Patent Publication Number: US-2012030372-A1

Title: Redundant ethernet connection system and method

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to communications and, in particular, to providing redundant Ethernet connections. 
     Control systems typically include multiple nodes. These nodes are typically in communication with one another, either directly or indirectly. One communication approach is to couple the node together through an Ethernet. 
     Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name came from the physical concept of the ether. The Ethernet protocol defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model as well as a common addressing format and Media Access Control at the Data Link Layer. 
     In today&#39;s environment there is much concern for redundancy to keep facilities that employ control systems up and running. This is an area of prime importance as the cost of downtime and lost production can often times make the difference between profit and loss. Communications connection redundancy is one area of prime importance because communication is the backbone of any effective control system. Accordingly, some or all devices in a control system may be coupled together by two different Ethernets. Stated differently, each device may be coupled to two different Ethernet switches, each of which is connected to a different Ethernet. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a system including redundant communication paths is disclosed. The system includes a first communication network including a first switch and a second switch connected to the first switch and a second communication network including a third switch and fourth switch coupled to the third switch. The system also includes a first computing device coupled to the first communications network through a first network interface controller (NIC) and coupled to the second communication network through a second NIC. The first computing device is configured to communicate through the first NIC first communication network until it determines that it is not receiving bridge protocol data units (BPDUs) and then to communicate through the second NIC. 
     According to another aspect of the present invention, a method of operating a control system is disclosed. The method of this embodiment includes monitoring communications at a first computing device received through a first network interface controller; determining that the first computing device is not receiving bridge protocol data units (BPDUs); and switching operation of the first computing device such that it receives communications through a second network interface controller different than the first network interface controller. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a block diagram of a system according to one embodiment; and 
         FIG. 2  is a flow chart showing a method according to one embodiment. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an example of a redundant control system  100  according to one embodiment. The redundant control system  100  (control system) includes at least two communication networks  102  and  104 . As shown, each communication network includes three switching devices (switches). Of course the number of switches forming the communication networks  102  and  104  is not limited to three and may include any number equal to or greater than two. 
     In the example redundant control system  100  shown in  FIG. 1 , the first communication network  102  includes a first switch  106 , a second switch  108  and a third switch  110 . The first switch  106  may be coupled to the second switch  108  by a first communication cable  107  and the second switch  108  may be coupled to the third switch  110  by a second communication cable  109 . 
     Similarly, the second communication network  104  includes a fourth switch  112 , a fifth switch  114  and a sixth switch  116 . The fourth switch  112  may be coupled by a third communications cable  113  to the fifth switch  114  and the fifth switch  114  may be coupled to the sixth switch  116  by a fourth communications cable  115 . Of course, in one embodiment, one or more of the communications cables  107 ,  109 ,  113  or  115  may be replaced by a wireless communication device. 
     Each switch may be able to receive data packets from other switches it is directly coupled to, inspect them and pass them on to the next switch. Of course, if the switch is coupled to the desired destination device (e.g., a particular computer), the switch does not pass the information on. Rather, it provides packets to the destination device coupled to it. 
     In one embodiment, the communication networks  102  and  104  may be Ethernet communication networks. Of course, the communication networks  102  and  104  could be other types of communication networks including, for example, a local area network, a wide area network, an intranet or a wireless communication network. 
     In one embodiment, the first communication network  102  may be coupled to the second communication network  104  via a crossover cable  118 . In one embodiment, the wires in the crossover cable  118  are “crossed” so that output signals from the transmitting device are properly sent as input signals to the receiving end and vice versa. In this manner, all communications on the first communication network  102  may be replicated on the second communication network  104  and vice versa. 
     The first switch  106  and the fourth switch  112  may be coupled to a first computing device  118 . In one embodiment, the first computing device  118  is coupled to the first switch  106  via first network interface controller (NIC)  122 . In this embodiment, a second NIC  124  couples the first computing device  118  to the fourth switch  112 . A network interface controller (NIC) is a hardware device that handles an interface to a computer network and allows a computing device to access that network. In this manner, the first computing device  118  is coupled to both first communications network  102  and the second communications network  104 . 
     The redundant control system  100  may include any number of computing devices coupled to the first and second networks. As illustrated in  FIG. 1 , a second computing device  126  and a third computing device  132  are provided. Similar to the first computing device  120 , the second computing device  126  and the third computing device  132  may both include at least two NICs. In particular, the second computing device  126  includes a third NIC  128  connected to the first communication network  102  via the second switch  108  and a fourth NIC  130  connected to the second communication network  104  via the fifth switch  114 . Similarly, the third computing device  132  includes a fifth NIC  134  connected to the first communication network  102  via the third switch  110  and a sixth NIC  136  connected to the second communication network  104  via the sixth switch  114 . 
     The computing devices  120 ,  126  and  132  may be any type of computing device. For example, the computing devices may be a computer or computing platform, and may include a terminal, wireless device, information appliance, device, workstation, mini-computer, mainframe computer, personal digital assistant (PDA) or other computing device. It shall be understood that the computing devices may include multiple computing devices linked together by a communication network. For example, there may exist a client-server relationship between two devices and processing may be split between the two. In one embodiment, the first computing device  120  may provide a human-machine interface (HMI) to a control system for operating a process. In one embodiment, the second computing device  126  is connected to a turbine and the third computing device  132  is connected to an exciter. 
     In one operation, the first computing device  120  communicates over only one of the NICs  122  and  124 . That is, the first computing device  120  is limited to communicating only over one NIC. The first computing device  120  may make a random decision as to which NIC to communicate over. The first computing device  120  does not typically change the NIC being utilized. 
     In one embodiment, one of the switches may be designated as the spanning tree root bridge under the spanning tree protocol. The spanning tree protocol allows a network design to include spare (redundant) links to provide automatic backup paths if an active link fails, without the danger of bridge loops, or the need for manual enabling/disabling of these backup links. Switches that may operate the spanning tree protocol include algorithms for electing one of the servers as the root bridge. The root bridge server periodically broadcasts spanning tree protocol packets. The packets are typically referred to as BPDUs (bridge protocol data units). 
     According to one embodiment, in the event that the first computing device  120  determines that it is not receiving the BPDUs, it switches the NIC it is communicating through. For example, in the embodiment illustrated in  FIG. 1 , if the first computing device  120  is communicating through the first NIC  122  and the fourth switch  112  fails, there is no way it can receive the BPDUs. Accordingly, the first computing device  120  will switch to an operating mode where it communicates through the second NIC  122 . In one embodiment, the second computing device  126  and third computing device  132  may communicate though one or more NICs simultaneously. Of course, in the event that the first computing device  120  includes more than two NICs, the computing device may select NICs until it begins to receive BPDUs. 
     It shall be understood that while the terms “first,” “second” and the like have been used to distinctly identify certain devices in the system  100 , in the appended claims, the ordering and naming of certain devices may vary depending on the context. 
       FIG. 2  is a block diagram showing a method according to one embodiment of the present invention. The method shown assumes that the first computing device  120  ( FIG. 1 ) is currently communicating to at least one other computing device through a redundant communication system. At block  202 , the first computing device, which is communicating through one of its NICs, is monitoring the communications it receives. At block  204 , the first computing device determines if BPDUs are being received. This may include monitoring communications for several predetermined time periods in which a BPDU would be expected. If one or more BPDUs are received, processing returns to block  202 . Otherwise, at block  206  the first computing device switches from the NIC it is currently communicating on to another of the NICs it contains. Processing then returns to block  202 . 
     In support of the teachings herein, various analysis components may be used, including digital and/or an analog system. The system may have components such as a processor, storage media, memory, input, output, communications link (wired, wireless, pulsed mud, optical or other), user interfaces, software programs, signal processors (digital or analog) and other such components (such as resistors, capacitors, inductors and others) to provide for operation and analyses of the apparatus and methods disclosed herein in any of several manners well-appreciated in the art. It is considered that these teachings may be, but need not be, implemented in conjunction with a set of computer executable instructions stored on a computer readable medium, including memory (ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, hard drives), or any other type that when executed causes a computer to implement methods of the present invention. These instructions may provide for equipment operation, control, data collection and analysis and other functions deemed relevant by a system designer, owner, user or other such personnel, in addition to the functions described in this disclosure. Accordingly, the present invention may include switching the operation of a computing device in a redundant computing system such that it communicates on a different NIC when it is determined that the computing device is not receiving BPDUs. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.