Abstract:
Communications interfaces are provided that include a connector port that has housing that defines a plug aperture and at least first through eighth contacts that extend into the plug aperture. These communications interfaces further include an Ethernet interface (e.g., an Ethernet switch) and a multi-drop communication interface (e.g., an RS-485 transceiver). First through fourth conductive paths are provided that electrically connect the respective first through fourth contacts of the connector port to the Ethernet interface. Fifth and sixth conductive paths are provided that electrically connect the respective fifth and sixth contacts of the connector port to the multi-drop communication interface.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application Ser. No. 61/569,385, filed Dec. 12, 2011, the entire content of which is incorporated by reference as if set forth fully herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to communications systems and, more particularly, to local area networks that may be used in applications such as the control of intelligent patching systems and to controllers and communications interfaces that are suitable for use in such local area networks. 
     BACKGROUND 
     Many businesses, government agencies and other organizations employ dedicated communications systems (also referred to herein as “networks”) that enable computers, servers, printers, facsimile machines and the like to communicate with each other through a private network, and with remote locations via a telecommunications service provider. Such communications systems may be hard-wired through, for example, the walls and/or ceilings of a building using communications cables and connectors. Individual communications connectors (which are also referred to herein as “connector ports”) such as RJ-45 style modular wall jacks are mounted in offices and other work areas throughout the building (referred to herein as “work area outlets”). Communications cables provide communications paths from the work area outlets to network equipment (e.g., network switches, servers, memory storage devices, etc.) that may be located in a computer room. 
     A commercial data center is a facility that may be used to run the computer-based applications that handle the core electronic business and operational data of one or more organizations and/or to provide large numbers of users simultaneous, secure, high-speed, fail-safe access to their web sites run by such organizations. These data centers may host hundreds, thousands or even tens of thousands of servers, routers, memory storage systems and other associated equipment. In these data centers, fiber optic communications cables and/or communications cables that include insulated conductive wires are typically used to provide a hard-wired communications system that interconnects the data center equipment. 
     The cables and connectors in conductive wire-based communication systems that are installed in both office buildings and data centers typically include eight insulated conductors (e.g., copper wires) that are arranged as four differential pairs of conductors. Each differential pair may be used to transmit a separate differential information signal. These conductive wire-based communications systems typically use RJ-45 plugs and jacks to ensure industry-wide compatibility. Pursuant to certain industry standards (e.g., the TIA/EIA-568-B.2-1 standard approved Jun. 20, 2002 by the Telecommunications Industry Association), the eight conductors in RJ-45 plug and jack connectors are aligned in a row in the connection region where the contacts of the plug mate with the contacts of the jack.  FIG. 1  is a schematic view of the front portion of an RJ-45 jack that illustrates the pair arrangement and positions of the eight conductors in this connection region that are specified in the type B configuration of the TIA/EIA-568-B.2-1 standard, which is the most widely used configuration. As shown in  FIG. 1 , under the TIA/EIA 568 type B configuration, conductors  4  and  5  comprise differential pair  1 , conductors  1  and  2  comprise differential pair  2 , conductors  3  and  6  comprise differential pair  3 , and conductors  7  and  8  comprise differential pair  4 . Herein, a differential pair of conductors may be referred to simply as a “pair.” 
     In both office network and data center communications systems, the communications cables that are connected to network equipment (e.g., network servers, memory storage devices, network switches, etc.) and to work area outlets may terminate into one or more communications patching systems that may simplify later connectivity changes. Typically, a communications patching system includes one or more “patch panels” that are mounted on equipment rack(s) or in cabinet(s), and a plurality of “patch cords” that are used to make interconnections between patch panel and/or network switch connector ports. As is known to those of skill in the art, a “patch cord” refers to a communications cable that has a connector such as, for example, an RJ-45 plug, on at least one end thereof. A “patch panel” refers to an inter-connection device that includes a plurality (e.g., 24 or 48) of connector ports. Each connector port (e.g., an RJ-45 jack) on a patch panel may have a plug aperture on a front side thereof that is configured to receive the connector of a patch cord (e.g., an RJ-45 plug), and the back end of each connector port may be configured to receive a communications cable. Consequently, each RJ-45 connector port on a patch panel acts to connect the eight conductors of the patch cord that is plugged into the front side of the connector port with the corresponding eight conductors of the communications cable that is terminated into the back end of the connector port. 
     In a typical office network, “horizontal” cables are used to connect each work area outlet to the back end of a respective connector port on one of a first set of patch panels. In an “interconnect” patching system, a single set of patch cords is used to directly connect the connector ports on the first set of patch panels to respective connector ports on a set of network switches. In a “cross-connect” patching system, two sets of patch panels are provided, and standard patch cords are used to connect the connector ports on the first set of patch panels to respective connector ports on the second set of patch panels, while single-ended patch cords (which are also sometimes referred to as equipment cords) are used to connect the connector ports on the second set of patch panels to respective connector ports on the network switches. 
     The connections between the work area outlets and the network switches may need to be changed for a variety of reasons, including equipment changes, adding or deleting users, office moves, etc. In an interconnect patching system, these connections are typically changed by rearranging the patch cords that are connected between the first set of patch panels and the network switches. In a cross-connect patching system, the connections between the work area outlets and the network switches are typically changed by rearranging the patch cords that are connected between the first set of patch panels and the second set of patch panels. Both types of patching systems allow a network administrator to easily implement connectivity changes by simply unplugging one end of a patch cord and then plugging it into a different connector port. 
     So-called “intelligent” patching systems are now available that automatically track and log the connectivity between the connector ports on the network switches and the work area outlets each time the patch cord connections are rearranged. These intelligent patching systems typically use special patch panels and/or patch cords that employ sensors, radio frequency identification tags, serial ID chips and the like to detect patch cord insertions and removals and/or to automatically track patching connections. These systems may further include a plurality of controllers such as rack managers that control operation of the intelligent patching functionality. These controllers may be interconnected via a local area network, and one (or more) of the controllers may act as a master controller (referred to herein as a “network manager”). The network manager may also have a connection to an external controller and/or database such as a system manager computer. 
     SUMMARY 
     Pursuant to embodiments of the present invention, communication interfaces are provided that include a connector port that has a housing that defines a plug aperture and at least first through eighth contacts that extend into the plug aperture. These communication interfaces further include an Ethernet interface (e.g., an Ethernet switch) and a differential multi-drop communication interface (e.g., an RS-485 transceiver). First through fourth conductive paths are provided that electrically connect the respective first through fourth contacts of the connector port to the Ethernet interface. Fifth and sixth conductive paths are provided that electrically connect the respective fifth and sixth contacts of the connector port to the multi-drop communication interface. 
     In some embodiments, the communications interface may also include a multi-drop communication termination that is electrically connected between the fifth and sixth conductive paths. A multi-drop communication termination control circuit may also be provided, and seventh and eighth conductive paths may be provided that electrically connect the respective seventh and eighth contacts to this multi-drop communication termination control circuit. The multi-drop communication termination may be a switch and a resistor that are disposed in series between the fifth and sixth conductive paths. 
     In some embodiments, the multi-drop communication termination control circuit may be a logic circuit that is configured to automatically sense if the multi-drop communication interface is electrically connected to a downstream device via a second communications connector. The multi-drop communication termination control circuit may be configured to close the switch in response to determining that the multi-drop communication interface is not electrically connected to the downstream device via the second communications connector or to open the switch in response to determining that the multi-drop communication interface is electrically connected to the downstream device via the second communications connector. 
     In some embodiments, the communications connector may be an RJ-45 jack, and the Ethernet interface may be an Ethernet switch that includes at least three input/output ports. The first through fourth conductive paths of the RJ-45 jack may be electrically connected to respective first through fourth contacts of a second RJ-45 jack via the Ethernet switch. The fifth and sixth conductive paths may be electrically connected to respective fifth and sixth contacts of the second RJ-45 jack, and the multi-drop communication interface may be connected to the fifth and sixth conductive paths via respective first and second tap lines. 
     According to further embodiments of the present invention, local area networks are provided that include a plurality of controllers. Each of these controllers may include a processor, an input RJ-45 connector port that includes first through eighth contacts, an output RJ-45 connector port that includes first through eighth contacts, an Ethernet interface and a multi-drop communication interface. In these controllers, a first conductive path may connect the fifth contact of the input RJ-45 connector port to the fifth contact of the output RJ-45 connector port and a second conductive path may connect the sixth contact of the input RJ-45 connector port to the sixth contact of the output RJ-45 connector port. In these controllers, the processor is electrically connected to the first through fourth contacts of the input RJ-45 connector port and the first through fourth contacts of the output RJ-45 connector port via the Ethernet interface, and is electrically connected to the fifth and sixth contacts of the input RJ-45 connector port and to the fifth and sixth contacts of the output RJ-45 connector port via the multi-drop communication interface. The local area network further includes a plurality of Ethernet cables. Each of these Ethernet cables may connect the input RJ-45 connector port on a respective one of the controllers to the output RJ-45 connector port on an adjacent controller so that the Ethernet cables connect the controllers in a daisy-chain configuration. 
     In some embodiments, each controller may also include a switch-activated matched termination that terminates a transmission line that includes the first conductive path and the second conductive path to a matched termination. Each controller may also include a multi-drop communication termination control circuit that controls a switch of the switch-activated matched termination. The switch-activated matched termination on each controller may comprise a resistor that is disposed in series with the switch. The Ethernet interface of each controller may be an Ethernet switch, and the multi-drop communication interface of each controller may be a multi-drop communication transceiver. 
     According to still further embodiments of the present invention, controllers are provided that include an input RJ-45 connector port that includes first through eighth input contacts, an output RJ-45 connector port that includes first through eighth output contacts, and a processor that is selectively electrically connected to the first through fourth input contacts and to the first through fourth output contacts. In these controllers, the fifth and sixth input contacts may be electrically connected to the fifth and sixth output contacts, and the processor may be electrically connected to the fifth and sixth input contacts and to the fifth and sixth output contacts via a multi-drop communication transceiver. 
     In some embodiments, the controller may also include an Ethernet switch that is configured to selectively route a differential signal that is received on the first and second input contacts to one of the first and second output contacts or to the processor, and which is further configured to selectively route a differential signal that is received on the third and fourth output contacts to one of the third and fourth input contacts or to the processor. The controller may also include a termination circuit that is configured to insert a resistance in series between the fifth input contact and the sixth input contact in response to a termination control signal. The controller can also include a termination control circuit that is coupled to at least one of the seventh and eighth input contacts. This termination control circuit may be configured to selectively activate the termination control signal. 
     According to further embodiments of the present invention, methods of operating a local area network that includes at least a first controller and a second controller that are interconnected by a first Ethernet cable and a third controller that is connected to the second controller by a second Ethernet cable are provided. Pursuant to these methods, it may be sensed that a first Ethernet transmission path between the first controller and the third controller that extends through the first and second Ethernet cables has been lost. Thereafter, a first signal may be transmitted from the first controller to the third controller over a multi-drop communication transmission path that extends through the first and second Ethernet cables in response to sensing that the first Ethernet transmission path was lost. 
     In some embodiments, the first Ethernet transmission path may be a first pair of twisted conductors of the first Ethernet cable and a first pair of twisted conductors of the second Ethernet cable. The multi-drop communication transmission path may be a second pair of twisted conductors of the first Ethernet cable and a second pair of twisted conductors of the second Ethernet cable. The methods may further involve transmitting a second signal over the first Ethernet transmission path and receiving a third signal over a second Ethernet transmission path, where the second Ethernet transmission path comprises a third pair of twisted conductors of the first Ethernet cable and a third pair of twisted conductors of the second Ethernet cable. A reference voltage may also be transmitted from the first controller to the third controller over a reference voltage transmission path, where the reference voltage transmission path comprises at least one conductor of a fourth pair of twisted conductors of the first Ethernet cable and at least one conductor of a fourth pair of twisted conductors of the second Ethernet cable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating the contact arrangement for a conventional 8-position communications jack (TIA 568B) as viewed from the front opening (plug aperture) of the jack. 
         FIG. 2  is a simplified, schematic view of an exemplary intelligent patching system on which the communications interfaces, controllers and/or local area networks according to embodiments of the present invention may be used. 
         FIG. 3  is a schematic diagram illustrating a local area network according to embodiments of the present invention that may be used to interconnect a plurality of intelligent patching system controllers according to embodiments of the present invention. 
         FIG. 4  is a block diagram of a controller according to embodiments of the present invention that may be used in the local area network of  FIG. 3 . 
         FIG. 5  is a block diagram of a controller according to further embodiments of the present invention that may be used in the local area network of  FIG. 3 . 
         FIG. 6  is a circuit diagram of the controller of  FIG. 5 . 
         FIG. 7  is a circuit diagram of a controller according to further embodiments of the present invention. 
         FIG. 8  is a circuit diagram of a controller according to still further embodiments of the present invention. 
         FIG. 9  is a flow chart diagram illustrating the operation of a local area network according to certain embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Pursuant to embodiments of the present invention, local area networks, controllers and communications interfaces are provided that may be used, for example, to implement control networks for intelligent patching systems. These intelligent patching control networks may comprise a plurality of controllers that are serially interconnected in a “daisy-chain” configuration using Ethernet patch cords. In some embodiments, the intelligent patching control network may support both (1) Ethernet (e.g., 10BASE-T or Ethernet 100BASE-TX) communications that are transmitted over first and second (transmit and receive) Ethernet transmission paths and (2) multi-drop communications that are transmitted over a separate differential multi-drop transmission path (i.e., a transmission path that supports multi-drop communications). Multi-drop communications refer to communications that are transmitted over a bus in which the components communicating over the bus are all connected to the same set of electrical wires, and some sort of arbitration process may be used to determine which component has the right to transmit information over these electrical wires at any given point in time, while the other devices listen to determine if any of the transmitted data is intended for them. Examples of multi-drop communications include RS-485 communications, Controller Area Network (“CAN”) communication interfaces, Thinnet and Thicknet communications, and multi-drop Low Voltage Differential Signaling (“LVDS”) communications. The Ethernet transmission paths may support high data rates that may facilitate implementing the full functionality of the intelligent patching system. If one or more of the plurality of controllers in the intelligent patching control network lose power or otherwise become inoperable, then the Ethernet transmission paths through such controller(s) may be lost, creating one or more break(s) in the daisy chain. However, through the provision of the multi-drop communication transmission path, controllers on either side of such a break may still communicate with each other over the slower multi-drop communication transmission path. 
     In some embodiments, adjacent controllers may be interconnected by a single patch cord that carries both the Ethernet and multi-drop communications. Moreover, the controllers may include a switched matched termination that may be used to match the multi-drop communication transmission line to a matched termination for controllers that are on either end of the daisy-chain. In some embodiments, the controllers may automatically sense whether or not this matched termination should be switched into place. 
     While the local area networks according to embodiments of the present invention may be suitable to interconnect a plurality of controllers of an intelligent patching system, it will be appreciated that these local area networks and the related controllers and communications interfaces that are disclosed herein may also be used in a variety of other applications. 
     Embodiments of the present invention will now be described with reference to the accompanying drawings. 
       FIG. 2  is a schematic view of a simplified intelligent cross-connect communications system  10  that may be used, for example, to connect computers, printers and other end devices that are located in work areas of a building to network equipment that is located, for example, in a computer room of the building. The local area networks disclosed herein may be used, for example, to interconnect the intelligent patching controllers of the communications system  10  or to interconnect the controllers of similar patching systems that may be used in data center environments. 
     As shown in  FIG. 2 , an exemplary computer  20  or other end device is located in a work area of the building. The computer  20  is connected by a patch cord  22  to a modular wall jack  24 . A communications cable  28  is routed from the back end of the wall jack  24  to a computer room. While only a single work area end device (computer  20 ) is shown in  FIG. 2 , it will be appreciated that there would be hundreds or thousands of work area end devices  20  and wall jacks  24  in a typical office environment, communications system, and hence there may be hundreds or thousands of cables  28  routed into the computer room. 
     A plurality of first equipment racks  30  are located in the computer room, two of which are shown in  FIG. 2 . A plurality of patch panels  32  are mounted on each first equipment rack  30 . Each patch panel  32  includes a plurality of RJ-45 connector ports  34 . The cables  28  from the wall jacks  24  are terminated into the back ends of respective ones of the connector ports  34  of the patch panels  32 . A plurality of second equipment racks  30 ′ are also located in the computer room, two of which are shown in  FIG. 2 . Each second equipment rack  30 ′ has a plurality of second patch panels  32 ′ mounted thereon. Each patch panel  32 ′ includes a plurality of RJ-45 connector ports  34 ′. A first set of patch cords  36  is used to interconnect the connector ports  34  on the patch panels  32  to respective ones of connector ports  34 ′ on the patch panels  32 ′. 
     A rack controller  40  is included in each first equipment rack  30  and each second equipment rack  30 ′. Each rack controller  40  may include an input port  42 , an output port,  44 , a processor  46  (not visible in  FIG. 2 ) and a user interface  48 . A plurality of patch cords  50  may be used to connect the input port  42  of each rack controller  40  to the output port  44  of an adjacent rack controller  40 . The input (or output) port  42  of one of the “end” rack controllers may be connected to a system manager  52  which may control operations of the rack controllers  40 . As a result of this interconnectivity, the rack controllers  40  can communicate in a common network as if they were a single controller. Each rack controller  40  may, for example, gather data from intelligent tracking capabilities of the patch panels  32 ,  32 ′ and/or may control operations of the intelligent patching system at the patch panel level. The interconnected rack controllers  40  and system manager  52  (if provided) may form an intelligent patching controller local area network  12 . 
     As is further shown in  FIG. 2 , network devices such as, for example, one or more network switches  54  and network routers and/or servers  58  are included, for example, in a third equipment rack  30 ″. Each of the switches  54  may include a plurality of connector ports  56 , and each network router and/or server  58  may also include one or more connector ports. One or more external communications lines  60  are connected to at least some of the network devices  58 . Single-ended patch cords  70  are used to connect the connector ports  56  on the switches  54  to respective ones of the back ends of the connector ports  34 ′ on the patch panels  32 ′. Patch cords  72  may be used to interconnect other of the connector ports  56  on the switches  54  with the connector ports provided on the network routers/servers  58 . In order to simplify  FIG. 2 , only a few of the patch cords  36 ,  70  and  72  are shown. 
     The communications patching system of  FIG. 2  may be used to connect each work area computer  20  or other work area end device to the network switches  54 , the network switches  54  to the network routers and servers  58 , and the network routers/servers  58  to the external communications lines  60 , thereby establishing the physical connectivity required to give devices  20  access to both local and wide area networks. In the cross-connect patching system of  FIG. 2 , connectivity changes are typically made by rearranging the patch cords  36  that interconnect the connector ports  34  on the patch panels  32  with the connector ports  34 ′ on the patch panels  32 ′. The rack controllers  40  and the system manager  52  may be used to automatically determine and/or confirm patching connections (i.e., determine and/or confirm the specific connector port pairs that are interconnected by patch cords) between the patch panels  32  mounted on the first equipment racks  30  and the patch panels  32 ′ mounted on the second equipment racks  30 ′, thereby allowing a network administrator to automatically generate and maintain a computer-based log of patching connections. 
     As will be discussed in detail below, controllers and communications interfaces according to embodiments of the present invention may be used to implement the intelligent patching controller local area network  12  included in the communications system  10  of  FIG. 2 . 
       FIG. 3  is a schematic diagram illustrating a local area network  100  according to certain embodiments of the present invention that is used to interconnect a plurality of controllers  110 - 1  through  110 - 8  (which are generically referred to herein as controllers  110 ). The controllers  110  may comprise, for example, rack controllers of an intelligent patching system such as the controllers  40  in  FIG. 2 . The local area network may correspond to the local area network  12  in  FIG. 2 . 
     As shown in  FIG. 3 , each controller  110  includes an input connector port  112 , an output connector port  114  and a processor (not shown in  FIG. 3 ). The connector ports  112 ,  114  are RJ-45 connector ports. The controllers  110 - 1  through  110 - 8  are interconnected by a plurality of patch cords  120 - 1  through  120 - 7  (which are generically referred to herein as patch cords  120 ). Each of the patch cords  120  is an Ethernet patch cord that includes eight insulated conductors that are arranged as four twisted pairs of conductors. Each pair of conductors is configured to carry a differential signal. A first of the differential pairs in each patch cord  120  may be used to carry Ethernet signals that are transmitted in a first direction along the local area network  100  (i.e., in the direction from controller  110 - 1  to controller  110 - 8 ), while a second of the differential pairs in each patch cord may be used to carry Ethernet signals that are transmitted in a second, opposite direction along the local area network  100  (i.e., in the direction from controller  110 - 8  to controller  110 - 1 ). Thus, the local area network  100  provides a two-way Ethernet transmission path  140  that any of the controllers  110  may use to communicate with any other of the controllers  110 . 
     As shown in  FIG. 3 , one of the controllers (here controller  110 - 1 ) may act as a network manager. The network manager controller  110 - 1  may be connected by a bridge connection  134  to another local area network  132  such as a local area network run by the entity that is using the intelligent patching system that includes local area network  100 . A system manager  130 , which may be a software program running on a computer, may be resident on the customer local area network  132  and may interface with the local area network  100  through the bridge connection  134  between the local area network  132  and the local area network  100 . As shown in  FIG. 3 , the controllers  110 - 1  through  110 - 8  are interconnected in series in “daisy-chain” fashion. Thus, for example, a communications from controller  110 - 2  to  110 - 6  will pass through patch cords  120 - 2  through  120 - 5  and through controllers  110 - 3  through  110 - 5  (i.e., through the intervening links on the daisy chain). 
     The Ethernet communications link  140  provides a high data rate communications link that the controllers  110  may use to communicate with each other and/or with the system manager  130 . However, if any of the controllers  110  lose power or otherwise become inoperable, then devices (e.g., controllers  110  and/or the system manager  130 ) on either side of the inoperable controller  110  cannot communicate with each other over the Ethernet communications link  140 . In order to maintain a communications capability, the local area network  100  further includes either an RS-422 or an RS-485 communications link  150  (herein the term “multi-drop communications link” refers to a communications link that operates under any differential multi-drop data transmission standard). 
     As is known to those of skill in the art, differential multi-drop communication interfaces are physical interfaces that are used by compliant drivers and receivers to transmit and receive communications over multi-drop communications. Examples of multi-drop communication interfaces include RS-485 interfaces, Controller Area Network (“CAN”) interfaces, Thinnet and Thicknet interfaces and multi-drop Low Voltage Differential Signaling (“LVDS”) interfaces. Before transmitting on a multi-drop communications link  150 , a controller (e.g., controller  110 - 2 ) will listen to see if any transmissions are currently being carried on the multi-drop communications link  150  in an effort to avoid collisions. If no transmissions are present, the controller may start transmitting, and may monitor the signal received over the communications link  150  to confirm that it is the same signal that is being transmitted (in order to detect collisions). While the multi-drop communications link  150  will typically comprise a lower data rate link as compared to the signals carried on the Ethernet communications link  140 , the provision of the multi-drop communications link  150  allows the intelligent patching system to continue operating (although perhaps, in some cases, with reduced functionality or at slower update speeds) even when a power loss, equipment malfunction or other disruption renders one or more of the devices on the daisy-chained local area network  100  inoperable. 
     The system manager  130  and the controllers  110 - 1  through  110 - 8  may use the local area network  100  to exchange control signals and data that are used to perform intelligent patching operations. By way of example, the controllers  110 - 1  through  110 - 8  may receive notifications from processors associated with patch panels and/or network switches of the intelligent patching system when patch cords are plugged into, or removed from, the connector ports on patch panels and/or network switches that are under the control of the controller  110 . Upon receiving such notifications, a controller  110  can notify other controllers  110  and/or the system manager  130  of these detected patch cord insertions and/or removals. As another example, intelligent patch panels and/or switches that are included in an intelligent patching network may exchange communications that allow these patch panels and/or switches to determine, for each connector port thereon, whether or not the connector port is connected via a patch cord to another connector port and, if so, the identity of the connector port that receives the far end of the patch cord (e.g., the identification of the patch panel or switch and the connector port thereon). This connection information may then be transmitted over the local area network  100  to, for example, the system manager  130  which maintains and updates a database of all of the patching connections in the intelligent patching communications system. The specific control and data signals that are transmitted over the local area network will depend upon the specific implementation of the intelligent patching network. U.S. patent application Ser. No. 13/110, 994, filed May 19, 2011 (“the &#39;994 application”), describes one exemplary intelligent patching system and various of the control and data communications that may be passed between rack controllers and between rack controllers and a system manager computer in that particular intelligent patching system. The entire content of the &#39;994 application is incorporated by reference herein as if set forth in its entirety. 
       FIG. 4  is a block diagram of a controller  200  according to embodiments of the present invention that may be used, for example, to implement any of the controllers  110 - 1  through  110 - 8  in the local area network  100  of  FIG. 3 . 
     As shown in  FIG. 4 , the controller  200  includes a processor  210  and a communications interface  220 . The processor  210  may comprise, for example, a microprocessor, an application specific integrated circuit (ASIC), a microcontroller or the like. The communications interface  220  includes an input connector  230 , an output connector  240 , an Ethernet interface  250  and a multi-drop communication interface  260 . Herein, the term “Ethernet interface” refers to a device that receives or generates an Ethernet signal. Likewise, the term “multi-drop communication interface” is used herein to refer to a device that receives and/or generates a multi-drop signal such as, for example, an RS-485 signal. In the embodiment of  FIG. 4 , each connector  230 ,  240  comprises a jack such as, for example, an RJ-45 jack. As shown in  FIG. 4 , the input connector  230  is electrically connected to the output connector  240 , the Ethernet interface  250  and the multi-drop communication interface  260 . The processor  210  is connected to both the Ethernet interface  250  and the multi-drop communication interface  260 . 
     Ethernet communications that are received at the input connector  230  are passed either to the processor  210  or the output connector  240  by the Ethernet interface  250 . Ethernet communications that are received at the output connector  240  are passed either to the processor  210  or to the input connector  230  via the Ethernet interface  250 . Ethernet communications may also be transmitted from the processor  210  to the input connector  230  or to the output connector  240  via the Ethernet interface  250 . Multi-drop communications that are received at the input connector  230  are passed to both the output connector  240  and to the processor  210  via the multi-drop communication interface  260 . Multi-drop communications that are received at the output connector  240  are passed to both the input connector  230  and the processor  210  via the multi-drop communication interface  260 . Multi-drop communications may also be transmitted from the processor  210  to the input connector  230  and the output connector  240  via the multi-drop communication interface  260 . 
       FIG. 5  is a block diagram of a controller  300  according to further embodiments of the present invention. As shown in  FIG. 5 , the controller  300  includes a processor  310  and a communications interface  320 . The processor  310  may comprise, for example, a microprocessor, an application specific integrated circuit (ASIC), a microcontroller or the like. The communications interface  320  includes an input connector  330 , an output connector  340 , a 3-port Ethernet switch  350 , a multi-drop communication transceiver  360 , a multi-drop communication termination  362 , a multi-drop communication termination control circuit  368  and a printed circuit board  390 . 
     The input connector  330  may comprise an RJ-45 jack that is mounted on the printed circuit board  390 . The RJ-45 jack  330  includes a plurality of input contacts  331 - 338  which may comprise, for example cantilevered jackwire contacts that are formed of a resilient metal such as beryllium-copper or phosphor-bronze. The output connector  340  may likewise comprise an RJ-45 jack that is mounted on the printed circuit board  390 . The RJ-45 jack  340  includes a plurality of output contacts  341 - 348  which may comprise, for example cantilevered jackwire contacts that are formed of a resilient metal such as beryllium-copper or phosphor-bronze. 
     It will be appreciated that while the connector ports  330  and  340  are referred to as an input connector port and an output connector port, the terms “input” and “output” are only used for ease of description to distinguish the two connector ports apart. As is made clear in the discussion above of the local area network  100  of  FIG. 3 , any of the controllers  110 - 1  through  110 - 8  can communicate with any of the other controllers and/or the system manager  130 , and thus it is apparent that communications may flow in both directions through the daisy-chain configuration of controllers. Accordingly, it will be appreciated that communications signals may enter the controller  300  at the “output” connector port  340  and may exit the controller  300  at the “input” connector  330 . The same is true with respect to the other embodiments of the present invention discussed herein. 
     As shown in  FIG. 5 , the three-port Ethernet switch  350  is interposed between the processor  310  and the input and output RJ-45 jacks  330 ,  340 . In particular, a first set of conductive traces  371 ,  372 ,  373 ,  376  (which may be traces that extend on a single layer of printed circuit board  390  or can be a plurality of traces that are on multiple layers of the printed circuit board  390  that are electrically connected by metal-filled vias or by other layer transferring techniques known to those skilled in the art) are provided on the printed circuit board  390  that connect contacts  331 ,  332 ,  333  and  336  (i.e., pairs  2  and  3 ) of input connector port  330  to Ethernet switch  350 . A second set of conductive traces  381 ,  382 ,  383 ,  386  are provided on the printed circuit board  390  that connect contacts  341 ,  342 ,  343  and  346  of output connector port  340  to Ethernet switch  350 . The three-port Ethernet switch  350  includes three input/output ports  351 - 353 . Port  351  is connected to conductive paths  371 ,  372 ,  373 ,  376 , port  352  is connected to conductive paths  381 ,  382 ,  383 ,  386  and port  353  is connected to processor  310 . The processor  310  may include an Ethernet Media Access Controller and a PHY chip, and may communicate through the port  353  via a media independent interface (not shown). The three-port Ethernet switch  350  may comprise, for example, a commercially available, printed circuit board mountable integrated circuit chip that receives Ethernet packets that arrive on any of the three ports  351 - 353  of the switch  350  and, based on the address information in those packets, routes the packets to the appropriate of the other ports  351 - 353  on the switch  350 . An example of a suitable three-port Ethernet switch  350  is the KSZ8863 integrated circuit chip available from Micrel. 
     The Ethernet switch  350  may operate, for example, as follows. An Ethernet signal that is received, for example, on contacts  331  and  332  of input jack  330  (pair  2 ) is passed by the corresponding conductive traces  371 ,  372  to port  351  on Ethernet switch  350 . The Ethernet switch  350  reads the header information on each received packet. If the header information indicates that the processor  310  is the intended recipient of the packet, then the Ethernet switch  350  passes the received packets to the processor  310 . If not, the Ethernet switch  350  passes the packet through to port  352  where it is passed to the conductive traces  381 ,  382  that are connected to contacts  341  and  342  of output jack  340  so that the packet may be passed to the next controller in the local area network (see  FIG. 3 ). 
     As is further shown in  FIG. 5 , contacts  334  and  335  of input jack  330  are connected by conductive traces  374 ,  375  on printed circuit board  390  to contacts  344  and  345 , respectively, of output jack  340 . Multi-drop communications that are input to controller  300  at contacts  334 ,  335  of input jack  300  are passed to output contacts  344 ,  345  of output jack  340  where they are passed to the next controller in the local area network (see  FIG. 3 ). Additionally, a conductive trace  384  electrically connects conductive trace  374  to the multi-drop communication receiver  360 , and a conductive trace  385  similarly electrically connects conductive trace  375  to the multi-drop communication receiver  360 . These conductive traces  384 ,  385  pass multi-drop communication signals that are input to the controller  300  (either at input jack  330  or output jack  340 ) to the multi-drop communication receiver  360  which recovers the data in the signal and provides this data to the processor  310 . The conductive paths  384 ,  385  are also used to pass multi-drop communication signals that are generated by the multi-drop communication transceiver  360  in response to the processor  310  to the conductive traces  374 ,  375  where they are passed to the local area network via contacts  334  and  335  of input jack  330  and contacts  344  and  345  of output jack  340 . 
     As is also shown in  FIG. 5 , a multi-drop communication termination circuit  362  is provided that may be used to terminate the multi-drop communication transmission line  322  formed by conductive traces  374 ,  375 . The termination circuit  362  may be designed to insert an impedance between the conductive traces  374  and  375  that matches the impedance of the multi-drop communication transmission line  322 . In the illustrated embodiment, the termination circuit  362  comprises a 100 ohm resistor  364  and a switch  366  that are disposed in series between conductive trace  374  and conductive trace  375 . If the controller  300  is at the end of a daisy-chained local area network such that no patch cord is connected into either the input jack  330  or the output jack  340 , then the switch  366  may be closed so that the resistor  364  provides a matched termination to the multi-drop communication transmission line  322  that may reduce signal reflections and associated return losses. 
     The controller  300  further includes a termination control circuit  368 . This termination control circuit  368  may be used to automatically terminate the transmission line  322  when no patch cord is received within either the input jack  330  or the output jack  340  by automatically closing the switch  366 . The termination control circuit  368  may be connected to conductive traces  377 ,  378  that are electrically connected to contacts  337  and  338  of input jack  330  and to contacts  347  and  348  of output jack  340  via conductive paths  387 ,  388 . The termination control circuit  368  may automatically sense whether or not contacts  337  and  338  of input jack  330  or contacts  347  and  348  of output jack  340  are open circuited and, if so, close the switch the  366 . Operation of the termination control circuit  368  will be explained below with respect to the discussion of the circuit diagram of  FIG. 6 . 
     Embodiments of the present invention may take advantage of the fact that lower throughput Ethernet communications such as 10BASE-T and 100BASE-TX communications only use two of the four differential pairs (pairs  2  and  3 ) of conductors that are provided in Ethernet connectors and cables (one pair is used for transmission, the second pair for receiving), thus leaving two additional differential pairs unused. Pursuant to embodiments of the present invention, a differential multi-drop communication signal may be transmitted over one of these unused differential pairs (pair  1 ), thereby providing a back-up communications path in the event that the Ethernet communications path is lost due to a power outage, an equipment failure or the like. The second unused differential pair (pair  4 ) may be used to as a signal return path to ground for the multi-drop communication signals. The use of such a well-defined ground path facilitates providing error-free or low error communications over the multi-drop communications path. 
     In addition, according to some embodiments of the present invention, the second unused differential pair (pair  4 ) may also be used for purposes of termination control. In particular, in order to obtain good signal quality on the multi-drop communication transmission line  322 , it is desirable to properly terminate both ends of the transmission line  322  to a matched impedance (which here would be the 100 ohm target impedance of a differential pair of an Ethernet patch cord). The termination control circuit  368  is provided to automatically sense whether or not the controller  300  is at the end of the daisy-chain in the local area network and, if so, to automatically terminate the multi-drop communication transmission line  322  to the matched termination  362  within the controller  300 . 
       FIG. 6  is a circuit diagram of the controller  300  of  FIG. 5  that provides additional details regarding one specific implementation of the communications interface  320  of the controller  300 . As shown in  FIG. 6 , in addition to the elements of the communications interface  320  discussed above with respect to  FIG. 5 , the communications interface  320  may further include a plurality of common mode chokes  302  that reduce any common mode emissions that enter the controller  300  on contact pairs  331 / 332 ,  333 / 336  and/or  337 / 338  of input RJ-45 jack  330  and any common mode emissions that enter the controller  300  on contact pairs  341 / 342 ,  343 / 346  and/or  347 / 348  of output RJ-45 jack  340 . The common mode chokes  302  likewise may reduce any common mode noise that may be emitted by the controller  300  onto the above-referenced contact pairs of the input and output RJ-45 jacks  330 ,  340 . Ethernet magnetics  304  are also included which may provide galvanic isolation with respect to the three-port Ethernet switch  350 . 
     The termination control circuit  368  is also depicted in  FIG. 6 . As shown in  FIG. 6 , the termination control circuit  368  includes a first circuit  368 - 1  that is connected to contacts  337  and  338  of input jack  330 , and a second circuit  368 - 2  that is connected to contacts  347  and  348  of output jack  340 . The termination control circuit  368 - 1  includes a resistor  391  and a diode  392  that are connected in series between a power supply voltage Vcc and a ground reference. The voltage of contact  337  passes through the common mode choke  302  and appears at terminal  393 . The termination control circuit  368 - 2  includes a resistor  394  and a diode  395  that are connected in series between a power supply voltage Vcc and a ground reference. The voltage of contact  348  passes through the common mode choke  302  and appears at terminal  396 . The termination control circuit  368  may be used to (1) carry a ground reference between adjacent controllers  300  in the LAN and (2) to automatically sense whether or not the input RJ-45 jack  330  and/or the output RJ-45 jack  340  are connected to another controller  300 . If it is determined that at least one of the input RJ-45 jack  330  or the output RJ-45 jack  340  is not connected to another controller  300 , then the termination control circuit  368  may generate one or more control signals that may be used to control the switch  366  in order to terminate the multi-drop communication transmission line to a matched termination using resistor  364 . 
     The following discussion explains the operation of the termination control circuit  368  in greater detail. For purpose of this discussion, it is assumed that the input RJ-45 jack  330  of the controller  300  of  FIG. 6  is connected to the output RJ-45 jack of a second controller  300 - 1 , and that the output RJ-45 jack  340  of the controller  300  of  FIG. 6  is connected to the input RJ-45 jack of a third controller  300 - 2  (neither controller  300 - 1  or  300 - 2  are illustrated in  FIG. 6 ). The controllers  300 - 1  and  300 - 2  may be identical to the controller  300  illustrated in  FIG. 6 . 
     Referring again to  FIG. 6 , it can be seen that contact  338  on input RJ-45 jack  330  is connected to the ground reference provided in termination control circuit  368 - 1  via the common mode choke  302 . Consequently, contact  338  will be set to a low level on the controller  300 . The same will be true for the contacts  338  of controllers  300 - 1  and  300 - 2  since each of these controllers are identical to controller  300 . Thus, when the output RJ-45 jack  340  of controller  300  is connected to controller  300 - 2 , then the ground reference in termination control circuit  368 - 1  on controller  300 - 2  will be carried into controller  300  via contact  338  on controller  300 - 2  and the cabling connection between controllers  300  and  300 - 2 , thereby pulling contact  348  on jack  340  on controller  300  to a low level. In this fashion, the ground reference from controller  300 - 2  may be provided to controller  300  (albeit the ground references may be offset by the voltage drop across the diode  395 ). Moreover, as is further shown in  FIG. 6 , contact  347  on output RJ-45 jack  340  of controller  300  is connected to the ground reference provided in termination control circuit  368 - 2  via the common mode choke  302 . Thus, if controller  300 - 2  is connected to output jack  340  of controller  300 , then both contacts  347  and  348  of controller  300  will be at a low level. In contrast, if controller  300 - 2  is not connected to controller  300 , then contact  348  on controller  300  will not be pulled to a low level and instead will be held at a high level by the power supply voltage Vcc. Accordingly, the voltage levels of contact  348  may be used to sense whether or not controller  300 - 2  is connected to controller  300 . 
     As noted above, contact  347  on output RJ-45 jack  340  is connected to the ground reference provided in termination control circuit  368 - 2  via the common mode choke  302 . Consequently, contact  347  will be set to a low level on all three of the controllers  300 ,  300 - 1  and  300 - 2 . Thus, when the input RJ-45 jack  330  of controller  300  is connected to controller  300 - 1 , then the ground reference in termination control circuit  368 - 2  on controller  300 - 1  will be carried into controller  300  via contact  347  on controller  300 - 1  and the cabling connection between controllers  300 - 1  and  300 , thereby pulling contact  337  on jack  330  of controller  300  to a low level. In this fashion, the ground reference from controller  300 - 1  may be provided to controller  300  (albeit the ground references may be offset by the voltage drop across the diode  392 ). Moreover, as is further shown in  FIG. 6 , contact  338  on input RJ-45 jack  330  of controller  300  is connected to the ground reference provided in termination control circuit  368 - 1  via the common mode choke  302 . Thus, if controller  300 - 1  is connected to input jack  330  of controller  300 , then both contacts  337  and  338  of controller  300  will be at a low level, and hence the voltage levels of contacts  337  and  338  may be used to sense whether or not controller  300 - 1  is connected to controller  300 . In some embodiments, a simple logic circuit may be provided that controls the switch  366  in response to the voltages that are present on some or all of contacts  337 ,  338 ,  347  and  348  so that the switch  366  is closed if any of those four voltages are, for example, at a high level. 
     Thus, as shown above, the termination control circuit  368  may be used to both carry a ground reference between adjacent controllers  300  in the LAN and to automatically sense whether or not the controller  300  is in the middle or the end of the daisy-chain and, if at the end, to automatically terminate the multi-drop communication transmission line to a matched termination. 
     A plurality of the controllers  300  of  FIGS. 5 and 6  may be used to implement the local area network  100  of  FIG. 3 . However, as shown in  FIG. 3 , in some embodiments it may be desirable to have the network manager controller  110 - 1  of  FIG. 3  interface with a system manager  130  on the customer&#39;s local area network  132  via a standard 10BASE-T or 100BASE-TX Ethernet connection  134 . The input and output jacks  330 ,  340  of the controller  300  of  FIGS. 5 and 6  may not be suitable for use on such a standard 10BASE-T or 100BASE-TX Ethernet connection  134 , as in a standard 10BASE-T or 100BASE-TX connection, the contacts of pair  1  (contacts  4  and  5 ) are shorted together and tied to ground. As such, the controller  300  of  FIGS. 5 and 6  may include an additional RJ-45 jack (not shown in  FIGS. 5 and 6 ) that may be used to support a standard 10BASE-T or 100BASE-TX Ethernet connection to such a system manager  130 . Pursuant to further embodiments of the present invention, controllers are provided that may support such a standard 10BASE-T or 100BASE-TX Ethernet connection through the same input and/or output jacks that are used to carry bother Ethernet and multi-drop communications, thereby eliminating any need for an additional Ethernet jack for connecting to the customer local area network  132 .  FIG. 7  is a circuit diagram of a communications interface  420  according to further embodiments of the present invention that can support a standard 10BASE-T or 100BASE-TX Ethernet connection to, for example, a system manager  130  through either the input jack or the output jack thereof. 
     As shown in  FIG. 7 , the communications interface  420  includes an input RJ-45 jack  430 , an output RJ-45 jack  440 , a 3-port Ethernet switch  450 , a multi-drop communication transceiver  460 , and a multi-drop communication termination  462 . The input RJ-45 jack  430 , the output RJ-45 jack  440 , the 3-port Ethernet switch  450  and the multi-drop communication transceiver  460  may be identical to the corresponding components  330 ,  340 ,  350  and  360  in the communications interface  320  of  FIGS. 5-6 , and hence further description of these elements will be omitted. 
     The communications interface  420  differs from the communications interface  320  in that the communications interface  420  includes a first set of three manual switches  412  that are used to configure the input RJ-45 jack  430  into one of either a standard Ethernet configuration or an Ethernet/multi-drop configuration, and a second set of three manual switches  414  that are used to configure the output RJ-45 jack  440  into one of either a standard Ethernet configuration or an Ethernet/multi-drop configuration. Herein, the term “Ethernet/multi-drop configuration” refers to a configuration where the jack is configured to support Ethernet communications over two of its differential pairs and multi-drop communications over a third of its differential pairs. In  FIG. 7 , the first set of switches  412  are shown set in a position that configures the input RJ-45 jack  430  to operate in an Ethernet/multi-drop configuration, and the second set of switches  414  is likewise set in a position that configures the output RJ-45 jack  440  to operate in an Ethernet/multi-drop configuration. In such a configuration, the jacks  430 ,  440  can transmit and receive either Ethernet or multi-drop communications in the manner described above for communications interface  320 . If each switch in the first set of switches  412  is flipped from the position illustrated in  FIG. 7  to its alternative position, then contacts  434  and  435  of jack  430  are disconnected from the multi-drop communication transmission line and are instead tied together and connected to ground (as would be the case with a standard 10BASE-T or 100BASE-TX Ethernet connection). In this configuration, the input RJ-45 jack  430  is appropriately configured to connect to a standard 10BASE-T or 100BASE-TX Ethernet connection. Likewise, if each switch in the second set of switches  414  is flipped from the position illustrated in  FIG. 7 , then contacts  444  and  445  of jack  440  are disconnected from the multi-drop communication transmission line and are instead tied together and connected to ground. In this configuration, the output RJ-45 jack  440  is similarly configured to connect to a standard 10BASE-T or 100BASE-TX Ethernet connection. Thus, with the communications connection interface  420  of  FIG. 7 , a network administrator may manually set the switches in the sets of switches  412  and  414  to a desired position to configure the input and output jacks  430  and  440  to be in a standard Ethernet connection (e.g., as would be the case for the input jack of network manager  110 - 1  of  FIG. 3 ) or to be in an Ethernet/multi-drop configuration (e.g., as would be the case for the input and output jacks on controllers  110 - 2  through  110 - 8  of  FIG. 3 ). 
     The communications interface  420  of  FIG. 7  also includes a third set of switches  416  that may be used to connect a pair of termination resistors  464  in between conductive paths  474  and  475  (i.e., the conductive paths that form the multi-drop communication transmission line  422 ) in order to terminate the multi-drop communication transmission line  422  when the communications interface  420  is set up to operate in its Ethernet/multi-drop configuration and input jack  430  and/or output jack  440  are not connected to an adjacent controller. The termination resistors  464  together operate like resistor  364  of communications interface  320 , and hence further description thereof will be omitted. In the circuit of  FIG. 7 , switch  416  may be automatically controlled based upon the position of the sets of switches  412  and  414  as indicated by the signals NMA_ENA_N and NMB_ENA_N. These two signals are high when their respective sets of switches  412  and  414  are set to the Ethernet/multi-drop configuration depicted in  FIG. 7 , and are low otherwise. If either set of switches  412  or  414  is not set to the Ethernet/multi-drop configuration as shown in  FIG. 7 , then the controller will be at the end of the multi-drop communications transmission line, and switch  416  may be automatically set to the closed position to properly terminate said multi-drop communications transmission line. 
     The communications interface  420  of  FIG. 7  also differs from the communications interface  320  of  FIGS. 5 and 6  in that the communications interface  420  does hot include the termination control circuits  368 - 1  and  368 - 2  that are included in the communications interface  320 . Instead, in the communications interface  420 , contacts  437  and  438  of jack  430  are tied together and connected to ground through a 100 ohm resistor  421 , and contacts  447  and  448  of jack  440  are likewise tied together and connected to ground through the 100 ohm resistor  421 . The simpler termination control circuit that is provided in communications interface  420  may be used since the multi-drop communication transmission line  422  may be automatically terminated based upon the positions of the sets of switches  412  and  416 , and hence automatic sensing as to whether or not adjacent controllers are connected to the input and output jacks  430  and  440  may be omitted. 
     Finally, the communications interface  420  of  FIG. 7  further differs from the communications interface  320  of  FIGS. 5 and 6  in that the communications interface  420  includes a fourth set of switches  418  that may be set to allow the controller that includes communications interface  420  to communicate with legacy controllers that only included a multi-drop communication transmission line on pair  1  of its input and output RJ-45 jacks. The signals PSENSE and DPSENSE may be used to allow the controllers in a daisy-chain configuration to automatically determine their respective positions in the daisy-chain. PSENSE is the input, and DPSENSE is the output. When connected in the daisy-chain, the DPSENSE output of one controller is connected to the PSENSE input of the next controller in the chain. 
       FIG. 8  is a circuit diagram of a communications interface  520  according to further embodiments of the present invention. The communications interface  520  is similar to the communications interface  420  of  FIG. 7 , except that the communications interface  520  is not configured to also support standard 10BASE-T and/or 100BASE-TX Ethernet communications (i.e., for connecting to a customer local area network). 
     As shown in  FIG. 8 , the communications interface  520  is almost identical to the interface  420 , except that the switches in the first set of switches  412  that connected to contacts  434  and  435  of jack  430  are omitted, as are the switches in the second set of switches  414  that connected to contacts  444  and  445  of jack  440 . These switches are not necessary in the interface  520  as the interface  520  is not designed to connect to a standard Ethernet interface in an external network. The switch  416 ′ provided in communications interface may be set by a network administrator to place resistors  464  in series between conductive paths  474  and  475  in order to terminate the transmission line  422  to a matched termination when one of jacks  430  or  440  are not connected to an adjacent controller. 
     Pursuant to further embodiments of the present invention, methods of operating a local area network that includes local area controllers according to embodiments of the present invention are provided.  FIG. 9  is a flow chart that illustrates one such exemplary method. The method of  FIG. 9  may be performed, for example, on a local area network that includes at least three controllers that are connected in a daisy-chain fashion with a first Ethernet cable connecting the first controller to the second controller and a second Ethernet cable connecting the second controller to the third controller. 
     As shown in  FIG. 9 , operations may begin with the transmission of an Ethernet signal such as, for example, an Ethernet control signal from the first controller to the second controller over the first Ethernet cable (block  600 ). Thereafter, the local area network (or a component thereof) may sense that an Ethernet transmission path between the first controller and the third controller has been lost (block  610 ). In some embodiments, the loss of the Ethernet transmission path may be detected by the link status bit in the Ethernet switch. A reference voltage that is used for the multi-drop communications may be transmitted from the first controller to the third controller over a reference voltage transmission path (block  620 ). In some embodiments, this reference voltage transmission path may comprise at least one conductor of a fourth pair of twisted conductors of the first Ethernet cable and at least one conductor of a fourth pair of twisted conductors of the second Ethernet cable. After the loss of the Ethernet transmission path has been detected and the reference voltage is transmitted, a signal may be transmitted from the first controller to the third controller over a multi-drop communication transmission path that extends through the first and second Ethernet cables (block  630 ). In some embodiments, the first Ethernet transmission path may comprise a first pair of twisted conductors of the first Ethernet cable and a first pair of twisted conductors of the second Ethernet cable, and the multi-drop communication transmission path may comprise a second pair of twisted conductors of the first Ethernet cable and a second pair of twisted conductors of the second Ethernet cable. 
     As is further shown in  FIG. 9 , the Ethernet transmission path may ultimately be restored, and the subsequent availability of the Ethernet transmission path may then be detected (block  640 ). In some embodiments, the detection of the re-availability of the Ethernet transmission path may be performed manually (e.g., input by a network administrator), while in other embodiments the re-availability of the Ethernet transmission path may be automatically detected. In response to detecting the re-availability of the Ethernet transmission path, a signal may be transmitted from the first controller to the third controller over the Ethernet transmission path (block  650 ). 
     It will be appreciated that many modifications may be made to the above-described embodiments without departing from the scope of the present invention. By way of example, in certain of the embodiments discussed above a logic circuit may be provided as part of the termination control circuit that generates one or more control signals that are used to set the switch in the multi-drop communication termination. It will be appreciated, however, that in other embodiments the switch may be controlled in other ways such as, for example, by control signals that are generated by firmware. 
     The present invention has been described with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments that are pictured and described herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It will also be appreciated that the embodiments disclosed above can be combined in any way and/or combination to provide many additional embodiments. 
     Unless otherwise defined, all technical and scientific terms that are used in this disclosure have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the above description is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this disclosure, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when an element (e.g., a device, circuit, etc.) is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     Herein, the term “Ethernet cable” refers to a cable that includes at least four twisted differential pairs of insulated conductors that are suitable for use as a transmission medium for computer communications. 
     Certain embodiments of the present invention have been described above with reference to flowchart illustrations. It will be understood that some blocks of the flowchart illustrations may be combined or split into multiple blocks, and that the blocks in the flow chart diagrams need not necessarily be performed in the order illustrated in the flow charts. It will also be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by computer program instructions. These computer program instructions may be provided to a processor to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, implement the functions/acts specified in the flowchart block or blocks. These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the function/act specified in the flowchart block or blocks. 
     The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart block or blocks. 
     In the drawings and specification, there have been disclosed typical embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.