Abstract:
An optical node capable of automatically detecting its interconnectivity is disclosed. The node includes a light switch, a light source, light detector, a control circuit having a unique identification. The node sends its identification via each of its ports and also listens to each of its ports for identification from other nodes. The node may store the interconnectivity information, forward the interconnectivity information to another node, or forward the interconnectivity information to a path router.

Description:
BACKGROUND  
         [0001]    The present invention relates to the art of data networks. More particularly, the present invention relates to data networks using optical switches.  
           [0002]    Because of ever increasing bandwidth requirements, data networks utilizing optical transmission systems are becoming popular. Optical transmission systems have a larger bandwidth compared to electrical transmission systems.  
           [0003]    [0003]FIG. 1 illustrates a simplified optical switching network  100  including a plurality of input lines represented by lines  102   a ,  102   b , and ellipsis  102   c  (collectively, “ 102 ”) and a plurality of output lines represented by lines  104   a ,  104   b , and ellipsis  104   c  (collectively, “ 104 ”). In the network  100 , three +optical nodes NA  110 , NB  120 , and NC  130  are illustrated. Although only three nodes are shown, the switching network  100  may include hundreds or even thousands of interconnected optical nodes.  
           [0004]    Node NA  110  has an optical switch  112 , a control circuit  114 , and a plurality of input lines and output lines, or ports, designated, for convenience, NA 0  to NAn where n is an integer. Typical values for n may be 15, 63, or 255. The ports—NA 0 , NA 1 , . . . and NAn—are ports of the node NA  110  as well as the ports of the switch  112 . The switch  112  may utilize micro mirrors, liquid, or gaseous elements (generically, “switching element”) to direct or reflect optical signals from a first port to a second port. Typically, the ports are bi-directional but is sometimes uni-directional. The control circuit  114 , connected to the switch  112 , controls the state of the switching elements to implement Node NA  110  as described herein above is known in the art.  
           [0005]    Nodes NB  120  and NC  130  are similarly configured to node NA  110 , and their ports are similarly denoted herein. A path router  140  is connected to nodes NA  110 , NB  120 , and NC  130 . The path router  140  contains physical path topology of the network  100  necessary to make connections as requested. The path router  140  contains the physical network topology of how the switches are connected.  
           [0006]    For instance, in order for the path router  140  to successfully direct an input signal at input line  102   b  to an output line  104   b , the path router  140  needs to know that (1) the input line  102   b  feeds into port NA 7 ; (2) port NA 9  is connected to port NB 1 ; (3 port) NB 8  is connected to port NC 7 ; and (4) port NC 9  is connected to the output line  104   b . With the information, the path router  140  signals node NA  110  to route its port NA 7  to its port NA 9 , signals node NB  120  to link its port NB 1  to its port NB 8 , and signals node NC  130  to link its port NC 7  to its port NC 9 . The physical path topology information may be entered directly into the path router  140  or supplied by an external controller system (not shown), connected to the path router  140 .  
           [0007]    In the illustrated configuration, port NA 9  is connected to port NB 1  (connection  150 ) and port NB 8  is connected to port NC 7  (connection  152 ). The other ports of nodes NA  110 , NB  120 , and NC  130  may be connected to ports of nodes not show in FIG. 1. As the number of nodes, thus the ports, grows in the network  100 , the number of possible connections grows exponentially. It is not uncommon to have a network with hundreds or even thousands of ports. Prior art requires that the physical topology be configured manually.  
           [0008]    Without a correct topology of the network  100  as defined by the connection information of the routing table, the network  100  does not operate effectively.  
           [0009]    The processes of manually defining the full network physical path topology for the path router  140  are susceptible to error. For example, an optical path can be made to an unintended port or to an unintended node. Or, incorrect data may be entered into the path router  140 . The problem is exacerbated by the fact that networks are becoming increasingly large and complex.  
           [0010]    Moreover, when new nodes are installed, connections are modified, or when error in connection information is suspected, the entire network must be manually analyzed, and the topology manually reconfigured. No dynamic or automated procedure exists to determine the network topology.  
           [0011]    Accordingly, there remains a need for an improved technique to determine the connections and topology of an optical network.  
         SUMMARY  
         [0012]    These needs are met by the present invention.  
           [0013]    According to one aspect of the present invention, an apparatus has an optical switch for routing optical signals, the optical switch including ports. The apparatus also includes a light source, a light detector, and a control circuit connected to the optical.  
           [0014]    According to a second aspect of the invention, an optical network including a plurality of optical nodes is disclosed. A node includes an optical switch for routing optical signals, the optical switch including ports. Further, the node has a light source, a light detector, and control circuit connected to the optical switch.  
           [0015]    According to a third aspect of the invention, a method of determining topology of a network is disclosed. First, connection information of a first port of a first node is determined. Then, a path router is updated with the connection information.  
           [0016]    According to a fourth aspect of the invention, a method of discovering an optical interconnect path is disclosed. First, a first identification is sent from a first port of a first node. Then, the first identification is received at a first port of a second node. The interconnect path is the between the first port of the first node and the first port of the second node.  
           [0017]    Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in combination with the accompanying drawings, illustrating by way of example the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a simplified illustration of an optical network including prior art optical nodes; and  
         [0019]    [0019]FIG. 2 is a simplified illustration of an optical network according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0020]    As shown in the drawings for purposes of illustration, the present invention is embodied in an optical node apparatus having an optical switch for routing optical signals, the optical switch including ports. The apparatus also includes a light source, a light detector, and a control circuit connected to the optical switch. The optical node sends its node identification via each of its ports, and also listens to each of its ports to detect node id&#39;s from other optical nodes connected to the optical node.  
         [0021]    Referring to FIG. 2, an optical network  200  includes a plurality of optical nodes. For brevity, only three nodes are shown in FIG. 2. They are, node ND  210 , node NE  220 , and node NF  230 . The network  200  includes a plurality of input lines represented by lines  202   a ,  202   b , and ellipsis  202   c  (collectively, “ 202 ”) and a plurality of output lines represented by lines  204   a ,  204   b , and ellipsis  204   c  (collectively, “ 204 ”). Although only three nodes are shown, the switching network  200  may include hundreds or even thousands of interconnected optical nodes.  
         [0022]    Node ND  210  has an optical switch  212 , a control circuit  214 , and a plurality of input lines and output lines, or ports, designated, for convenience, ND 0  to NDn where n is an integer. Typical values for n may be 15, 63, or 255. For brevity, the ports of node ND  210  are referred to, collectively, as ports  211 . For the illustrated embodiment, the ports  211  are ports of node ND  210  as well as ports of the switch  212 . The switch  212  may utilize micro mirrors, liquid, or gaseous elements (collectively, “switching element”) to direct or reflect optical signals from a first port to a second port.  
         [0023]    A light source  216  is connected to one of the ports  211  of the switch  212 . The light source  216  may be modulated to produce a light signal, which may be routed to any of the ports of the switch  212 . A light detector  218  is connected to another port of the switch  212 . The light detector  218  may be connected to any of the ports  211  of the switch  212  to detect light signal on the connected port. In the current technology, light sources may be implemented using or laser diodes. The light detectors may be implemented as photodiodes or phototransistors for example.  
         [0024]    Semiconductor light sources and detectors are well known in the industry and can be easily obtained from various manufacturers, for example, Agilent Technologies, Inc.  
         [0025]    The control circuit  214 , connected to the switch  212 , controls the state of the switching elements to implement routing of the optical signals from a first port to a second port. For instance, the control circuit  214  may cause the switch  212  to connect port ND 1  to port ND 9  to route an incoming optical signal from line  202   b , connected to port ND 1 , to be routed to port ND 9  for forwarding to port NE 1  of node NE  220 .  
         [0026]    The control circuit  214  may include a node id (for example, “ND”) for node ND  210 . Preferably, the node id uniquely identifies node ND  210  within the network  200 . The control circuit  214  is also connected to the light source  216  and the light detector  218 . Alternatively, the node id may be supplied by the path router as needed. The node id may further include a port identification portion that identifies the port (of the node) through which the communication is taking place.  
         [0027]    Node NE  220  is similarly configured to node ND  210  and has switch  222 , ports NEO through NEN (collectively, ports  221 ), light source  226 , light detector  228 , and control circuit  224 . The control circuit  224  is connected to the switch  222 , the light source  226 , and the light detector  228 , and has a node id (for example, “NE”) for node NE  220 .  
         [0028]    The technique of determining the topology, or the connection information, of network  200  can be explained using nodes NE  220  and ND  210 . Control circuit  224  causes light detector  226  to produce optical signals (“identification signal”) identifying node NE  220  such as signal corresponding to node id “NE”. The identification signal may be sent to each of the ports  221  by routing, using switch  222 , the identification signal to each of the ports  221 . Preferably, the identification signal also includes information regarding which port of node NE  220  the identification signal is being sent from.  
         [0029]    The identification signal is received by node ND  210 . Control circuit  214  of node ND  210  causes light detector  218  to receive optical signals from each of ports  211  of node ND  210 . When light detector  218  is connected to port ND 9 , light detector  218  receives the identification signal from port NE 1  of node NE  220 . The received identification signal is forwarded to control circuit  214 . With the received identification signal, control circuit  214  recognizes that its port ND 9  is connected to port NE 1  of node NE  220  and stores this connection information, forwards the connection information to a path router  240  to update the path router  240 , or both. The connection is illustrated by connection  250  in FIG. 2. Additionally, control circuit  214  may send the connection information to another node, not shown, such that the other node is informed about the connection  219 .  
         [0030]    Based on the available paths, the path router  240  can then make optical path connections as requested.  
         [0031]    The path router  240  may include the following components: (1) information on the physical path topology; (2) Switch configuration (number of ports, etc.); and (3) current list of requested optical path connections including dynamic requests to change optical paths. These requests need not know the physical topology of the network but rather specification of the endpoint to endpoint connection. The path router  240  maps the optical path connection requests to physical switch changes based upon the physical topology. The word “connection” includes, without limitation, relatively static port to port switch connections as well as the physical network topology, or how the switches are physically connected.  
         [0032]    The process also works in reverse. That is, node ND  210  sends its node identification “ND” via its ports  211  as identification signal. When the identification signal is sent on port ND 9 , node NE  220  detects the identification signal, recognizes that its port NE 1  is connected to port ND 9  of node ND  210 , and stores this connection information. The connection information is then reported to the path router  240 .  
         [0033]    Therefore, under the present invention, the topology of the network is dynamically determined using self-identifying nodes such as node ND  210  and node NE  220 . In one embodiment of the present invention, all nodes of the network  200  are similarly configured to illustrated nodes ND  210  or NE  220 . However, this is not required. In the network  200 , node NF  230  does not include a light source or a light detector; however, its route topology may be manually entered into the path router. In the case that such node is connected to nodes with node identification capability, such topology may be found.  
         [0034]    The connection information detection may be performed for unused ports. That is, for the ports for which no connection information exists. Alternatively, the connection information detection may be performed even for used ports using supervisory channels or bands.  
         [0035]    The path router  240  may maintain the connection information in a routing table. Alternatively, the connection information may be maintained in a distributed manner by the nodes themselves.  
         [0036]    From the foregoing, it will be appreciated that the present invention is novel and offers advantages over the current art. The present invention results in an automatic determination of connection information in an optical network, the connection information being less susceptible to errors. Although a specific embodiment of the invention is described and illustrated above, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. For example, each optical node such as node ND  210  may include a plurality of light sources, a plurality of light detectors, or both. Alternatively, light source  216  may be built outside the node  210  with the identification signals being sent to the node via one of the ports. Likewise, light detector  218  may be located outside the node  210  with the light signals being sent out to the external light detector for processing. The invention is limited only by the claims that follow.