Abstract:
A network apparatus includes an independent power supply providing a first power signal, and a data distribution device which is operably coupled to the independent power supply and a remote data distribution device, where the remote distribution data device exchanges data and provides a second power signal to the data distribution device, and further where the data distribution device selects the first power signal or the second power signal for operational power. A method includes scanning a plurality of sensors, each coupled to a plurality of power inputs, to ascertain if a power signal is present, determining whether a power signal associated with an independent power supply is present at a power input, sourcing power from the independent power supply if the power signal is associated with an independent power supply, and sourcing power from an alternative supply if the power signal is not associated with an independent power supply.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the invention generally relate to the power management of networking devices, and more particularly, networked data distribution devices having a plurality of selectable power supplies. Additional embodiments are directed to utilizing such data distribution devices in conjunction with Voice over Internet Protocol (VOIP) telephones. 
         [0003]    2. Description of the Background Art 
         [0004]    The IEEE Power over Ethernet (PoE) standard 802.3af may increase the flexibility and capability of existing Ethernet networks by providing power over the same connection media which is use to exchange data. Because PoE may provide power in a reliable manner over the same cables as data, it can improve the flexibility of the placement of network devices, which may be useful for various network devices, such as, for example, Voice over Internet Protocol (VoIP) telephones. Additionally, when the PoE source is supplemented with a UPS as a power backup, PoE may be able to permit a network device to function during an AC power outage, which may be especially useful for VoIP telephones in emergency situations. However, problems can arise if the PoE source is overburdened by too many devices drawing more current that the PoE supply can provide, or when one or more devices malfunction and draw too much power. This can cause the PoE source to malfunction and may reduce device and network system reliability. 
         [0005]    In a related area of endeavor, rapid advances in network technology have provided the opportunity for commodity network devices, such as, for example, personal computers, Ethernet switches, routers, etc., to communicate over networks using gigabit rates. This may present bottlenecks in the network as other legacy hardware, such as, for example, VoIP telephones, may not be able to switch data to downstream devices at gigabit rates. The performance of some legacy network devices may not be improved with high speed data rates, and moreover, such hardware may be expensive to upgrade. Therefore simply replacing the legacy hardware may not be an economical solution to network bottlenecks. 
         [0006]    Accordingly, there is a need for devices and methods which economically address network bottlenecks, and have the ability to select power from a plurality of power sources to improve reliability and ease power consumption over PoE sources. 
       SUMMARY OF THE EMBODIMENTS 
       [0007]    Various embodiments of the invention are presented herein which can address the abovementioned issues associated with the existing technology. Embodiments consistent with the present invention are directed to methods and apparatuses for data distribution devices having selectable power supplies. One embodiment consistent with the present invention is directed to a network apparatus which receives power from a plurality of power sources. The network apparatus includes an independent power supply providing a first power signal, and a data distribution device which is operably coupled to the independent power supply and a remote data distribution device, where the remote distribution data device exchanges data with, and provides a second power signal to, the data distribution device using a common connection, and further where the data distribution device selects either the first power signal or the second power signal for operational power. 
         [0008]    Another embodiment consistent the present invention is directed to a network switch which interfaces with a Voice over Internet Protocol (VoIP) telephone. The network switch includes a first circuit which exchanges data and receives power from a remote data distribution device, a second circuit which exchanges data and supplies power to the VoIP telephone, a third circuit which exchanges data with a networked based device, a power switching circuit which receives power from an independent power supply and from the first circuit, and a controller, functionally coupled to the power switching circuit, which instructs the power switching circuit to select power from either the first circuit or the independent power supply. 
         [0009]    Another embodiment consistent with the present invention is directed to a method for selecting a power source for a network switch. The method includes scanning a plurality of sensors, each coupled to a plurality of power inputs, to ascertain if a power signal is present, determining whether a power signal associated with an independent power supply is present at a power input, sourcing power from the independent power supply if the power signal is associated with an independent power supply, and sourcing power from an alternative supply if the power signal is not associated with an independent power supply. 
         [0010]    Yet another embodiment consistent the present invention is directed to an adapter interface for connecting a network device to a midspan or endspan product. The adapter interface includes a power over Ethernet (PoE) controller generating a first power signature for transmission to the midspan or endspan product, wherein the first power signature represents a request for a first power level and does not depend upon the value or presence of any other power signature request received by the adapter interface from the network device. 
         [0011]    Another embodiment consistent the present invention is directed to an adapter interface for connecting at least two devices to an endspan or midspan product. The adapter interface includes a Power over Ethernet (PoE) controller generating a first power signature for transmission to the endspan or midspan product, wherein the first power signature represents a request for a first power level, a first port for providing power to a first device of the at least two devices, and a second port for providing a communication path to a second device of the at least two devices. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    Further aspects and advantages of the present invention will become apparent upon reading the following detailed description taken in conjunction with the accompanying drawings summarized below. 
           [0013]      FIG. 1  shows an exemplary top-level block diagram of a data distribution device having alternate power supplies consistent with an embodiment of the invention. 
           [0014]      FIGS. 2A and 2B  depict exemplary block diagrams of a gigabit Ethernet switch having selectable power supplies for use with VoIP telephones consistent with another embodiment of the invention. 
           [0015]      FIG. 3  shows an exemplary detailed block diagram of a data distribution device consistent with an embodiment of the invention. 
           [0016]      FIG. 4  depicts an exemplary flow diagram consistent with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0017]    Embodiments consistent with the present invention are more specifically set forth in the following description with reference to the appended figures. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
         [0018]      FIG. 1  shows an exemplary configuration  100  including a data distribution device having a plurality power supplies consistent with an embodiment of the invention. Configuration  100  may include a data distribution device  105 , an independent power supply  115 , a remote data distribution device  110 , one or more network devices  125 - 1 - 125 -N, and one or more externally powered network devices  120 - 1 - 120 -N. 
         [0019]    Data distribution device  105  may exchange data with remote data distribution device  110  over a connection through a wall plate  114 . Wall plate  114  may be physically attached to wall  112 , and may typically be in local proximity to data distribution device  105  and remote proximity power from independent power supply  115 . Additionally, operational power for the data distribution device  105  may be provided by remote data distribution device  110  over the same connection used for data through wall plate  114 . Alternately, data distribution device  105  may select power over a dedicated power line connected to independent power supply  115 . Data distribution device may make this selection using an internal switch, the details of which are presented below. Data distribution device  105  may also exchange data with one or more externally powered network devices  120 - 1 - 120 -N and with one or more network device  125 - 1 - 125 -N. Typically, data distribution device  105  may not provide power to externally powered network devices  120 - 1 - 120 -N. Data may be exchanged may with other devices and/or networks through remote data distribution device  110 , or may be exchanged with other devices directly connected to data distribution device  105 . Additionally, data distribution device  105  may provide power to one or more network device  125 - 1 - 125 -N over the same connection used to exchange data. This power originates from the power source data distribution device  105  has selected. Moreover, data distribution device  105  may sense the amount of power required by one or more network devices  125 - 1 - 125 -N, and provide power accordingly. 
         [0020]    Data distribution device  105  may be any type of network device for distributing data using any physical networking standards and data communication protocols, including, for example, Ethernet and TCP/IP. Data Distribution device  105  may be a switch, a hub, a router, a patch panel, or any other type of network device known by one of ordinary skill in the art. Data distribution device  105  may exchange data with remote data distribution device  110 , externally powered network devices  120 - 1 - 120 -N, and/or network devices  125 - 1 - 125 -N using any known physical networking standards and data communication protocols, including, for example, Ethernet and/or TCP/IP. Data distribution device  105  may exchange data utilizing standard Ethernet cables and connectors, such as, for example, CAT5/5e, and/or CAT6 cabling, in conjunction with, for example, standard RJ-45 connectors. Data distribution device may operate at 10/100/1000 Mbit/sec data rates for data exchange, and thus, for example, may serve as a so called gigabit switch. 
         [0021]    Data distribution device may select from one of a plurality of power supplies to supply its own internal power, and/or to supply power to one or more network devices  125 - 1 - 125 -N. This switching may be performed using relays, transistors, or any other known switching devices. Details of one hardware switching approach are presented below in the description of  FIG. 3 . For sake of clarity, only two sources of power are illustrated in  FIG. 1 . As shown, data distribution device  105  may select power from independent power supply  115  or from remote data distribution device  110 . This selection may be based upon pre-defined logic rules within data distribution device  105 , and can be based upon the source of incoming power and/or the maximum available power from each power source. For example, if only one source of power is present, then data distribution device  105  will utilize that source for internal power. If both remote data distribution device  110  and independent power supply  115  are supplying power, logic within data distribution device may switch to using power from independent power supply  115  to reduce the power draw from remote data distribution device  110 , as it may be powering other devices over other Power over Ethernet (PoE) network connections (not shown). Additionally, data distribution device  105  may provide the appropriate feed-back to remote data distribution device  110  as to how much power it needs to allocate and/or offer to data distribution device  105 . This may be done, for example, using known IEEE 802.3af techniques by having data distribution device  105  present the appropriate resistive signature to remote data distribution device  110  based upon which power supply was selected. This signature may be in accordance with signatures associated with any class prescribed by 802.3af, including Class  0 ,  1 , 2 , and/or  3  power signatures. Data distribution device  105  may obtain power from remote data distribution device  110  operating in any configuration, including midspan and endspan configurations, associated with PoE under IEEE 802.3af. Using the selected power supply, data distribution device  105  can subsequently provide power for network devices  125 - 1 - 125 -N, if present. 
         [0022]    Independent power supply  115  may supply power to data distribution device  105  using either standard or customized cabling and connectors. Remote data distribution device  110  may supply power using the same physical medium used to exchange data. Power may be delivered over the physical data connection media using any technique known to one of ordinary skill in the art. Such techniques include, for example, techniques and configurations which comply with the IEEE 802.3af Power over Ethernet (PoE) standards, or any other power over data line techniques know in the art. 
         [0023]    Data distribution device  105  may in turn provide power to network devices  125 - 1 - 125 -N over the same physical media used to exchange data, and may use IEEE 802.3af PoE standards, or any other power over data line techniques know in the art. In accordance with the 802.3af standard, data distribution device  105  may first sense how much power network devices  125 - 1 - 1225 -N require for proper operation, and allocate and/or offer power in accordance with the sensed requirements. Techniques used to sense the power requirements are known and may be defined according to IEEE 802.3af standards, and may include Class  0 ,  1 ,  2 , and/or  3  power signatures. Moreover, data distribution device may provide a different power signature to remote distribution device  110  than it receives from one or more network devices  125 - 1 - 125 -N. Furthermore, the power signature which may be provided by the data distribution device to the remote data distribution device  110  may not depend upon the value or presence of any other power signature request received by the data distribution device  105  from one or more network devices  125 - 1 - 125 -N. 
         [0024]    Remote data distribution device  110  may be any type of network device for distribution data (e.g., a switch, a hub, a router, and/or a patch panel, etc.) using any known physical networking standards and data communication protocols, including, for example, Ethernet and/or TCP/IP Typically, remote data distribution device may be housed in a dedicated enclosure (such as, for example, a “closet”), and be used for a high speed communications (such as, for example, gigabit Ethernet), to serve as an interchange between upstream data communications with other networks and/or network devices (such as, for example, other local area networks, wide area networks, and/or the Internet, possibly through other external switches, routers, firewalls, patch panels, and/or hubs, etc., which are not shown in  FIG. 1 ), and downstream data communication with plurality of downstream network devices (e.g., externally powered network devices  120 - 1 - 120 -N and/or network devices  125 - 1 - 125 -N) through data distribution device  105 . Remote data distribution device  110  may have one or more dedicated power sources (not shown). Remote data distribution device  110  may have a main power source, such as a standard power source driven by AC wall power, or other standard power supplies known in the art. Remote data distribution device  110  may also include one or more backup power sources for redundancy or emergency purposes, such as for example, an uninterruptible power supply, which may include generator and/or battery backup, and/or any other type of backup known to those skilled in the art. 
         [0025]    Remote data distribution device  110  may interface with other devices to deliver power utilizing the same physical connection media for which data is exchanged. Typically, the physical connection media may be standard Ethernet cables and connectors (such as, for example, CAT5, CAT5e, and/or CAT6 cabling, using, for example, standard RJ-45 connectors). Power may be delivered over the physical connection media using any technique known to one of ordinary skill in the art. Such techniques include, for example, techniques and configurations which comply with the IEEE 802.3af Power over Ethernet (PoE) standards, which include sensing the power requirements of any downstream device requiring power (for example, data distribution device  105 ) and allocating and/or offering power in accordance with the sensed requirements. Such requirements may be defined according to IEEE 802.3af standards, and may include Class  0 ,  1 ,  2 , and/or  3  power signatures. 
         [0026]    Independent power supply  115  may be any type of power supply known in the art, and can include, for example, AC/DC power converters (such as, for example, so called “wall warts”), DC/DC power converters, switching power supplies, battery power supplies, and/or capacitive power supplies, etc.). While only one independent power supply is shown, one of ordinary skill in the art would appreciate that various embodiments of the invention could include more than one independent power supply. Independent power supply  115  may interface with data distribution device  105  using any method known in the art, including standard and/or custom power cables and connectors. 
         [0027]    Network Devices  125 - 1 - 125 -N may be any type of networkable device known in the art, using any known physical networking standards and data communication protocols, including, for example, Ethernet and TCP/IP. Network devices  125 - 1 - 125 -N may exchange data using 10/100/1000 Mbit/sec rates using known cabling and connectors (such as, for example, CAT5, CAT5e, and/or CAT6 cabling, using, for example, standard RJ-45 connectors), and may receive operational power supplied by data distribution device  105  using the same cabling and connectors which are used for data exchange. Power may be supplied using any known methods, included IEEE 802.3af PoE. Network devices  125 - 1 - 125 -N may include Voice over Internet Protocol (VoIP) telephones, video cameras, still cameras, wireless access points, and/or remote telemetry data collection devices. 
         [0028]    Externally powered network devices  120 - 1 - 120 -N may be any type of networkable device known in the art, using any known physical networking standards and data communication protocols, including, for example, Ethernet and TCP/IP. Network devices  125 - 1 - 125 -N may exchange data using 10/100/1000 Mbit/sec rates using known cabling and connectors (such as, for example, CAT5, CAT5e, and/or CAT6 cabling, using, for example, standard RJ-45 connectors). Externally powered network devices  120 - 1 - 120 -N may not receive power directly from data distribution device  105 , but will have power supplied to them through an external power supply which is not associated with data distribution device  105 . Externally powered network devices  125 - 1 - 125 -N may include personal computers, workstations, and/or laptops, routers, switches and/or hubs. 
         [0029]      FIG. 2A  depicts a gigabit Ethernet switch having selectable power supplies for use with VoIP telephones in a configuration  200 A having an independent power supply. This configuration includes a closet gigabit switch  210 , a Gigabit switch  205 , an independent power supply  115 , a personal computer  220 , and a VoIP telephone  215 . All of the data communications within this embodiment may utilize Ethernet and TCP/IP communication protocols. 
         [0030]    In configuration  200 A, gigabit switch  205  exchanges data over an Ethernet connection, through wall plate  114 , with closet gigabit switch  210 . Wall plate  114  may be mounted wall  112  which may be proximately located to gigabit switch  205 , and distally located to closet gigabit switch  210 . Closet gigabit switch  210  can serve a number of other connected devices throughout a network with data and power using IEEE 802.3af PoE (not shown). Gigabit switch  205  may further exchange data with personal computer  220 , and with VoIP telephone  215 . In one embodiment, gigabit switch  205  may exchange data with personal computer  220  and closet gigabit switch  210  at higher data rates, such as, for example, 1000 Mbps. Data exchanged between gigabit switch  205  and VoIP telephone  215  may occur at lower rates, such as, for example, 10/100 Mbps. 
         [0031]    Because the independent power supply  115  is present in this configuration, gigabit switch  205  may sense power present at independent power supply  115  and select power from this source for use as operational power, and may not select PoE power from closet gigabit switch  210 . Additionally, gigabit switch  205  may initially determine how much power VoIP telephone  215  requires using standard 802.3af sensing techniques, and subsequently supply power to VoIP telephone  215  using standard 802.3af PoE. 
         [0032]      FIG. 2B  depicts another configuration  200 B of gigabit switch  205  which does not have an independent power supply connected thereto. Here, gigabit switch  205  would not sense power coming from the independent power supply, and would then select power from closet gigabit switch  210 . Upon initialization, closet gigabit switch can determine how much operation power gigabit switch  210  requires utilizing 802.3af techniques, and allocate and supply the appropriate power amount over the same physical connection used for exchanging data. As described above, gigabit switch  205  can in-turn provide power to VoIP telephone  215  using 802.3af, PoE as described above, however, in configuration  200 B, the power would be sourced from closet gigabit switch  210 . As described above gigabit switch  205  may initially determine how much power VoIP telephone  215  requires using standard 802.3af sensing techniques, and subsequently supply the requested power thereto. The operation of gigabit switch  205  with respect data communication would be the same as described above for configuration  200 A shown in  FIG. 2A . One of ordinary skill in the art would appreciated that configuration  200 B may also include the case where independent power supply  115  is present, but for whatever reason(s), is not providing power to gigabit switch  205 . In this case, power from closet gigabit switch  210  may serve as backup power for the independent power supply. 
         [0033]    One practical advantage of configurations  200 A and  200 B is that they can permit high speed network communications with PC  220 , while permitting the user to maintain the use of existing VoIP telephones which may have an internal switches operating at lower bit rates. This permits high speed communications for PC  220  through a relatively inexpensive upgrade by adding gigabit switch  205 , while preserving the investment in the existing, slower speed VoIP telephone  215 . In other words, this allows the user to upgrade PC  220 , while avoiding having to upgrade to a relatively more expensive VoIP telephone having a high speed internal switch. 
         [0034]    A practical advantage of gigabit switch  205  having the capability of selecting different power supplies is that it affords greater operational reliability to VoIP telephone  215 . For example, independent power supply  115  may be utilized if closet gigabit switch  210  does not offer PoE, or in the event its PoE capabilities are overburdened by other connected devices. Also, independent power supply may be provided as a battery backup by the user in the event close gigabit switch  210  has a failure and cannot supply PoE. 
         [0035]      FIG. 3  shows a further detail of gigabit switch  205  consistent with an embodiment of the invention. Gigabit switch  205  may exchange data through uplink port  320 , unpowered port  310 , and powered port  315 . These ports may be any type of data port known in the art, and can include, for example, RJ-45 connectors. Data exchanged through uplink port  320  may originate from closet gigabit switch  210  and may operate at lower and higher data rates, such as, for example, 10/100/1000 Mbps. One of ordinary skill in the art would appreciate that closet gigabit switch  210  may be any type of data distribution device. Once presented at uplink port  320 , data from closet switch  210  may pass through PoE controller  360  and then through an impedance matching circuit  335 , and then onto data distributor module  305 . Data exchanged through unpowered port  310  may originate from personal computer  220  which may also operate at lower and higher data rates, such as, for example, 10/100/1000 Mbps. One of ordinary skill in the art would appreciate that personal computer  220  may be any type of network based device. Once presented at uplink port  310 , data from personal computer  220  may then pass through an impedance matching circuit  325  prior to being exchanged with data distributor module  305 . Data exchanged through powered port  315  may originate from VoIP telephone  215  which may operate at lower data rates, such as for example, 10/100 Mbps. One of ordinary skill in the art would appreciate that VoIP telephone may also be any type of networked device. Once presented at powered port  315 , data from VoIP telephone  215  may pass through an impedance matching circuit  330  and then onto data distributor module  305 . 
         [0036]    Data distributor module  305  may serve as an Ethernet switch which directs packets based upon their, MAC addresses and various routing tables and/or rules. Additionally, Data Distributor module  305  may also implement the features of a so called Multi-Layer Switch, and provide routing based on VLANs and the IP addresses themselves. A process controller  340  may provide one or more control signals to data distributor module for purposes configuration and operating parameters, either at initialization time or during the course of normal operation of the system. Data distributor module  305  may take the form of an integrated circuit and be any type of data distributor module known in the art, including multi-port gigabit Ethernet switch controllers. 
         [0037]    Process controller  340  may also receive signals from power detectors  350  and  355  which may indicate a source of power, and based upon these signals, process controller may select a power source through switch  380 . Power detectors may be either voltage or current detectors, and may be of any appropriate type known to one of ordinary skill in the art. Over uplink port  320 , power may be received using IEEE 802.3af PoE standards, which can be supplied by closet gigabit switch  210 . If power is present at this port, power detector  350 , which may connected to outputs coming from PoE controller  360 , will sense the power signal from uplink port  320 , and send a signal notifying process controller  340  that the closet gigabit switch  210  is providing a power signal. Similarly, power detector  355  may sense a power signal provided by independent power supply  115 , which may be fed power through standard A/C wall socket over plug and connector  390 . Power sensor  355  will then send a signal to process controller  340  that independent power supply  115  is providing a power signal which may be used for operational power. As discussed above, independent power supply could be any known power source, and additional independent power supplies may be utilized, along with additional power sensors, to accommodate additional power supply sources. 
         [0038]    Process controller  340  may then exercise various logic to determine which power supply to select. Such logic may be in the form of a program stored in on-board memory (not shown) within the process controller. Process controller and memory may be of any type known to one of ordinary skill in the art, and include. One form of logic which may be used could be to have process controller  340  use either PoE power from uplink port  320 , or power from independent power supply  115 , if only one of which is present. If both are sources are present, process controller  340  may select power from independent power supply  115  in order to minimize any aggregate PoE power draw closet gigabit switch  210  may experience. Details of the logic which may be used in this embodiment are further presented below in the description of  FIG. 4 . One of ordinary skill in the art would appreciate that other logic schemes may be used in accordance with the invention. 
         [0039]    Once process controller  340  determines which power supply to select, the selection may occur by process controller  340  sending a command signal to switch  380 . Switch  380  may be a relay, one or more transistors, or any other type of switch which may be controlled by an electronic signal. If process controller  340  selects independent power supply  115 , it may open switch  380  so that current flows through a diode assembly  385  to a Power Sourcing Equipment (PSE) controller and Power Controller  370 , hereinafter referred to as PCPC  370 . If process controller  340  selects PoE power over uplink port  320 , process controller  340  may close switch  380 , and current from uplink port  320  will flow through diode assembly  385  into PCPC  370 . Note that the voltage of independent power supply  115  may be chosen so, that if the independent power supply  115  is present and providing power, the appropriate diodes are back-biased, allowing current to flow from uplink port  320  into PCPC  370 , and blocking current from independent power supply  115 . 
         [0040]    Process controller  340  may provide a signal to PoE controller  360  in order to provide feedback to closet gigabit switch  210  regarding how much power to allocate and supply to gigabit switch  205 . PoE controller  360  may set up a signature resistance in accordance with IEEE 802.3af, to signal a class  0 ,  1 ,  2 , and/or  3  power signatures. The signature resistance may be sensed by closet gigabit switch  210  during initialization so the appropriate amount of power is provided to gigabit switch  205 . Moreover, close gigabit switch  210  may provide power in any configuration permitted under 802.3af, including, but not limited to endspan and/or midspan configurations. PoE controller  360  may take the form of an integrated circuit, or any other form known to one of ordinary skill in the art. The PoE controller may signal the process controller various conditions, which may include normal status, overload, instability of voltage source, voltage sag and others. Additionally, the process controller may calculate the total power needed by Switch  205  and provide that information to the PoE Controller  360  so that the PoE Controller  360  may report that information back to the closet switch in accordance with IEEE 802.3af or any other appropriate standards. 
         [0041]    Process controller  340  may also provide control signals to PCPC  370  which may include instructions for providing the appropriate amount of power to VoIP telephone  215 . Initially, PCPC  370  may first sense the power VoIP telephone  215  is requesting by measuring the signature resistance presented at powered port  315  by VoIP telephone  215 . This may be done in accordance with PoE standard 802.3af. Once the power signature is requested, which may be class  0 ,  1 ,  2 , or  3 , process controller  340  may instruct the power controller in PCPC  370  to provide powered port  315  with the appropriate amount of power for use by VoIP telephone  215 . This power may be provided over powered port  315  using PoE. The PSE controller may collect requested powering information from the device ( 215 ) connected to powered port  315  and report that information to Process Controller  340  for various purposes, including to report back to the closet switch  210  via PoE Controller  360  for power of switch  205 . 
         [0042]    In addition to receiving power from either uplink port  320  via closet gigabit switch  210  or independent power supply  115 , PCPC  370  may also receive initialization power from optional energy store  375 . Optional energy store  375  provides initialization power to gigabit switch  250  for a short period of time so that it may perform the power supply selection. Because only a small amount of power needs to be provided for a short period of time (for example, on the order of milliseconds), optional energy source does not have to supply a large amount of energy, and can take the form of a battery, a capacitor, or any other appropriate storage device known in the art. 
         [0043]      FIG. 4  depicts logic flow  400  consistent with an embodiment of the invention. This diagram shows an exemplary sequence gigabit switch  205  may execute in order to select a power supply. This logic sequence may assume that an administrator&#39;s overall power management strategy for a network is to minimize the power draw from closet gigabit switch  210 , and have independent power supply  115  selected whenever its power signal is detected, so other devices connected to closet gigabit switch  210  may benefit from sourcing power utilizing PoE. One of ordinary skill in the art would appreciate other logic sequences may be performed to accomplish other power management strategies. One of ordinary skill in the art would also appreciate that, since a power supply has yet to be selected, the logic  400  would be accomplished by the components in gigabit switch  205  using power supplied by optional energy store  375 . 
         [0044]    Initially, process controller  340  may scan each power detector  350  and  355  for an active power signal (S 410 ). Process controller  340  may then make the determination if power is present on power detector  355 , which monitors power signals coming from independent power supply  115  (S 415 ). If power is present on power detector  355 , process controller  340  may source power from independent power supply  115  (S 420 ). This can be accomplished by having process controller  340  send a signal to switching circuit  380  to open and prevent current from flowing from uplink port  320 . Process controller  340  may then send another signal to PoE controller  360 , which can set a signature resistance on uplink port  320  (in accordance with IEEE 802.3af standards) for signaling closet gigabit switch  210  that gigabit switch  205  does not require any power over the data line through uplink port  320  (S 425 ). Alternatively, if in step S 415 , power detector  350  signals process controller  340  that power is present on uplink port  320 , process controller  340  may send a signal to PoE controller  360  to configure the signature resistance across uplink port  320 , so that it will signal closet gigabit switch  210  to allocate and offer power to gigabit switch  205  (S 430 ). The amount of power offered may depend on the value of the signature resistance value presented by PoE controller  360  (which may be based upon IEEE 802.3af standards). Process controller  340  may then source power from the closet gigabit switch  210  over uplink port  320  (S 435 ). This may occur by having process controller  340  signal switching circuit  380  to close, thus allowing current to flow though diode arrangement  385 . Independent power supply  115  may be configured so that the two diodes in series with its current supply will be back-biased when power is being supplied through uplink port  320 , thus providing a way to economically and effectively block the power being supplied by independent power supply  115 . 
         [0045]    Although detailed embodiments and implementations of the present invention have been described above, it should be apparent that various modifications are possible without departing from the spirit and scope of the present invention.