Abstract:
A system and method for policing bad powered devices in power over Ethernet. Degradation of components within powered devices can lead to noise and ripple that exceed specified thresholds. This noise and ripple can adversely impact the operation of the power sourcing equipment. A noise detector implemented in the power sourcing equipment can detect the presence of such noise and ripple and modify the application of power to the particular port.

Description:
This application claims priority to provisional application No. 61/230,142, filed Jul. 31, 2009, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to power over Ethernet (PoE) and, more particularly, to a system and method for policing bad powered devices in PoE. 
     2. Introduction 
     In a PoE application such as that described in the IEEE 802.3af and 802.3 at specifications, a power sourcing equipment (PSE) can deliver power to a powered device (PD) over Ethernet cabling. Various types of PDs exist, including voice over IP (VoIP) phones, wireless LAN access points, Bluetooth access points, network cameras, computing devices, etc. 
     In accordance with IEEE 802.3af, a PSE can deliver up to 15.4 W of power to a single PD over two wire pairs. In accordance with IEEE 802.3 at, on the other hand, a PSE may be able to deliver up to 30 W of power to a single PD over two wire pairs. Other proprietary solutions can potentially deliver higher or different levels of power to a PD. A PSE may also be configured to deliver power to a PD using four wire pairs. 
     In the PoE process, a valid device detection is first performed. This detection process identifies whether or not a PSE is connected to a valid PD to ensure that power is not applied to non-PoE capable devices. After a valid PD is discovered, the PSE can optionally perform a power classification. In a conventional 802.3af allocation, each PD would initially be assigned a 15.4 W power classification after a Layer 1 discovery process. An optional classification process could then reclassify the PD to a lower power level. In more complex PoE schemes, a Layer 2 classification engine can be used to reclassify the PD. Layer 2 classification processes can be included in PoE systems such as 802.3af, 802.3 at or proprietary schemes. 
     PSEs are generally designed to manage a set of subscribing PDs. These PDs can be designed by various manufacturers and can be qualified based on standards of operational performance indicated by a PoE specification. While this qualification ensures that a PD can interoperate with a PSE from another manufacturer, it may not accurately reflect the potential degradation of PD performance over time due to aging of PD components. This degradation in PD performance can have a significant impact on PSE operation. What is needed therefore is a mechanism that enables a PSE to monitor and police PDs to determine when a PD&#39;s performance has degraded beyond a certain threshold. 
     SUMMARY 
     A system and method for policing bad powered devices in Power over Ethernet, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to describe the manner in which the above-recited and other advantages and features of the invention can be obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  illustrates an embodiment of a PoE system. 
         FIG. 2  illustrates a connection between a PSE and PD. 
         FIG. 3  illustrates a PSE according to the present invention. 
         FIG. 4  illustrates a band-pass filter implemented by a noise detector in the PSE. 
         FIG. 5  illustrates an example of a noise detector. 
         FIG. 6  illustrates a flowchart of a process of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the invention are discussed in detail below. While specific implementations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without parting from the spirit and scope of the invention. 
     In an enterprise environment, a PoE system can be used to power a network of PDs.  FIG. 1  illustrates an example of such a PoE system. As illustrated, the PoE system includes PSE  120  that transmits power to PD  140  over two wire pairs. Power delivered by PSE  120  to PD  140  is provided through the application of a voltage across the center taps of a first transformer that is coupled to a transmit (TX) wire pair and a second transformer that is coupled to a receive (RX) wire pair carried within an Ethernet cable. In general, the TX/RX pairs can be found in, but not limited to structured cabling. 
     The two TX and RX pairs enable data communication between Ethernet PHYs  110  and  130  in accordance with 10BASE-T, 100BASE-TX, 1000BASE-T, 10GBASE-T and/or any other Layer 2 PHY technology. Here, it should be noted that PoE does not require the presence of a PHY. 
     As is further illustrated in  FIG. 1 , PD  140  includes PoE module  142 . PoE module  142  includes the electronics that would enable PD  140  to communicate with PSE  120  in accordance with a PoE specification such as IEEE 802.3af (PoE), 802.3 at (PoE Plus), legacy PoE transmission, or any other type of PoE transmission. PD  140  also includes controller  144  (e.g., pulse width modulation (PWM) DC:DC controller) that controls power transistor (e.g., FET)  146 , which in turn provides constant power to load  150 . 
       FIG. 2  provides a simplified illustration of a connection (without showing the transformers) between a PSE and PD. As illustrated, PSE  210  provides power to a controller such as PWM DC:DC controller  222  within PD  220  via decoupling capacitor  224 . In a conventional implementation, decoupling capacitor  224  can be embodied as a 100 μF. aluminum electrolytic capacitor. 
     In IEEE 802.3af and IEEE 802.3 at, the PD power supply limits are specified as follows: 
                                                 Ripple and Noise, &lt;500 Hz   0.5 V pp             Ripple and Noise, 500 Hz to 150 kHz   0.2 V pp             Ripple and Noise, 150 kHz to 500 kHz   0.15 V pp             Ripple and Noise, 500 kHz to 1 MHz   0.1 V pp                          
This requirement is identical to the power feeding ripple and noise requirement that is specified for the PSE.
 
     In the present invention, it is recognized that one of the issues of concern is the degradation of the performance of the PD, which can lead to electromagnetic interference (EMI) pollution via radiation from the cables. One of the potential culprits is the aging of decoupling capacitor  224 . 
     A typical aluminum electrolytic capacitor is allowed by many PD vendors to have an equivalent series resistance (ESR) that can increase over three times from its initial value before the aluminum electrolytic capacitor is considered a wear-out failure. This wear-out failure of the aluminum electrolytic capacitor can determine the useful life of the entire PD itself. 
     More specifically, the increase in ESR of decoupling capacitor  224  can lead to a high voltage ripple being produced by PWM DC:DC controller  222  of PD  220  onto the cable. In one example, PWM DC:DC controller  222  can have a switching frequency of 100 or 125 kHz. This switching frequency can produce a high voltage ripple at a sub-harmonic or harmonic frequency. For example, a switching frequency of 125 kHz by PWM DC:DC controller  222  can produce a high voltage ripple at a sub-harmonic frequency of 62.5 kHz. The size of the voltage ripple would be greatly dependent on the ESR of decoupling capacitor  224 . 
     It is a feature of the present invention that the high voltage ripple produced by the PD can be detected by the PSE.  FIG. 3  illustrates an embodiment of such a detection mechanism in the PSE. As illustrated, PSE  300  includes power supply  302 , which is designed to provide power to a PD via a connected cable. Typically, the power output of PSE  300  is very quiet. Accordingly, the noise and ripple generated by PSE  300  is unlikely to affect the proper functioning of the PD. The noise and ripple generated by the PD, on the other hand, is highly variable due to the potential ESR changes of the decoupling capacitor at the input of the PD controller. Notwithstanding this fact, the ripple and noise requirements that are imposed on the PD are identical to the ripple and noise requirements that are imposed on the PSE. 
     The noise and ripple generated by the PD can significantly affect the functioning of the PSE. For this reason, PSE  300  includes noise detector  304 , which is coupled to the cable that delivers power to the PD. Noise detector  304  is generally designed to detect a voltage ripple generated by the PD. In one embodiment, noise detector  304  performs a voltage ripple measurement. As the voltage measurement can be dependent on the particular point of measurement, in an alternative embodiment, noise detector  304  performs a current ripple measurement. This current ripple measurement is advantageous in that the current ripple measurement can be performed anywhere on the cable. 
     In general, the detection of a ripple that exceeds the imposed requirement can lead to the modification of power that is applied to the PD. As illustrated in  FIG. 3 , this detection can lead to the cutting off of power to the PD using switch  308  that is under the control of controller module  306 . 
     As noted, the frequency of the voltage ripple can be located on a sub-harmonic or harmonic of the switching frequency of the PWM DC:DC controller. Accordingly, in one embodiment, noise detector  304  is further designed to implement a band-pass filter such as that illustrated in  FIG. 4  to capture the target frequency range of detection. The example band-pass filter of  FIG. 4  is generally designed to capture the ripple at sub-harmonic or harmonic frequencies. As would be appreciated, the particular design of the filtering implemented by the noise detector would be implementation dependent. 
       FIG. 5  illustrates an embodiment of a detection mechanism implemented by the noise detector in the PSE. As illustrates, noise detector  500  includes comparator  510  that is operative to compare an input value to a threshold value. The result of comparator  510  is used as an input to pulse counter  520 . Pulse counter  520  is designed to count the number of times the input value exceeds the threshold value during a measurement period (e.g., 100 ms) defined by counter  530 . A full value output by counter  530  is provided to one pulse generator  540 , which then outputs a reset signal to counters  520  and  530 . The full value output by counter  530  is also used as a load signal for register  550  to load the value of pulse counter  520 . The resulting value of pulse counter  520  provides an indication not only of a presence of a ripple that exceeds the threshold value, but also the number of times of such an occurrence within the measurement period. The value of register  550  will therefore provide an indication of the frequency of such a ripple signal (e.g., counter value of 25000 over 100 ms measurement period indicates a frequency of 25 kHz). An advantage of an implementation such as that illustrated in  FIG. 5  is that it enables the creation of a detailed EMI profile up to a certain frequency. 
     Having described an example implementation of a noise detection mechanism within a PSE, reference is now made to the flowchart of  FIG. 6  to illustrate further features of the present invention. As illustrated, the process begins at step  602 , where the PSE activates the noise detector for measurement on a selected port. In one embodiment, the noise detector can be activated to detect in a sequential manner the presence of a ripple signal on a plurality of ports that are connected to a previously detected PD. As would be appreciated, the noise detector can be designed to be turned on for a window of time that is sufficient to detect the presence of a ripple signal in a reliable manner. This window of time can be dependent on the quality and accuracy of the components used in the noise detector itself. 
     At step  604 , the noise detector would filter the input signal to determine the presence of a ripple signal in a given frequency range. This frequency range can be designed to cover the expected variations in switching frequency of the controllers of various PD manufacturers to which the PSE can be connected. As would be appreciated, the particular frequency range chosen would be implementation dependent. 
     At step  606 , the noise detector would determine whether a ripple voltage exists on the cable on the selected port. As noted, the ripple voltage determination can be based on various voltage or current measurements. Next, at step  608 , it is determined whether the detected ripple exceeds the ripple threshold. In one embodiment, the threshold is contained as part of EMI profile that covers a range of thresholds for a corresponding plurality of frequency ranges. Additionally, in one embodiment, multiple thresholds for a single frequency range can be used to enable detection of a degradation of performance by the PD prior to reaching a state of failure. 
     If, at step  608 , it is determined that the ripple does not exceed the threshold, then the process continues to step  602  where another port can be selected for analysis. If, on the other hand, at step  608 , it is determined that the ripple does exceed the threshold, then the process continues to step  610  where a controller in the PSE can modify the power delivered to the port under analysis. In one example, the controller can choose to cut off all power to that port. In another example, the controller can choose to lower the power level delivered to that port, thereby preserving some level of functionality on that PD prior to shutting down all power being delivered. 
     It should be noted that the principles of the present invention can be applied to various networks that use standard or non-standard (e.g., 2.5 G, 5 G, etc.) link rates, as well as future link rates (e.g., 40 G, 100 G, etc.). Also, the principles of the present invention can be applied to various single-pair, two-pair and four-pair PoE applications, or more generally, a power delivery application using at least a pair of conductors. 
     These and other aspects of the present invention will become apparent to those skilled in the art by a review of the preceding detailed description. Although a number of salient features of the present invention have been described above, the invention is capable of other embodiments and of being practiced and carried out in various ways that would be apparent to one of ordinary skill in the art after reading the disclosed invention, therefore the above description should not be considered to be exclusive of these other embodiments. Also, it is to be understood that the phraseology and terminology employed herein are for the purposes of description and should not be regarded as limiting.