Apparatus and method of implementing a universal home network on a customer premises ISDN bus

[0002] This application claims benefit of Ser. No. 60/163,239 filed Nov. 3, 1999.

[0003] 1. Field of the Invention

[0004] The present invention relates to network interfacing, and more particularly to methods and systems for controlling transmission of data between network stations connected to a telephone line medium.

[0005] 2. Background Art

[0006] Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) enabling network interface cards at each station to share access to the media.

[0007] Conventional local area network architectures use a media access controller operating according to half-duplex or full duplex Ethernet (ANSI/IEEE standard 802.3) protocol using a prescribed network medium, such as 10BaseT. Newer operating systems require that a network station be able to detect the presence of the network. In an Ethernet 10BaseT environment, the network is detected by the transmission of a link pulse by the physical layer (PHY) transceiver. The periodic link pulse on the 10BaseT media is detected by a PHY receiver, which determines the presence of another network station transmitting on the network medium based on detection of the periodic link pulses. Hence, a PHY transceiver at station A is able to detect the presence of station B, without the transmission or reception of data packets, by the reception of link pulses on the 10BaseT medium from the PHY transmitter at station B.

[0008] Efforts are underway to develop an architecture that enables computers to be linked together using conventional twisted pair telephone lines instead of established local area network media such as 10BaseT. Such an arrangement, referred to herein as a home network environment, provides the advantage that existing telephone wiring in a home may be used to implement a home network environment. However, telephone lines are inherently noisy due to spurious noise caused by electrical devices in the home, for example dimmer switches, transformers of home appliances, etc. In addition, the twisted pair telephone lines suffer from turn-on transients due to on-hook and off-hook and noise pulses from the standard POTS telephones, and electrical systems such as heating and air-conditioning systems, etc.

[0009] An additional problem in telephone wiring networks is that the signal condition (i.e., shape) of a transmitted waveform depends largely on the wiring topology. Numerous branch connections in the twisted pair telephone line medium, as well as the different associated lengths of the branch connections, may cause multiple signal reflections on a transmitted network signal. Telephone wiring topology may cause the network signal from one network station to have a peak to peak voltage on the order of 10 to 20 millivolts, whereas network signals from another network station may have a value on the order of one to two volts. Hence, the amplitude and shape of a received pulse may be so distorted that recovery of a transmitted clock or transmit data from the received pulse becomes substantially difficult.

[0010] An additional problem encountered in European telephone systems involves the use of a network termination basic access (NTBA) device, used as an interface between the residential customer premises and a central office of the public switched telephone network for transmission of Integrated Services Digital Network (ISDN)-based signals. In particular, NTBA devices map a two wire ISDN signal from a central office into a four wire S0 bus having a two wire send path and a two wire receive path for sending and receiving the ISDN-based signals throughout a customer premises. The ISDN-based signals generate harmonic reflections on the S0 bus that cause substantial interference with the higher-frequency network signals. Moreover, the zero crossing of an ISDN-based signal interferes substantially with the transmitted network signals, rendering the transmitted network signal unusable due to the harsh conditions on the four wire S0 signal bus.

[0011] In addition, manufacturers of NTBA devices and ISDN terminal devices may have internal capacitors to minimize electromagnetic interference (EMI) of the devices. These internal capacitors, however, induce capacitive loads on the bus. These capacitive, while compliant with ISDN amplitude and timing requirements, severely attenuate the higher frequency network signals and substantially limit the distance that the network signals can be transmitted.

[0012] There is need for an arrangement for interconnecting computer end stations in a home telephone network having a network termination basic access (NTBA) device and configured for sending ISDN-based signals on a four-wire bus.

[0013] There is also a need for an arrangement for a universal coupling mechanism for home networking signals on a four-wire S0 bus, regardless of variations in S0 bus circuitry within ISDN end equipment such as network terminators, private branch exchange (PBX) systems, or internal S0 bus systems of modem PBX systems.

[0014] These and other needs are attained by the present invention, where filters are coupled between each ISDN device and the four-wire S0 bus, insuring that the four-wire S0 bus is isolated from the capacitive influences of the ISDN devices. This isolation of the S0 bus insures the proper transmission of the higher frequency home network signals.

[0015] One aspect of the present invention provides a method of implementing a local area network in a home telephone network having a connector, configured for sending and receiving ISDN-based signals to and from a public switched telephone network, and a four-wire bus. The four-wire bus includes a two-wire send path and a two-wire receive path for sending and receiving the ISDN-based signals, respectively, between the connector and connected ISDN terminal devices. The method includes connecting a low pass filter between the two wires of the two-wire send path at an output terminal of the connector, the low pass filter configured for passing the ISDN-based signals and rejecting harmonics thereof and isolating capacitive influences of the connector from the two-wire send path. The method also includes isolating capacitive influences of each of the connected ISDN terminal devices from the two-wire send path, and transmitting by a network node a first home network signal onto the two-wire send path and a second home network signal, complementary to the first home network signal, onto the two-wire receive path. Connection of the low pass filter insures that any harmonics of the ISDN-based signals to not interfere with the home network signals. Moreover, the isolation of each of the connected ISDN terminal devices insures that the circuitry within the ISDN terminal devices does not induce any capacitive loads onto the two-wire send path that may adversely affect transmission of the home network signals. Finally, the transmission of the first and second home network signals onto the two-wire send path and the two-wire receive path enables the two-wire home network signal to be transmitted onto a four-wire bus, substantially increasing the effective diameter of the transmission medium and greatly improving transmission performance.

[0016] Another aspect of the present invention provides a computer network. The computer network includes a connector configured for sending and receiving ISDN-based signals to and from a public switched telephone network. The computer network also includes a four-wire bus having a two-wire send path and a two-wire receive path for sending and receiving the ISDN-based signals between the connector and ISDN terminal devices. A low pass filter, coupled between the two-wire send path and the connector, is configured for isolating capacitive influences of the connector from the two-wire send path and filtering ISDN harmonic signals occurring substantially at the frequencies of network data signals. The computer network also includes ISDN terminal filters, each configured for isolating capacitive influences of a corresponding one of the ISDN terminal devices from the two-wire send path, and first and second end stations configured for exchanging the network data signals at frequencies substantially higher than the ISDN-based signals via at least one of the two-wire send path and the two-wire receive path.

[0017] Additional advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the present invention may be realized and attained by means of instrumentalities and combinations particularly pointed in the appended claims.

[0018] Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent like elements throughout and wherein:

[0019] FIG. 1 is a block diagram illustrating a computer network implemented in a customer premises having ISDN-based wiring according to an embodiment of the present invention.

[0020] FIG. 2 is a diagram illustrating a delay performed by the low pass filter of FIG. 1 on the ISDN-based signals relative to the network data signals.

[0021] FIG. 3 is a diagram illustrating another computer network implemented in a customer premises having a PBX system according to an embodiment of the present invention.

[0022] FIG. 1 is a block diagram illustrating an Ethernet (IEEE 802.3) local area network 10 implemented in a home environment using ISDN-based signals according to an embodiment of the present invention. As shown in FIG. 1, the home environment includes a network termination basic access (NTBA) device 12, configured for sending and receiving Integrated Services Digital Network ISDN) signals to and from a public switched telephone network via a two-wire twisted pair. As recognized in the art, the NTBA device 12 is configured for outputting ISDN signals onto a four-wire S0 bus 14, having two wires for a send path 16 and two wires for a receive path 18. Typically implemented in European households, the S0 bus fourteen may have multiple connections, or “taps” 20 connected in parallel off the S0 bus 14. In addition, the S0 bus may be internal to a PBX system; as such, the NTBA 12 serves as a connector for the S0 bus 14 to the two-wire twisted pair from the public switched telephone network.

[0023] Conventional networking technologies assume a Category 5 twisted pair medium for transmission of network signals as differential signals. In the disclosed ISDN environment, however, the NTBA 12 maps the ISDN signals into a two-wire send path 16, and a two-wire receive path 18. As recognized in the art, the receive path 18 reflects the ISDN signal transmitted on the send path 16, with a 2-bit spacing relative to the ISDN clock frequency of about 200 kHz (e.g., 192 kHz). Hence, due to the high level of ISDN noise in the frequency used for home networking, referred to as home PNA by the Home Phone Network Alliance, transmissions of home PNA data on the ISDN S0 bus 14 is normally not possible.

[0024] According to the disclosed embodiment, a low pass filter 30 is installed in the send path 16 of the NTBA 12. The low pass filter 30 is illustrated as external to the NTBA 12, although the low pass filter 30 may also be integrated internally within the NTBA 12; in either case, the low pass filter 30 will be coupled to the output terminal of the NTBA device 12, either internally or externally.

[0025] The low pass filter 30 includes an inductor 32 (e.g., 2×4.7 millihenries) and a capacitor 34 (e.g., 1 nanofarad) that attenuates the high frequency noise caused by the harmonics of the 192 kHz ISDN signal. Hence, the send path 16 and receive path 18 are free of high frequency harmonics that may affect the home network signals between end stations 22aand 22b. In addition, the inductor 32, implemented for example as a common mode choke, isolates the capacitive influence of NTBA 12 from the two-wire send path 16, enabling the high frequency home network signals to be transmitted without capacitive loading by the NTBA 12.

[0026] As described above, capacitive loading may also be induced by circuitry of ISDN terminal devices 60 coupled to the S0 bus 14. Hence, the disclosed network 10 also includes ISDN terminal filters 62 configured for isolating each of the connected ISDN terminal devices 60 from the two-wire send path 16. Each ISDN terminal filter 62 is preferably implemented as a common mode choke (e.g., 2×4.7 millihenries) which is connected between the corresponding ISDN terminal device 60 and the two wire send path 16.

[0027] Hence, the low pass filter 30 and the ISDN terminal filters 62 isolate the respective ISDN devices from the two-wire send path 16, providing optimal conditions for transmission of the home network signals having a frequency of at least about 7.5 MHz.

[0028] An additional feature of the disclosed embodiment is that each end station 22 is coupled to a pair of commercially-available S0 transformers 64, for example from Vogt Electronic AG of Erlau, Germany. Specifically, the 4-wire tap 20aof end station 22ais coupled to the ends of the primary windings of transformers 64aand 64b. The 4-wire tap 20bof end station 22bis coupled to the end of the primary windings of transformers 64cand 64d. Note that the secondary windings of transformers 64a, 64b, 64c, and 64dare not used. Each primary winding includes a middle tap 66, coupled substantially in the middle (i.e., substantially the center) of the corresponding primary winding. Hence, the ends of transformers 64aand 64bare symmetrically connected to the two wires a1, b1 of the send direction 16 and the two wires a2, b2 of the S0 bus 14, respectively. Similarly, the ends of transformers 64cand 64dare symmetrically connected to the two wires a1, b1 of the send direction 16 and the two wires a2, b2 of the S0 bus 14, respectively.

[0029] Each end station 22 outputs the home network signal as a two-wire signal (i.e., a differential signal pair) on two-wire signal lines 68; hence, the end station 22asends and receives the differential home network signals on signal lines 68aand 68b, and the end station 22bsends and receives the differential home network signals on signal lines 68cand 68d.

[0030] As shown in FIG. 1, the signal lines 68a, 68b, and 68c, and 68dare coupled to the middle taps 66a, 66b, 66c, and 66d, respectively, enabling the two-wire home network signal to be transferred across the four-wire S0 bus 14. Hence, the end station 22 outputs a first home network signal to the middle tap 66aof the primary winding 64acoupled to the send path 16, and a second home network signal complementary to the first home network signal (i.e., the corresponding differential signal), to the middle tap 66bof the primary winding 64bcoupled to the receive path 18. Hence, the end station 22breceives the first home network signal from the send path 16, and the second home network signal from the receive path 18, resulting in substantially improved reception of the home network signal by optimizing of the loop resistance of the bus 14. Experimental testing of the disclosed arrangement has resulted in successful reception of 7.5 MHz home network signals on an S0 bus 14 where the end stations 22 transmit the home network signals across a distance of about 80 meters.

[0031] Filter 2 is a diagram illustrating the delay introduced by the filter 30. As shown in Filter 2, the filter 30 introduces a delay 40. This delay ensures that the zero crossings 46 of the ISDN signal 42 do not offset the network data signals 40 on the receive path 18.

[0032] FIG. 3 is a diagram illustrating an alternative implementation of the local area network 10 of FIG. 1 according to another embodiment of the present invention. As shown in FIG. 3, the network 200 includes a private branch exchange (PBX) 210. The PBX 210 includes an internal connector 212 for an internal S0 bus 214 having a send path 216 and a receive path 218. The internal connector 212 has circuitry that is configured for connecting the internal S0 bus 214 to the S0 bus 14 (also referred to as the external S0 bus) for communication with the public switched telephone network. As recognized in the art, the PBX 210 will typically have four to eight analog (tip-and-ring) connectors (not shown), one external connector for connection to the external S0 bus, and up to eight digital connections off the S0 bus 214.

[0033] The local area network 200 also includes the same filters 30 and 62 described above with respect to FIG. 1, and also includes taps 220 connected in parallel off the internal S0 bus 214 for connection to an ISDN terminal device 60, and home network end stations 22aand 22bcoupled to the internal S0 bus 214. In this regard, the features of providing filters 30 and 62 to isolate capacitive influences of the connector 212 and ISDN terminal devices 60 may also be applied to the internal S0 bus 214 of the PBX system 210. If desired, the filter 30 may be integrated within the PBX system 210.

[0034] While this invention has been described with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.