Apparatus and method for remotely powering access equipment over a 10/100 switched ethernet network

Apparatus for remotely powering access equipment over a 10/100 switched Ethernet network comprises an Ethernet switch card with a phantom power supply for remote access equipment and added circuitry for automatic detection of remote equipment being connected to the network; determining whether the remote equipment is capable of accepting remote power in a non-intrusive manner; delivering the phantom power to the remote equipment over the same wire pairs that deliver the data signals, and automatically detecting if the remote equipment is removed from the network.

FIELD OF THE INVENTION
 This invention broadly relates to the powering of 10/100 Ethernet
 compatible equipment. The invention more particularly relates to apparatus
 and methods for automatically determining if remote equipment is capable
 of remote power feed and if it is determined that the remote equipment is
 able to accept power remotely then to provide power in a reliable
 non-intrusive way.
 BACKGROUND OF THE INVENTION
 A variety of telecommunications equipment is remotely powered today.
 Telephones and Network Repeater devices are examples of remotely powered
 equipment. Obviously there are many advantages to remotely powering
 equipment, however this technique has not migrated to data communications
 equipment for several reasons. Data communications equipment has
 traditionally required high power levels to operate which has made it
 prohibitive to implement. The widely distributed nature as well as the use
 of shared media used in data networks has also made remote power
 impractical.
 The desire to add remotely powered devices to a data network is being
 pushed by the convergence of voice and data technologies. The advent of IP
 Telephony, Voice over IP and Voice over Packet technologies has brought
 traditional telephony requirements into the data environment. It is not
 desirable to have a phone powered by a local wall transformer. It is
 desirable to have a centrally powered system that can be protected during
 a power outage.
 It is therefore an object of the invention to provide methods and apparatus
 for reliably determining if a remote piece of equipment is capable of
 accepting remote power.
 It is another object of this invention to provide methods and apparatus for
 delivering remote power to remote equipment over 10/100 switched Ethernet
 segments and maintain compliance with IEEE 802.3 standards.
 SUMMARY OF THE INVENTION
 In accord with the objects of the invention an apparatus for remotely
 powering access equipment over a 10/100 switched Ethernet network
 comprises: automatic detection of remote equipment being connected to the
 network; determining whether the remote equipment is capable of accepting
 remote power in a non-intrusive manner; delivering the power to remote
 equipment over the same wire pairs that deliver the data signals;
 automatic detection of remote equipment being removed from the network.
 The complete apparatus comprises a data node adapted for data switching, an
 access device adapted for data transmission, at least one data signaling
 pair connected between the data node and the access device and arranged to
 transmit data therebetween, a main power source connected to supply power
 to the data node, a secondary power source arranged to supply power from
 the data node via the data signaling pair to the access device, sensing
 means for delivering a low level current from said main power source to
 the access device over the data signaling pair and sensing a resulting
 voltage level thereon, and control means responsive to said voltage level
 and adapted to control power supplied by the secondary power source to
 said access device in response to a preselected condition of the voltage
 level.
 The method includes the steps of delivering a low level current from the
 main power source to the access device over the data signaling pair,
 sensing a voltage level on the data signaling pair in response to the low
 level current, and controlling power supplied by the secondary power
 source to the access device in response to a preselected condition of the
 voltage level.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring now to FIG. 1 of the drawing, a remote access device 10 which is
 compatible with 10/100 Ethernet requirements is connected through a data
 communications network interface adapter to a high data rate network cable
 12. Remote access device 10 requires power to carry out its operation and
 includes an internal dc-dc switching supply which, in the absence of the
 present invention, would be supplied by an ac transformer adapter plugged
 in to the local 110 volt supply. Cable 12 is preferably Category 5 wiring
 such as 100BaseX suitable for 100 Mb/s data communications over a switched
 Ethernet network, and is connected to a port in a network data node 14,
 such as a switch or hub. Ethernet frames containing data are transmitted
 over cable 12 between node 14 and device 10, and from node 14 to and from
 the network in accordance with selected protocols in a conventional manner
 known in the art.
 In accordance with the present invention, a power source 16, which may be
 the same as the conventional main power supply used to power the node 14,
 is connected to cable 12 via lines 18 to supply a power level sensing
 potential to the remote access equipment 10 over one of the cable
 conductors. A return path from remote access equipment 10 is connected
 through a lead 20 to an automatic remote power detector, shown generally
 as 22. Detector 22 includes an A/D converter and microprocessor control
 unit 24, operating a detection circuit consisting of a resistor 26, with
 shunting switch 28, both connected in parallel to a resistor 30, providing
 a path to ground. Switch 28 is actually an internal software controlled
 switch depicted diagrammatically as actuated by operator 32.
 Automatic detection of remote equipment being connected to the network is
 accomplished by delivering a low level current (approx. 20 ma) to the
 network interface and measuring a voltage drop in the return path. There
 are three states which can be determined: no voltage drop, a fixed level
 voltage drop or a varying level voltage drop. If no voltage drop is
 detected then the remote equipment does not contain a dc resistive
 termination, and this equipment is identified as unable to support remote
 power feed. If a fixed voltage level is detected then the remote equipment
 contains a dc resistive termination (a "bob smith" is typical for Ethernet
 terminations), and this equipment is identified as unable to support
 remote power feed.
 If a varying voltage level is detected, this identifies the presence of
 dc-dc switching supply in the remote equipment. The varying level is
 created by the remote power supply beginning to start up but the low
 current level is unable to sustain the start up. This cycle continues to
 be repeated creating a "sawtooth" voltage level in the return path. When
 this cycle is confirmed, switch S1 is closed which increases the power
 output to the remote equipment. When the power to the remote equipment
 reaches the proper level the remote power supply turns on and the remote
 equipment becomes active. At this point a second, software level,
 confirmation takes place. The remote equipment must respond to a poll
 using a coded response with a unique MAC address. When this process is
 complete the remote equipment is identified as known access equipment
 capable of accepting remote power.
 Referring now to FIG. 2 of the drawing, a suitable remote power supply is
 shown generally as 34, which may be conveniently incorporated into an
 Ethernet 8 port switch card. A first center tap data transformer 36
 includes a transformer winding 38 with opposite ends connected by leads
 40, 42 to terminals 6, 3 respectively of an RJ45 connector 43. A second
 center tap transformer 44 with a transformer winding 46 has its opposite
 ends connected via leads 48, 50 to terminals 2, 1 respectively of the
 connector 43. Power feed is through a center tap lead 39 and power return
 is through a center tap lead 45. Inactive terminals 7, 8 of connector 43
 are connected via lead 52 to a resistor 54. Inactive terminals 1, 2 of
 connector 43 are connected via lead 56 to a resistor 58. A junction
 between resistors 54 and 58 is connected to ground via a capacitor 60.
 Remote power is delivered to the remote equipment over the existing data
 signaling pairs (phantom power feed). Although it is typical that all 8
 signal leads are delivered to remote equipment, only the 4 signaling leads
 are guaranteed in practice. See FIG. 2 for the power feed configuration.
 Once the remote equipment is operating and confirmed as a known remote
 power enabled device, the logic circuit shown in FIG. 1 begins to look for
 removal of the remote equipment or an overload fault condition. If the
 measured voltage level drops, then this indicates that the remote
 equipment has been removed and the logic circuit returns to the initial
 hunt state. If an overload condition is detected then the logic circuit
 returns to its initial state. It can then be programmed to either wait for
 the fault state to be cleared or continue to cycle through the state
 machine.
 FIG. 3 illustrates the physical layout of components corresponding to the
 schematic diagram of FIG. 1. The remote access equipment in this case is a
 telephone 62 equipped to handle data communications as well as voice and
 is connected through an access node 64 to premises wiring 66, comprising a
 Category 5 Ethernet 100BaseX cable of 4 sets of unshielded twisted pairs,
 which carry both data and power to the telephone 62. Wiring 66 is
 connected to one of the ports of an 8 port Ethernet switch 68 which is
 powered from a main power supply 70. The Ethernet switch card incorporates
 the automatic remote power detector 22 discussed in FIG. 1 and the remote
 power supply 34 discussed in FIG. 2. The power is provided over the wiring
 66 both to the remote access node 64 and telephone 62.
 While there is disclosed what is considered to be the preferred embodiment
 of the invention, other modifications will occur to those skilled in the
 art.