Abstract:
A system for providing power to telephone handsets and other appliances that are connected to a LAN switch. Telephone handsets with built-in Ethernet interfaces can be used to create an enterprise voice communications network which emulates the functions of a standard voice private branch exchange (PBX) switch. The disclosed LAN switch advantageously provides power directly to LAN telephone instruments within the system. The disclosed system may include a means for adding a power system to an existing LAN switch so that remote telephone handsets can receive power from a central location. Alternatively, power equipment may be integrated into a LAN switch itself. The primary benefit of a central power system for Ethernet appliances is that is more convenient to provide back-up power, so that the attached appliances can continue to operate in the event of a power failure. The present system has significant benefits over the most popular current approach, which requires a backup power supply at each telephone instrument or other LAN appliance.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority under 35USC §119( e ) to provisional application Ser. No. 60/174,674, entitled “LOCAL AREA NETWORK (LAN) PACKET SWITCH REMOTE POWER SYSTEM”, and filed Jan. 6, 2000. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    N/A  
         BACKGROUND OF THE INVENTION  
         [0003]    The present invention relates generally to the provision of power to individual telephone instruments and appliances when connected to an Ethernet LAN (Local Area Network) switch, and more specifically to a local area network (LAN) packet switch remote power system.  
           [0004]    As illustrated in FIGS.  2 ( a )-( c ), existing telephone systems for business use normally consist of a central switch or Private Branch exchange (PBX)  14 , which connects to telephones throughout the business via twisted pair wire shown as the station cable  17  and multipair cable  16 . In most cases the PBX  14  uses a single or dual twisted pair cable, shown as the station cable  17  in FIG. 2( a ), to connect with the telephone instrument. The telephone handset  11  and telephone handset  12  in FIG. 2( a ) are illustrative telephone instruments. The PBX  14  sends signals to the telephone instruments  11  and  12  via a frequency translated modem system, which operates according to the frequency plan shown in FIG. 2 ( b ). The telephone instruments  11  and  12  send signals to the PBX  14  using a similar technique. In order to avoid interference, the signals from the PBX  14  may occupy a different frequency spectrum than the signals from the telephone instruments  11  and  12 . Alternatively, transmit and receive signals may occupy the same spectrum envelope  18  shown in FIG. 2( b ). If the transmit and receive signals occupy the same spectrum, a technique called adaptive echo cancellation is used at each end to enable both the PBX  14  and the telephone handsets  11  and  12  to discriminate between their transmitted data and their received data.  
           [0005]    In either of the above existing approaches, the spectrum occupied by the telephone devices does not extend to zero frequency or direct current (“DC”). It is therefore possible to place a DC signal on the single twisted pair, from the PBX  14 , to the telephone instruments  11  and  12 . This DC signal can be used to power the telephone instruments  11  and  12 . The DC signal does not interfere with telephone signaling as there is a di-plexing filter at each end. This type of existing system is further illustrated in FIG. 2( c ). The di-plexing filter consists of Hi-pass  23  and Lo-pass  24  elements. The Hi-pass  23  and Lo-pass  24  elements permit the DC signal and the transmit and receive signals to be summed on the twisted pair wire leading from the PBX  14  to the telephone instruments  11  and  12 . Also, the di-plexing filter prevents the DC power from entering the sensitive signaling circuitry, on either end. An Adaptive Echo Canceller, shown as AEC  19  and  20  in FIG. 2( c ), is used at either end to prevent transmit data from interfering with receive data, since often they both occupy the same spectrum envelope  18 .  
           [0006]    DC Power  22  enters the cable via the Low-Pass Element  24 . The DC Power  22  power is conducted to the appliance or telephone and then conducted through another Lo-Pass Element  24  to the Telephone DC-DC Converter  21  within the appliance or telephone. The output of the DC-DC Converter  21  can then be used to power the telephone instrument.  
           [0007]    A technique for creating a “virtual” PBX is becoming popular in existing systems. In existing systems using this technique, the telephone instruments use an Ethernet cable, instead of a single twisted pair cable, to communicate with the PBX. In such systems, the PBX is a server with switch control software that is connected to the LAN, and the telephones are Ethernet devices that also communicate over the LAN. The advantage of this type of architecture, referred to as a “LAN-PBX”, is that the telephones can use the same wiring and data switches as the LAN data, thus resulting in increased flexibility and lower cost.  
           [0008]    One problem with LAN-PBX type existing systems is that Ethernet cables and switches make no provision for providing power. In Ethernet-based systems, power is provided at each station. As a further complication, Ethernet signals are what are known as “base-band” signals. This means that Ethernet signals include binary data representations that are not frequency shifted. Accordingly, Ethernet signals have frequency components that reach down to almost zero Hertz. For this reason, in existing systems, providing DC power on the same wire as the Ethernet signals is usually infeasible, and could potentially damage the Ethernet devices.  
           [0009]    It would therefore be desirable to have a system for providing centrally distributed power to telephone instruments in a LAN-PBX which does not interfere with Ethernet signals also transmitted between an Ethernet switch and the telephone instruments.  
         BRIEF SUMMARY OF THE INVENTION  
         [0010]    In accordance with principles of the invention, there is disclosed herein a power system for Ethernet LAN appliances, such as telephone instruments. The disclosed system employs two twisted pair wires to provide power to the LAN appliances. In an illustrative embodiment, the two twisted pair wires used to provide the power to the telephone instruments are unused twisted pair wires which may be found in many existing cable bundles. These two twisted pair wires carry DC power from the LAN switch to each LAN appliance. In a first embodiment, the disclosed power system includes a junction box that may be placed in relatively close proximity to an associated enterprise data LAN switch. The junction box is connectable to the LAN switch as well as the LAN appliances. The junction box includes a connection for obtaining external DC power, or alternatively, an internal DC power supply. The disclosed LAN appliances include an internal connection from the two twisted pair wires and their own DC-DC power supplies.  
           [0011]    In another illustrative embodiment, a power supply is placed within the LAN switch itself. With this approach, all ports on the switch may employ the previously unused twisted pair wires to supply DC power to LAN appliances. Existing 10megabit and 100megabit LAN adapters for many computer systems make no connection to the unused pair within the cable bundle. Accordingly, such devices would not usually be harmed by the power provided in accordance with the disclosed system. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0012]    The invention will be more fully understood by reference to the following detailed description of the invention in conjunction with the drawings, of which:  
         [0013]    [0013]FIG. 1 shows a high-level block diagram of an embodiment of the disclosed power system using a junction box;  
         [0014]    [0014]FIG. 2( a ) depicts an existing Private Branch Exchange (PBX);  
         [0015]    [0015]FIG. 2( b ) depicts an existing PBX cable frequency plan;  
         [0016]    [0016]FIG. 2( c ) depicts an existing PBX power diplexer filter;  
         [0017]    [0017]FIG. 3 depicts a schematic for a junction box in accordance with the disclosed LAN power system;  
         [0018]    [0018]FIG. 4 depicts a physical diagram showing an external power system in accordance with the disclosed system;  
         [0019]    [0019]FIG. 5 shows a physical depiction of a LAN switch with an internal power system in accordance with the present invention;  
         [0020]    [0020]FIG. 6 shows a schematic diagram of a power input circuit for a LAN appliance in accordance with an embodiment of the disclosed system;  
         [0021]    [0021]FIG. 7 shows an existing system using an uninterruptable power supply (UPS); and  
         [0022]    [0022]FIG. 8 shows an alternative embodiment of the disclosed system in which is illustrated a power supply for the junction box or internal switch power bus. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    The disclosures of provisional application serial No. 60/174,674, entitled “LOCAL AREA NETWORK (LAN) PACKET SWITCH REMOTE POWER SYSTEM”, and filed Jan. 6, 2000, to which this application claims priority under 35 USC §119( e ), are hereby incorporated by reference herein.  
         [0024]    [0024]FIG. 1 shows a high-level block diagram of the preferred embodiment. In this diagram, five main components are shown: LAN switch  1 , Junction Box  2 , Patch Panel  3 , Wall Jack  5  and Telephone Instrument  4 .  
         [0025]    In the illustrative embodiment of FIG. 1, the LAN switch  1  may, for example, consist of a conventional LAN switch or hub. Ordinarily, this device would be directly connected to a patch panel, such as patch panel or punch down block  3 , and from there be connected to a computer device. In FIG. 1, the LAN switch  1  is connected from a typical network port to the Junction Box  2 , via a standard Patch Cable  6 . One patch cable is used for each remote device or telephone, such as the Telephone Instrument  4 . The Junction Box  2  injects DC power onto the output Patch Cable  7 . The output Patch Cable  7  is used to connect to the Patch Panel  3 . The Patch Panel  3  is connected to the Wall Jack  5  via a Run Cable  9 . A Station Cord  10  is used to make the connection between the Wall Jack  5  and the Telephone Instrument  4 . While the LAN appliance powered by the disclosed system is shown as the Telephone Instrument  4  in the illustrative embodiment of FIG. 4, the disclosed system is not limited in application to this specific type of LAN appliance. Accordingly, those skilled in the art will recognize that the disclosed power distribution system is applicable to any type of LAN appliance, such as, for example, a computer system.  
         [0026]    Power enters the Junction Box  2  via an AC or DC Power connection. If an AC power connection is used, then the Junction Box contains a DC power supply. Internal to the Junction Box  2 , DC power is applied to the two unused twisted pairs on the connector to the Patch Cable  7  which leads to the Patch Panel  3 .  
         [0027]    Circuitry inside the Junction Box  2  monitors the current flow on each cable, individually. If the current flow is greater than a predetermined minimum threshold, for example 20 milli-amps, then the Power Port Indicator  8  is activated. This indicates that a LAN telephone or other LAN appliance is connected to the switch. If the current level exceeds a predetermined maximum, for example 500 milli-amps, then the current flow to the appliance via the Patch Cable  7  is interrupted, and the Power Fault Indicator  32  is activated. The current flow to the appliance may be reasserted by operation of a reset switch  35 , as shown in FIG. 1 and FIG. 3. Alternatively, the current flow to the appliance may be reasserted under such circumstances by way of a system management program executing on a remote station, from which a command is transmitted to the Junction Box  2  indicating that power to the appliance in question should be reasserted. Such a command may, for example, be provided using a network management protocol such as the Simple Network Management Protocol (SNMP), or through any other appropriate command protocol enabling management of the Junction Box  2  from a remote station. In this way power is regulated to the attached LAN appliances.  
         [0028]    Standard data grade cable  6 ,  7 ,  9 ,  10  is typically configured as four twisted pairs, or eight wires. For the disclosed system to be employed, all eight wires must be connected between the Junction Box  2  and the LAN appliance or Telephone Instrument  4 , through cables  7 ,  9 ,  10  as well as the Patch Panel  3  and Wall Jack  5 .  
         [0029]    A schematic for an illustrative embodiment of the disclosed Junction Box  2  of FIG. 1 is depicted in FIG. 3. As illustrated in FIG. 3, standard LAN data cable for Ethernet uses only two of the four twisted pairs it contains. As shown in the switch side connector  25  of FIG. 3, twisted pair  1   40 , through pins  1  and  2   42 , is used to convey Transmit Data from the switch. Twisted pair  2   44 , through pins  3  and  6   46 , is used for Receive Data. Twisted pairs  3   45  and  4   47  are unused. Pairs  3   45  and  4   47  are not connected on the switch side. The internal DC Power Bus  31  provides to all appliance side connector ports of the Junction Box. For example, the internal power bus  31  is used to provide Power  1   138  and Power  2   139  through two of the twisted pairs connected through the appliance side connector  27 . The other two twisted pairs connected through the appliance side connector  27  pass the Transmit Data  49  and Receive Data  51  as also provided on switch side connector  25 .  
         [0030]    The circuitry of FIG. 3 operates to give indication of proper use and to turn off the power if an over-current condition is detected. A Current Sensing Resistor  26  is used to provide a sense element for detection of conditions Current flowing through the Current Sensing Resistor  26  will develop a voltage that can be used by either or both of the Comparators  28  and  29 . The In-Use Comparator  29  will be “off” when no current is flowing in the Current Sensing Resistor  26 . When the current is above the minimum threshold, the In-Use Comparator  29  turns “on” , and provides power to the In-Use Indicator  30 . This will happen when a minimum current drain appliance is connected to the Appliance side connector  27 , via the Patch Cable  7 , Patch Panel  3 , Run Cable  9 , Wall Jack  5  and Station Cord  10 , as shown in FIG. 1. The In-Use Indicator  30  if FIG. 3 corresponds to the Power Port Indicator  8  as shown in FIG  1 .  
         [0031]    If the current passing through the Current Sensing Resistor  26  exceeds a predetermined maximum threshold, then the Current Limit Comparator  28  will turn “on”, causing voltage to be supplied to the Power Control Flip Flop  34 , resulting in the Power Control Flip Flop  34  being reset. The output of the Power Control Flip Flop  34  is connected to the FET Switch  33 . When the Power Control Flip Flop  34  is reset, then the FET Switch  33  is turned “off” halting current flow to the Appliance Side Connector  27 .  
         [0032]    When the FET Switch  33  is “off”, the Fault Indicator  32  is activated, thus indicating a fault condition. The indication of a fault condition can be reset by setting the Power Control Flip Flop  34  via momentary connection of the Reset Switch  35 . This will cause power to flow again unless the limit is still exceeded.  
         [0033]    The circuit of FIG. 3 is replicated for each Appliance Side Connector  27  in the Junction Box  2 . In this way each remote appliance has its own power control and fault interruption. This has the advantage of not allowing a fault in one appliance or cable to disrupt operation of the system with regard to other ports of the system.  
         [0034]    Referring now to FIG. 4, an external power system in accordance with an illustrative embodiment of the disclosed system is shown. An external AC source  50  (110/120v) is connected to an external power supply  52 . External power supply  52  provides appliance power at 48v via power bus  70 , which may, for example, consist of twisted pair or any other suitable connection. As further shown in FIG. 4, the LAN Switch  1  includes a number of Ethernet switch ports  61 , consisting, for example, of RJ-45 connectors. One of the Ethernet switch ports  61  is shown connected to a switch side connector of the junction box  2 , which in turn is shown having a connection to a LAN appliance.  
         [0035]    [0035]FIG. 5 depicts an embodiment of the disclosed system including an internal power supply  56  contained within a LAN switch  101 . The internal power supply  56  is, for example, a 48v power supply circuit, such as would be used to provide power over the power bus  31  in FIG. 3. For example, the power supply circuit  56  may be embodied as shown in the circuit  52  of FIG. 8. The circuitry shown within the Junction Box in FIG. 3 would, accordingly, be included within a circuit board  103  of FIG. 5. A switch power supply  102  is further shown in FIG. 5 providing power to all circuit boards within the switch  101 , and/or to the power supply circuit  56 . The circuit board  103  is shown including at least one Ethernet Switch port  104 , which may be connected to a LAN appliance for purposes of providing data communication and providing power.  
         [0036]    [0036]FIG. 6 shows an illustrative embodiment. of a 48v power input circuit included within an illustrative embodiment of a LAN appliance  156 . The power input circuit of FIG. 6 operates to receive 48v power from twisted pair lines  58   a  and  58   b  through a RJ-45connector  60 , and to pass the received power as input to a DC-DC converter  62 . The output of the DC-DC converter  62  is power for the LAN appliance  156 . The cable  112  is shown including twisted pairs for Transmit Data  115 , Receive Data  116 , Power  1   117  and Power  2   118 . The wires within the cable  112  are, for example 24 AWG wires. A smaller gauge wire could be employed alternatively. A zener diode  120  protects against overvoltage. A surge arrester  121 , for example a gaseous discharge surge arrester, is employed for surge and static protection. A pair of capacitors  122  located on either side of an inductor  123  are shown as an example of a noise filtering technique that may be employed in connection with the embodiment of FIG. 6. In an alternative embodiment, the DC-DC converter  62  may include the functionality of the other components in the power input circuit shown in FIG. 6.  
         [0037]    [0037]FIG. 7 shows an example of a prior solution to providing power to a computer system  200 . As shown in FIG. 7, an Uninterruptable Power Supply (UPS)  251  is used to provide AC power  252  to the network appliance  200 , shown for purposes of illustration as a computer system. The UPS  251  is shown including a DC power supply  71  and a DC to AC converter  72 , operating in connection with a pair of batteries  253 , and a power connector  250 . An advantage of the disclosed system is that it may be provisioned centrally, thus obviating the need for power supplies such as the UPS  251  to be located at every LAN appliance. In particular, it should be noted that the disclosed system may be applied to various LAN appliances, including LAN appliances consisting of computer systems having relatively small power requirements.  
         [0038]    Referring now to FIG. 8, an embodiment of the external power supply  52  used in the embodiment of FIG. 4 is described. As shown in FIG. 8, AC source  50  provides AC power to the Power Supply/Charger  66 . The Power Supply/Charger  66  is shown connected to 48v power bus  70  such that Junction Box  2  may be powered when the AC source  50  is active. A series of four 12v storage cells  68  are also charged when the AC source  50  is active, and supply power to the Junction Box  2  when the AC source  50  is inactive.  
         [0039]    While the invention is described through the above exemplary embodiments, it will be understood by those of ordinary skill in the art that modification to and variation of the illustrated embodiments may be made without departing from the inventive concepts herein disclosed. Accordingly, the invention should not be viewed as limited except by the scope and spirit of the appended claims.