Abstract:
A system and method for configuring a slot to be compatible with both modules that are compliant with the isolation requirements for power over Ethernet and modules that are not compliant.

Description:
RELATED APPLICATIONS 
   This application claims priority from a provisional application entitled SYSTEM AND METHOD FOR PROVIDING COMPATIBILITY WITH BOTH ELECTRICALLY ISOLATED AND NON-ISOLATED MODULES IN AN ETHERNET SYSTEM, filed Oct. 4, 2004, A/N 60/615,910, which is hereby incorporated by reference for all purposes. 

   BACKGROUND OF THE INVENTION 
   Incompatibility between new and existing products is a major problem in many technical disciplines including networking and signal switching. Often new products are developed having increased performance and speed but customers have invested heavily in legacy products. 
   Incompatibility is a particular problem with routing-platforms. Generally a router includes a chassis which can be rack mounted and has different types of slots into which cards and modules slide into, and also contains basic components such as power supply(s) and fan(s). The modules inserted into the slots are line cards which are the actual printed circuit boards that handle packet data and analog signaling ingress and egress. Line cards provide one or more interfaces over which traffic flows. Thus, depending on the number of slots and interfaces, a router can be configured to work with a variety of networking protocols. 
   In some cases slots compatible with a new versions of a module are incompatible with legacy modules. One example is where new modules are designed for receiving power in tandem with 10/100/1000 Mbps data according to the Power over Ethernet (PoE) standard (IEEE 802.3af). PoE modules must be isolated from the backplane and are provided with a second connector (−48VRET) coupled to the power supply for −48V return current. 
   However, a slot designed to received devices utilizing PoE is not compatible with legacy parts that are powered by conventional techniques. 
   The challenges in the field of communications continue to increase with demands for more and better techniques having greater flexibility and adaptability. Therefore, a need has arisen for a new system and method for providing reconfigurable slots in a router chassis. 
   BRIEF SUMMARY OF THE INVENTION 
   In one embodiment of the invention, a module includes identification information that is read when the module is inserted into a slot and prior to power being applied to the module. The identification information is utilized to determine whether the module is compliant with the power over Ethernet isolation requirements. If the module is compliant then current is returned via a −48V return line and the compliant module is isolated from the ground plane. If the module is non-compliant module then current is returned via the ground plane. 
   In another embodiment of the invention, a relay connects the −48V return line to the ground plane. If a compliant module is inserted the relay is opened to isolate the return line from ground. If a non-compliant module is inserted the relay is closed to couple the −48V return line to the ground plane. 
   In another embodiment of the invention, the relay is a normally closed relay that is closed when no power is applied to the relay and open when power is applied to the relay. 
   Other features and advantages of the invention will be apparent in view of the following detailed description and appended drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram depicting the connection between a PSE and a non-compliant module. 
       FIG. 2  is a block diagram depicting the connection between a PSE and a compliant module. 
       FIG. 3  is a flow chart for implementing an embodiment of the invention. 
       FIG. 4  is block diagram of an embodiment of the invention utilizing a normally closed relay. 
       FIG. 5  is a flow chart for implementing an embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to various embodiments of the invention. Examples of these embodiments are illustrated in the accompanying drawings. While the invention will be described in conjunction with these embodiments, it will be understood that it is not intended to limit the invention to any embodiment. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the various embodiments. However, the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
   An embodiment of the invention will now be described that is configurable to support devices powered by PoE having a −48V return that must be isolated from the ground plane and legacy devices that return −48V current through the ground plane. In the following the term “slot” refers to any structure that physically accepts a module and connects circuits in the module to other circuits in a system. 
     FIG. 1  is a block diagram of the power and return scheme for a non-compliant module that is not compliant with the isolation requirement of IEEE 802.3af.  FIG. 1  depicts a non-compliant module  10  having power and return terminals  12  and  14  and a PSE (power sourcing equipment)  20  having positive and negative terminals  22  and  24 . 
   In  FIG. 1  the positive terminal  22  of the PSE  20  is connected to the power terminal  12  of the non-compliant module  10  by a +48V power line and both the negative terminal  24  of the PSE  20  and the return terminal  14  of the non-compliant module  10  are connected to a ground plane. 
   Also, as depicted in  FIG. 1  the non-compliant module  10  includes a non-volatile memory (NVMEM)  16  that holds information about the module including identification information. This module is accessed by a controller  30  through a control bus  32 . The identification information is utilized by control software to determine whether the module is compliant with the IEEE 802.3af standard. 
     FIG. 2  is a block diagram of the power and return scheme for a compliant module that utilizes PoE and is compliant with the isolation requirements of IEEE 802.3af.  FIG. 1  depicts a compliant module  40  having power and return terminals  42  and  44  and PSE  20  having positive and negative terminals  22  and  24 . 
   In  FIG. 2  the positive terminal  22  of PSE  20  is coupled to the power terminal  42  of the compliant module  40  by the +48V power line and the negative terminal  24  of the PSE is connected to the return terminal  44  of the compliant module  40  by the −48VRET line. The return terminal  44  of the compliant module  40  must be isolated from the ground plane to be compatible with the isolation requirements of IEEE 802.3af. The compliant module  40  also included a NVMEM  16  holding compliance information that can be accessed by the controller  30 . 
   A technique for configuring a slot to be compatible with either a compliant or non-compliant will now be described with reference to the flow chart of  FIG. 3 . When a module is inserted into a host platform a controller on the host platform accesses the identification information stored in the NVMEM prior to applying power to the newly inserted module. 
   If the accessed identification information indicates that the newly inserted module is a compliant module then the return terminal of the newly inserted module is isolated from the ground plane and −48V return current is returned to the PSE utilizing a −48VRET line. 
   If the accessed identification information indicates that the newly inserted module is a non-compliant module then no action is required because a relay is already configured to connect the return terminal of the newly inserted module to a ground plane and −48V return current is returned to the PSE via the ground plane. 
   An embodiment of a system for selectively connecting the ground terminal of an inserted module to the −48VRET line or the ground plane will now be described with reference to  FIG. 4 . 
   In  FIG. 4  an inserted module  60  is has its power terminal  62  connected to the positive terminal  22  of the PSE  20  by a +48V power line and has its return terminal  64  coupled to the negative terminal  24  of the PSE  20  by the −48VRET line. The −48VRET line is coupled to the ground plane by a normally closed relay  70 . 
   The operation of the system depicted in  FIG. 4  will now be described with reference to the flow chart of  FIG. 5 . When the module is inserted the identification information in the NVMEM is accessed by the controller to determine whether the inserted module is compliant or non-compliant. 
   If the module is a compliant module then power is applied to open the relay to isolate the return terminal of the module from the ground plane so that −48V return current is returned to the PSE via the −48VRET line. 
   If the module is non-compliant power is not applied to the relay so that the −48VRET line remains coupled to the ground plane and −48V return current is returned to the PSE via the ground plane. 
   Relays may be damaged if current flows through the relay while it is changing state. Accordingly, the system is designed so that when power is off the relay is closed to protect the relay from damage if power to the system is lost or interrupted. 
   This is because for a compliant module where the relay is normally open current will continue to return via the −48VRET line even if the relay is switched to the closed position due to the higher resistance of the relay compared to the −48VRET line. However, for a non-compliant module, where the relay is normally closed, current would change from flowing through the relay to flowing through −48V return line if relay is switched to the open state. 
   Accordingly, by utilizing a relay that is normally closed, i.e., is closed when no power is applied, a loss of power will not cause the relay to change state when a non-compliant module is connected. 
   The invention may be implemented as program code, stored on a computer readable medium, that is executed by a digital computer. The computer readable medium may include, among other things, magnetic media, optical media, electro-magnetic fields encoding digital information, and so on. 
   The invention has now been described with reference to the preferred embodiments. Alternatives and substitutions will now be apparent to persons of skill in the art. Accordingly, it is not intended to limit the invention except as provided by the appended claims.