`(10) Patent N0.:
`US 6,762,675 B1
`
`Cafiero et a1.
`(45) Date of Patent:
`Jul. 13, 2004
`
`U3006762675B1
`
`,
`(75)
`
`(54) METHOD AND APPARATUS FOR REMOTE
`POWERING 0F DEVICE CONNECTED TO
`NETWORK
`.
`4
`,
`‘
`,
`4
`..
`s
`1
`lm'cmors‘ k;r:rfil:fifi:0lNlltldlloAélEEaIZAg‘;[JCS/{7
`(US); Thomas Edsall, Cupertino, CA
`(US); Karl Nakamura, Palo Alto, CA
`ESE} Soel Shm Hang, Sunnyvale, CA
`'
`('73) Assignee: Cisco Technology, Inc., San Jose, CA
`‘
`(US)
`
`(*) Notice:
`
`Subjectto any disclaimer, the term of this
`patent is extended or adjusted under 33
`U.S.C. 154(b) by 0 days.
`
`7
`
`(52) US. Cl.
`
`(21) Appl. N0.: 09/406,248
`(22
`Filed:
`Sep. 27, 1999
`(51)
`Int. Cl.
`......................... H04Q 5/22; 1104M 11/04;
`1-104-M 3/22; G061: 1/30
`
`340/1042; 340/3101”;
`379/210]; 713/300; 713/310
`(58) Field of Search ,,,,,,,,,,,,,,,,,,,,,,,,, 340/1042, 310.01,
`340/8255; 505! 524, 310.02, 310.06, 31007’
`568.1, 568.4, 571’ 572.1, 508.2, 351, 333,
`310.08 310.03 310.04 310.05 1034
`425.2; 71:3/200, 300; 710/02’ 8; 4155/5223
`379/2301 93.36
`’
`
`(:50)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,173,754 A * 11/1979 Feikei
`................... 340,610.02
`
`4.419.066 A + 12/1983 (J‘un' et a1.
`..
`....... 307/39
`4,703,300 A * 10/1987 Barritt
`.....
`. 340,810.08
`
`8/1996 Madonna .
`.. 370/352
`5.544.163 A *
`379/9107
`5,668,857 A *
`9/1997 MCIIale
`
`5,991,885 A * 11/1999 Chan et al.
`.. 713/300
`
`+
`/
`'
`.
`2/2000 Cromger et al.
`..
`.. 340/505
`6,021,493 A *
`6.218330 B1
`4,2001 katzenbelg et al.
`340/3100]
`OTIIER PUBLICATIONS
`Robert Bell. “P802.9f Draft Standard Local and Metropoli-
`tan Area Networks —Supplement to Integrated Services (IS)
`LAN Interface at the Medium Access Control (MAC) and
`1—24.
`Physical (PHY) Layers, ” IEEE .S‘mndurdstjeCt, 1997, pp.
`
`* cited by examiner
`Primary Examiner—Brian Zimmerman
`Assistant Examiner%1ara Yang
`(74) Attorney. Agent,
`or Fir171Warger
`McColIom, PC
`
`Johnson &
`
`ABSTRACT
`(57)
`A network node determines the suitability of coupled
`devices for being remotely line powered before actually
`powering them. The node scan its ports to determine which
`Ports are coupled to devieeS- The node then interrogates the
`coupled devices. A unique discovery tone or bit pattern is
`generated and sent to devices coupled to ports. The node
`then monitors the port for a return signal. If there is a return
`signal, it is compared to the transmitted discovery signal.
`The signal will be identical after allowing for line losses if
`the coupled device is suitable for remote Iine powering, if
`the comparison yields a match, the network node supplies
`remote line power to the device.
`
`30 Claims, 4 Drawing Sheets
`
`24
`
`
`
`
`ISLAN AU
`(NETWORK SWITCH)
`
`
` SWITCHED
`REMOTELY
`POWERED DEVICE
`
`
`
`
`
`NON—REMOTELY
`
`POWERED DEVICE
`
`26
`
`NETWORK—1 N1 -2002
`
`
`
`US. Patent
`
`Jul. 13, 2004
`
`Sheet 1 01'4
`
`US 6,762,675 B1
`
`14
`
`
`
`
`___________
`
`
`REMOTELY
`POWERED DEVICE
`
`
`ISLAN AU
`
`
`(NETWORK SWITCH)
`
`
`
`
`
`NON—REMOTELY
`
`POWERED DEVICE
`
`FIG.1
`(PRIOR ART)
`
`1‘5
`
`24
`
`
`SWITCHED
`REMOTELY
`POWERED DEVICE
`
`
`
`
`
`ISLAN AU
`
`(NETWORK SWITCH)
`
`..........
`___________
`
`
`
`
`NON—REMOTELY
`
`POWERED DEVICE
`
`
`26
`
`
`
`US. Patent
`
`Jul. 13, 2004
`
`Sheet 2 01'4
`
`US 6,762,675 B1
`
` 40
`GENERATE
`
`DISCOVERY SIGNAL
`
`
`
`SELECT FIRST PORT
`
`
`
`80
`
`LOOK FOR
`
`MARK
`
`NO
`10/100 LINK
`PORT AS
`ACTIVE SIGNAL,
`
`USED
`
`RECEOIVED
`
`
`
`
`START
`FROM FIRST
`
`UNUSED PORT
`
`
`
`70
`
`
`
`SELECT
`NEXT PORT
`
`SEND
`DISCOVERY SIGNAL
`
`MONITOR PORT
`FOR RETURN SIGNAL
`
`
`
`MARK
`PORT AS
`
`
`
`USED
`RETURN
`
`
`SIGNAL
`
`
`RECE‘PIVED
`200
`
`
`DISCONNECT
`PORT AS
`POWER
`
`USED
`
`
`RETURN
`SIGNAL MATCHES
`
`DISCOVERY
`
`SIG‘E‘JAL
`
`SATISFACTORY
`
`IDENTIFICATION
`
`PACKETS
`
`APPLY POWER
`
`
`THROUGH PORT
`
`
`FIG.3
`
`
`
`SEND INITIALIZATION
`PACKETS
`
`
`
`DEVICE SIDE
`
`
`
`
`
`mama'S'fl
`
`
`
`I700:‘91wt
`
`I7.10E133118
`
`THSL9‘Z9L‘9sn
`
`
`
`US. Patent
`
`Jul. 13, 2004
`
`Sheet 4 01'4
`
`US 6,762,675 B1
`
`260
`
`SELECT FIRST
`USEDPORT
`
`
`
`
`GO TO
`NEXT PORT
`
`
`
`
`PREEENT
`
`
`
` 266
`
`
` LINK
`SIGNAL STILL
`
`MARK PORT AS
`STILL USED
`
`
`
`18
`PORT
`POWERED
`
`268
`
`MARK PORT AS
`NOT USED
`
`FIG.5
`
`
`
`1
`METHOD AND APPARATUS FOR REMOTE
`POVVERING OF DEVICE CONNECTED TO
`NETWORK
`
`US 6,762,675 B1
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention is related to the field of devices
`used in networks, and more specifically to network nodes
`that verify the power configuration of a device before
`supplying power to it.
`2. Description of the Related Art
`Integrated Services Local Area Networks (ISLANs)
`include nodes such as switches, gateways, routers, bridges,
`repeaters, etc. Network nodes are referred to generally
`below as network switches, but include any device used for
`processing information in a network. Endpoints connected
`to the network, such as Internet phones, can receive power
`along with data from the network switch, Such endpoints are
`called line powered devices.
`An example of a line powered device is described with
`reference to FIG. 1. Anetwork node, such as ISLAN Access
`Unit (AU) 12, is connected to two devices 14 and [6. Device
`14 is a line powered telephone. Dev1ce 14 is connected to
`Port A of ISLAN AU 12 by a cable 14a. Switch 12 applies
`power remotely to device 14. Applied power is depicted by
`voltage VN traveling over cable 1411.
`A serious problem exists when network switch 12 inad-
`vertently applies power to a non-line powered device. In the
`example of FIG. 1, device 16 is unsuitable for remote line
`powering. Device 16 includes a network card 18 connected
`to Port B of ISLAN AU 12 by a cable 16a. Card 18 is not
`configured for receiving remote power from switch 12. If
`switch 12 applies power over cable 160,
`the incoming
`waveform VN can damage card 18, as shown by a flash 1811.
`In conventional circuit switched networks, telephones are
`often powered through the telephone lines. However, the
`telephones in packet switched networks may or may not be
`powered remotely by the network switch [2 over the net-
`work cable, In packet switched networks, the switch can
`detect a device coupled to a port (assuming the device
`already has power), but does not know whether the device
`is suitable for remote powering before power is applied to
`the device. What aggravates the problem is that such devices
`are often connected to the network switch at remote loca-
`tions. For example, telephones are typically powered from a
`central location (eg. a wiring closet) instead of locally (eg.
`in the same office). This makes it hard to configure the
`network for different line powered devices,
`The problem is worsened in the event of loss of power. In
`the case of telephones, users have come to expect service
`under all conditions, including loss of power. The device
`must
`therefore operate without
`interruption when local
`power is not available.
`Accordingly, a need exists for identifying line powered
`devices on a packet switched network.
`BRIEF SUMMARY OF THE INVENTION
`
`The present invention ascertains the suitability for remote
`powering a device from a network switch, before the net-
`work switch supplies power to the device. The network
`switch determines suitability by interrogating all coupled
`devices.
`The switch sends a discovery signal to the ports connected
`to remote devices and monitors each port for a return signal.
`
`10
`
`it!
`
`40
`
`55
`
`60
`
`65
`
`2
`If a return signal is received, it is compared to the transmit-
`ted discovery signal. If the signals are identical, accounting
`for the expected signal losses in the wire, the coupled device
`is deemed suitable for receiving power remotely from the
`network switch. Accordingly, the network switch then sup-
`plies power to the line powered devices. If the network
`switch fails to discover any device, the switch periodically
`retries this discovery signal in order to detect new devices
`that are connected. The network switch also monitors ports
`that have power applied, looking for loss of signal, indicat-
`ing that a device has been detached, Power then needs to be
`removed before another device is connected,
`The invention eliminates having to preprogram the net-
`work switch with the type of devices connected to each port.
`This reduces the amount of time required to initially pro-
`gram the switch, and also eliminates having to reprogram the
`switch every time a new device is connected. The invention
`also eliminates having to reprogram the switch after loss of
`power. The invention is particularly useful in network loca-
`tions without local power, or with a central power distribu-
`tion facility that uses an uninterrupted power supply.
`The foregoing and other objects, features and advantages
`of the invention will become more readily apparent from the
`following detailed description of a preferred embodiment
`which proceeds with reference to the drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG, 1 is a block diagram of a prior art network switch
`connected to a first
`line powered device and a second
`non-hne powered device.
`FIG. 2 is a block diagram of a network switch according
`to the invention interrogating connected devices before
`applying power to them.
`FIG. 3 is a flowchart showing how a network switch
`interrogates unused ports according to the invention.
`FIG. 4 is a circuit diagram of a network switch coupled to
`a telephone Via a cable, wherein the network switch inter-
`rogates the telephone according to the present invention.
`FIG. 5 is a flowchart showing how a network switch
`interrogates used ports to identify disconnected ports
`according to the invention.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT(S)
`The present invention identifies which devices connected
`to a network switch are suitable for remote powering. The
`network switch prevents accidental destruction of devices by
`first interrogating the devices before applying remote power.
`Referring to FIG. 2, ISLAN AU 22 (network switch) has
`least
`two ports, Port X and Port Y. These ports are
`at
`typically 10/100TX Ethernet ports with a physical interface
`(I’HY). Switch 22 is connected to devices 24 and 26 by
`cables 34 and 36, respectively. Device 24 is a telephone,
`although the person skilled in the art will discern easily that
`it can be any remotely powered device. Device 26 is a
`non-line powered device and includes a network card 28.
`Cables 34 and 36 each include at least two pairs of data lines,
`at least some of which are used for sending and receiving
`data signals.
`Switch 22 interrogates the device to determine its suit-
`ability for remote powering. Suitable devices (here only
`device 24, coupled to Port Y) are powered through their
`respective cables (here cable 34).
`Referring to FIGS. 2 and 3, switch 22 in step 40 generates
`a discovery signal. A variety of ways are possible for
`
`
`
`3
`generating the discovery signal. According to the preferred
`embodiment, the discovery signal is typically a discovery
`tone sent over cable 34. The discovery tone is uniquely
`identified from other packets sent over the network. For
`example,
`the discovery tone can be chosen to be a
`“10101010 .
`.
`. " pattern, that is easily generated by digital
`logic,
`As will be obvious to a person skilled in the art, any
`number of ways and sequences can be used to scan the ports
`to detect newly coupled devices that may need powering
`For example, the ports can be scanned continuously, serially
`or in parallel, or scanned during switch idle times. The ports
`are generally scanned simultaneously at a low frequency
`such as 0.5 Hz to 1 Hz. Alternatively,
`the ports can be
`scanned sequentially, as described below.
`Referring to step 70 in FIG. 3, a first port is selected. In
`step 80 the switch attempts to detect a 10/100 link active
`signal from a device connected to the port. If such a signal
`is detected,
`it
`is clear that
`the remote device is already
`powered and operational. That port is marked as used in step
`85. If no link signal is detected, either there is no device or
`an unpowered device.
`If the selected port was the last port in step 90, switch 22
`returns to normal operations in step 100. If not, the next port
`is selected in step 110, and interrogated in step 80. This is
`repeated for all ports. Alternately, the switch performs other
`steps after each port is interrogated, before interrogating the
`next port. If the switch is already powering the connected
`device in step 110, or the link signal is detected without
`power, no further interrogation takes place, and execution
`proceeds to the next port.
`If no link is detected in 80, the discovery tone is sent out
`through the port while keeping the power turned off, Refer-
`ring briefly to FIG. 2, for Port X the discovery tone is
`transmitted over a line pair in cable 36. The transmission is
`at a rate, or the tone is constructed such that it reliably
`transverses twice the maximum cable length allowed for
`signaling. The discovery tone transverses cable 36 reaching
`device 26.
`Referring back to FIGS. 2 and 3, a discovery tone is sent
`over a line pair in cable 36 X during process 130. Another
`line pair in cable 36 X is monitored for a return signal in step
`I40. The monitored line pair is the complement of the line
`pair over which the discovery tone was sent. If no return
`signal is received in step 150, the network switch 22 returns
`to step 90. There is no return signal if the far end of the cable
`36 is not connected to a device. The network switch 22 then
`does not apply power out Port X.
`In the example shown in FIG. 2, a device 26 is coupled to
`cable 36 but is not configured for receiving remote power
`over cable 36. The discovery tone is received by card 28 in
`device 26 at the end of cable 36, The interface card 28 does
`not recognize the discovery tone and, in turn, does not return
`the tone. However, device 26 may return a standard 10/100
`link signal. The switch 22 waits a predetermined time period
`for a returned tone. If no discovery tone (referenced as DP
`tone) is returned within a specified period of time,
`the
`network switch 22 does not apply power to the device.
`Referring back to HG. 3, execution then moves from step
`150 to step 90, and the next port interrogated in step 80. If
`the switch returns a return signal, then processing proceeds
`to step 160.
`Because the device 26 is not configured to receive line
`power, if device 26 returns a signal in step 150, the returned
`signal will be different than the discovery tone DP. In step
`160, the returned signal is compared to the discovery signal
`
`10
`
`20
`
`40
`
`55
`
`60
`
`65
`
`US 6,762,675 B1
`
`
`
`4
`DP. If there is no match, step 165 marks the port as used and
`execution moves to step 90. The next port is then interro-
`gated in step 110.
`The next port scanned in the example shown in FIG. 2 is
`Port Y. The process described above regarding Port X is
`repeated for Port Y However, in the case of Port X, device
`24 returns signal DPR. DPR is identical to DP, (except for
`ine losses), as explained in more detail in connection with
`FIG. 4. Since there is a match at step 160, network switch
`22 considers the device 24 a line powered device. Otherwise
`he port is marked as used (step 165).
`Optionally once a remote line powered device has been so
`identilied, the discovery tone is sent a few more times, and
`he return signal is accordingly recorded and confirmed. This
`reduces the probability of error.
`According to step 170, switch 22 applies power through
`cable 34 to device 24, The power is applied as phantom
`ower through the same pair of wires in cable 34 used for
`ransmitting data, or through a pair of wires in cable 34
`separate from the data lines.
`After power is applied to device 24, the link is established
`Jetween the switch and device. Then switch 22 sends one or
`more initialization packets in step 180. The initialization
`ackets inquire the type, serial number, version, etc, of
`device 24. The device 24 sends back identification packets
`in response to the initialization packets. Data in the identi-
`ication packets is processed by the network switch 22. If the
`data returned by device 24 is satisfactory in step 190, the
`ort is marked as used in step 195 and execution continues
`or the next port. If not, then power may be disconnected in
`step 200, before continuing to the next port.
`FIG. 4 shows an embodiment of the invention. An access
`unit 222 has a port 226 that connects through a cable 234 to
`erminal equipment 224, such as a telephone.
`Unit 222 includes a processor and associated signal
`detection circuits 238, a receive (RX) filter 240, a transmit
`(TX) filter 242, transformers 244 and 246, a voltage source
`VA,V and optional series circuit protection such as fuse F1.
`The voltage can be switched on and off through a switch SS,
`and applied through taps in the middle of transformers 244
`and 246. The fuse Fl has a high enough value so that it does
`not blow when a normal load is applied to port 226. The
`value of fuse F1 is low enough to ensure safety if the
`detection algorithm fails. One advantage of the invention is
`that it eliminates damage to ports that are not configured to
`receive power.
`Telephone 224 includes a RX filter 248, a TX filter 250
`and transformers 252 and 254. Device 224 further includes
`switches 81, S2, S3 and S4. These are interposed between
`transformers 252 and 254 and their respective RX and TX
`filters. This device is a line powered device. The switches
`51—84 are at a first position A or at a second position B.
`Switches 51784 are at position A before remote power is
`applied. The application of power throws switches 51—54 to
`position B.
`Cable 234 can be a Category 5 cable, having 8 lines that
`are organized in 4 line pairs. In this connection, pins 1 and
`
`
`
` 2 are differential transmitting signals TX+/—, and pins 3 and
`6 are di ‘erential receiving signals RX+/—.
`Returning to FIG. 4, processor 238 transmits discovery
`tone DP to transmit filter TX 242. The discovery tone DP
`passes through transformer 246, cable 234 (through lines 3,
`6), and through transformer 252. When the device is
`unpowered, switches 31—54 are inAposition. The discovery
`tone DP passes through switches S3, S4 to switches Sl, S2.
`The switches S1 and $2 relay the DP tone back through
`
`
`
`US 6,762,675 B1
`
`ID
`
`in
`
`40
`
`5
`transformer 254 and through cable 234 (lines 1, 2). The DP
`tone is received by processor 238 as signal DPR.
`The processor and detection circuits 238 compares DI’R
`to DP. If they are the same, the processor 238 infers that the
`device 224 is suitable for remote line powering, and applies
`power by closing switch $5. The voltage VN applied on
`cable 234 causes switches 8154 to move into position B.
`Then data and superimposed power VN is carried over the
`same lines to RX 248 and TX 250.
`After a link is established, it is important for the switch to
`interrogate used ports so that a device disconnection can be
`detected and the power
`removed from the port before
`another device can be reconnected. This detection of loss of
`link and removal of power should happen within 200—300
`msec or less.
`The isolation of the power supplied to the telephone 224
`can be optimized according to relevant IEEE standards.
`More specifically,
`IEEE Draft Standard 802.9f (1997
`version) specifies the details for providing power from an
`ISLAN Access Unit (AU) to an ISLAN-compliant Terminal
`Equipment (TE) via one of two methods: (a) PSI, powering
`over the signal pairs, and (b) P52, powering over additional
`cabling. For both methods the AU 222 provides power with
`adequate isolation and protection from shorts and transients
`to protect other AU ports and other functions within the TE '
`224 or any associated equipment.
`FIG. 5 is a flowchart showing how a network switch
`interrogates used ports to identify disconnected ports. In step
`260, the switch selects the first used port. If a link signal is
`still present on the port in decision step 262, the port is
`marked as used in step 270. If the link signal to that port is
`not still present in decision step 262. then at decision step
`264 it is determined whether the port is powered. If the port
`is not powered, the port is marked as not used in step 268.
`If the port is powered, then power is removed at step 266
`before marking the port as not used in step 268.
`After the link is marked as still used in step 270, or after
`the port is marked as not used in step 268, then at decision
`step 272 it is determined whether the currently interrogated
`port is the last port, If not, then execution moves to step 274,
`where the next port is selected. Then execution returns to
`decision step 262, and repeats the steps described above. If
`the currently interrogated port is the last port in decision step
`272, the network switch selects the first port in step 260, and
`repeats the steps described above.
`A person skilled in the art will be able to practice the
`present invention in view of the present description, where
`numerous details have been set forth in order to provide a
`more thorough understanding of the invention. In other
`instances, well-known features have not been described in
`detail in order not to obscure unnecessarily the invention.
`Having illustrated and described the principles of the
`invention in a preferred embodiment thereof, it should be
`readily apparent to those skilled in the art that the invention
`can be modified in arrangement and detail without departing
`from such principles.
`We claim all modifications coming within the spirit and
`scope of the accompanying claims.
`The invention claimed is:
`l. A method for remote line powering a network node
`comprising:
`receiving a discovery signal at a network device;
`relaying a return signal back to the network node corre-
`sponding to the discovery signal when the network
`device is configured for remote line powering and is not
`powered;
`
`LIIv).
`
`60
`
`65
`
`6
`sending no corresponding return signal when the network
`device is not configured for remote line powering
`whether that device is powered or unpowered;
`receiving remote power from the network node after
`sending the corresponding retum signal; and
`automatically switching from a discovery signal loopback
`relay position to a remote line powering position when
`receiving remote power.
`including receiving multiple
`2. The method of claim 1
`discovery signal retries before receiving power from the
`network node if the return signal matches the discovery
`signal,
`3. The method of claim 1 including receiving at least one
`initialization packet after receiving power from the network
`node.
`4. The method of claim 3 including sending an identifi-
`cation packet responsive to the received initialization packet
`and receiving power from the network node responsive to
`data in the identification packet.
`5. A network endpoint for connecting to a network cable
`comprising:
`a receive input for connecting to the network cable;
`a transmit output for connecting to the network cable; and
`a switching circuit having a
`first position relaying a
`discovery packet received on the receive input back out
`through the transmit output and automatically switch-
`ing to a second position receiving data and remote
`power at the input and outputting data and providing a
`power retum path at the output.
`6. A network endpoint according to claim 5 wherein the
`switching circuit includes an output power interface output-
`ting the rcmote power received at the receive input to a
`phone.
`7. The network endpoint according to claim 6 including a
`transformer circuit coupled between the receive input and
`the output power interface.
`8. The network endpoint according to claim 6 including a
`network device interface including a power connection and
`signaling connections.
`9. The network endpoint according to claim 8 wherein the
`network device interface includes a differential pair of
`receive lines, a differential pair of transmit signals and
`power signals.
`10. The network endpoint according to claim 5 wherein
`the switching circuit includes an interface outputting the
`data and the remote power to a phone.
`11. An article comprising a machine-accessible medium
`having associated data that, when accessed, results in a
`machine determining suitability of providing remote power
`to a network device, the machine-accessible medium com-
`prising:
`code for generating a discovery signal before the network
`device receives power;
`code for transmitting the discovery signal from the net-
`work node to the network device;
`code for monitoring for a return signal from the network
`device;
`code for comparing the return signal to the discovery
`signal if the return signal is received from the network
`device;
`code for determining that the network device is suitable
`for remote powering w hen the return signal matches the
`discovery signal; and
`code for determining that the network device is unsuitable
`for remote powering when the return signal
`is not
`
`
`
`
`
`7
`received or when the return signal, with the exception
`of line losses, does not match the discovery signal.
`12, The article acwrding to claim 11 wherein the code for
`determining that the network device is suitable for remote
`powering further comprises code for outputting a power
`signal from the network node for powering the network
`device when the network device loops back the discovery
`signal.
`13. The article of claim ll wherein the code for deter-
`mining suitability of providing remote power to a network
`device further comprises code for waiting for the network
`node to become idle before transmitting the discovery
`signal.14, The article of claim 11 wherein the code for deter-
`mining suitability of providing remote power to a network
`device further comprises:
`coc e for interrogating a first port on the network node for
`a connection to a first network device;
`cor e for transmitting the discovery signal and monitoring
`for the matching return signal on the first port when the
`first network device is connected to the first port;
`coce for interrogating a second port on the network node
`for a connection to a second network device;
`co
`e for transmitting the discovery signal and monitoring ,
`for the matching return signal on the second port when
`the second network device is connected to the second
`port;
`coee for powering the first network device remotely with
`the network node when the matching return signal is
`detected on the first port;
`coee for powering the second network device remotely
`with the network node when the matching return signal
`s detected on the second port; and
`co e for detecting disconnected devices and unpowering
`the port before another device is attached.
`15. A circuit, comprising:
`a first interface;
`a second interface; and
`a switching circuit having a first state for receiving a
`remote power discovery signal on the first interface and
`sending a reply signal out through the second interface
`and automatically switching to a second state for
`receiving data and remote power at the first interface
`and outputting data and providing a power return path
`at the second interface.
`16, A circuit according to claim 15 wherein the first
`interface includes receive terminals and the second interface
`includes transmit terminals
`17, The circuit acwrding to claim 15 wherein the switch-
`ing circuit
`includes a first switch and a second switch
`configured in the first switching circuit state to couple a first
`receive terminal on the first interface to a first
`transmit
`terminal on the second interface and configured in the
`second switching circuit state to couple the first receive
`
`40
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`LIIv).
`
`US 6,762,675 B1
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`10
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`it!
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`8
`terminal on the first interface and the first transmit terminal
`on the second interface to phone interface terminals.
`18. The circuit according to claim 17 wherein the switch-
`ing circuit
`includes a third switch and a fourth switch
`configured in the first switching circuit state to couple a
`second receive terminal on the first interface to a second
`transmit terminal on the second interface and configured in
`the second switching circuit state to couple the second
`receive terminal on the first interface and the second trans-
`mit
`terminal on the second interface to phone interface
`terminals.
`19. The circuit according to claim 15 including a power
`circuit coupled between the first and second interface and
`the switching circuit.
`20. The circuit according to claim [9 including taps on the
`power circuit for supplying power to an Internet phone.
`21. The circuit according to claim 19 wherein the power
`circuit includes a first transformer coupled between the first
`interfacx and the switching circuit and a second transformer
`coupled between the second interface and the switching
`circuit.
`22. The circuit according to claim 15 wherein the switch-
`ing circuit automatically switches from the first state to the
`second state when power is received across the first and
`second interface.
`23. The circuit according to claim 15 wherein the first
`interface includes a differential pair of receive signal con-
`tacts and the second interface includes a differential pair of
`transmit signal contacts.
`24. The circuit according to claim 15 wherein the switch-
`ing circuit when in a non-powered condition receives the
`discovery signal at the first interface and passes the discov-
`ery signal to the second interface.
`25. A device, comprising
`a circuit configured to loop hack signals on a network
`interface to indicate a remote power capability and
`further configured to change from looping back signals
`to connecting signals on the network interface to an
`endpoint interface when remote power is detected at the
`network interface.
`26. The device according to claim 25 including an output
`power interface for connecting to power received at
`the
`network interface.
`27. The device according to claim 26 including a trans-
`former circuit coupled between the network interface and
`the output power interface.
`28. The device according to claim 25 wherein the end-
`point
`interface is configured to connect to a Voice over
`Internet Protocol (Voll’) phone.
`29. The device according to claim 25 wherein the circuit
`loop backs signals when no power is applied to the circuit.
`30. The device according to claim 25 wherein the network
`interface includes a differential pair of receive contacts and
`a dilferential pair of transmit contacts.
`
`