Abstract:
A router line card is partitioned to separate the packet forwarding functions from physical port interfacing. For each packet forwarding card, at least one redundant port interface is provided. Identical input packets are transmitted via these redundant input port interfaces, one of which is eventually selected based on, for example, SONET standard criteria. If there is a failure, the router selects the interface path that is operating properly and rejects the path containing a failed element. Thus, the router decides locally how to correct the problem internally. Moreover, following an equipment failure the now offline failed interface path can be replaced, while the equipment remains in service using the duplicated interface path. The system can be restored to full duplex operation without affecting the existing traffic, providing for a hot replacement of a failed path. Because the interfaces are separate, a failed module can be renewed and replaced while the equipment is in service. If a failure occurs in an interface card between two peer routers, then packets flow between the two routers uninterrupted from exactly the same previous ports on one router to the same previous ports on the second router, using the same Internet protocol addresses as existed prior to the switching.

Description:
RELATED APPLICATIONS 
     This application is related to concurrently filed, co-pending, and commonly assigned U.S. application Ser. No. 09/703,043, filed Oct. 31, 2000, entitled “Router Line Card Protection Using One-for-N Redundancy” and to concurrently filed, co-pending, and commonly assigned U.S. application Ser. No. 09/703,064, filed October 31, 2000, entitled “Router Switch Fabric Protection Using Forward Error Correction,” the disclosures of both of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     This application relates to the field of optical communication networks, and particularly to large-scale routers for optical communication networks. 
     BACKGROUND 
     The Synchronous Optical Network (SONET) standard is used for communication on fiber optic cables between routers in a telecommunications network. The fiber network uses multiple cable paths operating in tandem, such that data that fails to arrive at a destination (due to a fault in one path) will arrive over the tandem fiber path. However, Internet Protocol (IP) routers that have optical ports based on Packet-over-SONET protocols have not been protected from optical receiver device failures or from optical fiber breaks with any kind of hot standby immediate patch protection mechanism. Typical designs depend upon external routing of IP packets and flows to restore packet traffic around an optical failure in either the outgoing or the incoming ports of the router. This method of protection is very slow and is very cumbersome to engineer and to administer. Without fast acting hot standby protection, a network must be engineered with duplex and multiple routers and with less than fully utilized traffic capacity on each port. Then in the event of a facility or port failure during operation, all traffic must be redirected from the failed port to another port, which is available but underutilized and which has enough intrinsic capacity to carry the additional traffic under such a failure circumstance. 
     The first problem is not what happens once the failure occurs, but the way the network must be engineered to provide this complex protection structure. Once duplex routers or multiple routers are engineered into the network to address this type of failure, then typically it is required to engineer additional link capacity into the network between those routers. Whereas an unprotected network might require only a single trunk that is 100% utilized between two routers, a protected network under current technology requires a second trunk. The utilization of each one of the trunks in the absence of failure falls to only 50%. This increases the cost not only of the equipment, but of the router itself that now includes redundancy, software costs relating to the intervening network capacity, fiber optic transmission capacity including increased overhead traffic between routers, and administrative and engineering effort. 
     In prior art schemes an internal failure within one part of a router would have to be protected by rerouting of the trunk outside of that router, perhaps encompassing several other routers in an existing network. Failure of a cable at a router can in fact propagate significantly far through a network, resulting in substantial confusion to the network as it adjusts to reconfigured routing. The network must broadcast to much of the Internet any IP addresses, for example, that have changed. Thus, small localized failures produce impacts that ripple out through the network, even though their original cause may not have been significant. 
     Not only do the packets get re-routed, but there is of necessity broadcast information that has to be sent to various routers to handle the re-routed traffic. In situations where outages occur from time to time, this can become overwhelming to a network. Even in the best case, the time to perform a repair and restore the original configuration can cause network traffic to slow dramatically. Again, this affects the capacity of a network, which in the initial stage would have to be engineered for higher capacity than would otherwise be necessary. 
     A common problem is an intermittent fault in a network, coming into and going out of service repetitively, thereby causing the generation of rerouting messages almost continuously through the network, known in the industry as “route-flap”, resulting in much non-useful traffic. 
     Consequently, there is a need in the optical network art for router systems and methods that provide protection in the event of a failure, with a smaller investment in equipment and engineering effort than in the prior art. Further, there is a need for router failure protection that requires minimal disruption and reconfiguration of the larger network, and that provides seamless continuity of service in the event of a single point of failure. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a system and method which involves partitioning the router line card to separate the packet forwarding functions from physical port interfacing. For each line card that has a set of packet forwarding functions, at least one redundant port interface is provided. Identical input packets are transmitted via these redundant input port interfaces, one of which is eventually selected, based on various optical data characteristics. In this application, a Synchronous Optical Network (SONET) line mechanism is utilized for detection of these optical data characteristics. 
     If there is a failure of a cable or fiber inside a router, or of a facility module on the router, or of an optical interface module in the equipment feeding the router, the system will switch locally (at the router) around the detected failure. In operation, the router will select the interface path that is operating properly, bypassing around the path that contains some failed element. Thus, the router will make a local decision as to how to correct the problem internally. In this manner, failures do not ripple throughout the network, but typically are contained within the router itself. 
     Moreover, after an equipment failure the now offline failed facility path can be replaced while the equipment remains in service using the duplicated protection facility path. The system can be brought back to full duplex operation without affecting the existing traffic. This provides for a hot replacement of a failed path. Because the facility interfaces are separate, a failed module can be renewed and replaced while the equipment is in service. If a particular facility module needs to be removed for maintenance purposes on one data bus, the duplicate data bus is maintained intact, allowing for hot replacement of any of the facility modules, working and protect, even if a packet forwarding module protection switch is in effect at the time, as described below in more detail. 
     According to the principles of the present invention, if two peer routers in a network are connected by a trunk between them, and a failure occurs on a working facility card and a protection switch occurs from the working facility card to a duplicate protection facility card, then packets that flow between the two routers continue to flow uninterrupted from exactly the same previous ports on one router to the same previous ports on the second router. The packets continue to use the same IP addresses as existed prior to the switching. In prior solutions, by contrast, the packets would have to be routed around the failed working facility card and around the usable port on the peer router to a different useable port on the source router and a different port on the peer router. IP packet addresses would have to be changed. 
     Various aspects of the invention are described in concurrently filed, co-pending, and commonly assigned U.S. application Ser. No. 09/703,043, filed Oct. 31, 2000, entitled “Router Line Card Protection Using One-for-N Redundancy” and to concurrently filed, co-pending, and commonly assigned U.S. application Ser. No. 09/703,064, filed Oct. 31, 2000, entitled “Router Switch Fabric Protection Using Forward Error Correction,” the disclosures of both of which are incorporated herein by reference. 
     Embodiments according to the present invention are designed to protect against all single fault occurrences. Single faults include a single fault of a module, a single fault of a cable, or a single fault of a path. Accordingly, although some double faults are protected against, double faults generally lie beyond the scope of primary objects of the present invention and thus are not in general protected against. 
     From the foregoing discussion, it will be evident that embodiments of the present invention provide substantial advantages over prior art systems. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIGS. 1A-1C  form a schematic diagram showing an overview of the data paths through a router, in an embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating data flow through facility modules in more detail; 
         FIG. 3  is a block diagram illustrating information flow through a typical packet forwarding module; 
         FIG. 4  is a schematic diagram illustrating an alternative implementation of the facility module shown in  FIG. 2 ; 
         FIG. 5  is an overview block diagram illustrating a network incorporating embodiments of the present invention; 
         FIG. 6  is a block diagram illustrating a network incorporating prior art routers, showing the method by which prior art deals with faulty information on one of a pair of bi-directional channels; and 
         FIG. 7  is a block diagram showing a simplified form of the prior art network of  FIG. 6  for ease of comparison with the network of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A-1C  form a schematic diagram showing an overview of the data paths through a router  10 , in an embodiment of the present invention. For ease of understanding,  FIGS. 1A-1C  are partitioned into three sequentially adjacent panels.  FIGS. 1A-1C  do not show how router system  10  is wired, but simply illustrates the flow of data. At the upper left portion of  FIG. 1A , an input  101 - 0  is a first SONET data channel, formatted as Packet-over-SONET in the present embodiment. Input  101 - 0  includes two optical fibers, namely a working input fiber  101 - 0 W and a protect input fiber  101 - 0 P. Fibers  101 - 0 W,  101 - 0 P carry duplicated information into router  10  from a peer source equipment e.g., another router or piece of SONET transmission equipment, compatible with the Packet-over-SONET format. Protect and working facility module cards  11 - 0 P and  11 - 0 W independently receive duplicate input from respective optic fibers  101 - 0 P and  101 - 0 W and perform an integrity check on the information by computing SONET parity and SONET framing words to determine if the information is valid, and independently check SONET protection switching ‘K’ Bytes. Both facility modules  11 - 0 W and  11 - 0 P perform essentially identical functions on the information. Each facility module independently evaluates the SONET frame and determines whether the information contained on it is valid. Facility modules  11 - 0 W and I- 0 P then extract packets from their respective SONET frames and transfer those packets over a packet bus  103  to a packet forwarding module (PFM)  13 - 0 . 
     Working facility module  11 - 0 W and protect facility module  11 - 0 P respectively provide duplicate input interfaces  103 - 0 W and  103 - 0 P to packet forwarding module  13 - 0 . A system controller (not shown in  FIGS. 1A-1C ) examines the status of facility modules  11 - 0 W and  11 - 0 P and selects as the in-service facility module the one that is receiving properly framed and bit-error-free packets on its input, in accordance with the SONET standard or as selected by SONET ‘K’ Bytes. Should the information coming into a facility module, for example facility module  11 - 0 P, have bit errors or other defects, then facility module  11 - 0 P raises an alarm at the system controller (not shown in  FIGS. 1A-1C ). The system controller then selects facility module  11 - 0 W as the source of input from that channel, and facility module  11 - 0 W strips the packets out of the SONET framing overhead and transfers those raw packets over industry standard bus  103 - 0 W to packet forwarding module  13 - 0 . Typically facility modules  11 - 0 W and  11 - 0 P, along with packet forwarding module  13 - 0 , are contained in a line shelf, denoted in  FIG. 1A  as ½ line shelf  142  (ingress) and described below in more detail. 
     There are actually N+ 1  multiple packet forwarding modules  13 - 0  through  13 -N. In  FIG. 1A , N equals 4, providing for four working packet forwarding modules  13 - 0  through  13 - 3  and a fifth designated protect packet forwarding module  13 - 4 . In this case protect packet forwarding module  13 - 4  is a spare module available to replace any working module  13 - 0  through  13 - 3 . Should any one of working packet forwarding modules  13 - 0  through  13 - 3  fail, then fifth packet forwarding module  13 - 4  can substitute for the failed packet forwarding module  13 - 0  through  13 - 3 . This protection configuration is known as “one-for-four” protection. Similarly, on the output side of router  10  shown in the right side portion of  FIG. 1C , packet forwarding modules  18 - 0  through  18 - 3  are all working modules, and packet forwarding module  18 - 4  is a spare protect packet forwarding module available as a replacement in the event of failure of any working packet forwarding module  18 - 0  through  18 - 3 . Typically packet forwarding modules  18 - 0  through  18 - 4  are contained in a line shelf, denoted in  FIG. 1C  as ½ line shelf  143  (egress) and described below in more detail. 
     Protection works through a daisy-chain data bus  105  cascading from Channel  0  to Channel  1 , to Channel  2 , to Channel  3 , and to Channel  4 , linking facility modules  11 - 0 W through  11 - 4 W. A duplicate data bus interconnects from Channel  4  up to Channel  0 , linking facility modules  11 - 4 P through  11 - 0 P. If for example packet forwarding module  13 - 1  were to fail, then input facility modules  11 - 1 P and  11 - 1 W send their traffic down data bus  105  linking facility modules  11 - 2  and  11 - 3  to facility module  11 - 4 , which then switches those inputs to protect packet forwarding module  13 - 4 . Thus if one channel fails, traffic, instead of going through the failed channel, goes down data bus chain  105  to designated protect module  13 - 4 . If a particular facility module needs to be removed for maintenance purposes on one data bus, the duplicate data bus is maintained intact, allowing for hot replacement of any of the facility modules, working and protect, even if a packet forwarding module protection switch is in effect at the time. Similarly on the output side of router  10 , output data is rerouted up a data bus chain  106  to Channel  1  and then out of router  10 . 
     In operation, if PFM  13 - 1  fails, a microprocessor in the line shelf containing the failed packet forwarding module detects the failure, notices if the system is configured for one-for-four protection, and instructs switches on facility modules  11 - 1  through  11 - 4  to switch traffic that used to be in Channel  1  down to Channel  4 . Channel  4  contains facility modules  11 - 4 P and  11 - 4 W on the input side and facility modules  12 - 4 P and  12 - 4 W on the output side respectively of router  10 . These modules are connected to optical inputs and outputs only when utilizing protect PFM  13 - 4  or  18 - 4  as a working module and not as protection for PFMs w  13 - 0  through  13 - 3  or  18 - 0  through  18 - 3 . If PFM  13 - 4  or  18 - 4  is a working module, then daisy chain bus  105 ,  106  is not utilized in any way, and there are simply 5 working inputs and 5 working outputs. Accordingly, two modes of operation are available; namely one-for-N protection, for example one-for-four; or zero-for-five protection, meaning no protect modules and five working modules. Without requiring any wiring changes, router system  10  will function in either mode. 
     An alternative operating mode designates input  101 -N and output  102 -N for lower priority traffic. That traffic would be deliberately interrupted in the event of a failure of any of the packet forwarding modules carrying higher priority traffic and requiring a protect packet forwarding module to service that failure. 
     Information is transferred from PFM  13 - 0  to internal optics modules (IOMs)  14  as chunk payloads of data, such that a chunk contains typically 400 bytes of payload data. Packets contained in virtual out queues of PFM  13 - 0  that are destined for the same egress PFM can be combined to form a single chunk payload of data. Thus, multiple small packets or just a segment of a larger packet can be loaded into a single chunk. A maximum of two chunks can be transferred from a PFM  13 - 0  to the IOMs  14 - 0 W 0  and  14 - 1 W 0  during each chunk period. The same chunks are replicated and transferred in parallel to IOMs  14 - 0 W 1  and  14 - 1 W 1 . 
     IOM modules  14  encapsulate FEC code words as multiple redundant check symbols into each of the chunks. The present implementation uses a conventional interleaved Reed-Solomon FEC coding. IO modules  14 - 0 W 0 ,  14 - 1 W 0  provide duplicate working module capacity for a working zero optical switch plane. Similarly IO modules  14 - 0 W 1 ,  14 - 1 W 1  provide duplicate working module capacity for a working one optical switch plane. Switch plane pairs in this case are not configured as working and protect, but as working zero and working one copies respectively, such that copy zero switch plane containing optical switch modules  15 - 1  through  15 - 6  and duplicate copy one switch plane containing optical switch modules  16 - 1  through  16 - 6  each provide 6 optical switches worth of capacity. 
     IO module  14 - 0 W 0  transfers information from PFM  13 - 0  to one of three optical switch modules  15 - 1 ,  15 - 2  and  15 - 3 . IO module  14 - 0 W 0  sends the information to the appropriate optical switch module based on the decisions of a central arbiter module (not shown in the figures). Illustratively, one input comes into an optical switch module and one output goes out from that same optical switch module. In an actual system, these inputs and outputs in fact provide connectivity across router system  10 .  FIG. 1B  shows optical switch module  15 - 1  connected to an egress side internal optics module  17 - 0 W 0  through an output fiber  110 - 1 . For clarity, six such optical switch modules  15 - 1  through  15 - 6  are shown in the top portion of  FIG. 1B . In fact, in one implementation each of these optical switch modules has 64 optical fibers in and 64 optical fibers out, with these 64 optical fiber pairs fanning out to a great many different line shelves. Different shelves have multiple fiber inputs and outputs. Six parallel optical switch modules  15 - 1  through  15 - 6  provide 6 times the data capacity of a single switch module. Other embodiments can have for example, 36 of these modules rather than six. 
     Chunks of information are sent individually through optical switch modules  15 - 1  through  15 -N and  16 - 1  through  16 -N and received by IO modules  17  on line shelves at the egress side of router  10 . IO module  17  checks the FEC check symbols to validate the accuracy of the data bits within the chunk. It then removes the FEC check symbols and transfers the resulting chunk payloads to packet forwarding module  18 - 0 ,  18 - 1 ,  18 - 2 ,  18 - 3 , or  18 - 4  as appropriate for each destination address. Similarly, the working one optical switch plane containing optical switch modules  16 - 1  through  16 -N does substantially the same thing in parallel. Thus, working zero and working one optical switch planes perform this process duplicatively and in parallel. This allows the packet forwarding modules on the egress side, such as PFM  18 - 0 , to select those chunk payloads that are error free either from working zero or from working one optical switch plane on a chunk by chunk basis. If there is an error in an optical switch, then egress PFM modules  18 - 0  through  18 -N can identify which working plane, zero or one, is accurate. Consequently errors in a switch are contained and do not ripple out through the network. 
     If there are only a few bit errors going through a switch, those errors can be corrected in real time by FEC decoding in IO modules  17 . If a path through a working zero optical switch fails completely, then a path through the working one optical plane can be utilized instead. Further, because each IO module  17  computes the corrupted bits and how many bits were corrected on every path of the system, IO modules  17  provide a detailed fault analysis not only of the failed fiber or optical switch plane, but even down to the level of an individual switch defect, which then can also be isolated. Importantly, the data flowing across for example OS Module  15 - 1  and the data flowing across OS Module  16 - 1  in the absence of failures in the system are identical, byte for byte. This provides a hot standby, chunk for chunk. 
     After selecting error-free chunk payloads, packet forwarding modules  18 - 0  through  18 -N then reassemble the chunks into individual IP packets and forward those packets across interface links  104 , as previously described. 
     In  FIGS. 1A-1C  for the purpose of clarity, corresponding input and output functions are shown on separate circuit cards in separate ½ line shelves  142  and  143  respectively. In some embodiments corresponding input and output functions are combined on a single circuit card in a single line shelf combining ½ line shelves  142  and  143 , thereby creating a folded configuration. For example, working input facility module  11 - 0 W and working output facility module  12 - 0 W can be combined on a single physical printed circuit card with two optical connectors, one in and one out. Similarly protect input facility module  11 - 0 P and protect output facility module  12 - 0 P can be combined on a single physical circuit card with two optical connectors, one in and one out. Likewise, input and output packet forwarding modules  13 - 0  and  18 - 0  also can be combined on a single physical circuit card in a single line shelf. In a folded configuration, if packet forwarding modules  13 - 0  and  18 - 0  share the sane physical card, then there is a single card for Channel  0 , likewise a single card each for, Channels  1 ,  2 ,  3 , and a fifth card for a Protect channel  4 . Because there is a single physical card for input and output functions, then if a card fails, the protection ratio is equal for both input and output modules on that card. In some embodiments internal optics modules  14 - 0 W 0  and  17 - 0 W 0  similarly share the same physical circuit card, which in the present implementation is contained in the same line shelf  142 ,  143  with combined input/output facility modules  11 ,  12  and combined input/output packet forwarding modules  13 ,  18 . 
       FIG. 2  is a block diagram illustrating data flow through facility modules  11 - 0 W and  12 - 0 W, for example, in more detail. Facility optical fibers are connected on the left through input and output interfaces  101 - 0 W and  102 - 0 W respectively. In a preferred embodiment shown in  FIG. 2 , for purposes of illustration input and output facility modules  11 - 0 W and  12 - 0 W occupy the same circuit board in the same line shelf in a folded configuration. In other embodiments, the input and output facility modules  11 - 0 W and  12 - 0 W are located on separate physical circuit cards. 
     A signal, e.g., a packet-over-SONET (POS) formatted IP packet, arrives at input  101 - 0 W to a signal processing module  201  typically in a ten-Gbit/sec OC192 SONET datastream. Processing module  201  contains an optical receiver, an optical multiplexer and associated demultiplexer, and a transmitter associated with those. For example, the received signal is demodulated from optical input  101 - 0 W into an electronic signal, and then demultiplexed from a single ten-Gbit-per-second datastream in this example down to a parallel bus at a lower data speed. That parallel bus of signals then leaves module  201  and goes into a processing module  202 . Module  202  contains an OC192 demultiplexer, which extracts a single 2.5 Gbit/second OC48 substream out of the OC192 stream and delivers a packet-over-SONET (POS) input to a framer  203 - 1 , which is an industry standard off the shelf component. Likewise, module  202  extracts the other three OC48 substreams and sends these to POS framers  203 - 2 ,  203 - 3 , and  203 - 4  respectively. At this point there are four parallel 2.5 Gbit/sec SONET streams, one to each of four POS framers  203 - 1  through  203 - 4 , which extract from each OC48 stream the individual IP packets. POS framers  203 - 1  through  203 - 4  first have to find the IP packets in the datastream and then have to extract the packets from the SONET continuous datastream. This is done on the four parallel OC48 streams. Once it has removed the packets from the SONET frame, each POS framer  203 - 1  through  203 - 4  delivers those packets to a facility ASIC  204 - 1  through  204 - 4  respectively. 
     The principal function of facility ASICs  204 - 1  through  204 - 4  is to send that information to an appropriate packet forwarding module (not shown in  FIG. 2 ), in this case through an interface  103 - 0 W consisting of four parallel interfaces for the four packet streams, or, if directed, to receive packets from an upstream neighboring facility ASIC on an interface  103 - 4 W and switch  103 - 4 W to  103 - 0 W in a protect mode. Otherwise, in a working mode of operation, a facility ASIC sends the information out through interface  103 - 0 W, and information input on  103 - 4 W is directed through cascading protection bus interface  105 - 0 W. The normal sequence is for a facility ASIC to take information from above and switch it below, letting the received traffic pass straight through onto interface  103 - 0 W. All four of facility ASIC switches  204 - 1  through  204 - 4  are ganged, such that they operate in parallel. With faster buses, faster framers, or faster facility ASICs, a single ASIC or bus, for example, could perform the above described functions instead of four required at the present state of technology. 
     Referring again to  FIG. 2 , on the egress side facility ASIC  204 - 1  directs the information packets through output link  211  to Packet-over-SONET framer  203 - 1 , which receives a packet, inserts it into a SONET frame, producing a 2.5 gigabit/second datastream or parallel bus equivalent, and sends that frame to OC192 add/drop multiplexer  202 . Multiplexer  202  combines four 2.5 gigabit/second streams from POS framers  203 - 1  through  203 - 4 , multiplexes them together into a 10 gigabit/second datastream, and delivers them to optical transceiver  201 . Transceiver  201  receives the 10 gigabit/second stream, which is formatted as a parallel bus, and multiplexes it into a single datastream, which modulates a laser diode. This produces a SONET ten-gigabit/second optical format, which is transmitted through outbound optical facility interface link  102 - 0 W. 
       FIG. 3  is a block diagram illustrating information flow through a typical packet forwarding module  13 - 0  ( 18 - 0 ). Facility ASICs  301 - 1  through  301 - 4  on the ingress side receive packets from facility modules working and protect  11 - 0 W and  11 - 0 P through single links  103 - 0 W 0  through  103 - 0 W 3 . A principal function of facility ASICs  301 - 1  through  301 - 4  on the ingress side is to select between the working and the protection facility modules, as represented by the information on, for example, incoming path  103 - 0 W 0  or  103 - 0 P 0 . That selection is made based on the standard SONET criteria for defining if one or both of those incoming facility modules is flawed or failed and also based on any detection of local errors or failures on working facility module  11 - 0 W or protect facility module  11 - 0 P. 
     In the egress direction, a principal function of facility ASICs  301 - 1  through  301 - 4  is to duplicate the packet stream coming out of egress ASIC  302  and to send that packet stream out across both outgoing paths  104 - 0 W 0  and  104 - 0 P 0  to facility modules  12 - 0 W and  12 - 0 P (see  FIG. 2 ). 
     Packet forwarding engines  306 - 1  through  306 - 4  are devices that inspect the packet headers of all of the incoming packets received on any of the selected working or protect facility modules that are associated with this particular packet forwarding module  13 - 0  ( 18 - 0 ). Based on the inspection of those headers, a determination of the intended destination of each packet can be made. The header information is stored by an ingress ASIC  304  in various queues and lists, which are used to determine for any given packet which output port of the router it should exit, when it should exit, and its relative priority. Actual packet data is stored by ingress ASIC  304  in an external RAM memory  305 . Packet forwarding engine  306 - 1  through  306 - 4  also determines if any particular packet is intended for a local destination within this particular router and redirects it toward the main control processor of the router instead of transmitting it downstream out one of the output ports of the router to a peer router across the network. 
     Ingress ASIC  304 , based on the states of the various queues that it maintains and based on the destination addresses of the various packets that are represented by headers in those queues, sends requests through optical transceiver units  308 -W and  308 -P across optical link  310  (typically multimode ribbon fiber) to the central arbiter (not shown in  FIG. 3 ). The central arbiter determines, based on all of the packets that are being processed through the router in aggregate at any given time, which of the requests from a particular ingress ASIC should be granted and when it should be granted for transmission across the optical switch. Grants of those requests return across optical link  310  through transceivers  308 -W and  308 -P back to ingress ASIC  304 . Ingress ASIC  304  uses that grant information to extract packets from memory  305  in the appropriate order and assembles them into chunk payloads. At the appropriate times ingress ASIC  304  sends those chunk payloads across channels  107 - 00  A through  107 - 03  to internal optics modules  14 - 0 W 0  through  14 -NW 1  (see  FIG. 1B ). 
     On the egress side, information chunk payloads are received from the optical switch matrix indirectly through internal optics modules  17 - 0 W 0  through  17 -NW 1  (see  FIG. 1B ) across links  108 - 00  through  108 - 03  into an egress ASIC  302 . Egress ASIC  302  reconfigures the chunks into packets and again stores the packets in a memory  303  in the form of queues and structures. Egress ASIC  302  subsequently reads those packets out again into one of the four facility ASICs  301 - 1  through  301 - 4 . At the facility ASIC, each of those packet streams is duplicated and sent in tandem to both working and protect facility modules  12 - 0 W and  12 - 0 P. 
     A line control processor  307  located on packet forwarding module  13 - 0  ( 18 - 0 ) is primarily responsible for controlling the facility protection switching function by examining the SONET error and failure indications from facility modules  11 - 0 W and  11 - 0 P and also by analyzing the indications that facility ASICs  301 - 1  through  301 - 4  develop from those incoming signals. The appropriate switching decisions are made in software and logic and are then implemented by line control processor  307 . 
       FIG. 4  is a schematic diagram illustrating an alternative implementation  400  of facility module  11 - 0 W ( 12 - 0 W) shown in  FIG. 2 . Facility module implementation  400  performs essentially the identical function described in connection with  FIG. 2 , except that, instead of having 10 gigabit/second single fiber input  101 - 0 W and single fiber output  102 - 0 W, it has four parallel 2.5 gigabit/second input fibers  101 - 0 W 1 ,  101 - 0 W 2 ,  101 - 0 W 3 , and  101 - 0 W 4  and four parallel 2.5 gigabit/second output fibers  102 - 0 W 1 ,  102 - 0 W 2 ,  102 - 0 W 3 , and  102 - 0 W 4  out. SONET standards include OC192 at 10 gigabits/second, and OC48 at 2.5 gigabits/second used in the embodiment of  FIG. 4 .  FIG. 4  employs of four parallel optical transceivers,  401 - 1  through  401 - 4 , which essentially replace transceiver module  201  and add/drop module  202  of  FIG. 2 . Interface links  214 - 1  and  215 - 1  from transceiver  401 - 1  to POS framer  203 - 1  in  FIG. 4  are identical to respective links  214 - 1  and  215 - 1  of  FIG. 2 . The difference is merely that of the optical interface to the facility. Facility ASICs  204 - 1  through  204 - 4 S, OC48 POS framers  203 - 1  through  203 - 4 , and switching operations, e.g. described in connection with  FIG. 2 , are identical for facility module implementations of  FIGS. 2 and 4 . 
     In a further alternative embodiment to that of  FIG. 2 , the ten-gigabit/second SONET facility interface  101 - 0 W and  102 - 0 W of  FIG. 2  is replaced with a ten-gigabit/second Ethernet interface. In this case since the input data stream contains packets in Ethernet and not SONET framing, input and output modules  201 ,  202 , and  203  are different, but facility ASICS  204 - 1  through  204 - 4  remain the same as those described in connection with  FIG. 2 . Between eight and ten parallel single-gigabit/second Ethernet modules are also possible in this case. This is similar to the embodiment of  FIG. 4 , except that transceivers  401  and POS framers  203  are replaced by single or multiple one-gigabit/second Ethernet interfaces instead of SONET interfaces. In the case of ten-gigabit/second Ethernet or one-gigabit/second Ethernet, current industry standards do not define facility protection functionality. Accordingly, only working facility modules  101 - 0 W,  102 - 0 W would be installed on any interface ports that utilize those standards. 
       FIG. 5  is an overview block diagram illustrating a network  50  incorporating embodiments of the present invention. Network  50  includes a switch fabric  501  combining the elements of internal optics modules  14 ,  17  and optical switch modules  15 ,  16  (see  FIGS. 1A-1C ). In this context a fabric is a collection of devices which cooperatively provides a general routing capability. Typically, communication moves between two routers  51  and  52  (for simplicity shown only partially in  FIG. 5 ) of network  50  over duplex optical channels  510  and  511 . This information arrives at facility module  11 W ( 12 W) and the same information arrives at facility module  11 P ( 12 P) and is passed to packet forwarding module (PFM)  13  ( 18 ), as described above in connection with  FIGS. 1A-1C . Assuming both optical channels  510 ,  511  are working properly, then packet forwarding modules  13  ( 18 ) determine which channel  510 ,  511  to utilize and, if both channels are equal then utilize a default channel, for example channel  510 . PFM  13  ( 18 ) passes the information on through network  50  to switch fabric  501  or as otherwise selected by SONET ‘K’ Bytes. 
     In the event of a fault on channel  510 , for example at point X, then because packet forwarding module (PFM)  13  ( 18 ) of router  51  is transmitting identical packets over both channels  510  and  511 , packet forwarding module working  13  ( 18 ) on router  52 , without any external network intelligence or intervention, can select that same traffic from channel  511 . A similar process occurs for packets transmitted in the reverse direction from router  52  to router  51 . This has the effect of limiting the impact of a failure of channel  510  strictly to the two routers  51  and  52 , and in fact strictly to the local intelligence that monitors packet forwarding modules  13  ( 18 ) and facility modules  11  ( 12 ) on each router  51 ,  52 . Note that a break in information coming into router  52  over channel  510  is detected at router  52 . Likewise, a break in information that is going towards router  51  over channel  510  is detected at router  51 . Accordingly, there is no need for communication between routers  51  and  52  with respect to rerouting any information, because each router  51 ,  52  independently makes the decision to accept the information moving on the surviving parallel bi-directional channel  511 . These decisions are made independently but are based upon the same occurrence, whether it be a break or simply faulty information on channel  510 . Information may of course be faulty in one direction only and, therefore, router  51  can accept and process information coming in its direction on channel  510 , whereas router  52  can concurrently process information coming in its direction on channel  511 , each router making independent decisions. Importantly, in all the above cases there is no involvement by any peer routers in a wider scale network outside of routers  51 ,  52  in making decisions with respect to how to respond to a particular fault in network  50 . 
       FIG. 6  is a block diagram illustrating a network  60  incorporating a typical prior art set of routers  61 ,  62 ,  63 , and  64 , showing the method by which prior art deals with the same problem of faulty information on one of a pair of bi-directional channels discussed above with respect to  FIG. 5 . Router  61  and router  63  typically are co-resident in a particular location. Router  62  and router  64  are similarly co-resident in a different particular location. Redundancy of channels between those locations is provided through bi-directional channel  610  between router  61  and  62  and bi-directional channel  611  between router  63  and  64 . Line cards (interface modules)  601 ,  602 , and  604  in  FIG. 6  each combine the functions of a single facility module and a single packet forwarding module, for example facility module  11 W ( 12 W) and packet forwarding module  13  ( 18 ) of  FIG. 5 . Assuming a break in channel  610 , neither router  61  nor router  62  can make the necessary adjustments to recover that traffic. On the contrary, it is necessary for router  61  and router  62  to notify upstream and downstream peer routers (not shown) which can be operating geographically remote from routers  61 - 64 , that a failure on channel  610  had occurred. These upstream and downstream peer routers then begin redirecting packet traffic that had been intended, for example, through routers  61  and  62  through alternative channels, for example through router  63  across channel  611  into router  64 , and then on to a downstream destination. 
     Upstream routers sending IP packets originally destined to go through router  62  and out of router  62  to an ultimate destination have to rewire their programming to recognize that same IP packet address now has to follow a different route through network  60 . Instead of sending it to ports  620 A, it now has to reroute an IP packet having the same destination address, instead, for example to ports  620 B, which then relay it to router  63 , which then in turn forwards it through router  64  and out through interface module  602  on router  64 . Accordingly, a fault between router  61  and router  62  has to be signaled to upstream peer routers such that they can rewire their routing tables. Similarly, downstream peer routers must rewire their routing tables, so that return packets also take an alternative route. Thus, in addition to router  61  and router  62  being affected by the failure, router  63  and router  64  are both affected, as well as all possible upstream peer routers and all possible downstream peer routers. 
     By contrast, in network  50  of  FIG. 5  embodying principles of the present invention, only router  51  and router  52  are affected by an equivalent fault, each of which routers makes its own determination as to what it is to do internally and need not communicate any of its decisions to any router external to itself. Router  51  and router  52  do not, in fact, alter their routing tables at all, because protection facility modules  11 P ( 12 P) do not change the port designation on which IP packets enter or exit switch fabric  501 . Therefore, under fault conditions the mapping between IP addresses and physical port numbers remains unchanged, both internal and external to network  50 . 
       FIG. 7  is a block diagram showing a prior art network  70  representing a simplified form of network  60  of  FIG. 6  for ease of comparison with network  50  of  FIG. 5 . Assuming that the total traffic under normal service conditions traveling from router  71  to router  72  is 100% of the channel capacity of either bi-directional channel  710  or  711  (or comparatively channel  510  or  511  in  FIG. 5 ), then the relative costs of these two approaches in order to maintain that channel capacity can be compared. In the case of  FIG. 5 , router  51  duplicates facility modules  11 W ( 12 W) and  11 P ( 12 P), each facility module having a capacity of 100%, but it does not duplicate packet forwarding module  13  ( 18 ). Router  51  has a single packet forwarding module  13  ( 18 ) with a capacity of 100%. In the event of failure of channel  510 , the channel capacity of PFM  13  ( 18 ) is redirected entirely to service channel  511 , thereby maintaining 100% channel capacity despite failure of channel  510 . In  FIG. 7 , to maintain the same 100% channel capacity under failure conditions, it is necessary to effectively duplicate the channel capacity of line card  702  and line card  703  completely, each of which includes the functionality and cost associated with both a facility module and a packet forwarding module, as described above in connection with  FIG. 6 . The capacity of switch fabric  701  is also included as part of that cost. 
     In network  50  shown in  FIG. 5 , implementation of fault protection consumes one port of switch fabric  501 , one packet forwarding module, and two facility modules. In network  70  shown in  FIG. 7 , fault protection implementation consumes two ports of switch fabric  701  and two packet forwarding modules  702  and  703 , each of which includes a single facility module. Accordingly, a total of two PFMs, two facility modules and two switch ports is required for fault protection in  FIG. 7 , whereas network  50  of  FIG. 5  requires only one switch port, one PFM and two facility modules for a comparable level of fault protection. 
     Referring again to  FIG. 3 , each packet forwarding module  13  packages chunk payloads as described earlier and sends identical streams of chunk payloads to both working  1  and working 0 copies of the optical switch fabric via internal optics modules (IOMs)  14 - 0 W 0  through  14 -NW 1  (see  FIG. 1B ), which encapsulates the chunk payloads into chunks. Working 0 copy of the optical switch fabric (see  FIG. 1B ) includes internal optics modules  14 - 0 W 0  and  14 - 1 W 0 , optical switch modules  15 - 1  through  15 - 6 , and internal optics modules  17 - 0 W 0  and  17 - 1 W 0 , whereas working 1 copy of the optical switch fabric includes internal optics modules  14 - 0 W 1  and  14 - 1 W 1 , optical switch modules  16 - 1  through  16 - 6 , and internal optics modules  17 - 0 W 1  and  17 - 1 W 1 . For example, IOM  14 - 0 W 0  and IOM  14 - 0 W 1  each receive simultaneous sequences of chunk payloads from each packet forwarding module  13  that is transmitting through those two IOMs. Similarly, on the egress side each packet forwarding module  18 - 0  through  18 -N (see  FIG. 1C ) receives a simultaneous sequence of chunk payloads from IOMs  17 - 0 W 0  and  17 - 0 W 1 , for example. In error-free normal working operation of both optical switch fabrics, the simultaneous sequences of chunk data delivered to each packet forwarding module are identical. In the event of a failure of any kind, either within a chunk or across multiple chunks on either copy zero or copy one of the optical switch fabric, the affected IOM is able to detect that failure based on comparison of the received FEC check sums with the calculated FEC check sums. When a failure on a particular chunk from either working zero or working one copy of the optical switch fabric is detected, the IOM inserts a failure indication downstream toward PFMs  18 . This forces PFM  18  to select the error-free chunk data from the alternate copy of the optical switch fabric. This can be done individually for each chunk payload delivered to a particular PFM. 
     Note that while embodiments of the invention have been described in terms of two SONET standards namely OC48 and OC192, alternative implementations of router  10  having an appropriate facility module can operate under other standards. 
     Embodiments according to the present invention are designed to protect against all single fault occurrences. Single faults include a single fault of a module, a single fault of a cable, or a single fault of a path. Accordingly, although some double faults are protected against, double faults generally lie beyond the scope of principal objects of the present invention and thus are not in general protected against. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.