WO2001067136A9

WO2001067136A9 - A ring interconnection architecture

Info

Publication number: WO2001067136A9
Application number: PCT/US2001/006863
Authority: WO
Inventors: Li Ming; Mark Soulliere; Richard Wagner
Original assignee: Corning Inc
Priority date: 2000-03-03
Filing date: 2001-03-02
Publication date: 2002-01-10
Also published as: WO2001067136A3; AU2001271236A1; WO2001067136A2

Abstract

A ring interconnection architecture (10) is disclosed that includes an interconnection switch (20) having a plurality of N x N switching fabrics that interconnect two or more optical channel shared protection rings. Each switching fabric (20) includes a plurality of switch states corresponding to a failure condition in either of the protection rings. The ring architecture (10) also provides a plurality of node switches disposed at each node in the optical channel shared protection rings. Each node switch includes a ring switch mode that is responsive to multi-channel failures and a span switch mode that is responsive to single wavelength channel failures. Thus, the interconnection architecture (10) provides independent protection for both multi-channel failures and single channel failures in any of the interconnected rings. The node switches act in concert with the interconnection switch to provide protection for both multi-channel failures, single channel failures, and switch fabric failures.

Description

A RING INTERCONNECTION ARCHITECTURE

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. Provisional Patent Application Serial No. 60/187,943 filed on March 3, 2000, the content of which is relied upon and incorporated herein by reference in its entirety, and the benefit of priority under 35 U.S.C. §119(e) is hereby claimed.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to optical channel shared protection rings, and particularly to protection switching in a ring interconnection architecture for interconnecting optical channel shared protection rings.

Technical Background

Optical protection ring topologies are currently being deployed by network providers because of their cost savings, survivability, and ability to self-heal. Ring topologies typically include a plurality of client access nodes that are interconnected by at least two optical fibers to form a ring. Traffic is transmitted from node to node around the ring. Wavelength

Add/Drop multiplexers (WADMs) are employed at each node to allow clients to gain access to the ring. Client transmitters are coupled to the add portion of the WADM to insert client traffic onto the ring, whereas client receivers are coupled to the drop portion of the WADM to receive ring traffic.

Optical protection rings can survive and self-heal from ring fault conditions by providing duplicate and geographically diverse paths for all of the client traffic propagating on the ring. In a two-fiber ring, this is accomplished by providing two fibers that carry working traffic in opposite directions. Each fiber reserves approximately half of its bandwidth for protection purposes. In a four fiber ring, two fibers are reserved for working channel traffic and two fibers are reserved for protection channel traffic. Thus, if a cable is cut between two nodes, or a wavelength channel transmitter becomes disabled at a particular node, or if there is a switch fabric failure, the ring will detect the fault condition, and route traffic around the damaged network component using the protection bandwidth until a repair can be effected. Conventional protection switching used to implement the self-healing features of protection ring have several shortcomings. First, most protection switches are not versatile enough to provide protection for both multi-channel failures and single channel failures. Second, most protection switches employ large switching fabrics. Thus, if the switching fabric itself experiences a failure, a single point failure severely impacting the operation of the entire ring may result. Third, conventional protection switches provide no architecture for interconnecting two or more four-fiber shared protection rings.

Thus, what is needed is a ring interconnection architecture that includes an interconnection switching fabric for interconnecting two or more four-fiber shared protection rings. An interconnection switching fabric is needed that will provide independent protection for both multi-channel failures and single channel failures in any of the interconnected rings. Further, the ring interconnection architecture should also include node switching fabrics that substantially reduce the possibility of single-point failures. Node switching fabrics are needed that are responsive to both multi-channel failures and single channel failures.

SUMMARY OF THE INVENTION

The present invention is directed to a ring interconnection architecture that includes an interconnection switching fabric for interconnecting two or more four-fiber shared protection rings. The ring interconnection architecture also includes node switching fabrics at every node in each protection ring. Thus, the interconnection architecture provides protection for both multi-channel failures, single channel failures, and switch fabric failures. The interconnection architecture also provides independent protection for both multi-channel failures and single channel failures in any of the interconnected rings.

One aspect of the present invention is a self healing ring interconnection switch for interconnecting at least two optical channel shared protection rings. Each optical channel shared protection ring includes at least one pair of optical fibers interconnecting a plurality of nodes within the optical channel shared protection ring. The optical fibers propagate a plurality of wavelength channels including a plurality of working wavelength channels dedicated to primary client traffic and a plurality of protection wavelength channels which may accommodate extra client traffic. The ring interconnection switch includes a monitor coupled to the at least two optical channel shared protection rings, the monitor being operative to detect at least one fault condition. A controller is coupled to the monitor, the controller being operative to respond to the at least one fault condition with one of a plurality of commands. A plurality of N x N space-division switching fabrics are coupled to the at least two optical channel shared protection rings to form a ring interconnection. Each switching fabric of the plurality of N x N space-division switching fabrics is connected to working wavelength channels and protection wavelength channels of a predetermined wavelength. Each switching fabric includes a plurality of switch states corresponding to the plurality of commands, whereby at least one working wavelength channel of the predetermined wavelength is directed into a predetermined fiber over at least one protection wavelength channel in accordance with one of the plurality of switch states.

In another aspect, the present invention includes a self healing ring interconnection architecture for interconnecting at least two optical channel shared protection rings. Each optical channel shared protection ring includes at least one pair of optical fibers interconnecting a plurality of nodes within the optical channel shared protection ring. Each optical fiber propagates a plurality of wavelength channels including a plurality of working wavelength channels dedicated to primary client traffic and a plurality of protection wavelength channels which may accommodate extra client traffic. The ring interconnection architecture includes a switch fabric controller coupled to the monitor, the controller being operative to respond to at least one multi-channel fault condition and at least one single channel fault condition with one of a plurality of commands. A plurality of N x N switching fabrics are coupled to the at least two optical channel shared protection rings and the switch fabric controller. Each N x N switching fabric of the plurality of N x N switching fabrics is connected to working wavelength channels and protection wavelength channels of a predetermined wavelength. Each switching fabric includes a plurality of switch states corresponding to the plurality of commands, whereby at least one working wavelength channel of the predetermined wavelength is directed into a predetermined fiber over at least one protection wavelength channel in accordance with the switch state. A plurality of node switches disposed at a plurality of nodes in the at least two optical channel shared protection rings. The node switch includes a ring switch mode that is responsive to multi-channel failures and a span switch mode that is responsive to single wavelength channel failures, whereby at least one working first wavelength channel is directed into a predetermined fiber in one protection ring by pre-empting a protection wavelength channel.

Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a ring interconnection switch in accordance with an embodiment of the present invention;

Figure 2 is a block diagram of an N x N MEMS movable mirror switch fabric according to one embodiment of the present invention;

Figure 3 is a block diagram of an N x N Mach-Zehnder switch fabric according to another embodiment of the present invention;

Figure 4 is a block diagram of a ring interconnection switch used in a network having M interconnected two-fiber optical channel protection rings;

Figure 5 is a block diagram of a ring interconnection switch used in a network having M interconnected four fiber optical channel protection rings; Figure 6 is a block diagram of a ring interconnection switch used in a network having

M interconnected four fiber optical channel protection rings and L-add/drop ports;

Figure 7 is a block diagram of a node switch disposed in each node of the ring interconnection architecture;

Figure 8 A is a diagrammatic depiction of two interconnected two-fiber optical channel protection rings using the node switch shown in Figure 7 and the interconnection switch depicted in Figure 1 ; , Figure 8B is a detail view of the interconnection switch depicted in Figure 8 A; Figure 9 A is an example of the operation of the two interconnected two-fiber optical channel protection rings during a multi-channel failure;

Figure 9B is a detail view of the interconnection switch depicted in Figure 9 A; Figure 10A is an example of the operation of the two interconnected two-fiber optical channel protection rings during a multi-channel failure in both rings;

Figure 1 OB is a detail view of the interconnection switch depicted in Figure 10 A; Figure 11A is an example of the operation of the two interconnected two-fiber optical channel protection rings during a single channel failure; Figure 1 IB is a detail view of the interconnection switch depicted in Figure 11A;

Figure 12A is an example of the operation of the two interconnected two-fiber optical channel protection rings during a switch fabric failure in the interconnection switch;

Figure 12B is a detail view of the interconnection switch depicted in Figure 12 A; Figure 13A is a diagrammatic depiction of two interconnected four-fiber optical channel protection rings;

Figure 13B is a detail view of the interconnection switch depicted in Figure 13 A; Figure 14A is an example of the operation of the two interconnected four-fiber optical channel protection rings during a multi-channel failure;

Figure 14B is a detail view of the interconnection switch depicted in Figure 14A; Figure 15A is an example of the operation of the two interconnected four-fiber optical channel protection rings during a multi-channel failure in both rings;

Figure 15B is a detail view of the interconnection switch depicted in Figure 10A; Figure 16A is an example of the operation of the two interconnected four-fiber optical channel protection rings during a single fiber cut; Figure 16B is a detail view of the interconnection switch depicted in Figure 16 A; and

Figure 17 is a detail view of the interconnection switch in the two interconnected four-fiber optical channel protection rings during a switch fabric failure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the ring interconnection switch of the present invention is shown in Figure 1, and is designated generally throughout by reference numeral 10. In accordance with the invention, the present invention for a ring interconnection architecture includes an interconnection switch having a plurality of N x N switching fabrics that interconnect two or more optical channel shared protection rings. Each N x N switching fabric is connected to the working wavelength channels and the protection wavelength channels of a predetermined wavelength. Each switching fabric includes a plurality of switch states corresponding to a failure condition in either of the protection rings. According to the present invention, the working wavelength channel is directed into a predetermined fiber using a protection wavelength in accordance with one of the plurality of switch states. The ring architecture also provides a plurality of node switches disposed at a plurality of nodes in the optical channel shared protection rings. Each node switch includes a ring switch mode that is responsive to multi-channel failures and a span switch mode that is responsive to single wavelength channel failures, whereby at least one working wavelength channel is directed into a predetermined fiber by pre-empting a protection wavelength channel.

The present invention provides several advantages. The present invention is directed to a ring interconnection architecture that includes an interconnection switching fabric for interconnecting two or more four-fiber shared protection rings. The ring interconnection architecture also includes node switching fabrics at every node in each protection ring. Thus, the interconnection architecture provides protection for both multi-channel failures, single channel failures, and switch fabric failures. The interconnection architecture also provides independent protection for both multi-channel failures and single channel failures in any of the interconnected rings.

As embodied herein, and depicted in Figure 1, a block diagram of a ring interconnection switch 10 in accordance with a first embodiment of the present invention is disclosed. Ring interconnection switch 10 includes demultiplexer 12 which is connected to a plurality of N x N space division switching fabrics. In one embodiment, ring interconnection switch 10 is adapted to interconnect two two-fiber protection rings. In this configuration, N = 4. In another embodiment, ring interconnection switch 10 is adapted to interconnect two or more four-fiber protection rings. In this configuration, N = 8. For clarity of illustration, only switch fabric 20 is shown. Switch fabric 20 is dedicated to wavelength channel 8j. Demultiplexer 12 separates the multi-wavelength transmission propagating on fibers FI 1, F12, F21, and F22 into four sets (in a two-fiber ring) of constituent wavelength channels (81 - 8N), and transmits them to their respective switch fabrics. After switching, multiplexer 14 re-multiplexes the wavelength channels (81 - 8N) and directs them into their respective fibers FI 1, F12, F21, and F22. Switch fabric 20 is also connected to controller 22. Controller 22 is coupled to monitor 24. Monitor 24 is operative to monitor the signal strength of each wavelength channel. Controller 22 interprets the inputs received from monitor 24. Based on the signal strengths of the wavelength channels, controller 22 recognizes both single channel failures and multi-channel failures. These failure conditions will be defined below. Controller 22 also monitors switch fabric 20 for switch fabric fault conditions. Controller 22 is operative to drive the plurality of switch fabrics 20 to predetermined switching states to self-heal a given fault condition. Controller 22 also provides inter-ring coordination between the node switches.

It will be apparent to those of ordinary skill in the pertinent art that controller 22 may be of any suitable type, but there is shown by way of example a microprocessor based system having a look-up table which includes all of the switching states of the plurality of switch fabrics 20. In another embodiment, controller 20 is implemented using application specific integrated chips (ASICs).

As embodied herein and depicted in Figure 2, switching fabric 20 is implemented using an N x N MEMS movable mirror switch fabric 20. MEMS switching fabric 20 is operative to direct a light signal from any one of N inputs to any one of N outputs. MEMS switch fabric 20 includes a substrate 200. A matrix of waveguides 202 are disposed in substrate 200. Trenches 204 are formed at the cross-points of waveguides 202. Movable switching element 206 is disposed in each trench 204. In this embodiment, switching element 206 includes a sliding MEMS mirror, a mirror anchor, and a MEMS actuator to slide the MEMS mirror into and out of the cross-point in accordance to the switch state command provided by controller 22. It will be apparent to those of ordinary skill in the pertinent art that modifications and variations can be made to MEMS movable mirror switch fabric 20 of the present invention depending on the fabrication techniques employed. For example, switching element 206 may be deployed on a second substrate and mated to substrate 200. Index-matching fluid may be disposed in trenches 204 to maintain beam collimation as a light signal propagates through the cross-points. Further, MEMS switch fabric 20 may be implemented as a free-space design, as opposed to the guided wave approach discussed above.

As embodied herein and depicted in Figure 3, switching fabric 20 is implemented using an N x N matrix of interconnected Mach-Zehnder switching units 210. Again, Mach-Zehnder switching fabric 20 is a space-division switch. A light signal can be directed from any input port into any output port. Mach-Zehnder switching unit 210 has full add/drop functionality and path-independent loss characteristics. In the embodiment depicted in Figure 3, switching unit 210 includes a two-stage dilated Mach-Zehnder design that is individually actuatable by controller 22. The two-stage Mach-Zehnder switching unit 210 employs two 1 x 2 Mach-Zehnder switches operating in tandem. It will be apparent to those of ordinary skill in the pertinent art that modifications and variations can be made to Mach-Zehnder switch fabric 20 of the present invention depending on the type of actuation used. For example, switching unit 210 can be actuated using thermooptic, piezoelectric, or electrooptic actuators. It will be apparent to those of ordinary skill in the pertinent art that switching fabric 20 may be of any suitable type, as long as a space-division switch is used in the design. As embodied herein and depicted in Figure 4, a block diagram of a ring interconnection switch 10 in accordance with another embodiment of the present invention is disclosed. In Figure 4, interconnection switch 20 (8j) and interconnection switch fabric 20' (8k) interconnect a network having M two-fiber optical channel protection rings. For M protection rings, a 2M x 2M switch fabric is required for each wavelength. The self healing features that apply to two interconnected rings apply to M interconnected rings, as well. Furthermore, this arrangement can be extended to four-fiber protection rings. Figure 5 is a block diagram of a ring interconnection switch used in a network having M interconnected four fiber optical channel protection rings. In the four-fiber ring case, two 2M x 2M switch fabrics are required for each wavelength.

As embodied herein and depicted in Figure 6, a block diagram of a ring interconnection switch having add/drop capability is disclosed. The network shown in Figure 6 has M interconnected four fiber optical channel protection rings and L-add/drop ports. In a two-fiber ring network, the switch fabric size for each wavelength must be 2(M + L) x 2(M + L). In the four-fiber ring network, two 2(M + L) x 2(M + L) switch fabrics are used. One of ordinary skill in the art will recognize that the MEMS or Mach-Zehnder switching fabrics depicted in Figures 2 and 3, respectively, can be cascaded to form the larger fabrics required when interconnecting M rings.

As embodied herein and depicted in Figure 7, a block diagram of node switch 30 disposed in each node of a two-fiber interconnected ring architecture is disclosed. In this embodiment, node switch 30 is implemented using an electrical switch design. Switch 30 includes a plurality of electrical node switch fabrics 300. Again, for clarity of illustration, only one switch fabric 300 dedicated to wavelength channels 8j and 8k is shown. Switch fabric 300 includes drop portion 302 and add portion 310. Drop portion 302 includes optoelectric converters 304 which are coupled to drop multiplexers 320 and 326. Optoelectric converters 304 provide electrical data signals to electrical switch fabric 306. Switch fabric 306 is coupled to electrooptical converters 308. Electrooptical converters 308 transmit to primary client 1, primary client 3, extra client 1, and extra client 3 using 13 lOnm short reach optics. Add portion 310 includes optoelectric converters 312 which receive optical transmissions from primary client 1, primary client 3, extra client 1, and extra client 3 using 1310nm short reach optics. Optoelectric converters 312 provide electrical data signals representing client traffic to electrical switch fabric 314. Switch fabric 314 is coupled to electrooptical converters 316. Electrooptical converters 316 provide client traffic in optical form to add multiplexers 322 and 324.

Both drop electrical switch fabric 306 and add electrical switch fabric 310 employ two 3 x 1 switches and two 2 x 1 switches. The 3 x 1 switches and the 2 x 1 switches are actuated in response to multi-channel failures, or a single channel failure. For example, in drop portion 302, the 2 x 1 switches are turned to an off-position to pre-empt extra client traffic. The 3 x 1 switches are actuated to route primary client data over the pre-empted signal pathways. Add portion 310 operates in a similar fashion. Thus, electrical switch fabric 30 includes a ring switch mode that is responsive to multi-channel failures and a span switch mode that is responsive to single wavelength channel failures. In one embodiment, the 3 x 1 switches and the 2 x 1 switches are implemented using gated logic. One of ordinary skill in the art will recognize that this scheme can easily be implemented using an application specific integrated chip (ASIC). One of ordinary skill in the art will also recognize that other implementation techniques can be utilized. For example, in another embodiment, electrical switch fabric 300 is replaced by an optical design.

As embodied herein and depicted in Figure 8 A, a diagrammatic depiction of the ring interconnection architecture of the present invention is disclosed. Ring 1 includes fiber 11 and fiber 12 which link Node A, Node B, Node C and interconnection Node D. A functional depiction of node switch 30 is shown at Node A. Ring 2 includes fiber 21 and fiber 22 which link Node E, Node F, Node G and interconnection Node D. A functional depiction of node switch 30'. is shown at Node G. A functional depiction of interconnection switch 10 is shown at Node D. Figure 8 A illustrates a normal operating mode of the interconnection architecture featuring the communications between Primary client 1 in ring 1 with Primary client 2 in ring 2. It also shows the communications between Primary client 3 in ring 1 with Primary client 4 in ring 2.

Figure 8B is a detail view of the interconnection switch depicted in Figure 8 A. In particular, it shows the operation of switch fabric 20 and switch fabric 20' under the normal operating mode depicted in Figure 8A. Each switch fabric connects one working channel and one protection channel from opposite directions on each ring. Demultiplexer 12 separates the incoming multiplexed wavelength channels into individual wavelength channels. Each wavelength channel of a predetermined wavelength is connected to the switch fabric that is dedicated to that predetermined wavelength. For example, working channel Wl l(8j) from fiber 11 is directed to switch fabric 20 which is dedicated to wavelength 8j. On the other hand, protection channel PI 1 (8k) from fiber 11 is directed to switch fabric 20' which is dedicated to wavelength 8k. Switch fabric 20 directs Wl 1 and PI 1 to fiber 21 and fiber 22, respectively. Note that under normal (no-fault) conditions, extra client traffic is supported by the interconnection architecture using protection capacity.

Figure 9 A is an example of the operation of the two interconnected two-fiber optical channel protection rings during a multi-channel failure. In this instance, the cable containing fiber 11 and fiber 12 is severed. The cable cut interrupts the primary connection between primary client 3 and primary client 4. In response to the cable cut in ring 1, node switch 30 and node switch 30' disconnect the extra traffic connection between extra client 1 and extra client 2. Node switch 30 performs a ring switch by using the protection capacity previously used by extra 1 and extra 3 to carry primary 3 traffic. Interconnection switch 10 at Node D connects the protection channel P12 on ring 1 to working channel W21 of ring 2. Protection channel PI 1 of ring 1 is also connected to working channel W22 of ring 2. Figure 9B is a detail view of interconnection switch 10 as depicted in Figure 9 A. Figure 10A is an example of the operation of the two interconnected two-fiber optical channel protection rings during a multi-channel failure in both rings. One salient feature of the present invention is that the self-healing capabilities of node switch 30 in ring 1 does not affect the self healing capabilities of the node switches in ring 2. In Figure 10A a second cable cut is experienced between Node D and Node E. The second cable cut interrupts the primary connection between Node D and Node G in ring 2. Node switch 30' senses the multi-channel failure and performs a ring switch whereby extra clients 2 and 4 are pre-empted by directing primary client 4 traffic over the protection bandwidth. Interconnection switch 10 responds to both cable cuts by connecting the protection wavelength channels from both rings. Figure 10B is a detail view of interconnection switch 10 as depicted in Figure 10A. Note that channels P12 and P21 shown at the input side of switch fabrics 20 and 20' now carry primary traffic by virtue of the action taken by node switches 30 and 30'.

Figure 11 A is an example of the operation of the two interconnected two-fiber optical channel protection rings during a single channel failure. In this case, both node switch 30 and node switch 30' perform a span switch. Node switch 30 drops extra traffic 3 and uses the capacity for primary client 3. Node switch 30' drops extra traffic 4 and uses the capacity for primary client 4 to restore connectivity between primary client 3 and primary client 4. Figure 1 IB is a detail view of interconnection switch 10 as depicted in Figure 11A. Interconnection switch 10 also plays a coordination role in this operation. Because node switch 30 and node switch 30' both perform span switching, coordination is required between the rings in order to avoid misconnection. Since interconnection switch 10 monitors both rings, this capability is resident in controller 22 of switch 10.

Figure 12A is an example of the operation of the two interconnected two-fiber optical channel protection rings during an interconnection switch fabric failure. Figure 12B is a detail view of interconnection switch 10 as depicted in Figure 12A. In this example, switch fabric 20 experiences a failure. To heal this failure, node switch 30 pre-empts extra 1 and extra 3 and performs a span switch in both directions by diverting working channel Wl 1 to protection channel PI 1. Node switch 30' also performs a span switch in both directions by diverting working channel W21 to protection channel P21. The remaining functional switch fabric 20' is actuated to connect PI 1 to P21 on both the input and output sides of fabric 20'. Thus, primary traffic between client nodes primary 1 and primary 2, and primary 3 and primary 4 are re-established.

As embodied herein and depicted in Figure 13 A, a diagrammatic depiction of two interconnected four-fiber optical channel protection rings is disclosed. The four-fiber optical channel protection rings include node switch 30, node switch 30', and interconnection switch 10. Interconnection switch 10 is shown in Figure 1. One of ordinary skill in the art will recognize that the node switch 30 and node switch 30' are adaptations of the node switch depicted in Figure 7. Ring 1 includes working fiber 11, working fiber 12, protection fiber 11, and protection fiber 12 which link Node A, Node B, Node C and interconnection Node D. A functional depiction of node switch 30 is shown at Node A. Ring 2 includes working fiber 21, working fiber 22, protection fiber 21, and protection fiber 22 which link Node E, Node F, Node G and interconnection Node D. A functional depiction of node switch 30' is shown at Node G. A functional depiction of interconnection switch 10 is shown at Node D. Figure 13 A illustrates a normal operating mode of interconnection architecture 10 featuring communications between Primary client 1 in ring 1, with Primary client 2 in ring 2, over wavelength 8j. It also shows the communications between Primary client 3 in ring 1, with Primary client 4 in ring 2, also over wavelength 8j. The extra client traffic carried by 8j is also shown as the connections between extra 1 and extra 2, and extra 3 and extra 4. Figure 13B is a detailed view of interconnection switch 10 showing the configuration of switch fabric 20 required to implement the traffic flow depicted in Figure 13 A. Note that switch fabric 20 is implemented by cascading 4 4 switch fabric 200 and 4 x 4 switch fabric 202. Figure 14A is an example of the operation of the two interconnected four-fiber optical channel protection rings during a multi-channel failure. In this example, the cable between node C and node D in ring 1 is severed. This interrupts the primary connection between primary client 3 and primary client 4. To restore the connection, node switch 30 and node switch 30' disconnect the extra traffic between extra client 1 and extra client 2. Node switch 30 performs a ring switch by connecting working traffic to the protection capacity. Figure 14B is a detail view of switch fabric 20 in the interconnection switch depicted in Figure 14A. Switch fabric 20 connects the protection channel of protection fiber P12 of ring 1 to the working channel of working fiber W12 of ring 2. Further, the working channel from working fiber W22 of ring 2 is connected to the protection channel of protection fiber PI 1 of ring 1. Thus, the connection between primary client 3 and primary client 4 is restored. Switch fabric 20 must have access to termination ports to terminate unwanted traffic generated by the switching.

Figure 15A is an example of the operation of the two interconnected four-fiber optical channel protection rings during a multi-channel failure in both rings. This example is analogous to the example depicted in Figure 10A. Again, a salient feature of the present invention is that the self-healing capabilities of node switch 30 in ring 1 does not affect the self healing capabilities of node switch 30' in ring 2. In Figure 15A a second cable is cut between Node D and Node E. The second cable cut interrupts the primary connection between Node D and Node G in ring 2. To re-route the traffic disrupted by the second cable cut, node switch 30' performs a ring switch by directing primary 4 traffic onto protection fibers P21 and P22. Figure 15B is a detail view of switch fabric 20 in interconnection switch 10. As shown, switch fabric 20 connects the two protection fibers in ring 1 with the two protection fibers in ring 2.

Figure 16A is an example of the operation of the two interconnected four-fiber optical channel protection rings during a single fiber cut. In this scenario, primary traffic between primary client 3 and primary client 4 is disrupted. One way of healing this fault is by having node switch 30 and node switch 30' perform a span switch. As a result, extra client 1, extra client 2, extra client 3, and extra client 4 are pre-empted, and replaced by working traffic between primary client 3 and primary client 4 on the same span. Figure 16B is a detail view of switch fabric 20 in interconnection switch 10. Note that the interconnections in fabric 20 are unchanged, however the working traffic is propagated through protection fibers PI 1, PI 2, P21, and P22, by virtue of the span switching performed in node switch 30 and node switch 30'. Although switch fabric 20 is not changed during this operation, interconnection switch 10 performs a critical role. Since both ring 1 and ring 2 have span switching being performed, interconnection switch 10 provides coordination between the two rings to avoid a traffic misconnection.

Figure 17 is a detail view of switch fabric 20 during a switch fabric failure. In this case, 4 x 4 component fabric 200 fails. To heal this failure, node switch 30 performs a span switch between Node A and Node D, wherein working fiber traffic from Wl 1 is directed into protection fiber PI 1. Node switch 30' also performs a span switch between node G and node D, wherein working fiber traffic from W21 is directed into protection fiber P21. No net change is needed in surviving component switch fabric 202. However, connections are disconnected and re-established in the healing process in order to avoid misconnecting primary traffic to extra traffic. Thus, the two rings are connected through fibers W12, PI 1, W22, and P21. Again, interconnection switch 10 performs a critical role by providing coordination between the two rings. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is;

1. A self healing ring interconnection switch for interconnecting at least two optical channel shared protection rings, each optical channel shared protection ring includes at least one pair of optical fibers interconnecting a plurality of nodes within the optical channel shared protection ring, the optical fibers propagating a plurality of wavelength channels including a plurality of working wavelength channels dedicated to primary client traffic and a plurality of protection wavelength channels which may accommodate extra client traffic, the ring interconnection switch comprising: a monitor coupled to the at least two optical channel shared protection rings, the monitor being operative to detect at least one fault condition; a controller coupled to the monitor, the controller being operative to respond to the at least one fault condition with one of a plurality of commands; and a plurality of N x N space-division switching fabrics coupled to the at least two optical channel shared protection rings to form a ring interconnection, each switching fabric of the plurality of N x N space-division switching fabrics being connected to working wavelength channels and protection wavelength channels of a predetermined wavelength, each switching fabric including a plurality of switch states corresponding to the plurality of commands, whereby at least one of the working wavelength channels is directed into a predetermined fiber over at least one protection wavelength channel in accordance with one of the plurality of switch states.

2. A self healing ring interconnection architecture for interconnecting at least two optical channel shared protection rings, each optical channel shared protection ring including at least one pair of optical fibers interconnecting a plurality of nodes within the optical channel shared protection ring, each optical fiber propagating a plurality of wavelength channels including a plurality of working wavelength channels dedicated to primary client traffic and a plurality of protection wavelength channels which may accommodate extra client traffic, the ring interconnection architecture comprising: a switch fabric controller coupled to the monitor, the controller being operative to respond to at least one multi-channel fault condition and at least one single channel fault condition with one of a plurality of commands; a plurality of N x N switching fabrics coupled to the at least two optical channel shared protection rings and the switch fabric controller, each N x N switching fabric of the plurality of N x N switching fabrics being connected to working wavelength channels and protection wavelength channels of a predetermined wavelength, each switching fabric including a plurality of switch states corresponding to the plurality of commands, whereby at least one working wavelength channel is directed into a predetermined fiber over at least one protection wavelength channel in accordance with one of the plurality of switch states; and a plurality of node switches disposed at a plurality of nodes in the at least two optical channel shared protection rings, the node switch including a ring switch mode that is responsive to multi-channel failures and a span switch mode that is responsive to single wavelength channel failures, whereby the at least one working wavelength channel is directed into a predetermined fiber by pre-empting a protection wavelength channel.

3. The interconnection architecture of claim 2, wherein the multi- wavelength channel failure is a cable cut severing one or both of the protection rings.

4. The interconnection architecture of claim 2, wherein the single wavelength channel failure includes an inoperative working wavelength channel in either of the protection rings.

5. The interconnection architecture of claim 2, further comprising an optical signal monitor coupled to the controller, the optical signal monitor being operative to detect multi-wavelength wavelength channel failures and single wavelength channel failures in either of the two-fiber optical channel shared protection rings.

6. The interconnection architecture of claim 2, wherein the at least two optical channel shared protection rings includes M optical channel shared protection rings.

7. The interconnection architecture of claim 6, wherein a 2M x 2M switching fabric is required for each wavelength.

8. The interconnection architecture of claim 6, wherein each switching fabric includes L add/drop ports, L being an integer.

9. The interconnection architecture of claim 8, wherein a 2(M + L) x 2(M + L) switching fabric is required for each wavelength.

10. The interconnection architecture of claim 2, wherein the at least one pair of optical fibers in each ring includes one pair of optical fibers to thereby form a two-fiber optical channel shared protection ring.

11. The interconnection architecture of claim 10, wherein the N x N fabric is a 4 x 4 switching fabric.

12. The interconnection architecture of claim 10, wherein each fiber in the pair of fibers propagates the plurality of wavelength channels in opposite directions.

13. The interconnection architecture of claim 12, wherein each fiber in the pair of fibers dedicates a first portion of its available bandwidth to working wavelength channels, and the remainder of the available bandwidth to protection wavelength channels.

14. The interconnection architecture of claim 2, wherein the at least one pair of optical fibers in each ring includes two pairs of optical fibers to thereby form a four-fiber optical channel shared protection ring.

15. The interconnection architecture of claim 14, wherein the N x N fabric is an 8 x 8 switching fabric.

16. The interconnection architecture of claim 14, wherein one fiber pair of the two pair includes one pair of fibers dedicated to working traffic, each fiber in the pair of fibers propagating the plurality of working wavelength channels in opposite directions.

17. The interconnection architecture of claim 14, wherein one fiber pair of the two pair includes one pair of fibers dedicated to protection traffic, each fiber in the pair of fibers propagating the plurality of protection wavelength channels in opposite directions.

18. The interconnection architecture of claim 2, wherein the plurality of N x N switching fabrics are comprised of Mach-Zehnder switching units.

19. The interconnection architecture of claim 18, wherein the Mach-Zehnder switching units are thermooptic switching units.

20. The interconnection architecture of claim 18, wherein the Mach-Zehnder switching units are piezoelectric switching units.

21. The interconnection architecture of claim 18, wherein the Mach-Zehnder switching units include polymer waveguide material.

22. The interconnection architecture of claim 18, wherein the Mach-Zehnder switching units include silica waveguide material.

23. The interconnection architecture of claim 18, wherein the Mach-Zehnder switching units include lithiύm-niobate waveguide material.

24. The interconnection architecture of claim 2, wherein the plurality of N x N switching fabrics are comprised of MEMS movable mirror switching units.

25. The interconnection architecture of claim 24, wherein the MEMS movable mirror switching units are disposed in free-space.

26. The interconnection architecture of claim 24, wherein the MEMS movable mirror switching units include a waveguide substrate.

27. The interconnection architecture of claim 26, wherein each movable mirror is disposed at an intersection of two waveguides.

28. The interconnection architecture of claim 2, wherein each N x N switching fabric includes at least one termination port to thereby terminate unwanted traffic.

29. The interconnection architecture of claim 2, wherein the N x N switching fabric is connected to either one working first wavelength channel or one protection first wavelength channel from each fiber in the at least two optical channel shared protection rings.

30. The interconnection architecture of claim 2, further comprising: an optical demultiplexer unit coupled to each fiber in the at least two optical channel shared protection rings and the plurality of N x N switching fabrics, the optical demultiplexer unit demultiplexing the plurality of wavelength channels from each fiber such that each N x N switching fabric receives the working wavelength channels and the protection wavelength channels of the predetermined wavelength; and an optical multiplexer unit coupled to each fiber in the at least two optical channel shared protection rings and the plurality of N x N switching fabrics, the optical multiplexer unit multiplexing the working wavelength channels and the protection wavelength channels received from each N x N switching fabric into a plurality of multi-wavelength channel transmissions corresponding to the plurality of fibers in the at least two optical channel shared protection rings.

31. The interconnection architecture of claim 2, wherein the switch fabric controller includes a look-up-table having stored therein the plurality of switch states and the plurality of commands corresponding to the at least one multi-channel fault condition, the at least one single channel fault condition, and a switch fabric fault condition.

32. The interconnection architecture of claim 2, wherein the ring switch mode is operative to switch a primary client's transmission signal from a working wavelength propagating on a first fiber of the at least one pair of optical fibers to a protection wavelength propagating on a second fiber of the at least one pair of optical fibers, the ring switch mode is also operative to switch the primary client's receive signal from a working wavelength propagating on the second fiber to a protection wavelength propagating on the first fiber, and pre-empt the extra client traffic.

33. The interconnection architecture of claim 2, wherein the span switch is operative to switch a primary client's transmission signal from a working wavelength propagating on the first fiber to a protection wavelength propagating on the first fiber, and switch a primary client's receive signal from a working wavelength propagating on a second fiber to a protection wavelength propagating on the second fiber.

34. The interconnection architecture of claim 2, wherein the plurality of node switches are comprised of optical switching fabrics.

35. The interconnection architecture of claim 2, wherein the plurality of node switches are comprised of electrical switching fabrics.