Abstract:
A network comprises a plurality of network devices, including a first network device coupled to a second network device and a third network in a daisy chain topology configuration. The first network device has a first device port connected to a first network port and a second device port connected to a second network port. A bypass switch is coupled to the first network device and creates a bypass path when the first network device is inoperable. The bypass switch is coupled to a processor in the first network device. The processor has a control function for closing the bypass path when the first network device is inoperable and for opening the bypass path when the first network device is operable. The bypass switch connects the first network port to the second network port when the device is inoperable.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     None.  
       TECHNICAL FIELD  
       [0002]     The invention generally relates to bypassing a network device on an Ethernet network having a daisy chain topology, and more particularly, the invention relates to bypass switch for creating a bypass path when the network device is inoperable and to a method for bypassing the network device.  
       BACKGROUND OF THE INVENTION  
       [0003]     In an Ethernet network, failure of one device can have a devastating affect on the information flow through the entire network. This is particularly true on a daisy chain topology network where the information is passed through one device to another.  
         [0004]     Generally, in a daisy chain topology each network device is connected to a device upstream and downstream from itself. The daisy chain topology allows computers and other peripheral devices to be easily connected to a network and requires relatively less cable length than other network topologies. However, there are several disadvantage to employing a daisy chain topology. For example, any device failure in the chain will disable the entire network and prevent the transmission of all information on the network. Additionally, if a device needs to be added in the middle of the chain, the entire network will be disabled while the new device is added.  
         [0005]     In order to overcome the failure of a single device causing the failure of the entire network, a star topology may be employed. In a star topology, each device has a cable leading back to a central hub. The most popular networks using a star topology are 10BASE-T Ethernet and Token Ring. A star network can simplify troubleshooting because devices can be disconnected from the hub one at a time until the problem is isolated without disabling the entire network. However, a star topology requires the added expense of a hub and utilizes more cable than a daisy chain topology which adds to the expense of the system. In addition, a hub failure can knock out the entire network.  
         [0006]     The present invention is provided to solve the problems discussed above and other problems, and to provide advantages and aspects not provided by prior networks of this type. A full discussion of the features and advantages of the present invention is deferred to the following detailed description, which proceeds with reference to the accompanying drawings.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention relates to an Ethernet network having a daisy chain topology. The network comprises a first network device coupled to a second network device and a third network device in a daisy chain topology configuration. The first network device has a first device port connected to a first network port and a second device port connected to a second network port. Additionally, the first network device may be coupled to a plurality of network devices in a daisy chain topology configuration.  
         [0008]     To avoid a failure of the network due to a problem with the first network device, a bypass switch is coupled to the first network device and creates a bypass path when the first network device is inoperable. The bypass switch may be coupled to a processor in the first network device. The processor has a control function for closing the bypass path when the first network device is inoperable and for opening the bypass path when the first network device is operable. The bypass switch connects the first network port to the second network port when the device is inoperable.  
         [0009]     The bypass switch can be integrally part of the network device or it can be located on a removable adapter. The removable adapter has a first connector for connecting to a power source and a second connector for connecting to the first network device. The first and second connectors can be used to transmit network information between the first network device and other network devices. The second connector has a plurality of conductors, including one conductor for controlling power supplied to the removable adapter. The power source supplies power to the removable adapter when the removable adapter is connected to the first network device thereby disabling the bypass path. This power source may be located on the first network device.  
         [0010]     According to another aspect of the invention, the present invention further includes a network device on an Ethernet network having a daisy chain topology. The network device may be coupled to a plurality of network devices in the daisy chain topology configuration. The network device includes a first device port for coupling the network device to a second network device in a daisy chain topology configuration and a second device port for coupling the network device to a third network device in a daisy chain topology configuration.  
         [0011]     The network device also includes a bypass switch for creating a bypass path when the network device is inoperable. The bypass switch is coupled to a processor in the first network device. The processor has a control function for closing the bypass path when the first network device is inoperable and for opening the bypass path when the first network device is operable. The bypass switch connects the first network port to the second network port when the device is inoperable.  
         [0012]     According to yet another aspect of the invention, the present invention further includes a method for creating a bypass path on an Ethernet network having a daisy chain topology. The method includes for providing a first network device includes a first device port connected to a first network port and a second device port connected to a second network port. The method further includes connecting the first network device to a second network device and a third network in a daisy chain topology configuration and coupling the first network device to a bypass switch. The method includes creating a bypass path connecting the first network port to the second network port when the first network device is inoperable. The method may further include coupling the first network device to a plurality of network devices in a daisy chain topology configuration and locating the bypass switch on a removable adapter.  
         [0013]     The method further includes removing the first network device from the network and connecting a fourth network device to the network in place of the first network device. Additionally, the method includes disabling the bypass path in response to the fourth network device being operable.  
         [0014]     Other features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     To understand the present invention, it will now be described by way of example, with reference to the accompanying drawings in which:  
         [0016]      FIG. 1  is a block diagram of a daisy chain Ethernet topology utilized in an industrial automation network;  
         [0017]      FIG. 2  is a block diagram of a daisy chain Ethernet topology having network devices comprising a bypass switch in accordance with the present invention;  
         [0018]      FIG. 3  illustrates a bypass switch implemented directly on a network device;  
         [0019]      FIG. 4  illustrates a removable adapter having a bypass switch located thereon;  
         [0020]      FIG. 5  illustrates power activation on the removable adapter of  FIG. 4 ;  
         [0021]      FIG. 6  illustrates an IP67 removable adapter;  
         [0022]      FIG. 7  illustrates an IP20 removable adapter using four-wire cabling;  
         [0023]      FIG. 8  illustrates an IP20 removable adapter using eight-wire cabling; and,  
         [0024]      FIG. 9  illustrates a removable adapter connected to a network device through an external power connection. 
     
    
     DETAILED DESCRIPTION  
       [0025]     While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated.  
         [0026]      FIG. 1  illustrates a daisy chain Ethernet topology that is typically utilized in an industrial automation network  10 . The network  10  is controlled by a PLC  12  which is coupled to a plurality of network devices  14 , such as network automation devices. Preferably, the PLC  12  is coupled to the network devices  14  using 10/100 megabits per second Ethernet copper cabling. Each network device  14  is coupled to the next using a connector  20 , such as an Ethernet connection, having a transmit port and receive port. Messages to and from the PLC  12  are transmitted through network devices  14  and must travel through all the network devices  14  between the PLC  12  and the network device  14  the message originated from or is intended for. However, if one of the network devices  14  between the PLC  12  and the network device  14  the message originated from or is intended for fails, the network  10  is disabled and the message will not be delivered.  
         [0027]     Referring to  FIG. 2 , the present invention overcomes the problems associated with prior daisy chained networks by providing a daisy chain Ethernet topology having network devices  14  comprising or coupled to a bypass switch  16 . The bypass switch  16  is utilized to prevent data loss on the Ethernet network  10  due to loss of devices by creating a bypass path. That is, the traffic path of data on the network  10  is maintained in the event that one or more of the plurality of network devices  14  becomes inoperable. It is preferable that all the network devices  14  include the bypass switch  16  such that if any network device  14  fails, the network  10  will continue to function.  
         [0028]     As will be described herein, there are several embodiments implementing the bypass path  16  on a network device  14 . In one embodiment, the bypass switch  16  is incorporated as an integral component directly of the network device  14 . In another embodiment, the bypass switch  16  is implemented on a separate adapter  40 , 60  that is removably connected directly to the network device  14 . In yet another embodiment, the bypass switch  16  is implemented on a separate adapter  40 , 60  that is connected to the network device  14  by a cable  63 , 65 .  
         [0029]     The bypass switch  16  may be a traditional relay such as reed type or optomos relay. An optomos relay operates based on optical CMOS technology. The optomos relay provides excellent emissions and immunity capability along with a nearly unlimited number of switching operations. Using normally closed and/or normally opened paths, information passed through the transmit  17  and receive  18  ports of connectors  20  can be sent from one port to another port or back out the same port in the event of partial or total power failure of the device  14 . This bypass path would allow traffic to continue to move across the network without delay.  
         [0030]     As illustrated in  FIG. 3 , in one embodiment, the bypass switch  16  is incorporated directly in the network device  14 . Specifically, the bypass switch  16  is located on a Media Device Interface (MDI) bus (not shown) between the connectors  20  and the respective network isolation components  22 , such as transformers. The bypass switch  16  utilized is a normally closed switch and may be of several types, as generally known by those skilled in the art. When the network device  14  is inoperable, such as not being powered or being broken, the normally closed bypass path is connected. Any traffic entering one of the ports  17 , 18  of the connector  20  is sent back out the respective port  17 , 18  on the other connector  20  without being transmitted through the network isolation component  22 . It is important to note that the bypass switch  16  connects the receive port of one connector  20  to the transmit port of the other connector  20 . Further, it is also important that the polarity be correctly maintained such that the negative stream remains connected to the negative stream and the positive stream remains connected to the positive stream.  
         [0031]     The network device  14  may be in a bypass mode or an operational mode. The network device  14  automatically enters the operational mode when the power on the network device  14  is stable and at an adequate level. Conversely, the network device  14  automatically enters a bypass mode with the loss of power or when the network device  14  is otherwise inoperable.  
         [0032]     If the network device  14  is in operational mode and power is applied to the network device  14 , the pole control  19  of the bypass switch  16  is brought to a logical one and the bypass path will be broken allowing the connectors  20  to operate normally. This may be done automatically by power from the network device  14  through a control line  21  or may be part of a control function by the processing logic of the network device  14  through the control line  21 , or a combination of both. In addition, the processing logic can place the network device  14  in bypass mode at any time during operation if desired.  
         [0033]     The control function of the bypass switch  16  requires the bypass switch  16  to be powered in order to be taken out of its normal state, thereby putting the network device  14  into bypass mode. It is preferable that the normal state of the bypass switch  16  is closed such that when the device  14  is not powered the information path of the device  14  is bypassed. When a logical one is driven to the control pin  21  of the bypass switch  16 , the switch  16  will be in an open state, thereby taking the device  14  out of bypass mode and into operational mode.  
         [0034]     The control line  21  to the pole control  19  of the bypass switch  16  may be managed by a general purpose I/O pin (not shown) from any source such as a Physical Layer chip, a MAC chip, or a processor, etc (not shown). This permits the network device  14  to be taken in and out of the information path as desired. In addition, loss of power will automatically cause the device  14  to enter a bypass mode. The control line  21  may also be tied to the power of a processor (not shown) on the network device  14  such that when the processor has power the information path will open and the network device  14  will turn off the bypass path.  
         [0035]     It is noted that proper isolation be maintained between the network ground  37 , where the Ethernet connectors  22  reside, and the logic ground  39  where the rest of the device components reside on the control line  21  to insure no unwanted emissions cross between the two ground planes. This isolation may be provided with a ferrite bead  23  using a DC logic state signal to control the bypass switch  16 . The use of a ferrite bead  23  is preferable if the control line  21  is tied to power and not to the general purpose I/O pin (not shown).  
         [0036]     In instances where the bypass switch  16  is implemented directly on the network device  14 , the information path may be disrupted while a failed network device  14  is replaced. To overcome this disruption of the information path for the replacement or repair of a failed device, the bypass switch  16  may be located on a removable adapter  40 , as shown in  FIG. 4 . Although the bypass switch  16  is located on a removable adapter, it comprises substantially the same structure and functionality of a bypass switch  16  located directly on the network device  14 .  
         [0037]     When a network device  14  fails, it is separated from the adapter  40 . The adapter  40  remains connected to the Ethernet cables from the network  10  leaving the information path intact. When the failed network device  14  is fixed or replaced, the network device  14  is reconnected to the network  10  through the removable adapter  40 , thereby reestablishing the network device  14  into the network  10 .  
         [0038]     Referring to  FIG. 4  the removable adapter  40  can be incorporated in an IP20 environment or a IP67 environment. Preferably, the removable adapter  40  has male connectors  42  on the side of the adapter  40  connected to the jacks  46  of the network device  14  and female connectors  44  on the side of the adapter connected to the network  10 . The size of the adapter  40  is dominated by the size of the male and female connectors  42 ,  44 . The bypass switch  16  located within the adapter  40  and any associated logic would take up relatively little space in comparison.  
         [0039]     IP20 is an industrial automation designation describing a relatively benign environment where the components inside of that environment are not required to be sealed against the hazards of the environment. The IP20 removable adapter  40  comprises two board-mounted male RJ-45 connectors  42 , two board-mounted RJ-45 receptacles  44 , the bypass switch  16 , a board (not shown) and a housing enclosing the components.  
         [0040]     Power to the removable adapter  40  may come from the network device  14  to which the adapter  40  will be connected. However, it is noted that the adapter may be powered by any means known to those of ordinary skill in the art. Preferably, the removable adapter  40  is not continuously powered as this may affect the Ethernet signal in a network  10  that does not support or use the removable adapter  40 . As a result, the present embodiment permits power to the be supplied to the removable adapter  40  from the supporting network device  14  when connected to the supporting network device  14  and the power to be inhibited from use when the removable adapter  40  is not present.  
         [0041]     The male and female RJ-45 connectors  42 ,  44  can support eight conductors. However, Ethernet information is sent on only four conductors for 10/100 Ethernet. As a result, the remaining four conductors may be set up to allow a simple resistor logic to act as an enable/inhibit line (not shown). One pin from the unused pins on one of the RJ-45 connectors  42  is the enable/inhibit line. Another pin from the unused pins of the RJ-45 connectors  42  is used to drive the control logic of the bypass switch  16 . When the network device  14  detects that the removable adapter  40  is connected and power is present on the network device  14 , the network device  14  opens the bypass path on the bypass switch  16 .  
         [0042]      FIG. 5  illustrates power activation on a removable adapter  40 . The network device  14  comprises power drive circuitry  50 , such as an Op Amp  50  or other non-inverting driver, to supply power to the removable adapter  40  over one of the unused pins of one of the RJ-45 connectors  42 . The Op Amp  50  drives power to the removable adapter  40  and the enable/inhibit signal is brought low with the connection of the removable adapter  40  to the network device  14 .  
         [0043]     The removable adapter  40  of the present invention may be inserted to and removed from the network device  14  when power is being applied to the network device  14 . Precautions maybe necessary to protect against in-rush current as the IP20 removable adapter  40  is inserted or connected to the network device  14  when the network device  14  is powered. As a result, the removable adapter  40  may comprise circuitry  52  to protect against in-rush current to the power and ground of the bypass switch  16 . Generally, the amount of current to drive the bypass switch  16  is low, thus small value resistors may be utilized if required.  
         [0044]     The circuit  52  of the IP20 removable adapter  40  to protect against in-rush current to the power and ground of the bypass switch  16  may be a pull-up resistor  52 . The output of the power drive circuitry  50  is coupled to the pull up resistor  52  to prevent driving the power out the RJ-45 connector  46  if the removable adapter  40  is not present. When the pull up resistor  52  is used and the adapter  40  is not in use, the output of the power drive circuit  50  uses a transistor or other logic (not shown) to isolate the pull up resistor  52  from the RJ-45 connector  46 . If a transistor or other logic is not used, the network device  14  may drive a DC voltage level over the RJ-45 connector  46  when the adapter is not in use. The network device  14  has an adaptable termination on the unused pins from the RJ-45 connector  46  to allow the use of enable/inhibit logic and the power logic. Typically some form of termination, such as the “Bob Smith” termination described in U.S. Pat. No. 5,321,372, is employed on unused pins in the Ethernet connection.  
         [0045]     As set forth above, an IP67 removable adapter  60  can be utilized, as illustrated in  FIG. 6 . IP67 is an industrial automation designation describing a relatively harsh environment where the components inside of that environment are required to be sealed against the hazards of the environment. Unlike the IP20 removable adapter  40 , the IP67 removable adapter  60  utilizes M12 connectors  62 . The M12 connector  62  is a type of connector with male and female components used in IP67 environments, that when connected together, seal the device and the cable from the outside elements.  
         [0046]     The M12 connectors  62  used in industrial networks have four pins and no extra pins upon which to send the enable/inhibit signal and the power. Therefore the enable/inhibit signal and power to the bypass switch  16  must be sent over two pins with the data. Consistent with this design, the enable/inhibit signal can not be a simple pull down resistor to ground since this would ground the data signal.  
         [0047]     In order to solve this problem, the network device  14  may have a power injector  67  to send power over a data pin if the power is terminated on the adapter  60 . This is to ensure that no power is leaked over the network  10  to the next network device  14 . The power injector  67  may be power over Ethernet which allows the electrical current necessary for the operation of each adapter  60  to be carried by the data cables rather than by power cords.  
         [0048]     In addition, the power injector can use an isolated driver (not shown), similar to the non-inverting driver  50  discussed above. This minimizes the number of wires that must be used in order to install the network  10 . The result is lower cost, less downtime, easier maintenance, and greater installation flexibility than with traditional wiring.  
         [0049]     Similar to the IP20 removable adapter  40 , precautions maybe necessary to protect the IP67 removable adapter  60  against in-rush current as it is inserted or connected to the network device  14  when the network device  14  is powered. Thus, the IP67 removable adapter  60  can include built in circuitry  69  to protect against in-rush current if it uses a power over Ethernet style power insertion. The amount of power driven to the IP67 removable adapter  60  is minimal and does not need to be sent off the adapter  60 . As such, the IP67 removable adapter  60  may include a cost effective low-drive tap  69 .  
         [0050]     In yet another embodiment, the bypass switch  16  is implemented on separate removable adapter that is cabled to the network device  14 . The removable adapter  40  may be a IP20 removable adapter  40  or a IP67 removable adapter  60 . Additionally, the removable adapter  40 , 60  may be coupled to the network device  14  using four-wire cabling of eight-wire cabling.  
         [0051]      FIG. 7  illustrates an IP20 removable adapter  40  using four-wire cabling and  FIG. 8  illustrates an IP20 removable adapter using eight-wire cabling. With reference to  FIG. 7 , the IP20 removable adapter  40  is coupled to the network device  14  utilizing IP20 (four-wire) industrial Ethernet cables  63 . Preferably, a four-wire version CAT-5E Ethernet cable, as those typically employed in industrial automation, is utilized to connect the removable adapter  40  to the network device  14 . In the network  10  of  FIG. 7 , male RJ-45 connectors  42  are attached to the ends of the industrial Ethernet cable  63 . The same power injection  67  employed in the IP67 removable adapter  60 , as described above, is used in the IP20 removable adapter  40  because only four conductors are available in this configuration of the Ethernet cable  63 . Additionally, built in circuitry  69  similar to the IP67 removable adapter  60  can be utilized to protect against in-rush current.  
         [0052]     Referring to  FIG. 8 , the IP20 removable adapter  40  utilizes an eight-wire Ethernet cable  65  to couple the removable adapter  40  with the network device  14 . In the removable adapter  40  of  FIG. 8 , male RJ-45 connectors  42  are attached to the ends of the Ethernet cable  65 . The RJ-45 connectors  42  support eight conductors. Ethernet information is transmitted on four conductors for 10/100 Ethernet. As a result, the remaining four conductors are set up to allow a simple resistor logic  52  to act as an enable/inhibit line to the network device  14 , in a manner similar to that described above.  
         [0053]     It is also contemplated that the power injection  67  utilized in the IP20 removable adapter  40  using four-wire cabling may also be utilized in the an IP20 removable adapter  40  using eight-wire cabling. Similarly, low-drive tap  69  may also be utilized in the IP20 removable adapter  40  using eight-wire cabling.  
         [0054]     In another embodiment, an external power connection  112  separated from the Ethernet connection connects the removable adapter  40 ,  60  to the network device  14 , as shown in  FIG. 9 . The external power connection  112  is utilized to detect and use power from the network device  14  that is to be protected or bypassed. The external power connection  112  may be utilized with both the IP20 removable adapter  40  and the IP67 removable adapter  60 . The removable adapters  40 , 60  may include built-in circuitry  52  to protect against in-rush current.  
         [0055]     When utilized with an IP20 removable adapter  40 , the external power connection  112  uses a standard bullet plug to connect the network device  14  to the removable adapter  40 . The external power connection  112  should use power cables that are rated for use in an IP20 environment. Preferably, the external power connection  112  has two male ends that connect to corresponding female power acceptors  114  on the network device  14  and the removable adapter  40 . In another embodiment, the external power connection  112  may be a single wire connecting a screw terminal on the network device  14  to a screw terminal on the removable adapter  40 .  
         [0056]     As noted, the external power connection  112  may also be utilized with an IP67 removable adapter  60 . In the IP67 environment, the power acceptors  114  on the network device  14  and the adapter  40  must be sealed against the environment. In addition, the external power connection  112  should use power cables that are rated for use in an IP67 environment.  
         [0057]     The adapters  40 , 60  may be physically secured to the network device  14  to which they are providing a bypass path. In an IP67 environment, only two attach points (not shown) are used as securing connections because the adapter  60  is relatively small and the M12 connectors  62  provide a very secure connection. However, a screw connection, or other type of fastener, on the IP67 adapter  60  that mates with a corresponding connector on the network device  14  may be utilized to provide addition attachment. An IP20 adapter  40  may be secured using the RJ-45 connectors  42 . Additional connections may be utilized to secure the IP20 adapter  40  to the network device  14  and provide protection against light stress or vibration loads. Female connectors may be used for all connections on the removable adapter  40 , 60  and network devices  14 . Standard cables may be used to connect the network device  14  and the removable adapter  40 , 60  thereby allowing convenient mounting.  
         [0058]     Similar to the control line  21  of the bypass switch  16  residing directly on the network device, the control line (not shown) to the removable adapter  40 ,  60  may be controlled by the power status of the network device  14 . For example, if the network device  14  is sufficiently powered, the removable adapter  40 , 60  is automatically taken out of bypass mode. Control may also be handled by intelligent logic on the network device  14  that places the removable adapter  40 , 60  into bypass mode if desired even though the network device  14  is powered. This may be used to perform maintenance on the network device  14  without removing the network device  14  from the network  10 .  
         [0059]     When the removable adapter  40 , 60  is connected to the network device  14  and the network device  14  is initially powered up, there is a need to ensure the network device  14  does not interrupt the current traffic on the network  10 . Firmware may be used to control the introduction of the network device  14  back into the network  10 . If the network  10  is busy when the network device  14  is inserted into the adapter  40 , 60 , the network device  14  will become active on the network  10  at an appropriate time that does not affect the flow of traffic on the network  10 .  
         [0060]     Preferably, the network device  14  includes logic to make an intelligent decision as to when it becomes active on the network  10 . Normally open relays on the signals going to and from the network device  14  within the removable adapter  40 , 60  may be used to ensure the network device  14  does not improperly drive or take control of the Ethernet connectors before the system is ready to pass control to the network device  14  or accept Ethernet traffic from the network device  14 . The transmit path on the removable adapter  40 , 60  (which is the receive path on the network device  14 ) may not require the normally open relays because the network device  14  does not drive these signals. Allowing the transmit paths to the network device  14  to be open will permit the network device  14  to snoop the traffic on the network  10 . The snooping capability permits the network device  14  to participate in the decision as to when to become active on the network  10 .  
         [0061]     While the specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying Claims.