Patent Publication Number: US-2007110360-A1

Title: Dynamic power allocation in system for providing power over communication link

Description:
This application claims priority of and incorporates by reference provisional U.S. patent application No. 60/736,328 filed on Nov. 15, 2005, and entitled “SYSTEM AND METHOD FOR SUPPORTING ADVANCED POWER OVER ETHERNET SYSTEM.” 
    
    
     TECHNICAL FIELD  
      This disclosure relates to power supply systems, and more particularly, to circuitry and methodology for performing dynamic power allocation in a system for providing power over a communication link, such as a Power over Ethernet (PoE) system.  
     BACKGROUND ART  
      Over the years, Ethernet has become the most commonly used method for local area networking. The IEEE 802.3 group, the originator of the Ethernet standard, has developed an extension to the standard, known as IEEE 802.3af, that defines supplying power over Ethernet cabling. The IEEE 802.3af standard defines a Power over Ethernet (PoE) system that involves delivering power over unshielded twisted-pair wiring from a Power Sourcing Equipment (PSE) to a Powered Device (PD) located at opposite sides of a link. Traditionally, network devices such as IP phones, wireless LAN access points, personal computers and Web cameras have required two connections: one to a LAN and another to a power supply system. The PoE system eliminates the need for additional outlets and wiring to supply  
      As defined in the IEEE 802.3af standard, PSE and PD are non-data entities allowing network devices to supply and draw power using the same generic cabling as is used for data transmission. A PSE is the equipment electrically specified at the point of the physical connection to the cabling, that provides the power to a link. A PSE is typically associated with an Ethernet switch, router, hub or other network switching equipment or midspan device. A PD is a device that is either drawing power or requesting power. PDs may be associated with such devices as digital IP telephones, wireless network access points, PDA or notebook computer docking stations, cell phone chargers and HVAC thermostats.  
      The main functions of the PSE are to search the link for a PD requesting power, optionally classify the PD, supply power to the link if a PD is detected, monitor the power on the link, and disconnect power when it is no longer requested or required. A PD participates in the PD detection procedure by presenting a PoE detection signature defined by the IEEE 802.3af standard.  
      If the detection signature is valid, the PD has an option of presenting a classification signature to the PSE to indicate how much power it will draw when powered up. Based on the determined class of the PD, the PSE applies the required power to the PD.  
      To make sure that PoE system will operate under worst case conditions, the PD should request power corresponding to its peak power usage. The PSE keeps track of power allocated to all PDs. For the most robust operation, the PSE should reserve the peak power for each PD that it powers up. This power allocation scheme is static. The power is allocated to each PD only once at power-up.  
      However, power available to support operations of the PDs is limited. PSE will deny request for power from an additional PD if the available power is not sufficient to support its peak power usage. Therefore, it would be desirable to create a flexible power allocation scheme that would be able to support the maximum number of PDs.  
     SUMMARY OF THE DISCLOSURE  
      The present disclosure offers a novel system and methodology for supplying power to a powered device over a communication link, such as an Ethernet link. In particular, the system of the present disclosure comprises a power supply device for providing power to a powered device (PD), and a dynamic power allocation mechanism for dynamically modifying power allocated to the PD in accordance with tasks of the PD.  
      In accordance with one aspect of the disclosure, the power supply device is configured for providing power to the PD over a physical layer of a data network, and the dynamic power allocation mechanism is responsive to information transferred over a link layer of the data network.  
      The dynamic power allocation mechanism may be configured to reduce power allocated to the PD when the PD switches to a first task associated with a decrease in power consumption, and to increase power allocated to the PD when the PD switches to a second task associated with an increase in power consumption.  
      The power supply device may be configured to provide power to multiple powered devices (PDs). The dynamic power allocation mechanism may modify power allocated to the PDs based on tasks of the respective PDs. For example, power allocated to each PD may be modified when the respective PD changes a task being performed.  
      When the dynamic power allocation mechanism reduces or removes power allocated to a first PD, this power may be reallocated to a second PD. For example, the first PD may switch to a task associated with a lower power consumption, whereas the second PD switches to a task associated with a higher power consumption. Also, power may be reallocated from one PD to another if a power shortage is detected.  
      The system may further comprise a priority mechanism for assigning priorities to the PDs. The dynamic power allocation mechanism may reduce or remove power allocated to a lower-priority PD before reducing or removing power allocated to a higher-priority PD if a power shortage is detected.  
      Further, power allocated to a lower-priority PD may be reduced or removed to satisfy power demand from a higher-priority PD if a power shortage is detected.  
      The priority mechanism may dynamically change priorities assigned to the PDs during operations of the PDs, for example, in accordance with their tasks.  
      A task keeping mechanism may be provided for maintaining information on tasks to be performed by the PD. For example, the task keeping mechanism may maintain information on power and/or current consumption associated with each of the tasks.  
      In accordance with another aspect of the disclosure, a dynamic current allocation mechanism may be provided to dynamically modify current supplied by the power supply device to the PD in accordance with a current consumption level associated with a task of the PD.  
      In accordance with a further aspect of the disclosure, a local area network may comprise at least a pair of network nodes, a network hub, and communication cabling for connecting the network nodes to the network hub to provide data communications. The network hub may have a power supply device for providing power to a powered device over the communication cabling, and a dynamic power allocation mechanism for dynamically modifying power allocated to the PD when operations performed by the PD change. The dynamic power allocation mechanism may be responsive to information transferred over a layer link of the local area network.  
      In accordance with a method of the disclosure, the following steps are carried out for providing power to a PD over an Ethernet link: 
          allocating power to the PD,     delivering the allocated power to the PD, and     changing a level of the allocated power in response to a predetermined condition.        

      The level of the allocated power may be changed when the PD switches from a first task to a second task.  
      Additional advantages and aspects of the disclosure will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present disclosure are shown and described, simply by way of illustration of the best mode contemplated for practicing the present disclosure. As will be described, the disclosure is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The following detailed description of the embodiments of the present disclosure can best be understood when read in conjunction with the following drawings, in which the features are not necessarily drawn to scale but rather are drawn as to best illustrate the pertinent features, wherein:  
       FIG. 1  is a diagram illustrating a PoE system of the present disclosure, and  
       FIG. 2  is a diagram illustrating a dynamic power allocation mechanism of the present disclosure. 
    
    
     DETAILED DISCLOSURE OF THE EMBODIMENTS  
      The present disclosure will be made using the example of a power supply device in a PoE system. It will become apparent, however, that the concepts described herein are applicable to any power supply system. For example, the system of the present disclosure may be provided in a local area network (LAN) having a plurality of nodes, a network hub and communication cabling connecting the nodes to the network hub for providing data communications. The network hub may include a power supply device for providing power to a powered device over the communication cabling, and a dynamic power allocation mechanism of the present disclosure.  
       FIG. 1  shows a simplified block-diagram illustrating a Power over Ethernet (PoE) system  10  including Power Sourcing Equipment (PSE)  12  having multiple ports  1  to  4  connectable to Powered Devices (PD 1  to PD 4 ) via respective links, each of which may be provided using  2  or  4  sets of twisted pairs within an Ethernet cable. Although  FIG. 1  shows four ports of the PSE  12 , one skilled in the art would realize that any number of ports may be provided to support power supply to the respective number of PDs.  
      The PSE  12  may interact with each PD in accordance with the IEEE 802.3af standard. In particular, the PSE  12  and the PD participate in the PD detection procedure, during which the PSE  12  probes a link to detect the PD. If the PD is detected, the PSE  12  checks the PD detection signature to determine whether it is valid or non-valid. The valid and non-valid detection signatures are defined in the IEEE 802.3af standard. While the valid PD detection signature indicates that the PD is in a state where it will accept power, the non-valid PD detection signature indicates that the PD is in a state where it will not accept power.  
      If the signature is valid, the PD has an option of presenting a classification signature to the PSE to indicate how much power it will draw when powered up. Based on the determined class of the PD, the PSE allocates the required power to the PD and powers up the PD.  
      In a conventional PoE system, the PD requests power corresponding to its peak power usage to support its operation under worst case conditions. The PSE keeps track of power allocated to all PDs. For the most robust operation, the PSE should reserve the peak power for each PD that it powers up. This power allocation scheme is static. The power is allocated to each PD only once at power-up. However, power available to support operations of the PDs is limited. The PSE will deny request for power from an additional PD if the available power is not sufficient to support its peak power usage.  
      In accordance with the present disclosure, the PSE  12  may utilize a dynamic power allocation scheme to dynamically modify power allocated to the PD in accordance with tasks performed by the PD. Referring to  FIG. 2 , a dynamic power allocation mechanism  100  of the present disclosure employs a PSE system controller  102  that controls ports  1 ,  2 , . . . , n of a PSE interface circuit to supply power from a power supply  104  to PDs  1 ,  2  . . . , n linked to the respective ports. The dynamic power allocation mechanism  100  involves a power allocation sub routine  106 , a PSE priority allocation algorithm  108 , and a PD priority table  110 . The dynamic power allocation mechanism  100  may be implemented in the PSE  12  or in a processing device arranged outside the PSE  12 .  
      As discussed in more detail later, the power allocation sub routine  106  controls allocation of power to each of the PDs in the PoE system. The PSE priority allocation algorithm  108  controls allocation of priority to each of the PDs. The PD priority table  110  may contain a list of priorities assigned to the PDs.  
      Each of the PDs may include a PD system controller  202  that controls operation of the respective PD, PD electronics  204  for carrying out tasks that may be performed by the PD, and a PD interface circuit  206  linked to the respective PSE interface port to support interaction between the PD and the PSE  12 . The PD system controller  202  has access to a power usage table  208  that lists tasks executable by the PD, and the power usage associated with each task. Alternatively, the table  208  may contain information on current consumption associated with each of the task, in addition to or instead of the power usage information.  
      A data exchange protocol may be established between the PSE  12  and the respective PD to support the dynamic power allocation mechanism  100 . For example, a two-way communication may be provided between the PSE interface port and the interface circuit of the respective PD. While power from the PSE  12  to PDs is provided over the physical layer of the Ethernet network linking the PSE  12  and the PDs, a data exchange between the PSE  12  and the PDs to support the dynamic power allocation mechanism  100  may be carried out over the link layer of the Ethernet network above the physical layer. For example, Link Layer Discovery Protocol (LLDP) ratified as IEEE standard 802.1AB-2005 may be employed to support the dynamic power allocation mechanism  100 . LLDP is a neighbor discovery protocol. It allows Ethernet network devices to advertise information about themselves to other nodes on the network and store the information they discover.  
      In particular, LLDP may be used to define a set of common messages for the PSE and PDs. These messages may be transmitted between the PSE and PDs in accordance with LLDP. In particular, LLDP messages may convey information required to support the dynamic power allocation mechanism  100 . Multiple LLDP messages may be transmitted in one LAN packet in the form of a type length value (TLV) field. As defined by the LLDP, the received messages may be stored in Management Information Base (MIB) arranged in accordance with IEEE-defined Simple Network Management Protocol (SNMP).  
      Alternatively, the communication between the PSE and the PDs may be provided over the physical layer. For example, parameters of signals involved in the PoE protocol may be modulated to transmit required information between the PSE and the PD. Examples of data communication between the PSE and the PD are described in copending patent application Ser. No. 11/273,255 filed on Nov. 15, 2005, entitled “PROVIDING DATA COMMUNICATION BETWEEN POWER SUPPLY DEVICE AND POWERED DEVICE IN SYSTEM FOR SUPPLYING POWER OVER COMMUNICATION LINK” and assigned to Linear Technology Corporation, the assignee of the present application.  
      As PD power consumption is a function of tasks performed by the PD, the dynamic power allocation scheme of the present disclosure provides dynamic modification of power allocated to PDs based on the performed tasks. Interaction between the PSE  12  and the PD to implement the dynamic power allocation scheme may be performed in a number of different ways. For example, after a particular PD is powered up, it may dynamically modify its requests for power in accordance with tasks being performed. As the PD switches from one task to another, the PD system controller  202  may access the power usage table  208  to obtain information on the power usage associated with the new task. Based on the power usage information, the PD system controller  202  generates a request for a new power level to support the new task.  
      Via the respective PSE port, the PD power request is transmitted to the PSE system controller  102  that controls the power allocation subroutine  106  to change the power allocated to the requesting PD based on the PD&#39;s request. In particular, the PSE system controller  102  may issue INCREMENT POWER USE command if the current power allocated to the PD is lower than the requested power. Alternatively, the PSE system controller  102  may issue DECREMENT POWER USE command if the currently allocated power is higher than the requested power.  
      The power allocation subroutine  106  receives an INPUT POWER SUPPLY SIZE signal from the power supply  104  indicating the amount of currently available power. If the available power is sufficient to increase the power allocated to the requesting PD, the power allocation subroutine  106  grants the PD&#39;s request for a higher power level. In response to this request, the PSE  12  raises power provided to the PD to the requested level. When the power is increased, the PD may acknowledge an increased power level.  
      However, if the available power is not sufficient to satisfy the PD&#39;s request, the power allocation subroutine  106  may respond with an OUT OF POWER signal to indicate that the PD&#39;s request is denied. The PD may repeat its request later to check whether an increased power level is available.  
      If the currently allocated power is higher than the power level requested by the PD, the power allocation subroutine  106  grants the PD&#39;s request and enables the PSE  12  to reduce power provided to the PD to the requested level.  
      Hence, the power allocated to a PD by the PSE  12  would be modified as the PD changes tasks being performed. For example, when a PD becomes idle, it would likely have a lower power consumption. When the PD notifies the PSE  12  that it is idle and requires a reduced power level, the PSE  12  is able to reallocate power, that previously was allocated to that PD, to other PDs. As a result, the PSE  12  is able to better manage the power allocation to a set of PDs.  
      Further, the dynamic power allocation mechanism  100  may enable the PSE  12  to recall or reduce the power allocated to a particular PD in case of power shortage. For example, when the PSE system controller  102  receives the OUT OF POWER signal from the power allocation subroutine  106  indicating that the power available from the power supply  104  is not sufficient, the PSE system controller  102  may notify any PD currently provided with power that there is a power shortage and the PD must reduce its power consumption. The power released after reducing the power level to that PD may be reallocated to another PD.  
      The PD may request the PSE  12  not to reduce its allocated power below a certain minimum level that may correspond to a power usage required to support operations performed to prevent the PD from being damaged. For example, the PD may indicate the power level required to keep its memory alive and support minimum functions. In response to this request, the power allocation subroutine  106  prevents the power allocated to that PD from being reduced below the requested minimum level.  
      To enable the PSE  12  to efficiently reallocate power among a set of PDs, the dynamic power allocation mechanism  100  may employ a PD priority scheme. The PSE system controller  102  may use the PSE priority allocation algorithm  108  to assign priorities to each PD linked to the PSE  12 . A priority may be assigned to a PD at its initial power-up and recorded in the PD priority table  110 . As the power available from the power supply  104  becomes restricted, the PSE system controller  102  may remove or reduce power allocated to a lower-priority PD in order to grant a request for power from a higher-priority PD. Also, the priority scheme enables the PSE  12  to reduce or remove power allocated to a lower-priority PD before reducing or removing power allocated to a higher-priority PD.  
      The PSE priority allocation algorithm  108  may dynamically change the priority of a PD along with a power request from that PD. Hence, the priority of a PD may be changed when that PD switches from one task to another. For example, a high priority may be assigned to a PD supplied with the minimum level of power required to prevent that PD from being damaged. As the PD requests a higher power level, the PSE  12  may assign a lower priority to that PD because the additional power may be needed for supporting optional features that are not required to perform essential operations. When the PD returns to performing essential functions, the PSE  12  may assign a higher priority to that PD to guarantee allocation of the required power level.  
      The dynamic power allocation mechanism  100  is able to support high-power PDs that may require more power than available in accordance with the IEEE 802.3af standard. For example, a PD may be powered up in a IEEE 802.3af standard-compliant mode. Thereafter, it may request a higher power level. If the PSE supports a higher-power mode and a sufficient amount of power is available, the PSE may grant the PD&#39;s request for higher power. If not, the PD may continue to operate in the IEEE 802.3af standard-compliant mode. The PD may request a higher power level at a later time to check whether the higher power level is available.  
      The dynamic power allocation scheme described in the present disclosure allows PDs to request power allocation based on their tasks. As one skilled in the art would understand, this scheme would also allow PDs to request current allocation based on their tasks. In this case, the PD table  108  may store a current consumption amount associated with each PD task. When a PD switches from one task to another task, it may request the PSE to change the existing current allocation to supply the PD with current required to perform the new task.  
      The foregoing description illustrates and describes aspects of the present invention. Additionally, the disclosure shows and describes only preferred embodiments, but as aforementioned, it is to be understood that the invention is capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein, commensurate with the above teachings, and/or the skill or knowledge of the relevant art.  
      The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with the various modifications required by the particular applications or uses of the invention.  
      Accordingly, the description is not intended to limit the invention to the form disclosed herein. Also, it is intended that the appended claims be construed to include alternative embodiments.