Abstract:
A system and method is provided which describe a self-healing bidirectional lines switch ring (BLSR) communication node. Two interconnected relay elements, having default and duplex input and output ports, enable bidirectional communications through a node. In the event of a ring failure, the relays can be enabled to return communications to a source node so that the ring remains unbroken.

Description:
RELATED APPLICATIONS 
   This application contains material related to the following commonly assigned U.S. patent applications incorporated herein by reference:
         Ser. No. 09/753,135 filed 2 Jan. 2001 for “SYSTEM AND METHOD FOR REDUNDANT PATH CONNECTIONS IN DIGITAL COMMUNICATIONS NETWORK”;   Ser. No. 09/753,134 filed 2 Jan. 2001 for “SYSTEM AND METHOD FOR DIAGNOSTIC MULTICAST SWITCHING”.       

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to bidirectional line switch ring (BLSR) communications and, more particularly, to a system and method for using integrated circuit (IC) relay devices in the formation of a self-healing BLSR network. 
   2. Description of the Related Art 
     FIG. 1   a  is a schematic block diagram of a bidirectional line switch ring (prior art). Communications networks often connect nodes with bidirectional communications, to form a ring of nodes. One well-known example is the synchronous optical network (SONET). Bidirectional line switch rings are a method of SONET transport where part of the communications are sent clockwise over a first fiber and the rest of the communications are sent counter-clockwise over a second fiber. 
     FIG. 1   b  is a schematic block diagram of  FIG. 1   a  where the ring has been broken due to a faulty fiber or broken node (prior art). Protection fibers  10  and  12  are shown that heal the ring by permitting communications to travel around the ring in the opposite direction. 
   Protection fiber systems can be enabled in software, however, the solution is complex and requires a complete knowledge of the network fiber system before installation. Alternately, redundant nodes can be provided in the network. However, the hardware can be expensive. Further, the solutions must be done at the box or system level. This type of redundancy can be a problem where space and power consumption are concerns. There is no standard practice redundancy practice in the implementation of BLSR networks. 
   It would be advantageous if a healing function could be easily implemented in ring network architecture. 
   It would be advantageous if the BLSR healing function could be implemented at the IC level to save space and switching complexity. 
   SUMMARY OF THE INVENTION 
   This invention is an IC relay device system that makes use of programmable features that allow the user to set the active data paths through the device and to monitor the possible data paths for integrity. In addition to this, it is possible to connect any input data path to any output data path while selectively bypassing the internal circuitry, to aid in network diagnostics as well as board level debug operations. More specifically, the invention has two identical inputs and two identical outputs, as well as two main blocks within the device, one for encoding and one for decoding. The input, output, and block connects are programmable. In one aspect of the invention, the relay devices are programmed to be a self-healing BLSR. If the transmit part of a ring breaks, the device can close the return path so that there is always a return connection in the network. 
   A method is also provided for forming a bidirectional line switch ring (BLSR) using a pair of integrated circuit (IC) digital communication relay devices. The method comprises: receiving bidirectional communications; for each relay device, selecting an input path to accept the received communications; and, for each relay device, selecting an output path to supply bidirectional communications. More specifically, the method comprises: selecting a mode of operation; and, selectively connecting the default and duplex input paths, for each relay device, in response to selecting the mode of operation. Additional details of the BLSR system and method follow. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1   a  is a schematic block diagram of a bidirectional line switch ring (prior art). 
       FIG. 1   b  is a schematic block diagram of  FIG. 1   a  where the ring has been broken due to a faulty fiber or broken node (prior art). 
       FIG. 2  is a detailed schematic block diagram of the present invention IC relay device. 
       FIG. 3  is a schematic block diagram of the present invention BLSR system using a pair of IC relay devices. 
       FIG. 4  is a diagram illustrating a digital wrapper or frame structure in which communications are embedded. 
       FIG. 5  is a flowchart depicting a method of forming a bidirectional line switch ring (BLSR) using a pair of integrated circuit (IC) digital communication relay devices. 
       FIG. 6  is a flowchart depicting a method of forming a BLSR using a pair of IC digital communication relay devices. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2  is a detailed schematic block diagram of the present invention IC relay device. This figure can be consulted for details of the relay node described below. 
     FIG. 3  is a schematic block diagram of the present invention BLSR system using a pair of IC relay devices. The system  100  comprises a first relay  102  and a second relay  104 . The first relay  102  includes an input switch  106  having a default input on line  108  and a duplex input on line  110  to receive communications. The input switch  106  also has a control port on line  112  to accept switch commands and an output on line  114  to supply the selected communications. The first relay also includes a default output on line  116  and a duplex output on line  118  connected to the default input. 
   Likewise, the second relay  104  includes an input switch  120  having a default input on line  122  and a duplex input on line  118  to receive communications. The input switch  120  has a control port on line  126  to accept switch commands and an output on line  128  to supply the selected communications. The second relay  106  has a default output on line  130  and a duplex output on line  110  connected to the default input. 
     FIG. 4  is a diagram illustrating a digital wrapper or frame structure in which communications are embedded. Each frame includes a sub-frame which can be a row, or series of rows. Each row includes sections of overhead bytes, payload bytes, and forward error correction (FEC) bytes. One well-known FEC scheme, the Reed-Solomon (RS), includes coded information. Degraded information in the payload or overhead sections can be recovered using the decoded information in the FEC section. In some aspects of the invention, the received and transmitted communications are typically organized in a digital wrapper or frame structure that includes forward error correction (FEC). 
   The first relay  102  further includes a decoder  140  having a input connected to the input switch output on line  114 . The decoder  140  supplies decoded and corrected communications at a decoder output on line  142 . An encoder  144  has an input connected to the decoder output on line  142 . The encoder  144  supplies encoded communications at an output connected to the first relay default output-on line  116 . 
   Likewise, the second relay  104  includes a decoder  146  having a input connected to the input switch output on line  128 . The decoder  146  supplies decoded and corrected communications at a decoder output on line  148 . An encoder  150  has an input connected to the decoder output on line  140 . The encoder  150  supplies encoded communications at an output connected to the second relay default output on line  130 . 
   As shown in  FIG. 3 , the duplex output of the first relay is connected to the duplex input of the second relay on line  110 . Likewise, the duplex output of the second relay is connected to the duplex input of the first relay on line  118 . 
   In some aspects of the invention, a monitor circuit  160  in the first relay  102  and a monitor circuit  162  in the second relay circuit  104  are used to determine whether the links are healthy. The monitor  160 / 162  may determine health based upon encoded communications received on line  114 / 128 . For example, the decision may be made based on the recognition of overhead bytes or frame synchronization bytes. The FEC communications are monitored for loss of signal, loss of clock, synchronization status (Loss of Frame and Out of Frame), and bit error rates (Signal Fail and Signal Degrade). 
   Alternately, the decision may be based upon information received from the decoder  144 / 146 . For example, the decision may be based upon the number of corrections required in decoding the communications. Monitor  160  also has an external connection on line  164 , and monitor  162  has an external connection of line  166 . In some aspects of the invention, the health decision is made by a device (not shown) external to the relays  102 / 104 . The decision is received via these external connections. 
   When the first, default mode of operation is selected, the bidirectional ring is operating normally. Clockwise communications are passed through first relay  102  and counter-clockwise communications are passed through the second relay  104 . When the first mode of operation is selected, the first relay input switch control port on line  112  accepts a command to select the default input on line  108 . Then, the first relay  102  decodes, encodes, and supplies communications received on the input switch default input to the default output on line  116 . 
   Likewise, the second relay input switch control port accepts a command on line  126  to select the default input on line  122 . The second relay  104  decodes, encodes, and supplies communications received on the input switch default input to the default output on line  130 . 
   When the second mode of operation is selected, the first relay input switch control port accepts a command on line  112  to select the duplex input. The first relay  102  decodes and encodes the communications, and the first relay  102  supplies communications received on the input switch duplex input on line  110  at the default output on line  118 . Likewise, the second relay input switch control port accepts a command on line  126  to select the duplex input on line  118 . The second relay  104  decodes and encodes the communications, and the second relay  104  supplies communications received on the input switch duplex input at the default output on line  110 . 
   Thus, the first relay default input accepts communications on line  108 , and supplies the communications at the duplex output  118 . These communications are “returned” to the source on the default output of the second relay  104  on line  130 . Likewise, the second relay input switch default input accepts communications on line  122 , and supplies the communications at the duplex output on line  110 . These communications are returned to their source on line  116  from the first relay  102 . Alternately, the communications are returned to an intervening relay node and indirectly returned to the source. 
     FIG. 5  is a flowchart depicting a method of forming a bidirectional line switch ring (BLSR) using a pair of integrated circuit (IC) digital communication relay devices. Although the method is depicted as a series of numbered step for clarity, no order should be inferred from the numbering unless explicitly stated. The method begins with Step  200 . Step  202  receives bidirectional communications. Step  204 , for each relay device, selects an input path to accept the received communications for each relay device. Step  206 , for each relay device, selects an output path to supply bidirectional communications for each relay device. 
   In some aspects of the invention, Step  203   a  selects a mode of operation. Step  203   b  selectively connects the default and duplex input paths, for each relay device, in response to selecting the mode of operation. 
   In some aspects, Step  205   a  decodes communications in response to the selecting of an input path. Step  205   b  encodes communications in response to selecting an input path. 
   In some aspects, Step  203   a  selects a first mode of operation. Step  203   b , for each relay device, accepts communications on a default input for each relay device. Step  205   a , decodes the communications. Step  205   b  encodes the communications. Step  205   c  supplies the encoded communications at a default output. 
   In some aspects, Step  203   a  selects a second mode of operation. For each relay device, Step  203   b  accepts communications on a duplex input. Step  205   a  decodes the communications. Step  205   b  encodes the communications. Step  205   c  supplies the encoded communications at a default output. For each relay device, Step  208  connects the default input to a duplex output. Step  210  connects the duplex input of a first device to the duplex output of a second device. Step  212  connects the duplex input of the second device to the duplex output of the first device. 
     FIG. 6  is a flowchart depicting a method of forming a BLSR using a pair of IC digital communication relay devices. The method begins with Step  300 . Step  302  receives a first communication from a first node. In a first mode of operation, Step  304  supplies the first communication to a second node. In a second mode of operation, Step  306  supplies the first communication to the first node. Step  308  receives a second communication from the second node. In the first mode of operation, Step  310  supplies the second communication to the first node. In the second mode of operation, Step  312  supplies the second communication to the second node. 
   In some aspects of the invention, Step  303   a  selectively decodes the first communication. Step  303   b  selectively encodes the first communication. 
   In some aspects of the invention, Step  309   a  selectively decodes the second communication. Step  309   b  selectively encodes the second communication. 
   The advantage of this invention is that it provides the user with the ability to create redundancy in the network, with a minimum of required space, power, and extra equipment. In addition, the invention makes installations easy to diagnose because of the integrated loopback functionality. The configurability offered by the invention allows savings in space, required test equipment, and cost of customer units. An example is presented of two relays connected to provide a redundant path in a ring network. However, the present invention concept, with the addition of other relay units, expands upon the above-described uses for such circuitry. Other variations and embodiments of the invention will occur to those skilled in the art.