Abstract:
A method for supplying power to a local area network node over communication cabling, the method comprising: injecting current-limited current into communication cabling connected to the local area network node; measuring a voltage developed in accordance with said injected current limited current across said communication cabling at three pre-determined intervals; and determining, as a consequence of said measured voltage at said three pre-determined intervals whether characteristics of the local area network node allow it to receive power over the communication cabling.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of U.S. patent application Ser. No. 10/218,739 filed Aug. 13, 2002 which is a continuation of U.S. patent application Ser. No. 09/365,584 filed Aug. 2, 1999 issued as U.S. Pat. No. 6,473,608, which claims priority from U.S. Provisional Patent Application Ser. No. 60/115,628 filed Jan. 12, 1999 and is a continuation-in-part of U.S. patent application Ser. No. 09/293,343 filed Apr. 16, 1999 issued as U.S. Pat. No. 6,643,566. The entire content of each of the above mentioned applications and patents are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to structured cabling systems and more particularly to structured cabling systems used in local area networks supplying power to at least one node.  
       BACKGROUND OF THE INVENTION  
       [0003]     Structured cabling systems are well known for use in institutional infrastructure. Such systems provide a standardized yet flexible platform for a dynamic communications environment. Typically structure cabling systems employ twisted copper pairs which are installed in accordance with predetermined criteria. Structured cabling systems are conventionally employed for telephone, data communications, as well as for alarms, security and access control applications.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention seeks to provide an enhanced structured cabling system and local area network employing such a system.  
         [0005]     There is thus provided in accordance with a preferred embodiment of the present invention a local area network including a hub, a plurality of nodes, communication cabling connecting the plurality of nodes to the hub for providing data communication; and a power supply distributor operative to provide at least some operating power to at least some of the plurality of nodes via the communication cabling.  
         [0006]     Further in accordance with a preferred embodiment of the present invention the communication cabling includes at least part of a structured cabling system.  
         [0007]     Still further in accordance with a preferred embodiment of the present invention the power supply distributor is located within the hub.  
         [0008]     Additionally in accordance with a preferred embodiment of the present invention the power supply distributor is located outside the hub.  
         [0009]     Moreover in accordance with a preferred embodiment of the present invention the power supply distributor is located partially within the hub and partially outside the hub.  
         [0010]     Still further in accordance with a preferred embodiment of the present invention the operating power supplied by said power supply distributor to at least some of said plurality nodes via said communication cabling includes backup power.  
         [0011]     Additionally in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner, and the communication cabling connects the data communication concentrator via the combiner to the nodes.  
         [0012]     Sill further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator and wherein the power supply distributor is also located within the hub.  
         [0013]     Additionally in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator and wherein the power supply distributor is also located within the hub and includes a power supply and a combiner, the combiner coupling power from the power supply to the communication cabling which also carries data from the data communication concentrator.  
         [0014]     Preferably the data communication concentrator comprises a LAN switch which functions as a data communication switch/repeater.  
         [0015]     Additionally in accordance with a preferred embodiment of the present invention the plurality of nodes includes at least one of the following types of nodes: wireless LAN access points, emergency lighting system elements, paging loudspeakers, CCTV cameras, alarm sensors, door entry sensors, access control units, laptop computers, IP telephones, hubs, switches, routers, monitors and memory backup units for PCs and workstations.  
         [0016]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a plurality of couplers, each of which is connected to an output of the power supply.  
         [0017]     Further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner comprises a plurality of couplers and a plurality of filters, each coupler being connected via a filter to an output of the power supply.  
         [0018]     Still further according to a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply.  
         [0019]     Moreover in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, and the power supply includes a power failure backup facility.  
         [0020]     Additionally or alternatively the hub includes a data communication concentrator; the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner comprises a plurality of couplers and a plurality of filters, each coupler being connected via a filter to an output of the power supply.  
         [0021]     Moreover according to a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply.  
         [0022]     Preferably the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a plurality of couplers and a plurality of filters, each coupler being connected via a filter to an output of the power supply.  
         [0023]     Additionally or alternatively the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner comprises a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply.  
         [0024]     Preferably the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a plurality of couplers and a plurality of filters, each coupler being connected via a filter to an output of the power supply.  
         [0025]     Additionally or alternatively the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply.  
         [0026]     Further in accordance with a preferred embodiment of the present invention the power supply distributor is operative to provide electrical power along the communication cabling without unacceptable degradation of the digital communication.  
         [0027]     Still further in accordance with a preferred embodiment of the present invention the communication cabling comprises at least one twisted wire pair connected to each node and wherein power is transmitted over a twisted wire pair along which data is also transmitted.  
         [0028]     Preferably the hub includes a data communication concentrator, the power supply distributor includes a power supply interface and a power supply, the communication cabling connects the data communication concentrator via the power supply interface to the nodes, and power supply interface includes a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each filter being connected via a SPEAR to an output of the power supply.  
         [0029]     Additionally in accordance with a preferred embodiment of the present invention the communication cabling comprises at least two twisted wire pairs connected to each node and wherein power is transmitted over a twisted wire pair different from that along which data is transmitted.  
         [0030]     Preferably the hub includes a data communication concentrator, the power supply distributor includes a power supply interface and a power supply, the communication cabling connects the data communication concentrator via the power supply interface to the nodes, and the power supply interface includes a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each filter being connected via a SPEAR to an output of the power supply.  
         [0031]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply, and each coupler has at least two ports, one of which is connected to a port of the data communication concentrator and the other of which is connected, via communication cabling, to one of the plurality of nodes.  
         [0032]     There is also provided in accordance with a preferred embodiment of the present invention a local area network node for use in a local area network including a hub, a plurality of nodes, communication cabling connecting the plurality of nodes to the hub for providing digital communication and a power supply distributor operative to provide at least some operating power to at least some of the plurality of nodes via the hub and the communication cabling, the local area network node including a communications cabling interface receiving both power and data and separately providing power to a node power input and data to a node data input.  
         [0033]     Further in accordance with a preferred embodiment of the present invention the communications cabling interface is internal to at least one of the plurality of nodes.  
         [0034]     Still further in accordance with a preferred embodiment of the present invention the communications cabling interface is external to at least one of the plurality of nodes.  
         [0035]     Additionally in accordance with a preferred embodiment of the present invention the power supply distributor is operative to provide electrical power along the communication cabling without unacceptable degradation of the digital communication.  
         [0036]     Still further in accordance with a preferred embodiment of the present invention the communication cabling includes at least one twisted wire pair connected to each node and wherein power is transmitted over a twisted wire pair along which data is also transmitted.  
         [0037]     Additionally in accordance with a preferred embodiment of the present invention the communication cabling includes at least two twisted wire pairs connected to each node and wherein power is transmitted over a twisted wire pair different from that along which data is transmitted.  
         [0038]     Preferably the power supply distributor is operative to provide electrical power along the communication cabling without unacceptable degradation of the digital communication.  
         [0039]     Additionally the communication cabling may include at least one twisted wire pair connected to each node and wherein power is transmitted over a twisted wire pair along which data is also transmitted.  
         [0040]     Further more in accordance with a preferred embodiment of the present invention the communication cabling includes at least two twisted wire pairs connected to each node and wherein power is transmitted over a twisted wire pair different from that along which data is transmitted.  
         [0041]     Preferably the power supply distributor is operative to provide electrical power along the communication cabling without unacceptable degradation of the digital communication.  
         [0042]     Further in accordance with a preferred embodiment of the present invention the communication cabling includes at least one twisted wire pair connected to each node and wherein power is transmitted over a twisted wire pair along which data is also transmitted.  
         [0043]     Still further in accordance with a preferred embodiment of the present invention the communication cabling includes at least two twisted wire pairs connected to each node and wherein power is transmitted over a twisted wire pair different from that along which data is transmitted.  
         [0044]     Moreover in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner, a management and control unit and a power supply, the communication cabling connects said data communication concentrator via the combiner to the node, the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of said power supply, and the SPEAR is operative to report to the management and control unit the current consumption of a node connected thereto.  
         [0045]     Further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, the combiner comprises a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply, and the SPEAR is operative to limit the maximum current supplied to a node connected thereto.  
         [0046]     Alternatively according to a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply, and the SPEAR is operative to automatically disconnect a node connected thereto displaying an overcurrent condition following elapse of a programmably predetermined period of time.  
         [0047]     Additionally in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply, and the SPEAR is operative to automatically disconnect power from a node connected thereto displaying an overcurrent condition following elapse of a programmably predetermined period of time and to automatically reconnect the node to power thereafter when it no longer displays the overcurrent condition.  
         [0048]     Moreover in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects said data communication concentrator via the combiner to the nodes, the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply, and the SPEAR includes a current sensor which receives a voltage input Vin from a power supply and generates a signal which is proportional to the current passing therethrough, and a multiplicity of comparators receiving the signal from the current sensor and also receiving a reference voltage Vref from respective reference voltage sources.  
         [0049]     Preferably the reference voltage sources are programmable reference voltage sources and receive control inputs from management &amp; control circuits.  
         [0050]     Additionally the outputs of the multiplicity of comparators may be supplied to a current limiter and switch which receives input voltage Vin via the current sensor and provides a current-limited voltage output Vout.  
         [0051]     Furthermore the outputs of the comparators are supplied to management &amp; control circuits to serve as monitoring inputs providing information regarding the DC current flowing through the SPEAR.  
         [0052]     Additionally in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a plurality of couplers each of which includes at least a pair of transformers, each having a center tap at a secondary thereof via which the DC voltage is fed to each wire of a twisted pair connected thereto.  
         [0053]     Further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a plurality of couplers each of which includes at least one transformer, which is characterized in that it includes a secondary which is split into two separate windings and a capacitor which is connected between the two separate windings and which effectively connects the two windings in series for high frequency signals, but effectively isolates the two windings for DC.  
         [0054]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a pair of capacitors which effectively block DC from reaching the data communication concentrator.  
         [0055]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner comprises two pairs of capacitors which effectively block DC from reaching the data communication concentrator.  
         [0056]     Additionally in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a self-balancing capacitor-less and transformer-less common mode coupling circuit.  
         [0057]     Preferably the communications cabling interface includes a separator and a pair of transformers, each having a center tap at a primary thereof via which the DC voltage is extracted from each wire of a twisted pair connected thereto.  
         [0058]     Additionally or alternatively the communications cabling interface includes a separator including at least one transformer, which is characterized in that it includes a primary which is split into two separate windings and a capacitor which is connected between the two separate windings and which effectively connects the two windings in series for high frequency signals, but effectively isolates the two windings for DC.  
         [0059]     Furthermore the communications cabling interface includes a separator comprising a pair of capacitors which effectively block DC from reaching a data input of a node connected thereto.  
         [0060]     Additionally in accordance with a preferred embodiment of the present invention the communications cabling interface includes a separator comprising two pairs of capacitors which effectively block DC from reaching a data input of a node connected thereto.  
         [0061]     Additionally or alternatively the communications cabling interface includes a separator includes a self-balancing capacitor-less and transformer-less common mode coupling circuit.  
         [0062]     There is further provided in accordance with a preferred embodiment of the present invention a local area network including a hub, a plurality of nodes, a communication cabling connecting said plurality of nodes to the hub for providing data communication, and a power supply distributor operative to provide at least some operating power to at least some of the plurality of nodes via the communication cabling, the power supply distributor including power management functionality.  
         [0063]     Preferably the power supply distributor includes a power management &amp; control unit which monitors and controls the power supplied to various nodes via the communications cabling.  
         [0064]     Additionally in accordance with a preferred embodiment of the present invention the power supply distributor includes a management workstation which is operative to govern the operation of the power management &amp; control unit.  
         [0065]     Preferably the management workstation governs the operation of multiple power management &amp; control units.  
         [0066]     Moreover in accordance with a preferred embodiment of the present invention the power management &amp; control unit communicates with various nodes via a data communication concentrator thereby to govern their current mode of power usage.  
         [0067]     Further in accordance with a preferred embodiment of the present invention the power management &amp; control unit communicates with various nodes via control messages which are decoded at the nodes and are employed for controlling whether full or partial functionality is provided thereat.  
         [0068]     Still further in accordance with a preferred embodiment of the present invention the power management &amp; control unit senses that mains power to said power supply distributor is not available and sends a control message to cause nodes to operate in a backup or reduced power mode.  
         [0069]     Preferably the node includes essential circuitry, which is required for both full functionality and reduced functionality operation, and non-essential circuitry, which is not required for reduced functionality operation.  
         [0070]     There is also provided with yet another preferred embodiment of the present invention a local area network power supply distributor for use in a local area network including a hub, a plurality of nodes and communication cabling connecting the plurality of nodes to a hub for providing digital communication therebetween, the power supply distributor being operative to provide at least some operating power to at least some of said plurality of nodes via the communication cabling.  
         [0071]     Further in accordance with a preferred embodiment of the present invention the supply distributor is located within the hub.  
         [0072]     Still further in accordance with a preferred embodiment of the present invention the power supply distributor is located outside the hub. Alternatively the power supply distributor is located partially within the hub and partially outside the hub.  
         [0073]     Additionally in accordance with a preferred embodiment of the present invention the operating power supplied by the power supply distributor to at least some of the plurality nodes via the communication cabling includes backup power.  
         [0074]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner, and the communication cabling connects the data communication concentrator via the combiner to the nodes.  
         [0075]     Moreover in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator and wherein the power supply distributor is also located within the hub.  
         [0076]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator and wherein said power supply distributor is also located within the hub and includes a power supply and a combiner, the combiner coupling power from the power supply to the communication cabling which also carries data from the data communication concentrator.  
         [0077]     Preferably the combiner includes a plurality of couplers, each of which is connected to an output of the power supply.  
         [0078]     Additionally in accordance with a preferred embodiment of the present invention the combiner includes a plurality of couplers and a plurality of filters, each coupler being connected via a filter to an output of the power supply.  
         [0079]     Furthermore the combiner may also include a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply.  
         [0080]     Additionally in accordance with a preferred embodiment of the present invention the power supply distributor includes a power supply, and the power supply includes a power failure backup facility.  
         [0081]     Still further in accordance with a preferred embodiment of the present invention the combiner includes a plurality of couplers and a plurality of filters, each coupler being connected via a filter to an output of the power supply.  
         [0082]     Preferably the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply.  
         [0083]     Moreover in accordance with a preferred embodiment of the present invention the combiner includes a plurality of couplers and a plurality of filters, each coupler being connected via a filter to an output of a power supply.  
         [0084]     Additionally the combiner may also include a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply.  
         [0085]     Furthermore the combiner may also include a plurality of couplers and a plurality of filters, each coupler being connected via a filter to an output of a power supply.  
         [0086]     Moreover in accordance with a preferred embodiment of the present invention the power supply distributor is operative to provide electrical power along the communication cabling without unacceptable degradation of the digital communication.  
         [0087]     Further in accordance with a preferred embodiment of the present invention the communication cabling includes at least one twisted wire pair connected to each node and wherein power is transmitted over a twisted wire pair along which data is also transmitted.  
         [0088]     Preferably the power supply distributor includes a power supply interface and a power supply, the communication cabling connects the data communication concentrator via the power supply interface to the nodes, and the power supply interface includes a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each filter being connected via a SPEAR to an output of the power supply.  
         [0089]     Additionally in accordance with a preferred embodiment of the present invention the communication cabling includes at least two twisted wire pairs connected to each node and wherein power is transmitted over a twisted wire pair different from that along which data is transmitted.  
         [0090]     Moreover in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a power supply interface and a power supply, the communication cabling connects the data communication concentrator via the power supply interface to said nodes, and the power supply interface includes a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each filter being connected via a SPEAR to an output of the power supply.  
         [0091]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply, and each coupler has at least two ports, one of which is connected to a port of the data communication concentrator and the other of which is connected, via communication cabling, to one of the plurality of nodes.  
         [0092]     Additionally in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner, a management and control unit and a power supply, the communication cabling connects said data communication concentrator via the combiner to the nodes, the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply, and the SPEAR is operative to report to the management and control unit the current consumption of a node connected thereto.  
         [0093]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply, and the SPEAR is operative to limit the maximum current supplied to a node connected thereto.  
         [0094]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply, and the SPEAR is operative to automatically disconnect a node connected thereto displaying an overcurrent condition following elapse of a programmably predetermined period of time.  
         [0095]     Additionally in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply, and the SPEAR is operative to automatically disconnect power from a node connected thereto displaying an overcurrent condition following elapse of a programmably predetermined period of time and to automatically reconnect the node to power thereafter when it no longer displays the overcurrent condition.  
         [0096]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, the combiner includes a plurality of couplers and a plurality of filters and a plurality of smart power allocation and reporting circuits (SPEARs), each coupler being connected via a filter and a SPEAR to an output of the power supply, and the SPEAR includes a current sensor which receives a voltage input Vin from a power supply and generates a signal which is proportional to the current passing therethrough, and a multiplicity of comparators receiving the signal from the current sensor and also receiving a reference voltage Vref from respective reference voltage sources.  
         [0097]     Preferably the reference voltage sources are programmable reference voltage sources and receive control inputs from management &amp; control circuits.  
         [0098]     Additionally the outputs of the multiplicity of comparators may be supplied to a current limiter and switch which receives input voltage Vin via the current sensor and provides a current-limited voltage output Vout.  
         [0099]     Furthermore the outputs of the comparators may be supplied to management &amp; control circuits to serve as monitoring inputs providing information regarding the DC current flowing through the SPEAR.  
         [0100]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes plurality of couplers each of which includes at least a pair of transformers, each having a center tap at a secondary thereof via which the DC voltage is fed to each wire of a twisted pair connected thereto.  
         [0101]     Additionally in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a plurality of couplers each of which includes at least one transformer, which is characterized in that it includes a secondary which is split into two separate windings and a capacitor which is connected between the two separate windings and which effectively connects the two windings in series for high frequency signals, but effectively isolates the two windings for DC.  
         [0102]     Further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner includes a pair of capacitors which effectively block DC from reaching the data communication concentrator.  
         [0103]     Still further in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner comprises two pairs of capacitors which effectively block DC from reaching the data communication concentrator.  
         [0104]     Additionally in accordance with a preferred embodiment of the present invention the hub includes a data communication concentrator, the power supply distributor includes a combiner and a power supply, the communication cabling connects the data communication concentrator via the combiner to the nodes, and the combiner comprises a self-balancing capacitor-less and transformer-less common mode coupling circuit.  
         [0105]     Preferably the power supply distributor includes power management functionality.  
         [0106]     Additionally the power supply distributor may include a power management &amp; control unit which monitors and controls the power supplied to various nodes via the communications cabling.  
         [0107]     Furthermore the power supply distributor may include a management workstation which is operative to govern the operation of said power management &amp; control unit.  
         [0108]     Furthermore in accordance with a preferred embodiment of the present invention the management workstation governs the operation of multiple power management &amp; control units.  
         [0109]     Preferably the power management &amp; control unit communicates with various nodes via a data communication concentrator thereby to govern their current mode of power usage.  
         [0110]     Additionally in accordance with a preferred embodiment of the present invention the power management &amp; control unit communicates with various nodes via control messages which are decoded at the nodes and are employed for controlling whether full or partial functionality is provided thereat.  
         [0111]     Additionally the power management &amp; control unit senses that mains power to the power supply distributor is not available and sends a control message to cause nodes to operate in a backup or reduced power mode.  
         [0112]     Furthermore the node includes essential circuitry, which is required for both full functionality and reduced functionality operation, and non-essential circuitry, which is not required for reduced functionality operation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0113]     The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:  
         [0114]      FIGS. 1A and 1B  are simplified block diagram illustrations of two alternative embodiments of a local area network including a power supply operative to provide electrical power to local area network nodes over communication cabling constructed and operative in accordance with one preferred embodiment of the present invention;  
         [0115]      FIGS. 2A and 2B  are simplified block diagram illustrations of two alternative embodiments of a local area network including a power supply operative to provide electrical power to local area network nodes over communication cabling constructed and operative in accordance with another preferred embodiment of the present invention;  
         [0116]      FIGS. 3A &amp; 3B  are simplified block diagrams of hubs useful in the embodiments of  FIGS. 1A and 1B  respectively;  
         [0117]      FIGS. 4A &amp; 4B  are simplified block diagrams of hubs and power supply subsystems useful in the embodiments of  FIGS. 2A &amp; 2B  respectively;  
         [0118]      FIG. 5  is a simplified block diagram illustration of a smart power allocation and reporting circuit useful in the embodiments of  FIGS. 3A, 3B ,  4 A and  4 B;  
         [0119]      FIG. 6  is a simplified schematic illustration of the embodiment of  FIG. 5 ;  
         [0120]      FIGS. 7A &amp; 7B  are simplified block diagram illustrations of LAN node interface circuits useful in the embodiments of  FIGS. 1A &amp; 2A  and  FIGS. 1B &amp; 2B  respectively;  
         [0121]      FIGS. 8A-8G  are simplified block diagram and schematic illustrations of various embodiments of a combiner useful in the embodiments of  FIGS. 3A and 4A ;  
         [0122]      FIGS. 9A-9G  are simplified block diagram and schematic illustrations of various embodiments of a separator useful in the embodiments of  FIGS. 1A, 2A  &amp;  7 A in combination with combiners of  FIGS. 8A-8G ;  
         [0123]      FIGS. 10A &amp; 10B  are simplified block diagram illustrations of two alternative embodiments of a communications network including power supply and management over communications cabling constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0124]      FIGS. 11A &amp; 111B  are simplified block diagram illustrations of two alternative embodiments of a local area network including power supply and management unit operative to provide electrical power to local area network nodes over communication cabling;  
         [0125]      FIGS. 12A &amp; 12B  are simplified block diagram illustrations of a hub useful in the embodiments of  FIGS. 10A &amp; 10B  respectively;  
         [0126]      FIGS. 13A &amp; 13B  are simplified block diagram illustrations of a hub and a power supply and management subsystem useful in the embodiments of  FIG. 11A &amp; 11B  respectively;  
         [0127]      FIGS. 14A &amp; 14B  are simplified block diagrams of two different node configurations useful in the embodiments of  FIGS. 10A, 10B ,  11 A &amp;  11 B;  
         [0128]      FIG. 15  is a simplified block diagram of a node configuration which combines the features shown in  FIGS. 14A &amp; 14B ;  
         [0129]      FIG. 16  is a generalized flowchart illustrating power management in both normal operation and reduced power modes of the networks of  FIGS. 10A, 110B ,  11 A &amp;  11 B;  
         [0130]      FIG. 17  is a generalized flowchart illustrating one step in the flowchart of  FIG. 16 ;  
         [0131]      FIGS. 18A and 18B  together are a generalized flowchart illustrating a preferred embodiment of the interrogation and initial power supply functionality which appears in  FIG. 17 ;  
         [0132]      FIGS. 19A, 19B ,  19 C and  19 D are generalized flowcharts each illustrating one possible mechanism for full or no functionality operation in an involuntary power management step in the flowchart of  FIG. 16 ;  
         [0133]      FIGS. 20A, 20B ,  20 C and  20 D are generalized flowcharts each illustrating one possible mechanism for full or reduced functionality operation in an involuntary power management step in the flowchart of  FIG. 16 ;  
         [0134]      FIGS. 21A, 21B ,  21 C and  21 D are generalized flowcharts each illustrating one possible mechanism for node initiated sleep mode operation in a voluntary power management step in the flowchart of  FIG. 16 ;  
         [0135]      FIGS. 22A, 22B ,  22 C and  22 D are generalized flowcharts each illustrating one possible mechanism for hub initiated sleep mode operation in a voluntary power management step in the flowchart of  FIG. 16 ;  
         [0136]      FIGS. 23A, 23B ,  23 C and  23 D are generalized flowcharts each illustrating one possible mechanism for full or no functionality prioritized operation in a voluntary power management step in the flowchart of  FIG. 16 ; and  
         [0137]      FIGS. 24A, 24B ,  24 C and  24 D are generalized flowcharts each illustrating one possible mechanism for full or reduced functionality prioritized operation in a voluntary power management step in the flowchart of  FIG. 16 .  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0138]     Reference is now made to  FIG. 1A , which is a simplified block diagram illustration of a local area network constructed and operative in accordance with a preferred embodiment of the present invention. As seen in  FIG. 1A , there is provided a local area network (LAN) comprising a hub  10  which is coupled, by cabling  11 , preferably a structured cabling system, to a plurality of LAN nodes, such as a desktop computer  12 , a web camera  14 , a facsimile machine  16 , a LAN telephone, also known as an IP telephone  18 , a computer  20  and a server  22 .  
         [0139]     Cabling  11  is preferably conventional LAN cabling having four pairs of twisted copper wires cabled together under a common jacket. In the embodiment of  FIG. 1A , as will be described hereinbelow, at least one of the pairs of twisted copper wires is employed for transmitting both data and electrical power to nodes of the network. Typically two such pairs are employed for transmitting both data and electrical power along each line connecting a hub to each node, while one such pair carries data only and a fourth pair is maintained as a spare and carries neither data nor power.  
         [0140]     In accordance with a preferred embodiment of the present invention there is provided a power supply subsystem  30  which is operative to provide at least some operating or backup power to at least some of said plurality of nodes via the hub  10  and the communication cabling connecting the hub to various LAN nodes.  
         [0141]     In the illustrated embodiment of  FIG. 1A , subsystem  30  is located within the hub  10  and includes a power supply  32  which supplies operating power and/or backup power to various LAN nodes via the communication cabling. The communication cabling connects a LAN switch  34  via a combiner  36  to the various LAN nodes. The combiner couples electrical power from the power supply  32  along the communication cabling to at least some of the LAN nodes. Bidirectional data communications from LAN switch  34  pass through the combiner  36 , substantially without interference.  
         [0142]     It is seen that the communication cabling  11  from the hub  10  to the desktop computer  12 , facsimile machine  16  and computer  20  carries both data and backup power, while the communication cabling from the hub  10  to the hub camera  14  and LAN telephone  18  carries both data and operating power and the communication cabling from the hub to the server  22  carries only data, in a typically LAN arrangement constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0143]     It is a particular feature of the embodiment of  FIG. 1A  that both data and power are carried on the same twisted copper pair.  
         [0144]     It is appreciated that each of the LAN nodes  12 - 20  which receives power over the communication cabling includes a separator for separating the electrical power from the data. In the illustrated embodiment of  FIG. 1A , the separators are typically internal to the respective nodes and are not separately designated, it being appreciated that alternatively discrete separators may be employed.  
         [0145]     Reference is now made to  FIG. 1B , which is a simplified block diagram illustration of a local area network constructed and operative in accordance with another preferred embodiment of the present invention. As seen in  FIG. 1B , there is provided a local area network (LAN) comprising a hub  60  which is coupled, by cabling  61 , preferably a structured cabling system, to a plurality of LAN nodes, such as a desktop computer  62 , a web camera  64 , a facsimile machine  66 , a LAN telephone, also known as an IP telephone  68 , a computer  70  and a server  72 .  
         [0146]     Cabling  61  is preferably conventional LAN cabling having four pairs of twisted copper wires cabled together under a common jacket. In the embodiment of  FIG. 1B , in contrast to the arrangement described above with respect to  FIG. 1A  and as will be described hereinbelow, at least one of the pairs of twisted copper wires is employed only for transmitting electrical power to nodes of the network and at least one of the pairs of twisted copper wires is employed only for transmitting data. Typically two such pairs are employed for transmitting data only and two such pairs are employed only for supplying electrical power along each line connecting a hub to each node.  
         [0147]     In accordance with a preferred embodiment of the present invention there is provided a power supply subsystem  80  which is operative to provide at least some operating or backup power to at least some of said plurality of nodes via the hub  60  and the communication cabling  61  connecting the hub to various LAN nodes.  
         [0148]     In the illustrated embodiment of  FIG. 1B , subsystem  80  is located within the hub  60  and includes a power supply  82  which supplies operating power and/or backup power to various LAN nodes via the communication cabling. The communication cabling connects a LAN switch  84  via a power supply interface  86  to the various LAN nodes. The power supply interface  86  distributes electrical power from the power supply  82 , along twisted pairs of the communication cabling  61  which are not used for carrying data, to at least some of the LAN nodes. Bidirectional data communications from LAN switch  84  pass through the power supply interface  86 , substantially without interference.  
         [0149]     It is seen that the communication cabling  61  from the hub  60  to the desktop computer  62 , facsimile machine  66  and computer  70  carries both data and backup power along separate twisted pairs, while the communication cabling  61  from the hub  60  to the hub camera  64  and LAN telephone  68  carries both data and operating power along separate twisted pairs and the communication cabling  61  from the hub  60  to the server  72  carries only data, in a typically LAN arrangement constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0150]     It is a particular feature of the embodiment of  FIG. 1B  that data and power are carried on separate twisted copper pairs of each communication cabling line.  
         [0151]     It is appreciated that each of the LAN nodes  62 - 70  which receives power over the communication cabling  61  includes a connector for connecting the twisted pairs carrying electrical power to a node power supply and separately connecting the twisted pairs carrying data to a data input of the node. In the illustrated embodiment of  FIG. 1B , the connectors are typically internal to the respective nodes and are not separately designated, it being appreciated that alternatively discrete connectors may be employed.  
         [0152]     It is appreciated that  FIGS. 1A and 1B  illustrates two embodiments of a system providing electric power to plural LAN nodes via a hub and communication cabling connecting the hub to various LAN nodes. Another two embodiments of a system providing electric power to plural LAN nodes via a hub and communication cabling connecting the hub to various LAN nodes are illustrated in  FIGS. 2A &amp; 2B .  FIGS. 2A &amp; 2B  illustrate a local area network including a power supply operative to provide electrical power to local area network nodes over communication cabling.  
         [0153]     In the illustrated embodiment of  FIG. 2A , a conventional hub  100  does not provide electrical power over the communication cabling  101  and a power supply subsystem  130  is located externally of hub  100  and includes a power supply  132  which supplies operating power and/or backup power to various LAN nodes via the communication cabling  101 . The communication cabling connects a LAN switch  134  of conventional hub  100  to a combiner  136  in power supply subsystem  130  and connects the combiner to the various LAN nodes. The combiner  136  provides electrical power from the power supply  132  along the communication cabling to at least some of the LAN nodes. Bidirectional data communications from LAN switch  134  pass through the combiner  136 , substantially without interference.  
         [0154]     Cabling  101  is preferably conventional LAN cabling having four pairs of twisted copper wires cabled together under a common jacket. In the embodiment of  FIG. 2A , as will be described hereinbelow, at least one of the pairs of twisted copper wires is employed for transmitting both data and electrical power to nodes of the network. Typically two such pairs are employed for transmitting both data and electrical power along each line connecting the power supply sub-system  130  to each node, while one such pair carries data only and a fourth pair is maintained as a spare and carries neither data nor power.  
         [0155]     It is seen that the communication cabling  101  from the power supply sub-system  130  to the desktop computer  112 , facsimile machine  116  and computer  120  carries both data and backup power, while the communication cabling from the power supply sub-system  130  to the hub camera  114  and LAN telephone  118  carries both data and operating power and the communication cabling from the hub  100  to the server  122  carries only data and may, but need not pass through subsystem  130 , in a typically LAN arrangement constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0156]     It is a particular feature of the embodiment of  FIG. 2A  that both data and power are carried on the same twisted copper pair.  
         [0157]     In the illustrated embodiment of  FIG. 2A , each of the LAN nodes  112 - 120  which receives power is provided with an external separator for separating the data from the electrical power coupled to the communication cabling. The external separators associated with respective nodes  112 - 120  are designated by respective reference numbers  142 - 149 . Each such separator has a communication cabling input and separate data and power outputs. It is appreciated that some or all of the nodes  112 - 120  may alternatively be provided with internal separators and that some or all of the nodes  112 - 120  may be provided with external separators.  
         [0158]     It is appreciated that in addition to the LAN nodes described hereinabove, the present invention is useful with any other suitable nodes such as, for example, wireless LAN access points, emergency lighting system elements, paging loudspeakers, CCTV cameras, alarm sensors, door entry sensors, access control units, laptop computers, network elements such as hubs, switches and routers, monitors and memory backup units for PCs and workstations.  
         [0159]     In the illustrated embodiment of  FIG. 2B , a conventional hub  150  does not provide electrical power over the communication cabling  151  and a power supply subsystem  180  is located externally of hub  150  and includes a power supply  182  which supplies operating power and/or backup power to various LAN nodes via the communication cabling  151 . The communication cabling connects a LAN switch  184  of conventional hub  150  to a power supply interface  186  in power supply subsystem  180  and connects the power supply interface  186  to the various LAN nodes. The power supply interface distributes electrical power from the power supply  182  along the communication cabling to at least some of the LAN nodes. Bidirectional data communications from LAN switch  184  pass through the power supply interface  186 , substantially without interference.  
         [0160]     Cabling  151  is preferably conventional LAN cabling having four pairs of twisted copper wires cabled together under a common jacket. In the embodiment of  FIG. 2B , in contrast to the arrangement described above with respect to  FIG. 2A  and as will be described hereinbelow, at least one of the pairs of twisted copper wires is employed only for transmitting electrical power to nodes of the network and at least one of the pairs of twisted copper wires is employed only for transmitting data. Typically two such pairs are employed for transmitting data only and two such pairs are employed only for supplying electrical power along each line connecting a hub to each node.  
         [0161]     It is seen that the communication cabling  151  from the hub  150  to the desktop computer  162 , facsimile machine  166  and computer  170  carries both data and backup power, while the communication cabling from the hub  150  to the hub camera  164  and LAN telephone  168  carries both data and operating power and the communication cabling from the hub  150  to the server  172  carries only data and may, but need not pass through subsystem  180 , in a typically LAN arrangement constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0162]     It is a particular feature of the embodiment of  FIG. 2B  that data and power are carried on separate twisted copper pairs of each communication cabling line.  
         [0163]     In the illustrated embodiment of  FIG. 2B , each of the LAN nodes  162 - 170  which receives power is provided with an external connector for separately providing data and electrical power from the communication cabling. The external connector associated with respective nodes  162 - 170  are designated by respective reference numbers  192 - 199 . Each such connector has a communication cabling input and separate data and power outputs. It is appreciated that some or all of the nodes  162 - 170  may alternatively be provided with internal connectors and that some or all of the nodes  162 - 170  may be provided with external connectors.  
         [0164]     It is appreciated that in addition to the LAN nodes described hereinabove, the present invention is useful with any other suitable nodes such as, for example, wireless LAN access points, emergency lighting system elements, paging loudspeakers, CCTV cameras, alarm sensors, door entry sensors, access control units, laptop computers, network elements, such as hubs, switches and routers, monitors and memory backup units for PCs and workstations.  
         [0165]     Reference is now made to  FIG. 3A , which is a simplified block diagram of a hub, such as hub  10 , useful in the embodiment of  FIG. 1A . Hub  10  preferably comprises a conventional, commercially available, LAN switch  34  which functions as a data communication switch/repeater and is coupled to combiner  36 . Combiner  36  typically comprises a plurality of couplers  220 , each of which is connected via a filter  222  to a smart power allocation and reporting circuit (SPEAR)  224 . Each SPEAR  224  is connected to power supply  32  for receiving electrical power therefrom. It is appreciated that power supply  32  may be physically located externally of the hub  10 . Power supply  32  may be provided with a power failure backup facility, such as a battery connection.  
         [0166]     Each coupler  220  has two ports, one of which is preferably connected to a port of LAN switch  34  and the other of which is preferably connected, via communication cabling, to a LAN node.  
         [0167]     Couplers  220  are preferably operative to couple electrical power to the communication cabling substantially without interfering with the data communication therealong.  
         [0168]     Filters  222  are preferably operative to avoid unwanted interport and interpair coupling, commonly known as “crosstalk” and to block noise from the power supply  32  from reaching the communication cabling.  
         [0169]     A central management and control subsystem  226 , typically embodied in a microcontroller, preferably controls the operation of the power supply  32 , the LAN switch  34 , the couplers  220 , the filters  222  and the SPEARs  224 .  
         [0170]     Reference is now made to  FIG. 3B , which is a simplified block diagram of a hub, such as hub  60 , useful in the embodiment of  FIG. 1B . Hub  60  preferably comprises a conventional, commercially available, LAN switch  84  which functions as a data communication switch/repeater and is coupled to power supply interface  86 . Power supply interface  86  typically comprises a plurality of filters  272 , each connected to a smart power allocation and reporting circuit (SPEAR)  274 . Each SPEAR  274  is connected to power supply  82  for receiving electrical power therefrom. It is appreciated that power supply  82  may be physically located externally of the hub  60 . Power supply  82  may be provided with a power failure backup facility, such as a battery connection.  
         [0171]     Filters  272  are preferably operative to avoid unwanted interport coupling, commonly known as “crosstalk” and to block noise from the power supply  82  from reaching the communication cabling.  
         [0172]     A central management and control subsystem  276 , typically embodied in a microcontroller, preferably controls the operation of the power supply  82 , the LAN switch  84 , the filters  272  and the SPEARs  274 .  
         [0173]     It is seen that in the embodiment of  FIG. 3B , couplers are not provided inasmuch as power and data are transmitted over separate twisted pairs. The data carried on conductors via the power supply interface is substantially unaffected by the operation of the power supply interface.  
         [0174]     Reference is now made to  FIG. 4A , which is a simplified block diagram of hub  100  and the power supply subsystem  130  employed in the embodiment of  FIG. 2A . Hub  100  preferably comprises a conventional, commercially available, LAN switch  134  which functions as a data communication switch/repeater and is coupled to combiner  136  forming part of power supply subsystem  130 . Combiner  136  typically comprises a plurality of couplers  320 , each of which is connected via a filter  322  to a smart power allocation and reporting circuit (SPEAR)  324 . Each SPEAR  324  is connected to power supply  132  ( FIG. 2A ) for receiving electrical power therefrom. It is appreciated that power supply  132  may be physically located externally of the power supply subsystem  130 . Power supply  132  may be provided with a power failure backup facility, such as a battery connection.  
         [0175]     Each coupler  320  has two ports, one of which is preferably connected to a port of LAN switch  134  and the other of which is preferably connected, via communication cabling, to a LAN node.  
         [0176]     Couplers  320  are preferably operative to couple electrical power to the communication cabling substantially without interfering with the data communication therealong.  
         [0177]     Filters  322  are preferably operative to avoid unwanted interport and interpair coupling, commonly known as “crosstalk” and to block noise from the power supply  132  from reaching the communication cabling.  
         [0178]     A central management and control subsystem  326 , typically embodied in a microcontroller, preferably controls the operation of the power supply  132 , the couplers  320 , the filters  322  and the SPEARs  324 .  
         [0179]     Reference is now made to  FIG. 4B , which is a simplified block diagram of hub  150  and the power supply subsystem  180  employed in the embodiment of  FIG. 2B . Hub  150  preferably comprises a conventional, commercially available, LAN switch  184  which functions as a data communication switch/repeater and is coupled to power supply interface  186  forming part of power supply subsystem  180 . Power supply interface  186  typically comprises a plurality of filters  372  each coupled to a smart power allocation and reporting circuit (SPEAR)  374 . Each SPEAR  374  is connected to power supply  182  ( FIG. 2B ) for receiving electrical power therefrom. It is appreciated that power supply  182  may be physically located externally of the power supply subsystem  180 . Power supply  182  may be provided with a power failure backup facility, such as a battery connection.  
         [0180]     Filters  372  are preferably operative to avoid unwanted interport and interpair coupling, commonly known as “crosstalk” and to block noise from the power supply  182  from reaching the communication cabling.  
         [0181]     A central management and control subsystem  376 , typically embodied in a microcontroller, preferably controls the operation of the power supply  182 , filters  372  and the SPEARs  374 .  
         [0182]     It is seen that in the embodiment of  FIG. 4B , couplers are not provided inasmuch as power and data are transmitted over separate twisted pairs. The data carried on conductors via the power supply interface is substantially unaffected by the operation of the power supply interface.  
         [0183]     It is appreciated that power supply  32  ( FIG. 3A ), power supply  82  ( FIG. 3B ), power supply  132  ( FIG. 4A ) and power supply  182  ( FIG. 4B ) provide output power to SPEARs  224  ( FIG. 3A ), SPEARs  274  ( FIG. 3B ),  324  ( FIG. 4A ) and  374  ( FIG. 4B ) respectively along a pair of conductors, one of which is designated as a positive conductor and indicated by (+) and the other of which is designated as a negative conductor and indicated by (−). The voltages supplied to the respective positive and negative conductors are designated respectively as+Vin and −Vin. The difference therebetween is designated as Vin.  
         [0184]     Reference is now made to  FIG. 5 , which is a simplified block diagram illustration of a smart power allocation and reporting circuit (SPEAR)  400  useful in the embodiments of  FIGS. 3A, 3B  and  FIGS. 4A, 4B  particularly when DC current is coupled to the communication cabling.  
         [0185]     SPEAR  400  preferably comprises a current sensor  402  which receives a voltage input +Vin from a power supply and generates a signal which is proportional to the current passing therethrough. A voltage input −Vin received from the power supply  32  ( FIG. 3A ),  82  ( FIG. 3B ),  132  ( FIG. 4A ) or  182  ( FIG. 4B ) provides a voltage output −Vout which is typically unchanged from voltage input −Vin.  
         [0186]     The output of current sensor  402  is supplied to a multiplicity of comparators  404  which also receive respective reference voltages Vref from respective programmable reference voltage sources  406 , typically implemented in A/D converters. Programmable reference voltage sources  406  receive control inputs from management &amp; control circuits  226  ( FIG. 3A ),  276  ( FIG. 3B ),  326  ( FIG. 4A ) and  376  ( FIG. 4B ) preferably via a bus  407 . Alternatively, voltage sources  406  need not be programmable.  
         [0187]     The outputs of comparators  404  are supplied to a current limiter and switch  408  which receives input voltage Vin via the current sensor  402  and provides a current-limited voltage output Vout. Output voltages +Vout and −Vout are applied as inputs to an A/D converter  409  which outputs a digital indication of Vout, which is the difference between +Vout and −Vout, to the management &amp; control circuits  226  ( FIG. 3A ),  276  ( FIG. 3B ),  326  ( FIG. 4A ) and  376  ( FIG. 4B ) preferably via bus  407 . The outputs of comparators  404  are supplied to management &amp; control circuits  226  ( FIG. 3A ),  276  ( FIG. 3B ),  326  ( FIG. 4A ) and  376  ( FIG. 4B ) preferably via bus  407  to serve as monitoring inputs providing information regarding the DC current flowing through the SPEAR.  
         [0188]     The outputs of some of comparators  404  are supplied directly to current limiter and switch  408 , while the outputs of others of comparators  404  are supplied thereto via a timer  410  and a flip/flop  412 . The comparators whose outputs are supplied directly to current limiter and switch  408  provide immediate current limiting at a relatively high threshold, while the comparators whose outputs are supplied to current limiter and switch  408  via timer  410  and flip/flop  412  provide delayed action current cut-off at a relatively low threshold.  
         [0189]     Flip-flop  412  is responsive to external inputs which enable remote control of the operation of the current limiter and switch  408  by the management &amp; control circuits  226  ( FIG. 3A ),  276  ( FIG. 3B ),  326  ( FIG. 4A ) and  376  ( FIG. 4B ) via bus  407 .  
         [0190]     It is appreciated that the above described SPEAR circuitry may also be operated on the negative lead. In such a case a short-lead would be connected between the Vin and the Vout.  
         [0191]     It is further appreciated that the components of the SPEAR may also be organize in an alternative sequence.  
         [0192]     Reference is now made  FIG. 6 , which is a simplified schematic illustration of a preferred implementation of the embodiment of  FIG. 5 . Inasmuch as identical reference numerals are employed in both  FIGS. 5 and 6 , the schematic illustration of  FIG. 6  is believed to be self-explanatory and therefore, for the sake of conciseness, no additional textual description thereof is provided herein.  
         [0193]     Reference is now made to  FIG. 7A , which is a simplified block diagram illustration of a LAN node interface circuit useful in the embodiments of  FIGS. 1A and 2A  for example as external separators  142 - 149 . It is appreciated that the circuitry of  FIG. 7A  alternatively may be built-in to LAN nodes, as shown, for example in  FIG. 1A .  
         [0194]      FIG. 7A  shows typical constituent elements of a network node  500 , including a data transceiver  502 , a mains-fed power supply  504  and various other elements  506  depending on the functionality of the node. The interface circuitry typically comprises a separator  508  which is operative to receive data and electrical power over communication cabling and to provide a data output to the data transceiver  502  and a separate power output to a communications cabling-fed power supply  510 , preferably forming part of network node  500 , which preferably powers the data transceiver  502  and possibly any other suitable circuitry.  
         [0195]     Reference is now made to  FIG. 7B , which is a simplified block diagram illustration of a LAN node interface circuit useful in the embodiments of  FIGS. 1B and 2B  for example as external connectors  192 - 199 . It is appreciated that the circuitry of  FIG. 7B  alternatively may be built-in to LAN nodes, as shown, for example in  FIG. 1B .  
         [0196]      FIG. 7B  shows typical constituent elements of a network node  550 , including a data transceiver  552 , a mains-fed power supply  554  and various other elements  556  depending on the functionality of the node. The interface circuitry typically comprises a connector  558  which is operative to receive data and electrical power over communication cabling and to provide a data output to the data transceiver  552  and a separate power output to a communications cabling-fed power supply  560 , preferably forming part of network node  550 , which preferably powers the data transceiver  552  and possibly any other suitable circuitry.  
         [0197]     Reference is  FIGS. 8A-8E , which are simplified block diagram illustrations of various embodiments of a coupler useful in the embodiments of  FIGS. 3A and 4A . The various embodiments have the common purpose of coupling DC power to the communication cabling without upsetting the balance therealong, while producing a minimal change in the line impedance thereof and preventing saturation or burnout of line transformers coupled thereto.  
         [0198]      FIG. 8A  describes a coupler  600 , such as coupler  220  ( FIG. 3A ) or coupler  320  ( FIG. 4A ) suitable for use with a LAN in accordance with a preferred embodiment of the present invention and which includes a pair of additional transformers  610  for each channel. Transformers  610  are typically 1:1 transformers which are characterized in that they include a center tap at the secondary via which the DC voltage is fed to both wires of a twisted pair.  
         [0199]     This structure maintains the balance of the line and prevents core saturation. This structure also has the advantage that due to the fact that the same voltage is carried on both wires of the twisted pair simultaneously, the occurrence of a short circuit therealong will not cause a power overload. An additional advantage of this structure is that it will not cause burnout of a LAN node which is not specially adapted for receive power over the twisted pair.  
         [0200]      FIG. 8B  describes a coupler  620 , such as coupler  220  ( FIG. 3A ) or coupler  320  ( FIG. 4A ) suitable for use with a LAN in accordance with a preferred embodiment of the present invention and which includes a pair of additional transformers  630  for each channel. Transformers  630  are typically 1:1 transformers which are characterized in that they include a secondary  632  which is split into two separate windings  634  and  636 . A capacitor  640  is connected between windings  634  and  636 . The capacitor effectively connects the two windings in series for high frequency signals, such as data signals, but effectively isolates the two windings for DC.  
         [0201]     This structure enables the two windings to carry respective positive and negative voltages via the same twisted pair. An advantage of this structure is that it applies a net zero DC current via the twisted pair and thus eliminates the magnetic field that would otherwise have existed had the twisted pair carried DC current in the same directions.  
         [0202]      FIG. 8C  describes a coupler  650 , such as coupler  220  ( FIG. 3A ) or coupler  320  ( FIG. 4A ) suitable for use with a LAN in accordance with a preferred embodiment of the present invention and which includes a pair of capacitors  660  which effectively block DC from reaching the LAN switch. This structure is relatively simple and does not require an additional transformer.  
         [0203]      FIG. 8D  describes a coupler  670 , such as coupler  220  ( FIG. 3A ) or coupler  320  ( FIG. 4A ) suitable for use with a LAN in accordance with a preferred embodiment of the present invention and which includes two pairs of capacitors  680  and  690  which effectively block DC from reaching the LAN switch. This structure is also relatively simple and does not require an additional transformer.  
         [0204]     This structure also has the advantage that due to the fact that the same voltage is carried on both wires of the twisted pair simultaneously, the occurrence of a short circuit therealong will not cause a power overload. An additional advantage of this structure is that it will not cause burnout of a LAN node which is not specially adapted for receive power over the twisted pair.  
         [0205]      FIG. 8E  describes a coupler  700 , such as coupler  220  ( FIG. 3A ) or coupler  320  ( FIG. 4A ) suitable for use with a LAN in accordance with a preferred embodiment of the present invention and which is a self-balancing common mode coupling circuit. Combiner  700  comprises two pairs of adjustable active balancing circuits  702  and  704 , which are operative in conjunction with respective sensing and control circuits  706  and  708 .  
         [0206]     It is a particular feature of the embodiment of  FIG. 8E  that the two pairs of adjustable active balancing circuits  702  and  704 , which are operative in conjunction with respective sensing and control circuits  706  and  708  are operative to maintain precisely identical voltages on each of the two wires comprising a twisted pair coupled thereto.  
         [0207]     Normally the output of a LAN switch is coupled to communication cabling via an isolation transformer  710 , which is not part of the coupler  700 . When precisely identical voltages, as aforesaid, are applied to each of the two wires comprising the twisted pair, there is no DC voltage across the secondary windings of the isolation transformer  710  and thus no DC current flows therethrough. This obviates the need for DC isolating capacitors and thus improves the balancing and impedance matching behavior of the combiner.  
         [0208]     It is appreciated that whereas in a theoretically ideal system there would not be any need for active balancing as provided in the embodiment of  FIG. 8E , in reality due to variations in the DC resistance along the entire communication cabling system, the DC voltages on each of the two wires of the twisted pair would not be identical in the absence of active balancing, thus creating a DC voltage drop across the secondary of transformer  710  which could cause either saturation or burnout of transformer  710 .  
         [0209]     Reference is now made  FIG. 8F , which is a simplified schematic illustration of a preferred implementation of the embodiment of  FIG. 8E . Inasmuch as identical reference numerals are employed in both  FIGS. 8E and 8F , the schematic illustration of  FIG. 8F  is believed to be self-explanatory and therefore, for the sake of conciseness, no additional textual description thereof is provided herein.  
         [0210]     Reference is now made  FIG. 8G , which is a simplified schematic illustration of a preferred implementation of the embodiment of  FIG. 8E . Inasmuch as identical reference numerals are employed in both  FIGS. 8E and 8G , the schematic illustration of  FIG. 8G  is believed to be self-explanatory and therefore, for the sake of conciseness, no additional textual description thereof is provided herein.  
         [0211]     Reference is now made to  FIGS. 9A-9G  which are simplified block diagram and schematic illustrations of various embodiments of a separator useful in the embodiments of  FIGS. 1A, 2A  &amp;  7 A preferably in combination with the respective combiners of  FIGS. 8A-8G .  
         [0212]     In addition to the components included in  FIGS. 9A  to  9 G, these separators may also include appropriate filters to avoid interpair and interport crosstalk.  
         [0213]     The various embodiments have the common purpose of decoupling DC power from the communication cabling without upsetting the balance therealong, while producing a minimal change in the line impedance thereof and preventing saturation or burnout of line transformers coupled thereto.  
         [0214]      FIG. 9A  describes a separator  1600 , such as separator  142  ( FIG. 2A ), suitable for use with a LAN in accordance with a preferred embodiment of the present invention and which includes a pair of additional transformers  1610  for each channel. Transformers  1610  are typically 1:1 transformers which are characterized in that they include a center tap at the primary via which the DC voltage is extracted from both wires of a twisted pair.  
         [0215]     This structure maintains the balance of the line and prevents core saturation. This structure also has the advantage that due to the fact that the same voltage is carried on both wires of the twisted pair simultaneously, the occurrence of a short circuit therealong will not cause a power overload. An additional advantage of this structure is that it will not cause burnout of a LAN node which is not specially adapted for receive power over the twisted pair.  
         [0216]      FIG. 9B  describes a separator  1620 , such as separator  142  ( FIG. 2A ) suitable for use with a LAN in accordance with a preferred embodiment of the present invention and which includes a pair of additional transformers  1630  for each channel. Transformers  1630  are typically 1:1 transformers which are characterized in that they include a primary  1632  which is split into two separate windings  1634  and  1636 . A capacitor  1640  is connected between windings  1634  and  1636 . The capacitor effectively connects the two windings in series for high frequency signals, such as data signals, but effectively isolates the two windings for DC.  
         [0217]     This structure enables the two windings to carry respective positive and negative voltages via the same twisted pair. An advantage of this structure is that it applies a net zero DC current via the twisted pair and thus eliminates the magnetic field that would otherwise have existed had the twisted pair carried DC current in the same directions.  
         [0218]      FIG. 9C  describes a separator  1650 , such as separator  142  ( FIG. 2A ), suitable for use with a LAN in accordance with a preferred embodiment of the present invention and which includes a pair of capacitors  1660  which effectively block DC from reaching the node circuits. This structure is relatively simple and does not require an additional transformer.  
         [0219]      FIG. 9D  describes a separator  1670 , such as separator  142  ( FIG. 2A ), suitable for use with a LAN in accordance with a preferred embodiment of the present invention and which includes two pairs of capacitors  1680  and  1690  which effectively block DC from reaching the node circuits. This structure is also relatively simple and does not require an additional transformer.  
         [0220]     This structure also has the advantage that due to the fact that the same voltage is carried on both wires of the twisted pair simultaneously, the occurrence of a short circuit therealong will not cause a power overload. An additional advantage of this structure is that it will not cause burnout of a LAN node which is not specially adapted for receive power over the twisted pair.  
         [0221]      FIG. 9E  describes a separator  1700 , such as separator  142  ( FIG. 2A ), suitable for use with a LAN in accordance with a preferred embodiment of the present invention and which is a self-balancing common mode coupling circuit. Separator  1700  comprises two pairs of adjustable active balancing circuits  1702  and  1704 , which are operative in conjunction with respective sensing and control circuits  1706  and  1708 .  
         [0222]     It is a particular feature of the embodiment of  FIG. 9E  that the two pairs of adjustable active balancing circuits  1702  and  1704 , which are operative in conjunction with respective sensing and control circuits  1706  and  1708  are operative to maintain precisely identical voltages on each of the two wires comprising a twisted pair coupled thereto.  
         [0223]     Normally the input of a LAN node is coupled to communication cabling via an isolation transformer  1710 , which is not part of the separator  1700 . When precisely identical voltages, as aforesaid, are maintained on each of the two wires comprising the twisted pair, there is no DC voltage across the primary windings of the isolation transformer  1710  and thus no DC current flows therethrough. This obviates the need for DC isolating capacitors and thus improves the balancing and impedance matching behavior of the separator.  
         [0224]     It is appreciated that whereas in a theoretically ideal system there would not be any need for active balancing as provided in the embodiment of  FIG. 9E , in reality due to variations in the DC resistance along the entire communication cabling system, the DC voltages on each of the two wires of the twisted pair would not be identical in the absence of active balancing, thus creating a DC voltage drop across the primary of transformer  1710  which could cause either saturation or burnout of transformer  1710 .  
         [0225]     Reference is now made  FIG. 9F , which is a simplified schematic illustration of part of a preferred implementation of the embodiment of  FIG. 9E , including elements  1702  and  1706  thereof. Inasmuch as identical reference numerals are employed in both  FIGS. 9E and 9F , the schematic illustration of  FIG. 9F  is believed to be self-explanatory and therefore, for the sake of conciseness, no additional textual description thereof is provided herein.  
         [0226]     Reference is now made  FIG. 9G , which is a simplified schematic illustration of part of a preferred implementation of the embodiment of  FIG. 9E , including elements  1704  and  1708  thereof. Inasmuch as identical reference numerals are employed in both  FIGS. 9E and 9G , the schematic illustration of  FIG. 9G  is believed to be self-explanatory and therefore, for the sake of conciseness, no additional textual description thereof is provided herein.  
         [0227]     The circuits of  FIGS. 9F and 9G  is provided to ensure that the voltage is identical on both leads of the twisted pair to which they are coupled in order to prevent current flow through transformers  1710  ( FIG. 9E ). This is accomplished by the circuits of  9 F and  9 G by changing the current flowing through the active filters  1702  and  1704  under the control of elements  1706  and  1708  respectively.  
         [0228]     Reference is now made to  FIG. 10A , which is a simplified block diagram illustration of a communications network including power supply and management over communications cabling constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0229]     As seen in  FIG. 10A , there is provided a local area network (LAN) comprising a hub  2010  which is coupled, by cabling, preferably a structured cabling system, to a plurality of LAN nodes, such as a desktop computer  2012 , a web camera  2014 , a facsimile machine  2016 , a LAN telephone, also known as an IP telephone  2018 , a computer  2020  and a server  2022 .  
         [0230]     In accordance with a preferred embodiment of the present invention there is provided a power supply subsystem  2030  which is operative to provide at least some operating or backup power to at least some of said plurality of nodes via the hub  2010  and the communication cabling connecting the hub to various LAN nodes.  
         [0231]     In the illustrated embodiment of  FIG. 10A , subsystem  2030  is located within the hub  2010  and includes a power supply  2032  which supplies operating power and/or backup power to various LAN nodes via the communication cabling. The communication cabling connects a LAN switch  2034  via a combiner  2036  to the various LAN nodes. The combiner couples electrical power from the power supply  2032  along the communication cabling to at least some of the LAN nodes. Bidirectional data communications from LAN switch  2034  pass through the combiner  2036 , substantially without interference.  
         [0232]     In accordance with a preferred embodiment of the present invention, there is provided in hub  2010  a power management &amp; control unit  2038  which monitors and controls the power supplied by subsystem  2030  to the various LAN nodes via the communications cabling. The power management &amp; control unit  2038  preferably communicates with a management workstation  2040 , preferably via a LAN or a WAN. Management workstation  2040  is operative, preferably under the control of an operator, to govern the operation of power management &amp; control unit  2038 .  
         [0233]     It is appreciated that a management workstation  2040  may govern the operation of multiple power management &amp; control units  2038 . The power management &amp; control unit  2038  may also communicate with various LAN nodes via LAN switch  2034  by providing standard LAN messages to the nodes thereby to govern their current mode of power usage. For example, power management &amp; control unit  2038  may send control messages which are decoded at the LAN nodes and are employed by controllers in the circuitry of  FIGS. 14A &amp; 14B  for controlling whether full or partial functionality is provided thereat.  
         [0234]     In one specific case, when the power management &amp; control unit  2038  senses that mains power to power supply  2032  is not available, it may send a control message via LAN switch  2034  to cause the various LAN nodes to operate in a backup or reduced power mode.  
         [0235]     It is seen that the communication cabling from the hub  2010  to the desktop computer  2012 , facsimile machine  2016  and computer  2020  carries both data and backup power, while the communication cabling from the hub  2010  to the hub camera  2014  and LAN telephone  2018  carries both data and operating power and the communication cabling from the hub to the server  2022  carries only data, in a typically LAN arrangement constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0236]     It is appreciated that each of the LAN nodes  2012 - 2020 , which receives power over the communication cabling, includes a separator for separating the electrical power from the data. In the illustrated embodiment of  FIG. 10A , the separators are typically internal to the respective nodes and are not separately designated, it being appreciated that alternatively discrete separators may be employed.  
         [0237]     It is a particular feature of the embodiment of  FIG. 10A  that both data and power are carried on the same twisted copper pair.  
         [0238]     It is appreciated that  FIG. 10A  illustrates one embodiment of a system providing electric power to plural LAN nodes via a hub and communication cabling connecting the hub to various LAN nodes. Another embodiment of a system providing electric power to plural LAN nodes via a hub and communication cabling connecting the hub to various LAN nodes is illustrated in  FIG. 11A .  FIG. 11A  illustrates a local area network including a power supply and management unit operative to provide electrical power to local area network nodes over communication cabling.  
         [0239]     Reference is now made to  FIG. 10B , which is a simplified block diagram illustration of a communications network including power supply and management over communications cabling constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0240]     As seen in  FIG. 10B , there is provided a local area network (LAN) comprising a hub  2060  which is coupled, by cabling, preferably a structured cabling system, to a plurality of LAN nodes, such as a desktop computer  2062 , a web camera  2064 , a facsimile machine  2066 , a LAN telephone, also known as an IP telephone  2068 , a computer  2070  and a server  2072 .  
         [0241]     In accordance with a preferred embodiment of the present invention there is provided a power supply subsystem  2080  which is operative to provide at least some operating or backup power to at least some of said plurality of nodes via the hub  2060  and the communication cabling connecting the hub to various LAN nodes.  
         [0242]     In the illustrated embodiment of  FIG. 10B , subsystem  2080  is located within the hub  2060  and includes a power supply  2082  which supplies operating power and/or backup power to various LAN nodes via the communication cabling. The communication cabling connects a LAN switch  2084  via a power supply interface  2086  to the various LAN nodes. The power supply interface provides electrical power from the power supply  2082  along the communication cabling to at least some of the LAN nodes. Bidirectional data communications from LAN switch  2084  pass through the power supply interface  2086 , substantially without interference.  
         [0243]     In accordance with a preferred embodiment of the present invention, there is provided in hub  2060  a power management &amp; control unit  2088  which monitors and controls the power supplied by subsystem  2080  to the various LAN nodes via the communications cabling. The power management &amp; control unit  2088  preferably communicates with a management workstation  2090 , preferably via a LAN or a WAN. Management workstation  2090  is operative, preferably under the control of an operator, to govern the operation of power management &amp; control unit  2088 .  
         [0244]     It is appreciated that a management workstation  2090  may govern the operation of multiple power management &amp; control units  2088 . The power management &amp; control unit  2088  may also communicate with various LAN nodes via LAN switch  2084  by providing standard LAN messages to the nodes thereby to govern their current mode of power usage. For example, power management &amp; control unit  2088  may send control messages which are decoded at the LAN nodes and are employed by controllers in the circuitry of  FIGS. 14A &amp; 14B  for controlling whether full or partial functionality is provided thereat.  
         [0245]     In one specific case, when the power management &amp; control unit  2088  senses that mains power to power supply  2082  is not available, it may send a control message via LAN switch  2084  to cause the various LAN nodes to operate in a backup or reduced power mode.  
         [0246]     It is seen that the communication cabling from the hub  2060  to the desktop computer  2062 , facsimile machine  2066  and computer  2070  carries both data and backup power, while the communication cabling from the hub  2060  to the hub camera  2064  and LAN telephone  2068  carries both data and operating power and the communication cabling from the hub to the server  2072  carries only data, in a typically LAN arrangement constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0247]     It is appreciated that each of the LAN nodes  2062 - 2070 , which receives power over the communication cabling, includes a connector for separately providing electrical power and data. In the illustrated embodiment of  FIG. 10B , the connectors are typically internal to the respective nodes and are not separately designated, it being appreciated that alternatively discrete connector may be employed.  
         [0248]     It is a particular feature of the embodiment of  FIG. 10B  that data and power are carried on separate twisted copper pairs of each communication cabling line.  
         [0249]     It is appreciated that  FIG. 10B  illustrates one embodiment of a system providing electric power to plural LAN nodes via a hub and communication cabling connecting the hub to various LAN nodes. Another embodiment of a system providing electric power to plural LAN nodes via a hub and communication cabling connecting the hub to various LAN nodes is illustrated in  FIG. 11B .  FIG. 11B  illustrates a local area network including a power supply and management unit operative to provide electrical power to local area network nodes over communication cabling.  
         [0250]     In the illustrated embodiment of  FIG. 11A , a conventional hub  2100  does not provide electrical power over the communication cabling and a power supply and management subsystem  2130  is located externally of hub  2100  and includes a power supply  2132  which supplies operating power and/or backup power to various LAN nodes via the communication cabling as well as a power management &amp; control unit  2133 .  
         [0251]     The communication cabling connects a LAN switch  2134  of conventional hub  2100  to a combiner  2136  in power supply and management subsystem  2130  and connects the combiner to the various LAN nodes. The combiner  2136  couples electrical power from the power supply  2132  along the communication cabling to at least some of the LAN nodes. Bidirectional data communications from LAN switch  2134  pass through the combiner  2136 , substantially without interference.  
         [0252]     In accordance with a preferred embodiment of the present invention, there is provided in power supply and management subsystem  2130  power management &amp; control unit  2133  which monitors and controls the power supplied by subsystem  2130  to the various LAN nodes via the communications cabling. The power management &amp; control unit  2133  preferably communicates with a management workstation  2140 , preferably via a LAN or a WAN.  
         [0253]     Management workstation  2140  is operative, preferably under the control of an operator, to govern the operation of power management &amp; control unit  2133 . It is appreciated that a management workstation  2140  may govern the operation of multiple power management &amp; control units  2133  and may also govern the operation of multiple hubs  2100 .  
         [0254]     It is seen that the communication cabling from the hub  2100  to the desktop computer  2112 , facsimile machine  2116  and computer  2120  carries both data and backup power, while the communication cabling from the hub  2100  to the hub camera  2114  and LAN telephone  2118  carries both data and operating power and the communication cabling from the hub  2100  to the server  2122  carries only data and may, but need not pass through subsystem  2130 , in a typically LAN arrangement constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0255]     In the illustrated embodiment of  FIG. 11A , each of the LAN nodes  2112 - 2120  which receives power is provided with an external separator for separating the data from the electrical power coupled to the communication cabling. The external separators associated with respective nodes  2112 - 2120  are designated by respective reference numbers  2142 - 2150 . Each such separator has a communication cabling input and separate data and power outputs. It is appreciated that some or all of the nodes  2112 - 2120  may alternatively be provided with internal separators and that some or all of the nodes  2112 - 2120  may be provided with external separators.  
         [0256]     It is appreciated that in addition to the LAN nodes described hereinabove, the present invention is useful with any other suitable nodes such as, for example, wireless LAN access points, emergency lighting system elements, paging loudspeakers, CCTV cameras, alarm sensors, door entry sensors, access control units, laptop computers, network elements, such as hubs, switches and routers, monitors and memory backup units for PCs and workstations.  
         [0257]     In the illustrated embodiment of  FIG. 1B , a conventional hub  2150  does not provide electrical power over the communication cabling and a power supply and management subsystem  2180  is located externally of hub  2150  and includes a power supply  2182  which supplies operating power and/or backup power to various LAN nodes via the communication cabling as well as a power management &amp; control unit  2183 .  
         [0258]     The communication cabling connects a LAN switch  2184  of conventional hub  2150  to a power supply interface  2186  in power supply and management subsystem  2180  and connects the combiner to the various LAN nodes. The power supply interface  2186  provides electrical power from the power supply  2182  along the communication cabling to at least some of the LAN nodes. Bidirectional data communications from LAN switch  2184  pass through the power supply interface  2186 , substantially without interference.  
         [0259]     In accordance with a preferred embodiment of the present invention, there is provided in power supply and management subsystem  2180  power management &amp; control unit  2183  which monitors and controls the power supplied by subsystem  2180  to the various LAN nodes via the communications cabling. The power management &amp; control unit  2183  preferably communicates with a management workstation  2190 , preferably via a LAN or a WAN.  
         [0260]     Management workstation  2190  is operative, preferably under the control of an operator, to govern the operation of power management &amp; control unit  2183 . It is appreciated that a management workstation  2190  may govern the operation of multiple power management &amp; control units  2183  and may also govern the operation of multiple hubs  2150 .  
         [0261]     It is seen that the communication cabling from the hub  2150  to the desktop computer  2162 , facsimile machine  2166  and computer  2170  carries both data and backup power, while the communication cabling from the hub  2150  to the hub camera  2164  and LAN telephone  2168  carries both data and operating power and the communication cabling from the hub  2150  to the server  2172  carries only data and may, but need not pass through subsystem  2180 , in a typically LAN arrangement constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0262]     In the illustrated embodiment of  FIG. 11B , each of the LAN nodes  2162 - 2170  which receives power is provided with an external connector for separately providing data and electrical power from the communication cabling. The external connectors associated with respective nodes  2162 - 2170  are designated by respective reference numbers  2192 - 2199 . Each such connector has a communication cabling input and separate data and power outputs. It is appreciated that some or all of the nodes  2162 - 2170  may alternatively be provided with internal connectors and that some or all of the nodes  2162 - 2170  may be provided with external connectors.  
         [0263]     It is appreciated that in addition to the LAN nodes described hereinabove, the present invention is useful with any other suitable nodes such as, for example, wireless LAN access points, emergency lighting system elements, paging loudspeakers, CCTV cameras, alarm sensors, door entry sensors, access control units, laptop computers, network elements, such as hubs, switches and routers, monitors and memory backup units for PCs and workstations.  
         [0264]     Reference is now made to  FIG. 12A , which is a simplified block diagram illustration of a hub, such as hub  2010 , useful in the embodiment of  FIG. 10A . Hub  2010  preferably comprises a conventional, commercially available, LAN switch, such as LAN switch  2034  ( FIG. 10A ), which functions as a data communication switch/repeater and is coupled to a coupler and filter unit  2037  which includes couplers  220  and filters  222  as shown in  FIG. 3A  and forms part of combiner  2036  ( FIG. 10A ).  
         [0265]     The coupler and filter unit  2037  is connected to a plurality of smart power allocation and reporting circuits (SPEARs)  2224 . Each SPEAR  2224  is connected to power supply  2032  ( FIG. 10A ) for receiving electrical power therefrom. It is appreciated that power supply  2032  may be physically located externally of the hub  2010 . Power supply  2032  may be provided with a power failure backup facility, such as a battery connection.  
         [0266]     Power management &amp; control unit  2038  ( FIG. 10A ), preferably includes SPEAR controllers  2160  which are preferably connected via a bus  2162  to a microprocessor  2164 , a memory  2166  and communication circuitry  2168 , which typically includes a modem. The power management &amp; control subsystem  2038  is preferably operative to control the operation of all of the couplers, filters and SPEARs in combiner  2036  as well as to control the operation of the power supply  2032 . Power management &amp; control subsystem  2038  preferably communicates with management work station  2040  ( FIG. 10A ) in order to enable operator control and monitoring of the power allocated to the various LAN nodes in various operational modes of the system.  
         [0267]     Reference is now made to  FIG. 12B , which is a simplified block diagram illustration of a hub, such as hub  2060 , useful in the embodiment of  FIG. 10B . Hub  2060  preferably comprises a conventional, commercially available, LAN switch, such as LAN switch  2084  ( FIG. 10B ), which functions as a data communication switch/repeater and is coupled to a filter unit  2087  which includes filters  222  as shown in  FIG. 3B  and forms part of power supply interface  2086  ( FIG. 10B ).  
         [0268]     The filter unit  2087  is connected to a plurality of smart power allocation and reporting circuits (SPEARs)  2274 . Each SPEAR  2274  is connected to power supply  2082  ( FIG. 10B ) for receiving electrical power therefrom. It is appreciated that power supply  2082  may be physically located externally of the hub  2060 . Power supply  2082  may be provided with a power failure backup facility, such as a battery connection.  
         [0269]     Power management &amp; control unit  2088  ( FIG. 10B ), preferably includes SPEAR controllers  2276  which are preferably connected via a bus  2278  to a microprocessor  2280 , a memory  2282  and communication circuitry  2284 , which typically includes a modem. The power management &amp; control subsystem  2088  is preferably operative to control the operation of all of the filters and SPEARs in power supply interface  2086  as well as to control the operation of the power supply  2082 . Power management &amp; control unit  2088  preferably communicates with management work station  2090  ( FIG. 10B ) in order to enable operator control and monitoring of the power allocated to the various LAN nodes in various operational modes of the system.  
         [0270]     Reference is now made to  FIG. 13A , which is a simplified block diagram illustration of a hub and a power supply and management subsystem useful in the embodiment of  FIG. 11A . Hub  2100  ( FIG. 11A ) preferably comprises a conventional, commercially available, LAN switch  2134  which functions as a data communication switch/repeater and is coupled to combiner  2136  forming part of power supply subsystem  2130 .  
         [0271]     Combiner  2136  includes a coupler and filter unit  2137  which include couplers  320  and filters  322  as shown in  FIG. 4A .  
         [0272]     The coupler and filter unit  2137  is connected to a plurality of smart power allocation and reporting circuits (SPEARs)  2324 . Each SPEAR  2324  is connected to power supply  2132  ( FIG. 11A ) for receiving electrical power therefrom. It is appreciated that power supply  2132  may be physically located externally of the power supply and management subsystem  2130 . Power supply  2132  may be provided with a power failure backup facility, such as a battery connection.  
         [0273]     Power management &amp; control unit  2133  ( FIG. 11A ), preferably includes SPEAR controllers  2360  which are preferably connected via a bus  2362  to a microprocessor  2364 , a memory  2366  and communication circuitry  2368 , which typically includes a modem. The power management &amp; control unit  2133  is preferably operative to control the operation of all of the couplers, filters and SPEARs in combiner  2136  as well as to control the operation of the power supply  2132 .  
         [0274]     Power management &amp; control subsystem  2133  preferably communicates with management work station  2140  ( FIG. 11A ) in order to enable operator control and monitoring of the power allocated to the various LAN nodes in various operational modes of the system.  
         [0275]     Reference is now made to  FIG. 13B , which is a simplified block diagram illustration of a hub and a power supply and management subsystem useful in the embodiment of  FIG. 11B . Hub  2150  ( FIG. 11B ) preferably comprises a conventional, commercially available, LAN switch  2184  which functions as a data communication switch/repeater and is coupled to power supply interface  2186  forming part of power supply subsystem  2180 .  
         [0276]     Power supply interface  2186  includes a filter unit  2187  which includes filters  372  as shown in  FIG. 4B .  
         [0277]     The filter unit  2187  is connected to a plurality of smart power allocation and reporting circuits (SPEARs)  2374 . Each SPEAR  2374  is connected to power supply  2182  ( FIG. 11B ) for receiving electrical power therefrom. It is appreciated that power supply  2182  may be physically located externally of the power supply and management subsystem  2180 . Power supply  2182  may be provided with a power failure backup facility, such as a battery connection.  
         [0278]     Power management &amp; control unit  2183  ( FIG. 11B ), preferably includes SPEAR controllers  2376  which are preferably connected via a bus  2378  to a microprocessor  2380 , a memory  2382  and communication circuitry  2384 , which typically includes a modem. The power management &amp; control unit  2183  is preferably operative to control the operation of all of the filters and SPEARs in power supply interface  2186  as well as to control the operation of the power supply  2182 .  
         [0279]     Power management &amp; control unit  2183  preferably communicates with management work station  2190  ( FIG. 11B ) in order to enable operator control and monitoring of the power allocated to the various LAN nodes in various operational modes of the system.  
         [0280]     Reference is now made to  FIGS. 14A &amp; 14B , which are simplified block diagrams of two different node configurations useful in the embodiments of  FIGS. 10A, 10B , A and  11 B.  
         [0281]     The circuitry seen in  FIG. 14A  includes circuitry which is preferably embodied in a node, parts of which circuitry may alternatively be embodied in a separator or connector associated with that node.  
         [0282]     The node, whatever its nature, for example any of nodes  2012 - 2020  in  FIG. 10A ,  2062 - 2070  in  FIG. 101B ,  2112 - 2120  in  FIG. 11A  or  2162 - 2170  in  FIG. 11B , typically includes circuitry which is required for both full functionality and reduced functionality operation, here termed “essential circuitry” and designated by reference numeral  2400 , and circuitry which is not required for reduced functionality operation, here termed “non-essential circuitry” and designated by reference numeral  2402 . For example, if the node comprises an IP telephone, the essential circuitry  2400  includes that circuitry enabling a user to speak and hear over the telephone, while the non-essential circuitry  2402  provides ancillary functions, such as automatic redial, telephone directory and speakerphone functionality.  
         [0283]     The circuitry  2400  and  2402  which is typically part of the node is indicated by reference numeral  2404 . Other circuitry, which may or may not be incorporated within the node will now be described. A power supply  2406 , such as power supply  510  ( FIG. 7A ) or  560  ( FIG. 7B ) receives electrical power via communication cabling from a separator, such as separator  508  shown in  FIG. 7A  or from a connector, such as connector  558  shown in  FIG. 7B . The power supply  2406  supplies electrical power separately to the essential circuitry  2400  and via a switch  2410  to the non-essential circuitry  2402 . Switch  2410  may also receive and control the transfer of electrical power from a power supply  2412  which is connected to mains power.  
         [0284]     Switch  2410  receives a control input from a controller  2414  which is typically a conventional microcontroller providing a binary output. Controller  2414  receives a control input from a sensor  2416 . Preferably controller  2414  also receives a control input from power supply  2412 .  
         [0285]     Sensor  2416  may be implemented in a number of possible ways. It may, for example, sense the voltage level of the electrical power being supplied to power supply  2406 . Additionally or alternatively, it may sense a control signal transmitted thereto, such as a signal transmitted via the communication cabling from the power management &amp; control unit  2038  via the combiner  2036  ( FIG. 10A ) or from similar circuitry in the embodiment of  FIG. 11A . Alternatively, it may sense a control signal transmitted thereto, such as a signal transmitted via the communication cabling from the power management &amp; control unit  2088  via the power supply interface  2086  ( FIG. 10B ) or from similar circuitry in the embodiment of  FIG. 11B .  
         [0286]     The sensor  2416  may receive inputs from either or both the power and data outputs of separator  508  ( FIG. 7A ) or connector  558  ( FIG. 7B ). The input that it receives from the data output of separator  508  or connector  558  may be tapped from an input to the essential circuitry which may include control signal decoding functionality, but preferably may be derived from an output of the essential circuitry which provides a decoded control signal.  
         [0287]     The functionality of controller  2414  may be summarized as follows: When the controller  2414  receives a control input from power supply  2412  indicating that mains power is available, it operates switch  2410  such that power is supplied to both essential circuitry  2400  and non-essential circuitry  2402 .  
         [0288]     When mains power is not available via power supply  2412 , but sensor  2416  indicates that sufficient power is available via the communications cabling, controller  2414  operates switch  2410  such that power is supplied to both essential circuitry  2400  and non-essential circuitry  2402 .  
         [0289]     When, however, mains power is not available via power supply  2412  and sensor  2416  indicates that sufficient power is not available, controller operates switch  2410  such that adequate power is supplied with highest priority to the essential circuitry  2400 . If additional power beyond that required by essential circuitry  2400  is also available, it may be supplied to the non-essential circuitry  2402  via switch  2410 .  
         [0290]     Alternatively, the operation of switch  2410  by the controller  2414  may not be determined solely or at all by the power available, but rather solely by control signals sensed by sensor  2416 , wholly or partially independently of the available power.  
         [0291]     Reference is now made to  FIG. 14B . The circuitry seen in  FIG. 14B  includes circuitry which is preferably embodied in a node, parts of which circuitry may alternatively be embodied in a separator or connector associated with that node. A power supply  2436 , such as power supply  510  ( FIG. 7A ) or  560  ( FIG. 7B ) receives electrical power via communication cabling from a separator, such as separator  508  shown in  FIG. 7A  or from a connector, such as connector  558  shown in  FIG. 7B . The power supply  2436  supplies electrical power via a switch  2438  to the circuitry  2440  of the node. Switch  2438  may also receive electrical power from a power supply  2442  which is connected to mains power.  
         [0292]     Switch  2438  receives a control input from a controller  2444  which is typically a conventional microcontroller providing a binary output. Controller  2444  receives a control input from a sensor  2446  as well as a control input from monitoring circuitry  2448 . Monitoring circuitry  2448 , which is continually powered by power supply  2436  or power supply  2442 , senses a need of the LAN node to shift to full-functionality from sleep mode functionality. It may sense this need, for example, by receiving a user input indicating an intention to use the node or by receiving a control message via the communications cabling. Controller  2444  may also receive a control input from power supply  2442 .  
         [0293]     Sensor  2446  may be implemented in a number of possible ways. It may, for example, sense the voltage level of the electrical power being supplied to power supply  2446 . Additionally or alternatively, it may sense a control signal transmitted thereto, such as a signal transmitted via the communication cabling from the power management &amp; control unit  2038  via the combiner  2036  ( FIG. 10A ) or from similar circuitry in the embodiment of  FIG. 11A . Alternatively, it may sense a control signal transmitted thereto, such as a signal transmitted via the communication cabling from the power management &amp; control unit  2088  via the power supply interface  2086  ( FIG. 110B ) or from similar circuitry in the embodiment of  FIG. 11B .  
         [0294]     The functionality of controller  2444  may be summarized as follows: In the absence of an indication to the contrary from the monitoring circuitry  2448  or from sensor  2446 , the controller operates switch  2438  so that circuitry  2440  does not operate. When a suitable input is received either from the monitoring circuitry  2448  or from sensor  2446 , indicating a need for operation of circuitry  2440 , the controller  2444  operates switch  2438  to cause operation of circuitry  2444 .  
         [0295]     Reference is now made to  FIG. 15 . The circuitry seen in  FIG. 15  includes circuitry which is preferably embodied in a node, parts of which circuitry may alternatively be embodied in a separator associated with that node.  
         [0296]     The node, whatever its nature, for example any of nodes  2012 - 2020  in  FIG. 10A ,  2062 - 2070  in  FIG. 10B ,  2112 - 2120  in  FIG. 11A  or  2162 - 2170  in  FIG. 11B , typically includes circuitry which is required for both full functionality and reduced functionality operation, here termed “essential circuitry” and designated by reference numeral  2500 , and circuitry which is not required for reduced functionality operation, here termed “non-essential circuitry” and designated by reference numeral  2502 . For example, if the node comprises an IP telephone, the essential circuitry  2500  includes that circuitry enabling a user to speak and hear over the telephone, while the non-essential circuitry  2502  provides ancillary functions, such as automatic redial, telephone directory and speakerphone functionality.  
         [0297]     The circuitry  2500  and  2502  which is typically part of the node is indicated by reference numeral  2504 . Other circuitry, which may or may not be incorporated within the node will now be described.  
         [0298]     A power supply  2506 , such as power supply  510  ( FIG. 7A ) or  560  ( FIG. 7B ) receives electrical power via communication cabling from a separator, such as separator  508  shown in  FIG. 7A  or connector  558  shown in  FIG. 7B . The power supply  2506  supplies electrical power separately via a switch  2508  to the essential circuitry  2500  and via a switch  2510  to the non-essential circuitry  2502 . Switches  2508  and  2510  may also receive and control the transfer of electrical power from a power supply  2512  which is connected to mains power.  
         [0299]     Switches  2508  and  2510  each receive a control input from a controller  2514  which is typically a conventional microcontroller providing a binary output. Controller  2514  receives a control input from a sensor  2516 . Preferably controller  2514  also receives a control input from power supply  2512 .  
         [0300]     Sensor  2516  may be implemented in a number of possible ways. It may, for example, sense the voltage level of the electrical power being supplied to power supply  2506 . Additionally or alternatively, it may sense a control signal transmitted thereto, such as a signal transmitted via the communication cabling from the power management &amp; control unit  2038  via the combiner  2036  ( FIG. 10A ) or from similar circuitry in the embodiment of  FIG. 11A . Alternatively, it may sense a control signal transmitted thereto, such as a signal transmitted via the communication cabling from the power management &amp; control unit  2088  via the power supply interface  2086  ( FIG. 10B ) or from similar circuitry in the embodiment of  FIG. 111B .  
         [0301]     The sensor  2516  may receive inputs from either or both the power and data outputs of separator  508  ( FIG. 7A ) or connector  558  ( FIG. 7B ). The input that it receives from the data output of separator  508  or from connector  558  may be tapped from an input to the essential circuitry which may include control signal decoding functionality, but preferably may be derived from an output of the essential circuitry which provides a decoded control signal.  
         [0302]     Monitoring circuitry  2540 , which is continually powered by power supply  2506  or power supply  2512 , senses a need of the LAN node to shift to full-functionality from sleep mode functionality. It may sense this need, for example, by receiving a user input indicating an intention to use the node or by receiving a control message via the communications cabling.  
         [0303]     The functionality of controller  2514  may be summarized as follows: When the controller  2514  receives a control input from power supply  2512  indicating that mains power is available, it operates switches  2508  and  2510  such that power is supplied to both essential circuitry  2500  and non-essential circuitry  2502 .  
         [0304]     When mains power is not available via power supply  2512 , but sensor  2516  indicates that sufficient power is available via the communications cabling, controller  2514  operates switches  2508  and  2510  such that power is supplied to both essential circuitry  2500  and non-essential circuitry  2502 .  
         [0305]     When, however, mains power is not available via power supply  2512  and sensor  2516  indicates that sufficient power is not available, controller operates switch  2508  such that adequate power is supplied with highest priority to the essential circuitry  2500 . If additional power beyond that required by essential circuitry  2500  is also available, it may be supplied to the non-essential circuitry  2502  via switch  2510 .  
         [0306]     Alternatively, the operation of switch  2510  by the controller  2514  may not be determined solely or at all by the power available, but rather solely by control signals sensed by sensor  2516 , wholly or partially independently of the available power.  
         [0307]     In the absence of an indication to the contrary from the monitoring circuitry  2540  or from sensor  2516 , the controller operates switch  2508  so that circuitry  2500  does not operate. When a suitable input is received either from the monitoring circuitry  2540  or from sensor  2516 , indicating a need for operation of circuitry  2500 , the controller  2514  operates switch  2508  to cause operation of circuitry  2500 .  
         [0308]     In accordance with a preferred embodiment of the present invention, the power supply  2406  in the embodiment of  FIG. 14A, 2436  in the embodiment of  FIGS. 14B and 2506  in the embodiment of  FIG. 15  may be constructed to include rechargeable energy storage elements. In such an arrangement, these power supplies provide limited back-up power for use in the case of a power failure or any other suitable circumstance. They may also enable intermittent operation of LAN nodes in situations where only very limited power may be transmitted over the communication cabling.  
         [0309]     Reference is now made to  FIG. 16 , which is a generalized flowchart illustrating power management in both normal operation and reduced power modes of the networks of  FIGS. 10A, 10B ,  11 A and  11 B. As seen in  FIG. 16 , the power management &amp; control unit  2038  ( FIG. 10A ),  2088  ( FIG. 10B ),  2133  ( FIG. 11A ) or  2138  ( FIG. 11B ) governs the supply of power to at least some LAN nodes via the communications cabling, preferably in accordance with a predetermined functionality which is described hereinbelow with reference to  FIG. 17 .  
         [0310]     The power management &amp; control unit  2038  ( FIG. 10A ),  2088  ( FIG. 10B ),  2133  ( FIG. 11A ) or  2138  ( FIG. 11B ) monitors and manages the power consumption of those LAN nodes. It senses overcurrent situations and effects power cutoffs as appropriate. The power management &amp; control unit  2038  ( FIG. 10A ),  2088  ( FIG. 10B ),  2133  ( FIG. 11A ) or  2138  ( FIG. 11B ) may operate in either an involuntary power management mode or a voluntary power management mode. Normally the mode of operation is selected at the time that the LAN is configured, however, it is possible for mode selection to take place thereafter.  
         [0311]     In an involuntary power management mode of operation, if the power management &amp; control unit senses a situation of insufficient power availability for power transmission over the communications cabling to the LAN nodes, it supplies a reduced amount of power to at least some of the LAN nodes and may also provide control messages or other control inputs to the LAN nodes to cause them to operate in a reduced power mode. In a voluntary power management mode of operation, reduced power availability is mandated by management at certain times of reduced activity, such as nights and weekends, in order to save energy costs  
         [0312]     Reference is now made to  FIG. 17 , which illustrates a preferred methodology for supply of electrical power to at least some of the LAN nodes in accordance with the present invention.  
         [0313]     Following initialization of hub  2010  ( FIG. 10A ),  20260  ( FIG. 10B ) or power supply and management subsystem  2130  ( FIG. 11A ),  2180  ( FIG. 1B ) the communications cabling connection to nodes, to which it is intended to transmit power over the communications cabling, is interrogated.  
         [0314]     Initialization of hub  2010  ( FIG. 10A ),  20260  ( FIG. 10B ) or subsystem  2130  ( FIG. 11A ),  2180  ( FIG. 11B ) preferably includes automatically actuated test procedures which ensure proper operation of the elements of the hub  2010  ( FIG. 10A ),  20260  ( FIG. 10B ) or subsystem  2130  ( FIG. 11A ),  2180  ( FIG. 1B ) communication with management work station  2040  ( FIG. 10A ),  2090  ( FIG. 10B ),  2140  ( FIG. 11A ) or  2190  ( FIG. 1B ) if present to determine desired operational parameters of the hub for each node and setting up an internal data base including desired operational parameters for each node. During normal operation of the system, the various operational parameters for each node may be modified by an operator employing the management work station  2040  ( FIG. 10A ),  2090  ( FIG. 10B ),  2140  ( FIG. 11A ),  2190  ( FIG. 11B ).  
         [0315]     The interrogation is described hereinbelow in greater detail with reference to  FIGS. 18A and 18B .  
         [0316]     If the node being interrogated is determined to have power-over-LAN type characteristics and is classified in the internal data base as a node to which it is intended to transmit power over the communications cabling, the SPEAR parameters are set based on the contents of the internal data base and power is transmitted to the node via the communications cabling. Where appropriate, suitable signaling messages are sent to the remote node and the status of the line connected to the node is reported to the management work station  2040 .  
         [0317]     The foregoing procedure is then repeated sequentially for each line of the hub  2110  or subsystem  2130 , to which it is intended to transmit power over the communications cabling.  
         [0318]     Reference is now made to  FIGS. 18A and 18B , which together are a flowchart illustrating a preferred embodiment of the interrogation and initial power supply functionality which appears in  FIG. 17 .  
         [0319]     As seen in  FIGS. 18A &amp; 18B , initially the voltage is measured at the output of the SPEAR  224  ( FIG. 3A ),  274  ( FIG. 3B ),  324  ( FIG. 4A ) or  374  ( FIG. 4B ) corresponding to a line to which it is intended to transmit power over the communications cabling. If the absolute value of the voltage is higher than a predetermined programmable threshold V1, the line is classified as having a voltage present thereon from an external source. In such a case power is not supplied thereto over the communications cabling.  
         [0320]     If the absolute value of the voltage is not higher than the predetermined programmable threshold V1, the SPEAR current limit  10  is set to a predetermined programmable value IL1. SPEAR switch  408  ( FIG. 5 ) is turned ON.  
         [0321]     The voltage and the current at the output of the SPEAR are measured, typically at three predetermined programmable times T1, T2 and T3. Times T1, T2 and T3 are typically determined by a time constant determined by the inductance of typical NIC transformers and the maximum roundtrip DC resistance of a maximum allowed length of communications cabling between the hub and a node. Typically, T1, T2 and T3 are equal to 1, 2 and 10 times the above time constant.  
         [0322]     Typical values for T1, T2 and T3 are 4 msec, 8 msec and 40 msec, respectively.  
         [0323]     Based on these measurements the status of the node and the line to which it is connected are determined. A typical set of determinations is set forth hereinbelow:  
                                                                                 NO LOAD   WHEN Vout &gt; V2 AND THE           ABSOLUTE VALUE OF 10 &lt; I2           FOR ALL T1, T2, T3           SHORT CIRCUIT WHEN Vout &lt; V3 AND THE           ABSOLUTE VALUE OF IO           FOR ALL T1, T2, T3           NIC LOAD   WHEN VoutT3 &lt; V4 AND           THE ABSOLUTE VALUE OF IOT1&lt;IOT2&lt;IOT3           POL LOAD   WHEN Vout T1&gt;V5 AND VoutT2&gt;V5           AND VoutT3&gt;V5                AND THE ABSOLUTE VALUE OF IOT1&gt;I5 OR                THE ABSOLUTE VALUE OF IOT2&gt;I5 OR           THE ABSOLUTE VALUE OF IOT3&gt;I5.                WHERE                      
 
         [0324]     A NO LOAD condition is one in which a node is not connected to the line.  
         [0325]     A SHORT CIRCUIT condition is one in which a short circuit exists across the positive and negative conductors of the line upstream of the node or in the node.  
         [0326]     A NIC LOAD condition is one in which a Network Interface Card line transformer is connected across the line at the node.  
         [0327]     A POL LOAD condition is one in which a Power Over LAN separator is connected across the line at the node.  
         [0328]     V0 is the voltage at the output of the SPEAR.  
         [0329]     V1 is a predetermined programmable value which is preferably arrived at by measuring the highest peak value of voltage Vout for a period of a few minutes when switch  408  is OFF. This value is typically multiplied by 2 to arrive at V1. V1 is typically equal to 3 Volts.  
         [0330]     V2 is a predetermined programmable value which is preferably arrived at by measuring the lowest value of voltage Vout for a period of a few minutes when switch  408  is ON and when no load is connected between +Vout and −Vout at the output of each coupler  220  ( FIG. 3A ) and  320  ( FIG. 4A ). A typical value of V2 is 80% of Vin.  
         [0331]     V3 is a predetermined programmable value which is preferably arrived at by measuring the highest peak value of voltage Vout for a period of a few minutes when switch  408  is ON and when a resistance, which corresponds to the maximum roundtrip DC resistance of a maximum allowed length of communications cabling between the hub and a node, typically 50 ohms, is connected between +Vout and −Vout at the output of each coupler  220  ( FIG. 3A ) and  320  ( FIG. 4A ). This value is typically multiplied by 2 to arrive at V1. V1 is typically equal to 3 Volts.  
         [0332]     V4 is a predetermined programmable value which is preferably arrived at by measuring the highest peak value of voltage Vout for a period of a few minutes when switch  408  is ON and when a resistance, which corresponds to the maximum roundtrip DC resistance of a maximum allowed length of communications cabling between the hub and a node and the resistance of a NIC transformer, typically totaling 55 ohms, is connected between +Vout and −Vout at the output of each coupler  220  ( FIG. 3A ) and  320  ( FIG. 4A ). This value is typically multiplied by 2 to arrive at V1. V1 is typically equal to 3 Volts.  
         [0333]     V5 is a predetermined programmable value which is preferably 50% of Vin, which represents a typical threshold value of Vin at which power supply  510  ( FIG. 7 ) commence operation. 
        VoutT1 is Vout measured at time T1;     VoutT2 is Vout measured at time T2;     VoutT3 is Vout measured at time T3;     IO is the current flowing +Vout to −Vout which is measured by sensor  402  ( FIG. 5 )        
 
         [0338]     IL1 is the predetermined programmable value of the current limit of switch  408  ( FIG. 5 ) and is determined by the maximum allowable DC current through the NIC transformer which does not result in saturation or burnout thereof. IL1 is typically in the vicinity of 10 mA.  
         [0339]     12 is a predetermined programmable value which is preferably arrived at by measuring the maximum peak value of the current  10  for a period of a few minutes when switch  408  is ON and when no load is connected between +Vout and −Vout at the output of each coupler  220  ( FIG. 3A ) and  320  ( FIG. 4A ). A typical value of 12 is 1 mA.  
         [0340]     13 is a predetermined programmable value which is preferably arrived at by measuring the minimum value of the current  10  for a period of a few minutes when switch  408  is ON and when a resistance, which corresponds to the maximum roundtrip DC resistance of a maximum allowed length of communications cabling between the hub and a node, typically 50 ohms, is connected between +Vout and −Vout at the output of each coupler  220  ( FIG. 3A ) and  320  ( FIG. 4A ). 13 is typically equal to 80% of IL1.  
         [0341]     I5 is a predetermined programmable value which is preferably arrived at by measuring the maximum peak value of the current  10  for a period of a few minutes when switch  408  is ON and when no load is connected between +Vout and −Vout at the output of each coupler  220  ( FIG. 3A ) and  320  ( FIG. 4A ). This maximum peak value is multiplied by a factor, typically 2. A typical value of 15 is 2 mA. 
        IOT1 is IO measured at time T1;     IOT2 is IO measured at time T2;     IOT3 is IO measured at time T3;        
 
         [0345]     Reference is now made to  FIGS. 19A-19D ,  20 A- 20 D,  21 A- 21 D,  22 A- 22 D,  23 A- 23 D and  24 A- 24 D, which illustrate various functionalities for monitoring and managing power consumption in accordance with a preferred embodiment of the present invention. Most or all of the functionalities described hereinbelow employ a basic monitoring and managing technique which is now described:  
         [0346]     In accordance with a preferred embodiment of the present invention, the functionality for monitoring and managing power consumption during normal operation includes sensing current on all lines. This is preferably carried out in a generally cyclic manner. The sensed current is compared with programmably predetermined reference values for each line. Alternatively or additionally, voltage may be sensed and employed for this purpose. On the basis of this comparison, each node is classified as being over-current, under-current or normal. The over-current classification may have programmably adjustable thresholds, such as high over-current, and regular over-current. The normal classification may have sub-classifications, such as active mode, sleep mode, and low-power mode.  
         [0347]     The system is operative to control the operation of nodes classified as being over-current in the following manner: If the current at a node exceeds a regular over current threshold for at least a predetermined time, power to that node is cut off after the predetermined time. In any event, current supplied to a node is not permitted to exceed the high over-current threshold. In accordance with a preferred embodiment of the present invention, various intermediate thresholds may be defined between the regular over-current threshold and the high over-current threshold and the aforesaid predetermined time to cut-off is determined as a function of which of such intermediate thresholds is exceeded.  
         [0348]     The system is operative to control the operation of nodes classified as being under-current in the following manner: Within a relatively short predetermined time following detection of an under-current node, which predetermined time is selected to avoid undesired response to noise, supply of current to such node is terminated.  
         [0349]     In parallel to the functionality described hereinabove, the overall current flow to all of the nodes over all of the lines is monitored. This monitoring may take place in a centralized manner or alternatively may be based on an extrapolation of information received in the line-by-line monitoring described hereinabove.  
         [0350]     The sensed overall current is compared with a programmably predetermined reference value. On the basis of this comparison, the entire hub and the nodes connected thereto are together classified as being over-current or normal. The over-current classification may have programmably adjustable thresholds, such as high over-current, and regular over-current.  
         [0351]     The system is operative to control the operation of hubs classified as being over-current in the following manner: If the overall current exceeds a regular overall over-current threshold for at least a predetermined time, power to at least some nodes is either reduced or cut off after the predetermined time. In any event, the overall current is not permitted to exceed the high overall over-current threshold. In accordance with a preferred embodiment of the present invention, various intermediate thresholds may be defined between the regular overall over-current threshold and the high overall over-current threshold and the aforesaid predetermined time to cut-off is determined as a function of which of such intermediate thresholds is exceeded.  
         [0352]     Additionally in parallel to the functionality described hereinabove, the system is operative to report either continuously or intermittently, the current level classification of each node and of the entire hub to an external monitoring system.  
         [0353]     Further in parallel to the functionality described hereinabove, the system is operative to notify nodes of the impending change in the current supply thereto.  
         [0354]     Reference is now made to  FIGS. 19A, 19B ,  19 C and  19 D, which are generalized flowcharts each illustrating one possible mechanism for full or no functionality operation in an involuntary power management step in the flowchart of  FIG. 16 .  
         [0355]      FIG. 19A  illustrates a basic technique useful for full or no functionality operation in involuntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 19A , the system initially determines the total power available to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power availability (TPA) is then determined.  
         [0356]     If TPC/TPA is less than typically 0.8, additional nodes are supplied full power one-by-one on a prioritized basis. If TPC/TPA is greater than typically 0.95, power to individual nodes is disconnected one-by-one on a prioritized basis.  
         [0357]     If TPC/TPA is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires power. If so, and a node having a lower priority is currently receiving power, the lower priority node is disconnected from power and the higher priority node is connected to power.  
         [0358]      FIG. 19B  illustrates a technique useful for full or no functionality operation with emergency override in involuntary power management in accordance with a preferred embodiment of the present invention. The technique of  FIG. 19B  can be used in the environment of the functionality of  FIG. 19A .  
         [0359]     As seen in  FIG. 19B , the system senses an emergency need for power at a given node. In such a case, the given node is assigned the highest priority and the functionality of  FIG. 19A  is applied. Once the emergency situation no longer exists, the priority of the given node is returned to its usual priority and the functionality of  FIG. 19A  operates accordingly.  
         [0360]      FIG. 19C  illustrates a technique useful for full or no functionality operation having queue-controlled priority in involuntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 19C , the system initially determines the total power available to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power availability (TPA) is then determined.  
         [0361]     If TPC/TPA is less than typically 0.8, additional nodes are supplied full power one-by-one on a queue-controlled, prioritized basis, typically on a first come, first served basis. If TPC/TPA is greater than typically 0.95, power to individual nodes is disconnected one-by-one on a prioritized basis.  
         [0362]     If TPC/TPA is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires power. If so, that node is added to the bottom of the queue.  
         [0363]      FIG. 19D  illustrates a technique useful for full or no functionality operation having queue-controlled priority in involuntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 19D , the system initially determines the total power available to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power availability (TPA) is then determined.  
         [0364]     If TPC/TPA is less than typically 0.8, additional nodes are supplied full power one-by-one on a time-sharing, prioritized basis, typically on a basis that the node having the longest duration of use is cut off first. If TPC/TPA is greater than typically 0.95, power to individual nodes is disconnected one-by-one on a prioritized basis.  
         [0365]     If TPC/TPA is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires power. If so, and a node having a lower priority, in the sense that it has been receiving power for a longer time, which is above a predetermined minimum time, is currently receiving power, the lower priority node is disconnected from power and the higher priority node is connected to power.  
         [0366]     It is appreciated that normally it is desirable that the node be informed in advance in a change in the power to be supplied thereto. This may be accomplished by signally along the communications cabling in a usual data transmission mode or in any other suitable mode.  
         [0367]     Reference is now made to  FIGS. 20A, 20B ,  20 C and  20 D, which are generalized flowcharts each illustrating one possible mechanism for full or reduced functionality operation in an involuntary power management step in the flowchart of  FIG. 16 .  
         [0368]      FIG. 20A  illustrates a basic technique useful for full or reduced functionality operation in involuntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 20A , the system initially determines the total power available to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power availability (TPA) is then determined.  
         [0369]     If TPC/TPA is less than typically 0.8, additional nodes are supplied full power one-by-one on a prioritized basis. If TPC/TPA is greater than typically 0.95, power to individual nodes is reduced one-by-one on a prioritized basis.  
         [0370]     If TPC/TPA is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires additional power. If so, and a node having a lower priority is currently receiving power, the lower priority node has its power supply reduced and the higher priority node is provided with additional power.  
         [0371]      FIG. 20B  illustrates a technique useful for full or reduced functionality operation with emergency override in involuntary power management in accordance with a preferred embodiment of the present invention. The technique of  FIG. 20B  can be used in the environment of the functionality of  FIG. 20A .  
         [0372]     As seen in  FIG. 20B , the system senses an emergency need for additional power at a given node. In such a case, the given node is assigned the highest priority and the functionality of  FIG. 20A  is applied. Once the emergency situation no longer exists, the priority of the given node is returned to its usual priority and the functionality of  FIG. 20A  operates accordingly.  
         [0373]      FIG. 20C  illustrates a technique useful for full or reduced functionality operation having queue-controlled priority in involuntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 20C , the system initially determines the total power available to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power availability (TPA) is then determined.  
         [0374]     If TPC/TPA is less than typically 0.8, additional nodes are supplied additional power one-by-one on a queue-controlled, prioritized basis, typically on a first come, first served basis. If TPC/TPA is greater than typically 0.95, power to individual nodes is reduced one-by-one on a prioritized basis.  
         [0375]     If TPC/TPA is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires additional power. If so, that node is added to the bottom of the queue.  
         [0376]      FIG. 20D  illustrates a technique useful for full or reduced functionality operation having queue-controlled priority in involuntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 20D , the system initially determines the total power available to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power availability (TPA) is then determined.  
         [0377]     If TPC/TPA is less than typically 0.8, additional nodes are supplied additional power one-by-one on a time-sharing, prioritized basis, typically on a basis that the node having the longest duration of use is cut off first. If TPC/TPA is greater than typically 0.95, power to individual nodes is disconnected one-by-one on a prioritized basis.  
         [0378]     If TPC/TPA is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires additional power. If so, and a node having a lower priority, in the sense that it has been receiving power for a longer time, which is above a predetermined minimum time, is currently receiving full power, the lower priority node has its power supply reduced and the higher priority node is provided with additional power.  
         [0379]     Reference is now made to  FIGS. 21A, 21B ,  21 C and  21 D are generalized flowcharts each illustrating one possible mechanism for node initiated sleep mode operation in a voluntary power management step in the flowchart of  FIG. 16 .  
         [0380]      FIG. 21A  illustrates a situation wherein a node operates in a sleep mode as the result of lack of activity for at least a predetermined amount of time. As seen in  FIG. 21A , the time duration TD1 since the last activity of the node is measured. If TD1 exceeds typically a few seconds or minutes, in the absence of a user or system input contraindicating sleep mode operation, the node then operates in a sleep mode, which normally involves substantially reduced power requirements.  
         [0381]      FIG. 21B  illustrates a situation wherein a node operates in a sleep mode as the result of lack of communication for at least a predetermined amount of time. As seen in  FIG. 21B , the time duration TD2 since the last communication of the node is measured. If TD2 exceeds typically a few seconds or minutes, in the absence of a user or system input contraindicating sleep mode operation, the node then operates in a sleep mode, which normally involves substantially reduced power requirements.  
         [0382]      FIG. 21C  illustrates a situation wherein a node operates in a sleep mode in response to clock control, such that the node is active within a periodically occurring time slot, absent an input from the system or the user. As seen in  FIG. 21C , the time slots are defined as times TD3 while the remaining time is defined as TD4. The node determines whether it is currently within the time slot TD3. If not, i.e. during times TD4, it operates in the sleep mode.  
         [0383]      FIG. 21D  illustrates a situation wherein a node operates in a sleep mode as the result of a sensed fault condition. As seen in  FIG. 21D , the node periodically performs a self-test. The self test may be, for example, an attempt to communicate with the hub. If the node passes the test, it operates normally. If the node fails the test, it operates in the sleep mode.  
         [0384]     Reference is now made to  FIGS. 22A, 22B ,  22 C and  22 D, which are generalized flowcharts each illustrating one possible mechanism for hub initiated sleep mode operation in a voluntary power management step in the flowchart of  FIG. 16 .  
         [0385]      FIG. 22A  illustrates a situation wherein a node operates in a sleep mode as the result of lack of activity for at least a predetermined amount of time. As seen in  FIG. 22A , the time duration TD1 since the last activity of the node as sensed by the hub is measured. If TD1 exceeds typically a few seconds or minutes, in the absence of a user or system input contraindicating sleep mode operation, the node then operates in a sleep mode, which normally involves substantially reduced power requirements.  
         [0386]      FIG. 22B  illustrates a situation wherein a node operates in a sleep mode as the result of lack of communication for at least a predetermined amount of time. As seen in  FIG. 22B , the time duration TD2 since the last communication of the node as sensed by the hub is measured. If TD2 exceeds typically a few seconds or minutes, in the absence of a user or system input contraindicating sleep mode operation, the node then operates in a sleep mode, which normally involves substantially reduced power requirements.  
         [0387]      FIG. 22C  illustrates a situation wherein a node operates in a sleep mode in response to clock control from the hub, such that the node is active within a periodically occurring time slot, absent an input from the system or the user. As seen in  FIG. 22C , the time slots are defined as times TD3 while the remaining time is defined as TD4. The node determines whether it is currently within the time slot TD3. If not, i.e. during times TD4, it operates in the sleep mode.  
         [0388]      FIG. 22D  illustrates a situation wherein a node operates in a sleep mode as the result of a fault condition sensed by the hub. As seen in  FIG. 22D , the hub periodically performs a test of the node. The self test may be, for example, an attempt to communicate with the hub. If the node passes the test, it operates normally. If the node fails the test, it operates in the sleep mode.  
         [0389]     Reference is now made to  FIGS. 23A, 23B ,  23 C and  23 D, which are generalized flowcharts each illustrating one possible mechanism for full or no functionality operation in a voluntary power management step in the flowchart of  FIG. 16 .  
         [0390]      FIG. 23A  illustrates a basic technique useful for full or no functionality operation in voluntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 23A , the system initially determines the total power allocated to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power allocation (TPL) is then determined.  
         [0391]     If TPC/TPL is less than typically 0.8, additional nodes are supplied full power one-by-one on a prioritized basis. If TPC/TPL is greater than typically 0.95, power to individual nodes is disconnected one-by-one on a prioritized basis.  
         [0392]     If TPC/TPL is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires power. If so, and a node having a lower priority is currently receiving power, the lower priority node is disconnected from power and the higher priority node is connected to power.  
         [0393]      FIG. 23B  illustrates a technique useful for full or no functionality operation with emergency override in voluntary power management in accordance with a preferred embodiment of the present invention. The technique of  FIG. 23B  can be used in the environment of the functionality of  FIG. 23A .  
         [0394]     As seen in  FIG. 23B , the system senses an emergency need for power at a given node. In such a case, the given node is assigned the highest priority and the functionality of  FIG. 23A  is applied. Once the emergency situation no longer exists, the priority of the given node is returned to its usual priority and the functionality of  FIG. 23A  operates accordingly.  
         [0395]      FIG. 23C  illustrates a technique useful for full or no functionality operation having queue-controlled priority in voluntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 23C , the system initially determines the total power allocated to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power allocation (TPL) is then determined.  
         [0396]     If TPC/TPL is less than typically 0.8, additional nodes are supplied full power one-by-one on a queue-controlled, prioritized basis, typically on a first come, first served basis. If TPC/TPL is greater than typically 0.95, power to individual nodes is disconnected one-by-one on a prioritized basis.  
         [0397]     If TPC/TPL is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires power. If so, that node is added to the bottom of the queue.  
         [0398]      FIG. 23D  illustrates a technique useful for full or no functionality operation having queue-controlled priority in voluntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 23D , the system initially determines the total power allocated to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power allocation (TPL) is then determined.  
         [0399]     If TPC/TPL is less than typically 0.8, additional nodes are supplied full power one-by-one on a time-sharing, prioritized basis, typically on a basis that the node having the longest duration of use is cut off first. If TPC/TPL is greater than typically 0.95, power to individual nodes is disconnected one-by-one on a prioritized basis.  
         [0400]     If TPC/TPL is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires power. If so, and a node having a lower priority, in the sense that it has been receiving power for a longer time, which is above a predetermined minimum time, is currently receiving power, the lower priority node is disconnected from power and the higher priority node is connected to power.  
         [0401]     It is appreciated that normally it is desirable that the node be informed in advance in a change in the power to be supplied thereto. This may be accomplished by signally along the communications cabling in a usual data transmission mode or in any other suitable mode.  
         [0402]     Reference is now made to  FIGS. 24A, 24B ,  24 C and  24 D, which are generalized flowcharts each illustrating one possible mechanism for full or reduced functionality operation in a voluntary power management step in the flowchart of  FIG. 16 .  
         [0403]      FIG. 24A  illustrates a basic technique useful for full or reduced functionality operation in voluntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 24A , the system initially determines the total power allocated to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power allocation (TPL) is then determined.  
         [0404]     If TPC/TPL is less than typically 0.8, additional nodes are supplied full power one-by-one on a prioritized basis. If TPC/TPL is greater than typically 0.95, power to individual nodes is reduced one-by-one on a prioritized basis.  
         [0405]     If TPC/TPL is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires additional power. If so, and a node having a lower priority is currently receiving power, the lower priority node has its power supply reduced and the higher priority node is provided with additional power.  
         [0406]      FIG. 24B  illustrates a technique useful for full or reduced functionality operation with emergency override in voluntary power management in accordance with a preferred embodiment of the present invention. The technique of  FIG. 24B  can be used in the environment of the functionality of  FIG. 24A .  
         [0407]     As seen in  FIG. 24B , the system senses an emergency need for additional power at a given node. In such a case, the given node is assigned the highest priority and the functionality of  FIG. 24A  is applied. Once the emergency situation no longer exists, the priority of the given node is returned to its usual priority and the functionality of  FIG. 24A  operates accordingly.  
         [0408]      FIG. 24C  illustrates a technique useful for full or reduced functionality operation having queue-controlled priority in voluntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 24C , the system initially determines the total power allocated to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power allocation (TPL) is then determined.  
         [0409]     If TPC/TPL is less than typically 0.8, additional nodes are supplied additional power one-by-one on a queue-controlled, prioritized basis, typically on a first come, first served basis. If TPC/TPL is greater than typically 0.95, power to individual nodes is reduced one-by-one on a prioritized basis.  
         [0410]     If TPC/TPL is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires additional power. If so, that node is added to the bottom of the queue.  
         [0411]      FIG. 24D  illustrates a technique useful for full or additional functionality operation having queue-controlled priority in voluntary power management in accordance with a preferred embodiment of the present invention. As seen in  FIG. 24D , the system initially determines the total power allocated to it as well as the total power that it is currently supplying to all nodes. The relationship between the current total power consumption (TPC) to the current total power allocation (TPL) is then determined.  
         [0412]     If TPC/TPL is less than typically 0.8, additional nodes are supplied additional power one-by-one on a time-sharing, prioritized basis, typically on a basis that the node having the longest duration of use is cut off first. If TPC/TPL is greater than typically 0.95, power to individual nodes is disconnected one-by-one on a prioritized basis.  
         [0413]     If TPC/TPL is equal to or greater than typically 0.8 but less than or equal to typically 0.95, an inquiry is made as to whether a new node requires additional power. If so, and a node having a lower priority, in the sense that it has been receiving power for a longer time, which is above a predetermined minimum time, is currently receiving full power, the lower priority node has its power supply reduced and the higher priority node is provided with additional power.  
         [0414]     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and sub-combinations of various features described hereinabove as well as modifications and variations thereof which would occur to persons skilled in the art and which are not in the prior art.