Abstract:
A system and method for connecting traffic along a communications network is accomplished by rerouting traffic upon the detection of a fault condition along a primary connection path. Signals are divided into different wavelength regions labeled red and blue, respectively. The wavelength bands between transmit and receive channels are alternated between red and blue band regions and then combined, multiplexed or “bundled” together by a wideband wavelength division multiplexer in a single non wavelength specific transmission medium for connection to a single uni-directional Optical Cross Connect System (OCCS) port. Additionally, the receiving end of a single medium is connected to a wavelength division multiplexer which unbundles the combined red and blue band signals upon reception.

Description:
RELATED APPLICATIONS 
     This application is a Continuation-in-Part application of U.S. patent application serial No. 08/707,440, filed Sep. 4, 1996, entitled OPTICAL COMMUNICATION SYSTEM, now U.S. Pat. No. 5,933,258. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to communications systems and specifically to fault tolerant fiber optic communication networks. 
     2. Description of the Related Art 
     Fiber optic communication systems are traditionally deployed in a point-to-point terminal configuration along a single path. A problem occurs if the connection path is somehow interrupted either due to equipment failure or a physical disruption in the connection. 
     Sonet self healing ring architectures may be a solution that protects against service disruption and node failure along a given primary path. Referring to FIG. 1, a ring architecture is presented, with nodes  120 ,  130 ,  140  and  150  all residing on ring  110 . If a message to be transmitted from node  150  to node  130  clockwise along path A-B of ring  110  cannot be completed due to a failure in path B, then the message is routed counter-clockwise along alternate path D-C. In fact, in this architecture messages from node  120  intended for any node are also routed counter-clockwise to the intended destination node. 
     Drawbacks to the above system include the requirement for having expensive add/drop multiplexers and associated support equipment present in each node. 
     Most installed networks are point-to-point systems. Balancing traffic around a ring can be difficult. Further, managing an all-ring network and provisioning demands across several interconnected rings is more difficult and expensive than in a point to point network. 
     There is accordingly a need for a new method and apparatus for inexpensively and easily rerouting traffic between nodes in a communication network when a given path becomes unusable in order to solve or ameliorate one or more of the above-described problems. 
     SUMMARY OF THE INVENTION 
     According to a preferred embodiment of the present invention, a system and method for connecting traffic along a communications network is accomplished by rerouting traffic upon the detection of a fault condition along a primary connection path. 
     In an embodiment of the present invention, wavelengths are divided into different regions labeled red and blue, respectively. The wavelength bands between transmit and receive channels are alternated between red and blue band regions and then combined, multiplexed or “bundled” together by a non wavelength specific wideband wavelength division multiplexer in a single transmission medium for connection to a single uni-directional Optical Cross Connect System (OCCS) port. The different number of regions may be any even number of regions as long as the wavelengths are alternated. 
     Additionally, the receiving end of a single medium is connected to a wavelength division demultiplexer which unbundles the combined red and blue band signals upon reception. 
     In other words, a red band signal is bundled with a blue band signal for transmission through a single medium where it is received and then unbundled into its red and blue components by a wavelength division multiplexer at the receiver. 
     An analogous method and apparatus is used to transmit a signal in the opposite direction when and if required for full duplex operation. 
     Further features of the above-described invention will become apparent from the detailed description hereinafter. 
     The foregoing features together with certain other features described hereinafter enable the overall system to have properties differing not just by a matter of degree from any related art, but offering an order of magnitude more efficient use of processing time and resources. 
     Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate preferred embodiments of the apparatus and method according to the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a prior art self healing ring architecture. 
     FIG. 2 illustrates a block diagram of a minimized rerouting switch of the present invention. 
     FIG. 3 illustrates a block diagram of a wavelength division multiplexer. 
     FIG. 4 illustrates a flowchart of the method of operation of rerouting a signal. 
     FIG. 5 is a more detailed block diagram of the system block diagram of the present invention. 
    
    
     Note that generally the first digit of an item corresponds to the first figure in which that item is illustrated. 
     DETAILED DESCRIPTION 
     Referring now to FIG. 2, communications system  200  includes Node 1   210  and Node 2   212  connected via communication link  244 , which in the preferred embodiment is a fiber optic connection with its associated switching components (not shown). 
     Node 1   210  and Node 2   212  are also operably connected by redundant communication links  235 , 236 . Optical cross connect switches (OCCS)  238 , 240  are placed in the connection path. OCCS  238  is associated with Node 1   210  and OCCS  240  is associated with Node 2   212 . OCCSes  238 , 240 , typically 16×16 mechanical fiber optic switches in a preferred embodiment, serve to switch traffic among a number of desired routes via various fiber optic paths physically connected to each OCCS output port (not shown). The OCCSes need not be mechanical and may be M×N sized. 
     Connected between Nodes  210 , 212  and OCCSes  238 , 240  are wavelength division multiplexers  232 , 234 . Wavelength division multiplexers  232 , 234  serve to bundle  2  or more signals from distinct fiber optic cables into a single cable prior to entry into the OCCS. As the OCCS is an expensive device with finite capacity, bundling is desirable as it at least doubles the capacity of a port of the OCCS. Wavelength division multiplexers  232 , 234  are bi-directional devices which transmit and receive in opposite directions along separate fiber cables. Forward signals of a given wavelength λ 1    216  (red) and λ 2    218  (blue) are transmitted from Node 1   210  to wavelength division multiplexer  232  where they are bundled together for transmission to OCCS  238 , transmitted to OCCS  240  via fiber optic cable  236 . The bundled signal is then routed to wavelength division multiplexer  224 , where it is unbundled into its constituent components λ 1    222  (red) and λ 2    228  (blue) for transmission to Node 2   212 . 
     Only 2 nodes and a single matched pair of OCCSes are shown for simplicity. Any number of nodes, wavelength division multiplexers and OCCSes with associated cabling may be used. 
     Control routing information is provided to each component over a data control link  242 , 246 , 248 , 250  from an external control source, or may be supplied from in-band signalling. The link may be any type of central or distributed control architecture. In the preferred embodiment, an X.25 distributed link is used to reduce the possibility of catastrophic single point failures. However, it is possible to collocate the control source with the individual component to be controlled. 
     The return communication process system will now be described. Such a process would be included in a full duplex communication system, for example, as well as with other communication system types. 
     Signals λ 3    226  red and λ 0    224  blue are transmitted from Node 2   212  to wavelength division multiplexer  234  where they are bundled into a composite signal, and transmitted on fiber optic cable to OCCS  240  where it is switched onto cable  235 . Communication link  235  is routed to OCCS  238  where the signal is switched and routed to wavelength division multiplexer  232 , unbundled into constituent components, λ 3    220  and λ 4    219  before being sent to Node 1   210 . 
     Again, control and routing information is provided in an analogous manner as with the forward connection path. 
     Referring now to FIG. 3, the block diagram of a wavelength division multiplexer  300  will now be described. Signals intended to be sent in a forward direction are sent in fiber optic inputs  302 , 304 . Fiber optic inputs  302 , 304  are wavelength translated in first and second wavelength converters  306 , 308 , respectively, set to a predetermined wavelength (frequency). If either input  302 , 304  does not need to have its wavelength translated, then the wavelength converter is set appropriately. The translated input signals are then sent along path  314 , 316  to optical combiner  318  where the signals are summed. The resultant bundled signal is output from the wavelength division multiplexer along fiber optic path  320 . 
     As the wavelength division multiplexer is a bi-directional device, it is capable of handling communication signals along a two way path. In an analogous fashion, signals intended to be sent in a reverse direction are input in fiber optic inputs  322 , 324 . Fiber optic inputs  322 , 324  are wavelength translated in third and fourth wavelength converters  326 , 328 , respectively, set to a predetermined wavelength (frequency). If either input  322 , 324  does not need to have its wavelength translated, then the wavelength converter is set appropriately. The translated input signals are then sent along path  334 , 336  to optical combiner  338  where the signals are summed. The resultant bundled signal is output from the wavelength division multiplexer along fiber optic path  340 . 
     Referring now to FIG. 4, flowchart  400  depicts the method of operation of the instant invention. In step  410 , a fault along main communication path  244  (FIG. 2.) has been detected by an external detection device and a signal indicating the requirement,for rerouting optionally is sent to Nodel  210  and wavelength division multiplexers  232 , 234 . However, in a preferred embodiment of the present invention, the, rerouting information need only be sent to OCCSes  238 , 240 . An appropriate communication routing path is then configured according to a predetermined algorithm delivered from an external source along communication paths  242 , 244 ,  246 , 248 . 
     In step  420 , forward signals of a given wavelength λ 1    216  (red) and λ 2    218  (blue) are transmitted from Node 1   210  to wavelength division multiplexer  232  where they are bundled in step  430  together for transmission to OCCS  238 , transmitted to OCCS  240  in step  440  via fiber optic cable  236 . In step  450 , the bundled signal is then routed to wavelength division multiplexerr  234  where it is unbundled into its constituent components λ 1    222 (red) and λ 2    228  (blue) for transmission to Node 2   212 . 
     In step  460 , the process is repeated in an analogous fashion with similar references to the reverse channel depicted in FIG. 2 if it is decided that a full-duplex or a return channel is desired. 
     FIG. 5 illustrates another embodiment of the present invention in which the red band is defined to be approximately 1547.5-1561.0 nm and the blue band is defined to be approximately 1527.5-1542.5 nm. 
     Line Terminating Equipment  502 , 504  (LTE), for example, Nortel S/DMS OC-12, OC-48 or OC-192 are connected via main connection path  554  which utilizes wavelength division multiplexers  516 , 518 , 520 , 522  and OCCSes  524 , 526  in a manner similar to that described above with respect to FIG.  2 . The main difference is that LTE  502 , 504  has already delivered the signals already in the red and blue band wavelengths so that no signal conversion is required. At LTE  502  red and blue forward transmit signals are bundled together by wavelength division multiplexer  516 , and switched in OCCS  524  for transmission over link  554 , switched at OCCS  526 , unbundled by wavelength division multiplexer  522  for reception at LTE  504 . 
     Likewise, LTE  504  transmits return red and blue transmit signals which are bundled by wavelength division multiplexer  520 , switched by OCCS  526 , transmitted on link pair  554 , switched by OCCS  524  and unbundled by wavelength division multiplexer  518  before transmission to LTE  502 . 
     Upon a failure reported for any portion of link pair  554 , traffic is rerouted between LTEs  502 , 504  through OCCSes  524 , 526 , 546 . Note that the addition of OCCS  546  allows illustration of alternate routing through other portions of the network and re-use of alternate paths for: different nodes in the network which are not shown. 
     Control and predetermined routing information is again supplied from an external source through control links labeled C. 
     Note that wavelength division multiplexers  528 , 530 , 532 , 534 , 540 , 542 , 548 , 550  along with optical repeaters  536 , 538 , 544 , 552  are used if signal regeneration across a long distance is required. Such components may be eliminated or replaced with more expensive wideband optical repeaters when feasible. 
     Other such embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is readily apparent that the above described invention may be implemented in any type of fiber optic communication system including both Asynchronous and Synchronous Optical Network (SONET) configuration with any number of underlying transmission protocols such as Asynchronous Transfer Mode, (ATM). However, it is intended that the above described invention has applications in any type of communication system through any type or combination of transmission media or with any compatible protocol. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.