shown as being used as the switch 205. This switch has the capability to send ' any of the 16 inputs to any of its outputs. However, it may be possible to use different sized switches. For example, 2, 8x8 switches may be used instead, which will allow less switching redundancy, since each one input 200 will only be switchable to one of eight different outputs 210. An important part of this system is that, the transceivers 102,112 shown in Figure 1 are no longer necessary since the system is all optical. This may prove to be a significant cost savings.

[0016] However, in the system shown in figure 2, it may still be necessary for the routers 215 to provide information back to the switch 205. Otherwise, the switch 205 will not be able to determine error information in the routers 215. A signaling system may be used in the optical domain to carry out this operation. The signaling may occur over a line 222 or alternatively may be the standard SONET/SDA signaling. [0017] A first embodiment of the signaling system is shown in figure 3. In this system, the routers such as 215 place an optical signal shown as 300 on their optical line. The optical signal travels back towards the switch. The line 300 is monitored by an element 310 which may obtain a sample of the optical signal, the sample may represent 5 to 10 percent of the optical power in the line 300. The sample 315 is coupled to an optical to electrical converter 320, which converts the signal to an electrical signal 325. The electrical signal 325 is then framed by a framer 330 and output. The output 335 represents similar information to that in the Kl, K2 bits and is coupled to the control circuitry 340 within the optical switch 205. In this way, each router input and output may receive optical switch information.

[0018] A second embodiment defines the failure information using an optical tone system. In this embodiment, a serial bit sequence may be added to the optical signal 305 traveling to the router 215. The signal may be amplitude modulated over the digital signal; e.g. as a 5 percent amplitude variation. The signal may be a specific tone signal, on the order of 2 MHz, with a specific tone frequency assigned to each wavelength. The signal may represent the information in the Kl, K2 bits. For example, these serial bits sequence may be defined as a frame of 10 consecutive bytes, including two framing bytes. After transmitting and receiving the frame, the next frame may be transmitted and received. The framing bytes delineate the frame, within which is contained the information.

[0019] The outgoing transmitted signal includes a tone on the order of 2 MHz, but each specific tone frequency represents a specific wavelength among the channels. The system can therefore extract the tone in the presence of multiple signals, and extract amplitude modulation information that is superimposed on the tones. The system may then process the messages per application. Since each wavelength has a slightly different tone modulation frequency, when the tone is detected, the wavelength is correspondingly detected. Another embodiment, shown in figure 4, may provide an optional redundancy block in the optical switch. In this embodiment, two different optical switches 500,505 each receive the operation signals, and provide their outputs to the redundancy block 510. An error or fault in either optical switch 500,505 will still be corrected by the redundancy.

[0020] Other embodiments are possible based on the disclosed embodiment.

Claims

1. A signal switching system, comprising: a signal switching part, receiving a plurality of inputs and switching any of said plurality of inputs to any of a plurality of outputs; an optical router, receiving said signals from said outputs, and optically routing said signals, said optical router including a fault detecting element therein, which produces a fault signal to said signal switching part, said signal switching part responding to said fault signal to switch one of said inputs to one of said outputs based on said fault signal.

2. A signal switching system as in claim 1, wherein said signal switching part includes n by n switch, and wherein at least a plurality of said n channels are redundancy channels.

3. A signal switching system as in claim 1, wherein said signal switching part includes an optical switch.

4. A signal switching system as in claim 3 wherein said signals switching part includes a 16 x 16 optical switch.

5. A signal switching system as in claim 3, wherein said signal switching system includes an 8 by 8 optical switch.

6. A system as in claim 3, wherein said optical switch includes an optical detecting element, which detects a signal on one of said optical lines.

7. A system as in claim 6, wherein said signal is formed as an amplitude modulated signal on said optical lines.

8. A method, comprising: sending a plurality of channels to a plurality of routers, where the plurality of routers have spare capability for failed routers; and providing an optical signal from said routers indicating failure in said routers.

9. A method as in claim 8, wherein said optical signal is provided as a modulation on at least one of said plurality of channels.

10. A method as in claim 9, wherein said modulation is an amplitude modulation.

11. A method as in claim 8, further comprising sampling and optical signal as part of said sending, to determine said failure signal.

12. A method as in claim 11, wherein said optical signal is an amplitude modulated signal.

13. A method as in claim 12, wherein said signal includes information indicative of a frequency of said error.

14. A system, comprising: an all optical switch, capable of switching any of a plurality of inputs to any of a plurality of outputs, said switch including a control mechanism which controls said switching; and a router array, producing an optical error signal indicative of errors in said router array, said optical error signal being coupled to said optical switch and being used by said control mechanism.

15. A system as in claim 14, wherein said optical error signal is modulated on one of said outputs.

16. A system as in claim 15, wherein said optical error signal is amplitude modulated on one of said elements.

17. A system as in claim 15, further comprising, as part of said optical switch, an optical sampling element which produces a sample indicative of said optical error signal .

18. A system as in claim 15, wherein said control mechanism operates based on electrical signals.

19. A system as in claim 18, wherein said optical sampling element includes an optical to electrical converter element, and a framer element, producing an electrical signal which is used by said control mechanism.

20. A system as in claim 18, wherein said optical switch is an n by n switch which can switch any of its n inputs to any of its n outputs, based on said control mechanism.

21. A system as in claim 20, wherein said optical switch is a 16 by 16 switch.

22. A system as in claim 18, wherein said optical switch includes two, 8 by 8 switches.

23. A method, comprising: carrying out all optical switching between a plurality of channels and a plurality of routers.

24. A method as in claim 23, further comprising providing signaling from said plurality of routers to effect said optical switching.

25. A method as in claim 24, wherein said signaling comprises determining errors in said routers, and producing signals indicative of said errors.

26. A method as in claim 25, wherein said signaling comprises inducing a signal indicative of said error on one of said optical channels.

27. A method as in claim 26, wherein said inducing comprises amplitude modulating said signal on said optical channel .

28. A method as in claim 26, wherein said inducing comprises adding an indication of a channel number to said signal indicative of said error.

29. A method as in claim 23, wherein said switching comprises compensating for errors in said routers.

30. A method as in claim 29, wherein said compensating comprises forming a switching path which sends signals to routers which do not signal errors therein.

31. A system, comprising: an optical switching matrix, having an optical switch which enables switching a plurality of inputs to a plurality of outputs, and also having an optical detecting device, which detects a control signal which is modulated on one of said signals being switched.