Data, power and supervisory signaling over twisted pairs

[0001] This application claims priority of U.S. Provisional Patent Application No. 60/644,280 filed Jan. 14, 2005 entitled POWER AND SUPERVISORY SIGNALLING OVER 1000BASE-T ETHERNET.

[0002] N/A

[0003] The present invention relates generally to data communication and more specifically to the provision of supervisory signaling and power over the same twisted pairs as are employed for data signaling in accordance with a high speed data communication protocol.

[0004] Data communication over 100BASE-T and 1000BASE-T in accordance with the Ethernet protocols are well known. Using these protocols, Ethernet signals may be transmitted over twisted pairs such as CAT5, CAT 5e, CAT6 or any similar cable that includes four twisted pairs. The twisted pairs may be shielded or unshielded. A separate Ethernet signal is typically transmitted over each of the twisted pairs as a differential signal. In a 1000BASE-T Ethernet system, the lowest frequency that must be passed over an Ethernet pair unimpaired is 100 kHz.

[0005] While the use of cabling such as CAT5 permits the transmission of four Ethernet signals over the four twisted pairs, numerous circumstances arise in which it would be desirable to provide additional signaling capabilities and to supply power to a remote device without incurring the expense associated with the procurement and installation of additional wiring.

[0006] In accordance with the present invention, a system and method for providing power and supervisory control signaling over four twisted pairs is disclosed. More specifically, in one embodiment, power and supervisory control signaling are provided over the same twisted pairs that carry Ethernet communications using 1000BASE-T signaling (1 gigabit Ethernet), 100BASE-T signaling (100 megabit Ethernet) or 10 BASE-T signaling (10 megabit Ethernet).

[0007] High speed data signals from the Ethernet PHY devices are coupled to each of first, second, third and fourth twisted pairs in a manner that DC isolates the PHYs from the respective twisted pairs. In particular, the PHYs may be coupled to the twisted pairs capacitively or via a coupling transformer. First and second signaling transformers, each having a primary winding and a center-tapped secondary winding, are provided for coupling power and supervisory control signals to the first and second twisted pairs and the third and fourth twisted pairs respectively as is explained in greater detail below.

[0008] The ends of a center-tapped inductor are coupled to the wires of each twisted pair on the wire side of the coupling capacitors or coupling transformer at each end of the twisted pair. The ends of the secondary winding of each signaling transformer are coupled to the center-taps of the center-tapped inductors. For example, one end of the secondary winding of the first signaling transformer is coupled to the center-tap of the inductor that is connected to the wires of the first twisted pair so as to couple the signal on the first end of the first signaling transformer in common mode to both wires of the first twisted pair. Similarly, the second end of the secondary of the first signaling transformer is coupled to the center-tap of the inductor that has its ends connected to the wires of the second twisted pair so as to couple the signal on the second end of the secondary winding of the signaling transformer to both wires of the second twisted pair as a common mode signal. Accordingly, the first supervisory signal does not affect the differential high speed Ethernet signals that are communicated over the first and second twisted pairs.

[0009] Similar connections are made using the second signaling transformer and inductors coupled between the wires of the third and fourth twisted pairs to superimpose a second supervisory signal on the third and fourth twisted pairs. The second supervisory signal likewise does not affect the differential high speed Ethernet signals that are communicated over the respective third and fourth twisted pairs.

[0010] A DC power source having first and second voltage rails is connected at one end of the cable in such a manner as to make the DC output voltage available to power circuitry at the other end of the cable. More specifically, the first voltage rail or the power source is connected to the center tap of the secondary winding of the first signaling transformer and the second voltage rail of the power source is connected to the center tap of the secondary winding of the second signaling transformer. Thus, the voltage on the first volage rail is conveyed over both wires of both the first and second twisted pairs, and the voltage on the second voltage rail is conveyed over both wires of both the third and fourth twisted pairs.

[0011] The same circuit configuration is employed at both ends of the four twisted pairs to permit recovery of the supervisory signals and DC power in addition to the four Ethernet signals communicated over the twisted pairs. Additionally, since the same circuit configuration is employed at both ends, bidirectional communication via the supervisory signals is possible and power may be sourced at either end of the cable.

[0012] Other features, aspects and advantages of the presently disclosed method and system for providing power and supervisory signaling over four twisted pairs that are used for high speed data communication signaling will be apparent to those of ordinary skill in the art from the following Detailed Description of the Invention.

[0017] The present application incorporates by reference the entirety of the disclosure of U.S. Provisional Patent Application No. 60/644,280 filed Jan. 14, 2005 and entitled POWER AND SUPERVISORY SIGNALLING OVER 1000BASE-T ETHERNET.

[0018] A system and method for providing supervisory signaling and power over the same twisted pairs that are employed for data communications in accordance with a predetermined data communications protocol is disclosed. FIG. 1 depicts a system in which Ethernet PHYs and interface magnetics are generally co-located at respective ends of a communication cable 100. The cable 100 includes four twisted pairs that extend between a magnetic interface 90 at a first end of the cable 100 and a magnetic interface 92 at a second end of the cable as depicted in FIG. 1. The magnetic interfaces 90 and 92 provide an interface for coupling power and supervisory signaling to the twisted pairs within the cable at one end of the cable and for recovering power and supervisory signaling at the other end of the cable 100.

[0019] The Ethernet PHYs may be integrated into a computer, network device, Ethernet appliance or the like along with the magnetic interfaces 90, 92 as illustrated in FIG. 1. Alternatively, as depicted and later discussed in connection with FIG. 3, the Ethernet PHYs may be integrated into a computer, network device, Ethernet appliance or the like and the magnetic interfaces may be spaced from the computer, network device, Ethernet appliance, etc and coupled by a communication cable at one or both ends. In the embodiment depicted in FIG. 1, in compliance with the 1000BASE-T standard, the length of the cable 100 is no greater than a predetermined distance, e.g. 100 meters.

[0020] Referring to FIG. 1, the cable 100 includes first, second, third and fourth twisted pairs 100a, 100b, 100c, and 100d (which may be shielded or unshielded) for carrying four high speed data signals, such Ethernet signals using the 100BASE-T or 1000BASE-T signaling protocols. The Ethernet signals are generated and received by Ethernet physical interfaces (PHYs) 102a-102d, 104a-104d as known in the art. When the Ethernet protocol comprises a gigabit Ethernet protocol compliant with the 100BASE-T specifications, the data transfer rate across the four twisted pairs is equal to 1 gigabit. As is known, in 1000BASE-T systems (gigabit Ethernet) a gigabit signal is segmented into four signal components and each of the four signal components is transmitted over one of the four twisted pairs within the cable 100 from a transmit side interface. The signal transmitted over each twisted pair is transmitted at approximately 250 megabits/second to achieve a 1 gigabit/second data transfer rate in the aggregate. Ethernet signals may be transmitted over the respective twisted pairs bi-directionally. The Ethernet signals that are transmitted and received by the Ethernet PHYs are capacitively coupled to both wires of the first, second, third and fourth twisted pairs 100a-100d via coupling capacitors 106. The four signal components are received at a receive side interface and combined to obtain the original gigabit signal.

[0021] One magnetic interface 90 at the first end of the cable 100 includes center-tapped inductors 108a and 108b and a transformer 110. This magnetic interface is coupled to the first and second twisted pairs 100a and 100b. Another magnetic interface 90 at the first end of the cable 100 includes center-tapped inductors 108c and 108d and a transformer 112. This magnetic interface is coupled to the third and fourth twisted pairs 100c and 100d.

[0022] Similarly at the second end of the cable a magnetic interface 92 includes center-tapped inductors 109a and 109b and a transformer 114. This magnetic interface is coupled to the first and second twisted pairs 100a and 100b. Additionally, another magnetic interface 92 includes center-tapped inductors 109c and 109d and a transformer 116. This magnetic interface is coupled to the third and fourth twisted pairs 100c and 100d as depicted in FIG. 1.

[0023] Center-tapped inductors 108a-108d are coupled between the wires of the twisted pairs 100a-100d respectively on the twisted pair side of the coupling capacitors 106 at a first end of the cable 100 and center-tapped inductors 109a-109d are coupled between wires of the twisted pairs 100a-100d on the twisted pair side of the coupling capacitors 106 at a second end of the cable 100 as depicted in FIG. 1.

[0024] First and second signals, such as supervisory, control or monitor signals (referred to herein generally as a “supervisory signal”), are applied to first and second transformers 110, 112 as illustrated in FIG. 1. The transformers 110, 112 have primary windings 110a, 112a, secondary windings 110b, 112b and center-taps 110c, 112c on the secondary windings 110b, 112b.

[0025] One end of the secondary winding 110b of the first transformer 110 is coupled to the center-tap of the center-tapped inductor 108a which spans the wires of the first twisted pair 100a at the first end of the cable 100. The other end of the secondary winding 110b is coupled to the center-tap of the inductor 108b which spans the wires of the second twisted pair 100b at the first end of the cable 100. Thus, the signal applied to the center-tap of the inductor 108a is coupled to both wires in the twisted pair 100a as a common mode signal. Similarly, the signal that is applied to the center-tap of the inductor 108b is coupled to both wires of the twisted pair 100b as a common mode signal. Thus, differential receivers within the PHYs 104a, 104b are not affected by the coupling of the differential components of the first signal to both wires of the first and second twisted pairs 100a, 100b.

[0026] Additionally, a second supervisory signal is superimposed on the third and fourth twisted pairs in the manner discussed above with respect to the first signal. More specifically, the second signal is applied to the primary of the second transformer 112. One end of the secondary winding 112b of the second transformer 112 is coupled to the center-tap of the center-tapped inductor 108c which spans the wires of the third twisted pair 100c at the first end of the cable 100 and the other end of the secondary winding 112b is coupled to the center-tap of the inductor 108d which spans the wires of the second twisted pair 100d at the first end of the cable 100 as depicted in FIG. 1. Thus, the component of the second signal applied to the center-tap of the inductor 108c is coupled to both wires of the third twisted pair 100c as a common mode signal. Similarly the component of the second signal that is applied to the center-tap of the inductor 108d is coupled to both wires of the twisted pair 100d as a common mode signal. Thus, differential receivers within the PHYs 104c, 104d are not affected by the coupling of the differential components of the second signal to both wires of the third and fourth twisted pairs 100c, 100d.

[0027] The circuitry at the second end 92 of the cable is coupled to the four twisted pairs 100a-100d in the same manner as described above with respect to the first end 90. More specifically, Ethernet PHYs 104a-104d are coupled to the respective twisted pairs 100a-100d via coupling capacitors 106. Center-tapped inductors 109a-109d are coupled between the wires of the respective twisted pairs 100a-100d on the cable side of the coupling capacitors 106. Transformers 114 and 116 include primary windings 114a, 116a and secondary windings 114b, 116b. The secondary windings 114b, 116b have respective center-taps 114c, 116c.

[0028] One end of the secondary winding 114b is coupled to the center-tap of the inductor 109a at the second end of the cable 100a. The other end of the second winding 114b is coupled to the center-tap of inductor 109a that is connected to both wires of the second twisted pair 100b at the second end 92 of the cable 100.

[0029] One end of the secondary winding 116b is coupled to the center-tap of the inductor 109c that is connected between the two wires of the third twisted pair 100c at the second end 92 of the cable 100. The other end of the secondary winding 116b is coupled to the center-tap of inductor 109d that is connected to both wires of the fourth twisted pair 100d at the second end 92 of the cable 100.

[0030] The operation of the circuitry and system is generally as described below.

[0031] Ethernet PHYs 102a and 104a, 102b and 104b, 102c and 104c, and 102d and 104d transmit and receive Ethernet packets over twisted pairs 100a-100d respectively. Ethernet PHYs 102a-102d and 104a-104d are capacitively coupled to the twisted pairs 100a-100d via the coupling capacitors 106. The Ethernet PHYs 102a-102d and 104a-104d include differential drivers and receivers for differential transmission and reception over the balanced twisted pairs, and thus do not react to common mode signals appearing on both wires of any given twisted pair.

[0032] The first signal, such as the first supervisory or control signal, is applied to the primary winding 110a of the transformer 110. One end of the secondary winding 110b is coupled to the center-tap of the inductor 108a and the other end of the secondary winding 110b is coupled to the center-tap of the inductor 108b. By reason of the use of the center-tapped inductors 108a and 108b, the signal appearing on the center-tap of the inductor 108a is superimposed on the Ethernet signal communicated over both wires of the first twisted pair 100a as a common mode signal. Similarly, the signal appearing on the center-tap of the inductor 108b is superimposed on the Ethernet signal communicated over both wires of the second twisted pair 100b as a common mode signal.

[0033] Power is supplied over the 4 twisted pairs as described below.

[0034] A first voltage rail of a power source or supply (not shown) is coupled to the center-tap 110c of the secondary winding 110b of the first transformer 110 and a second voltage rail of the power source or supply is coupled to the center-tap 112c of the secondary winding 112b of the second transformer 112 at the first end 90 of the cable 100. The voltage on the first voltage rail is DC coupled through the secondary winding 110b and the inductors 108a and 108b to both wires of the first and second twisted pairs 100a, 100b. At the second end 92 of the cable 100, the voltage from the first voltage rail is coupled through the center-tapped inductors 109a and 109b and through the secondary winding 114b to the secondary winding center-tap 114c.

[0035] The voltage on the second voltage rail is DC coupled through the secondary winding 112b and the inductors 108c and 108d to both wires of the third and fourth twisted pairs 100c, 100d. At the second end 92 of the cable 100, the voltage from the second voltage rail is coupled through the center-tapped inductors 109d and 109d and through the secondary winding 116d to the secondary winding center-tap 116c. Power is thereby available at the second end 92 of the cable between the voltage from the first voltage rail appearing on the center-tap 114c of the secondary winding 114b and the voltage on the second voltage rail appearing on the center-tap 116c of the secondary winding 116b.

[0036] The differential signal between the signals on the center-tap of the inductor 109a and 109b corresponds to the first signal input at the primary winding 110a. This differential signal is ac coupled from the winding 114b to the winding 114a and is available for control or monitoring purposes at the second end 92 of the cable. The first signal may comprise a binary data signal or any other suitable signal for conveying data from the first end 90 of the cable 100 to the second end 92 of the cable 100.

[0037] Similarly, the differential signal between the signals on the center-tap of the inductor 109c and 109d corresponds to the second signal input at the primary winding 112a. This differential signal is ac coupled from the winding 116b to the winding 116a and is available for control or monitoring purposes at the second end 92 of the cable. The second signal may also comprise a binary data signal or any other suitable signal for conveying data from the first end 90 of the cable 100 to the second end 92 of the cable 100.

[0038] The cable 100 may comprise a CAT5 cable, a CAT5e cable, a CAT6 cable or any other suitable cable containing twisted pairs which may be shielded or unshielded.

[0039] The PHYs may alternatively be DC isolated from the twisted pairs either at one end or at both ends of the cable 100 using coupling transformers 120a-120d and coupling transformers 122a-122d as illustrated in FIG. 2. In this circumstance, the center-tapped inductors 108a-108d and 109a-109d discussed in connection with FIG. 1 form the secondary winding of the transformers 120a-120d and 122a-122d with the primary winding of the coupling transformers coupled to the respective PHYs. It should also be appreciated that capacitive coupling of the PHYs may be employed at one end of the cable and transformer coupling of the PHYs may be employed at the other end of the cable.

[0040] While in the above-described example, signaling is described as being from the first end of the cable to the second end of the cable, it should be recognized that the signals may sourced at either end of the cable 100. Additionally, the first signal may be sourced at one end of the cable 100 and the second signal may be sourced at the other end of the cable.

[0041] Multiple signals may be carried over the path traversed by the first signal or the second and the respective signals may be transmitted in both directions as the circuits at both ends are generally symmetrical. For example, signals having different frequencies may be transmitted over the path traversed by the first signal or the second signal and may be transmitted in the same or opposite directions. More specifically, using one supervisory signaling channel, a first signal having a 50 khz carrier may be transmitted over the channel and modulated on and off to provide binary signaling. Additionally, a second signal having a 1.6 megahertz carrier may be transmitted over the same supervisory channel and modulated on and off to provide binary signaling for the second signal. Thus, in the instant example, the first and second signals are multiplexed over the first supervisory channel. It should be recognized that the frequencies may be varied based on specific design objectives. Other signaling techniques may also be employed to multiplex signaling over one or both supervisory signaling channels.

[0042] The embodiment illustrated in FIG. 3 depicts a system in which the magnetic interfaces are spaced from the respective PHYs and are coupled to the PHYs via the communication cable. By way of example, in a 1 system operative in accordance with the 1000 BASE-T standard, the maximum length of the communication cable 200 between the respective PHYs is 100 meters. Accordingly, the total of the lengths of the cable portions 300a.1, 300a.2 and 300a.3 would need to be no greater than 100 meters. Similarly, the total of the lengths of the cable portions 300b.1, 300b.2 and 300b.3 would need to be no greater than 100 meters, the total of the lengths of the cable portions 300c.1, 300c.2 and 300c.3 would need to be no greater than 100 meters and the total of the lengths of the cable portions 300d.1, 300d.2 and 300d.3 would need to be no greater than 100 meters. Otherwise, the description of the circuitry of Fig. is the same as discussed above with respect to FIG. 1.

[0043] By spacing the magnetic interfaces from the PHYs, the PHY may be incorporated into a computer, network device or appliance and the magnetic interface may be fabricated external to the device. Accordingly, in this embodiment, there is no need to couple a power supply (such as a 48V power supply) or supervisory signal source to the computer, network device or Ethernet appliance that houses the respective PHY.

[0044] While FIG. 3 depicts magnetic interfaces coupled to respective PHYs via communication cables (4 twisted pairs) at each end, it should be recognized that at either end of the communication system, the respective PHYs may be directly coupled to the magnetic interfaces as depicted in FIG. 1 or alternatively, spaced therefrom and coupled via a communication cable as illustrated in FIG. 3.

[0045] Similarly, at the destination or unpowered end, the supervisory signaling and/or power can be recovered and employed to perform control functions, control light emitting diodes (LEDs) or to perform other control or monitoring functions. As illustrated in FIG. 3 the magnetic interfaces may be provided at intermediate points of the cable and power and signaling may thus be provided or recovered at such intermediate points.

[0046] While in the illustrated embodiments the physical interfaces (PHYs) are DC isolated from the respective twisted pairs via isolation capacitors, it should be recognized that DC isolation may alternatively be achieved via the use of transformers between the PHYs and the twisted pairs.

[0047] It should also be appreciated that the presently disclosed system may be employed to provide power over Ethernet without supervisory signaling capabilities. In such event, the transformers 110, 112, 114 and 116 could be omitted and the voltage rails or voltage outputs, as applicable, coupled directly to the center-taps of the inductors 108a, 108b, 108c, 108d, 109a, 109b, 109c and 109d. By way of example, if supervisory signaling is not necessary, the voltage rail V+ may be connected directly to the center-tap of the inductor 108a if power is conveyed over two wires and the voltage rail V+ may be connected to the center-tap of inductors 108a and 108b if power is conveyed over four wires. Similarly, the voltage rail V− may be connected directly to the center-tap of the inductor 108c if power is conveyed over two wires and the voltage rail V− may be connected to the center-tap of inductors 108c and 108d if power is conveyed over four wires.

[0048] With respect to the outputs, if supervisory signaling is not employed, the positive output rail V+ may be connected to the center-tap of the inductor 109a if power is conveyed over two wires and may be connected to the center-taps of both inductors 109a and 109b if power is conveyed over four wires. Similarly, the negative output rail V− may be connected to the center-tap of the inductor 109c if power is conveyed over two wires and may be connected to the center-taps of both inductors 109c and 109d if power is conveyed over four wires.

[0049] It should also be appreciated that other modifications to and variations of the above-described system and method for providing supervisory signaling and power over the same twisted pairs that are utilized for data signaling in accordance with a predetermined data communication protocol may be made without departing from the inventive concepts described herein. Accordingly, the invention should not be viewed as limited except by the scope and spirit of the appended claims.