More particularly, the present invention relates to a data communication network in which both voice signal and LAN data are simultaneously transmitted and received through telephone wiring existing home or in an office. Also, the present invention is directed to a data transceiver for using in the communication network.

Background Art Internet being used as means for collecting and transmitting various information has settled down as an indispensable communication network. The most common method for any individual to access the Internet is accessing through the Public Services Telephone Network (PSTN) by use of a dial-up modem. According to the method, digital data is converted to an analog signal and transmitted through a copper wire. However, data transmission through the PSTN is inefficient in that it is substantially impossible to transmit data in a rate higher than 56 kbps. The result is that the PSTN cannot carry a moving picture signal or large amount of text data in a speed high enough. As an alternative for increasing the data rate, Internet access through Integrated Services Digital Network (ISDN) is widely being used. Since the ISDN available nowadays is still a circuit-switched network based on the copper wire, however, the ISDN does not increase the data rate exceedingly compared with the PSTN.

Several approaches utilizing an optical network have been made in order to increase the data rate. An ideal optical network is the fiber- to-the-home (FTTH) network, in which an optical fiber extends to each home individually. However, FTTH network has a drawback in that each home has to be equipped with an optical network unit (ONU). Further, it takes so much expenses and time to install the optical fiber to each home, and thus it will not take so short time for each user at home to access Internet through the FTTH network. Accordingly, another approach of the fiber-to-the-curb (FTTC) network has been proposed, in which a plurality of home shares an optical fiber. In the FTTC network, the optical fiber extends to the curb of the road where the ONU is installed, and a copper wire connects the ONU and customer premises at home. The FTTC network is advantageous in that the economical burden of each home is reduced because of the sharing of the optical fiber and the ONU. However, the FTTC network still has the drawback in that the optical fiber has to be installed to the curb and the ONU is required.

Thus, another approaches are focused on utilizing of an existing cable television network or the copper wire instead of the optical cable.

In an Internet subscriber network utilizing the cable television network, a subscriber of the cable television system purchases a cable modem and installs it to the computer to access the Internet. In most countries, however, the cable television is not popularized enough yet and it is expected to take considerable time for most home users to enjoy the cable television and the high-speed Internet service utilizing the cable television network. The Hybrid fiber coax (HFC) network using the optical network to the ONU and connecting the ONU and each home by a coaxial cable has a similar problem.

Meanwhile, according to the digital subscriber loop (DSL) system in which data is modulated in accordance with a digital modulation scheme rather than an analog modulation scheme and transmitted through the PSTN, the switching office of any service area has to be equipped with a DSL equipment and the switching office has to be connected to the Internet through a high-speed dedicated line. The result is that Internet service providers other than telephone service providers have some substantial difficulties in implementing such systems.

In this regard, an international patent application W098/54901 filed by INLINE COMMUNICATION CORPORATION on June 1,1998 and entitled TWISTED PAIR COMMUNICATION SYSTEM discloses a system in which voice signal and data signal is mixed to be transmitted through a twisted pair and the mixed signal is separated by use of a highpass filter and a lowpass filter. According to the communication system, a high-speed Internet subscriber network can be implemented easily with low investment because the network utilizes telephone wiring already installed at home or an office building.

Basically, in such a communication system, all signals including uplink data signal from a computer to an external data network, downlink data signal from the external data network to the computer, and uplink and downlink voice signals are transmitted through a single twisted pair.

Even though the frequency band of the voice signal is almost different from that of the Manchester-coded data signal, it cannot be said that these signals do not interfere with each other at all. Meanwhile, it is needless to say that the cut-off characteristics of the lowpass filter and the highpass filter are not perfect. Accordingly, the voice signal transmitted along with the data signal acts as a noise on the data signal,

which has negative effect on the channel capacity or the data rate of the system.

Disclosure of the Invention To solve the above problem, one object of the present invention is to provide a data communication system, in which a plurality of data terminals may be coupled to a telephone cable and each of the plurality of data terminals can multiplex voice signal and LAN data to transmit the multiplexed signal through the telephone cable and can receive another multiplexed signal to demultiplex such a signal into a voice signal and a LAN data signal, of which data rate may be maximized particularly in case that uplink and downlink traffic are unsymmetrical.

Another object of the present invention is to provide, in a communication network in which voice signal and LAN data can be coupled and transmitted through a single telephone cable, a data transceiver allowing a plurality of data terminals to be coupled to the telephone cable.

A data communication network for achieving one of the above objects includes a hub, a center module, and a plurality of in-building subsystems, and allows each of the plurality of in-building subsystems to transmit and receive data signal to and from an external data network and to transmit and receive voice signal to and from an external telephone network.

The center module is coupled to the plurality of in-building subsystems respective four-wiring telephone cables each of which is provided for each of the plurality of in-building subsystems and to the hub and the external telephone network through respectively predetermined channels. The center module multiplexes a downlink data signal from the hub and a downlink telephone signal from the

external data network to transmit a multiplexed downlink signal to one of the plurality of in-building subsystems through a first wire pair of respective telephone cable. Also, the center module extracts an uplink voice signal mixed with the downlink data signal in the first wire pair of the respective telephone cable to transmit to the external telephone network, and receives an uplink data signal through a second wire pair of the respective telephone cable to transmit to the hub.

Each of the in-building subsystems includes at least one wall outlet and a subscriber module. The wall outlet is coupled to the four- wiring telephone cable and has a subscriber module connection port having a shape of a socket. Also, the wall outlet includes a switched termination circuit for preventing the data signal from being transferred to or from a direction opposite to the center module when the data terminal is coupled through the subscriber module engaging with the wall outlet.

The subscriber module has a plug for being engaged with the subscriber module connection port and allows one selected from a group consisting of a telephone, a data terminal, and a combination thereof to be connected to the respective telephone cable. In the subscriber module, a data terminal connection port allows the data terminal to be connected to the four-wiring telephone cable. A telephone connection port allows the telephone to be connected to the four-wiring telephone cable. A highpass filter receives the multiplexed downlink signal through the wall outlet and the piug and selectively passes the downlink data signal to provide the downlink data signal to the data terminal connection port. A lowpass filter receives the multiplexed downlink signal and selectively passes the downlink voice signal to provide the downlink voice signal to said data telephone connection port.

It is preferable to implement the data communication network by employing a serial expansion module or a parallel expansion module, both of which are related to another one of the above objects. The parallel expansion module is disposed between the center module and the at least one wall outlet, in case that the telephone wiring is routed in series, to increase the number of the wall outlets capable of being simultaneously coupled to the center module. Also, the serial expansion module is disposed between the parallel expansion module or the center module and the at least one wall outlet (40), in case that the telephone wiring is routed in a parallel shape, to increase the number of said wall outlets capable of being simultaneously coupled to said center module.

In the data communication network, the data signal and the voice signal is frequency-division multiplexed in the four-wiring cable and separated by respective filters in a receiving stage of each device.

Accordingly, it is possible to transmit both the data signal and the voice signal through a four-wiring telephone cable.

Brief Description of the Drawings The above objectives and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which : FIG. 1 illustrates an embodiment of a data communication network according to the present invention ; FIG. 2 is a circuit diagram of the center module shown in FIG. 1; FIG. 3 is a circuit diagram of the wall outlet shown in FIG. 1 ; FIG. 4 is a circuit diagram of the subscriber module shown in FIG.

1 ; FIG. 5 is a perspective view of a preferred embodiment of the subscriber module ;

FIG. 6 is a circuit diagram of the parallel expansion module shown in FIG. 1 ; FIG. 7 is a circuit diagram of the serial expansion module shown in FIG. 1; FIG. 8 illustrates an example of a network in a building according to the present invention; FIG. 9 illustrates another example of the network in a building according to the present invention ; and FIG. 10 illustrates yet another example of the network in a building according to the present invention.

Embodiments Referring to FIG. 1, a preferred embodiment of a data communication network according to the present invention, which is suitable for implementing an Internet subscriber network, includes a switching hub 10, a center module 20, and a plurality of in-building subsystems 30. The network of FIG. 1 can be installed for each apartment house, an aisle in an apartment house, or each floor or office in an office building. In case that the network is installed in the apartment house, the switching hub 10 and the center module 20 may be located in or near a main distributing frame (MDF) of the apartment house. Similarly, when the network is installed in the office building, switching hub 10 and the center module 20 may be located in or near the MDF of the building or in the communication room of the building.

In the preferred embodiment of the present invention, the switching hub 10 and the center module 20 are installed and maintained by an Internet service provider (ISP). The switching hub 10 is connected to a host system of the Internet service provider to exchange Internet traffic according to TCP/IP protocol or the Ethernet protocol.

The switching hub 10 transfers a downlink traffic received from the Internet, via the center module 20, to one of the in-building subsystems 30 which is specifically dictated by an address contained in the traffic.

Also, the switching hub 10 receives an uplink traffic from the in-building subsystems 30 via the center module 20 and regenerate the signal level of such a signal to transmit the regenerated signal to the Internet.

The center module 20 has an RJ-45 port on its front panel to be connected to the switching hub 10 and a plurality of RJ-11 ports to be connected to the in-building subsystems 30 through four-wiring telephone cables. Also, the center module 20 includes a thirty-seven- pin connector in its rear panel and is connected with a public services telephone network (PSTN) via the connector. The center module 20 multiplexes downlink data signal from the switching hub 10 and downlink voice signal from the PSTN to transfer the multiplexed signal to an appropriate in-building subsystem 30. Also, the center module 20 demultiplexes the signal received from each of the in-building subsystems 30 through respective four-wiring telephone cable into uplink data signal and uplink voice signal to transmit the data signal to the switching hub 10 and the voice signal to an exchange of the PSTN.

However, in case that the network is installed in an office building equipped with a private automatic branch exchange (PABX), the center module 20 may be coupled with the PSTN via the PBX. In the present embodiment, one wire pair of the four-wired telephone cable is used to transmit one of the uplink and downlink data signals along with the voice signal while another wire pair is used to transmit another one of the uplink and downlink data signals.

Each of the in-building subsystems 30 is installed each home or each floor of the office building. Hereinbelow, it is assumed that the in-

building subsystems 30 is installed each home for the sake of the simplicity of the description. The in-building subsystems 30 includes wall outlets 40a through 40e (which are simply denoted by"40" hereinbelow except where a precise denotation is required) and subscriber modules 50a, 50c, and 50e (which is simply denoted by"50" hereinbelow except where a precise denotation is required). The wall outlets 40, which are installed on the wall of the house similarly to conventional phone outlets, allows the user to couple subscriber premises, i. e., a data terminal 90 and/or a telephone, by use of the subscriber module 50. When being stuck onto the wall outlet 40, the subscriber module 50 multiplexes the uplink data signal from the data terminal 90 and the voice signal from the telephone 92 and demultiplexes a received downlink signal into a downlink data signal and a downlink voice signal to provide such signals to the data terminal 90 and the telephone 92, respectively.

On the other hand, a plurality of wall outlets 40a through 40e may be connected in the in-building subsystem 30 as shown in the figure. As described below, however, it is not preferable to couple any data terminal onto the wall outlets 40b, 40d, and 40e which are located behind the outlets 40a and 40c coupled to data terminals 90 in consideration of any data collision even though telephones 92 may be connected to such wall outlets. Accordingly, a parallel expansion module 60 or a serial expansion module 70 is provided in the in-building subsystem 30 so that a plurality of data terminals can simultaneously be connected to the network. The parallel expansion module 60 increases the number of ports which allows the connection of the data terminals in the in-building subsystem 30 having a parallel wiring scheme. The serial expansion module 70 increases the number of ports which allows

the connection of the data terminals in a serially-wired in-building subsystem.

The data communication network according to the present invention can be implemented in conventional buildings, as well as a new building, by use of the telephone cables already installed. When the network is implemented in a conventional house or office building, it is preferable to employ the parallel expansion module 60 to expand the ports for connecting the data terminals in case that the conventional telephone cable is routed in a parallel shape while it is preferable to employ the serial expansion module 70 to expand the ports in case that the conventional cable is routed in series. Of course, the in-building subsystem 30 may employ both at least one parallel expansion modules 60 and at least one serial expansion modules 60 depending on the telephone wiring scheme of the building or the number of data terminals to be used.

FIG. 2 shows an embodiment of the center module 20 in detail.

The center module 20 includes a switching hub connection port 22, an outside telephone line connection port 24, a high pass filter (HPF) 26, and a low pass filter (LPF) 28. In the preferred embodiment, the HPF 26 which selectively passes data signal has a cut-off frequency of 100 kilohertz (kHz) and the LPF 28 selectively passing voice signal has a cut-off frequency of 10 kHz. Two transmission terminals TX+ and TX-in the switching hub connection port 22 are coupled to a first wire pair L11 of the in-building telephone cable through the HPF 26 and two reception terminals RX+ and RX-are directly coupled to a second wire pair L12.

Terminals RING and TIP of the outside telephone line connection port 24 are coupled to the first wire pair L11 via the LPF 28.

The multiplexed signal received from the in-building subsystem 30 through the first wire pair L12 is demultiplexed by the HPF 26 and the

LPF 28. The uplink data signal selected by the HPF 26 is transmitted to the switching hub 10 through the terminals TX+ and TX-of the switching hub connection port 22 and the uplink voice signal selected by the LPF 28 is transmitted to the PSTN exchange through the outside telephone line connection port 24. Meanwhile, the downlink data signal from the switching hub is transferred to the in-building subsystem 30 through the second wire pair L12. Also, the downlink voice signal received from the outside telephone line is transferred to the in-building subsystem 30 through the first wire pair L11.

FIG. 3 shows an embodiment of the wall outlet 40 in detail. The wall outlet 40 includes a subscriber module connection port 42 and a termination and switching circuit 44. The termination and switching circuit 44 includes a switching unit 46 and a LPF 48. The subscriber module connection port 42 has four holes for receiving protrusions of the subscriber module and four terminals 42a through 42d respectively formed in the holes, so that the subscriber module 50 according to the present invention or a conventional phone plug can be stuck and electrically connected thereto. Meanwhile, the subscriber module 50 according to the present invention are categorized into two types: a phone connection dedicated module 50e similar to the conventional phone plug as shown in FIG. 1 and a general purpose module 50a or 50c for connecting just a data terminal or a data terminal along with a phone to the telephone cable. The operation of the wall outlet 40 will be described below.

In case that the phone connection dedicated module 50e or the conventional phone plug is inserted to the holes of the wall outlet 40, the switches of the switching unit 46 switch to the positions shown in FIG. 3.

At this time, the first and the second wire pairs L41 and L42 of the center module side are coupled to the terminals 42a through 42d of the

subscriber module connection port 42 and the wire pairs L51 and L52 of rear side. Thus, a voice channel may be set up through the wall outlet 40 shown in the figure and a telephone coupled thereon while another telephone or a data terminal may be installed behind the wall outlet 40.

In case that the general purpose subscriber module 50a or 50c is inserted to the holes of the wall outlet 40, the switches of the switching unit 46 switch to the positions opposite to those shown in FIG. 3. Since the first and the second wire pairs L41 and L42 of the center module side are coupled to the terminals 42a through 42d of the subscriber module connection port 42, a data terminal connected to the subscriber module connection port 42 via the subscriber module 50a or 50c can perform data communication with the switching hub. However, the downlink data signal from the first wire pair L41 of the center module side cannot be transferred to the first wire pair L51 of rear side because of the LPF 48. Also, the uplink data signal from the first wire pair L51 of rear side cannot be transferred to the first wire pair L41 of the center module side since they are electrically isolated. On the other hand, a voice channel may be set up for a telephone installed in the rear side, i. e. along the wire pair L51, since the first wire pair L41 of the center module side and the first wire pair L51 of rear side are electrically connected at low frequencies. Accordingly, when the general purpose subscriber module 50a or 50c is inserted to the holes of the wall outlet 40, any wall outlet behind such a wall outlet cannot be used for data communication but for voice communication.

In the preferred embodiment, a separate switch is provided to the wall outlet 40, so that the switching unit 46 switches depending on the type of the subscriber module 50 inserted to the wall outlet 40. One example of such a switch is a toggle switch by which the user can change the switching position manually depending on the depending on

the type of the subscriber module 50. In another example, however, a pressure sensor switch is provided in the wall outlet 40 and a protrusion for pressing the pressure sensor switch is formed in the front face of the general purpose subscriber module. In the operation of the switching unit 46, the separate switch generates a switching control signal CONT, so that the switching unit 46 changes its switching position in response to the switching control signal CONT. Alternatively, however, the switching unit 46 may change its switching position mechanically.

In the wall outlet 40 of FIG. 3, inductors of the LPF 48 perform an impedance matching operation between the first and the second wire pair L41 of the center module side and L51 of rear side and between the first wire pair L41 and the subscriber module connection port 42 in addition to the filtering operation of selectively passing of the telephone signal. Such an impedance matching operation facilitates a long- distance transmission of data and mitigates any limitation in the data communication which may arise from the length of the telephone cable at home.

FIG. 4 illustrates an embodiment of the subscriber module 50 of FIG. 1 in detail. The subscriber module 50 includes a plug 52, a data terminal connection port 54, a HPF 56, a telephone connection port 58, and a LPF 59. FIG. 5 is a perspective view of a preferred embodiment of the subscriber module 50. As shown in the figure, the subscriber module 50 substantially has a shape of a hexahedron and has the plug comprising of four protruding connectors on its front face. On one side of the subscriber module 50, there is provided the data terminal connection port 54, i. e. the RJ-45 connector. Further, on the bottom face of the subscriber module 50, there is provided the telephone connection port 58, i. e. the RJ-11 connector.

Referring back to FIG. 4, the HPF 56 has a cut-off frequency of 100 kHz so as to selectively pass data signal and the LPF 59 has a cut- off frequency of 10 kHz so as to selectively pass voice signal. Terminals RX+ and RX-of the data terminal connection port 54 are coupled to first and second terminals 52a and 52b of the plug 52, respectively, via the HPF 56. Terminals TX+ and TX-of the data terminal connection port 54 are coupled to second and fourth terminals 52c and 52d of the plug 52, respectively. RING and TIP terminals of the telephone connection port 58 are coupled to the first and the second terminals 52a and 52b of the plug 52, respectively, via the LPF 59.

Uplink data signal received from a data terminal coupled to the data terminal connection port 54, through the terminal RX+ and RX- thereof, is provided to the first and the second terminals 52a and 52b of the plug 52. Thus, the uplink data signal and the uplink voice signal are mixed or frequency-division-multiplexed at the first and the second terminals 52a and 52b of the plug 52 to be transmitted to the center module 20. Also, the downlink voice signal received through the first and the second terminals 52a and 52b of the plug 52 is selected by the LPF 59 and transmitted to the telephone via the telephone connection port 58. Here, the HPF 56 prevents the voice signal component of the signal in the first wire pair from being transferred to the data terminal coupled to the data terminal connection port 54. Meanwhile, the downlink data signal received from the LAN through the third and the fourth terminals 52c and 52d of the plug 52 is transmitted to the data terminal through the TX+ and TX-terminals of the data terminal connection port 54.

FIG. 6 illustrates an embodiment of the parallel expansion module 60 of FIG. 1 in detail. The module of FIG. 6, which expands the data terminal connection ports in parallel, includes a hub 62, HPFs 64,66

and 67, and a LPF 68. In the preferred embodiment, the parallel expansion unit 60 additionally includes a telephone connection port 69 for connecting the telephone. The hub 62 includes an uplink port connected to a telephone cable of the center module side and a first and second downlink ports connected to telephone cables of a first and a second channels, respectively.

TX+ and TX-terminals of the uplink port are coupled to a first wire pair L11 of the telephone cable of the center module side via the HPF 64, and RX+ and RX-terminals thereof are directly coupled to a second wire pair L12. RX+ and RX-terminals of the first downlink port are coupled to a first wire pair L21 of the telephone cable of the first channel via the HPF 66, and TX+ and TX-terminals thereof are directly coupled to a second wire pair L22. RX+ and RX-terminals of the second downlink port are coupled to a first wire pair L31 of the telephone cable of the second channel via the HPF 67, and TX+ and TX-terminals thereof are directly coupled to a second wire pair L32.

Meanwhile, the LPF 68 is connected between the first wire pair L11 and the first wire pairs L21 and L31 of the first and the second channels.

Of signals existing in the first wire pair L11 of the center module side, the downlink voice signal is selectively bypassed via the LPF 68 and mixed with the downlink data signal in the first wire pairs L21 and L31 of the first and the second channels. Of mixed signals existing in the first wire pairs L21 and L31 of the first and the second channels, the uplink voice signal is selectively bypassed via the LPF 68 and mixed with the uplink data signal in the first wire pair L11 of the center module side. Meanwhile, the downlink data signal received from the second wire pair L12 of the center module side is demultiplexed by the hub 62 to be transmitted to the second wire pairs L22 and L32 of the first and the second channels. Of uplink mixed signals received from the first

wire pairs L21 and L31 of the first and the second channels, the uplink data signals are selected by the HPFs 66 and 67 and multiplexed by the hub 62 to be transmitted to the first wire pair L11 of the center module side.

FIG. 7 illustrates an embodiment of the serial expansion module 70 of FIG. 1 in detail. The module of FIG. 7, which expands the data terminal connection ports serially, includes a hub 72, HPFs 74 and 76, a LPF 77, a data terminal connection port 78, and a telephone connection port 79. The hub 72 includes an uplink port connected to a telephone cable of the center module side and a third and fourth downlink ports.

TX+ and TX-terminals of the uplink port are coupled to a first wire pair L21 of the telephone cable of the center module side via the HPF 74, and RX+ and RX-terminals thereof are directly coupled to a second wire pair L22. RX+ and RX-terminals of the third downlink port are coupled to a first wire pair L41 of the telephone cable behind the serial expansion module 70, and TX+ and TX-terminals thereof are directly coupled to a second wire pair L42. The fourth downlink port of the hub 72 is coupled to the data terminal connection port 78. Meanwhile, the LPF 68 is disposed between the first wire pair L21 and the first wire pair L41.

Of signals existing in the first wire pair L21 of the center module side, the downlink voice signal is selectively passed via the LPF 77 and mixed with the downlink data signal in the first wire pair L41. Also, the downlink voice signal is provided to the telephone connection port 79.

Of mixed signals existing in the first wire pair L41, the uplink voice signal is selectively bypassed via the LPF 77 and mixed with the uplink data signal in the first wire pair L21 of the center module side. Meanwhile, the downlink data signal received from the second wire pair L22 of the center module side is demultiplexed by the hub 72 to be transmitted to

the data terminal connection port 78 or the second wire pair L42. Of uplink mixed signals received from the first wire pair L41, the uplink data signal is selected by the HPF 76 and multiplexed by the hub 72 to be transmitted to the first wire pair L21 of the center module side.

In the data communication network described above, the voice signal and the data signal is multiplexed and transmitted without any interference between them. In case of the voice signal channel, traffic exists only when any telephone is in an off-hook state or a call is received by the telephone (s). However, the data signal channel may be active always regardless of the call channel setup through the PSTN. In other words, the data communication network according to the present invention, which utilizes the in-building telephone wirings, bypasses the switch of the PSTN and directly connected to the host of the Internet service provider via the hub 10. Thus, the data communication network works like a high speed dedicated line. Particularly, the data terminal connection port 54 and 78 may be connected to the network adapter such as an Ethernet adapter of the data terminal, i. e. a personal computer. In such a system, data is transferred according to the Ethernet protocol.

FIG. 8 illustrates an example of a network in a building according to the present invention. In the network shown in FIG. 8, a plurality of wall outlets 40 are serially connected along the telephone cable. A personal computer of a LAN user is connected to one of the wall outlets 40, while plural telephones are connected to some of the other wall outlets 40. When connecting the telephone to the wall outlet 40, the user may use either a phone plug 99 or the general-purpose subscriber module 50 according to the present invention.

At each telephone, the voice signal is transmitted or received through the first wire pair of the telephone cable. Meanwhile, the uplink

data signal transmitted by the Ethernet adapter of the personal computer is mixed with the voice signal by the subscriber module 50 and transmitted to the center module through the telephone cable. The downlink data signal from the center module is provided to the personal computer via the subscriber module 50. Here, the termination and switching circuit 44 impedance-matches between the components of the wire pairs so as to enable the long-distance transmission of the signal.

Also, the termination and switching circuit 44 blocks the data signal being transferred to the telephone and prevents the attenuation of the high frequency data signal by capacitors in the telephone. Thus, the user may dispose and connect the subscriber module 50 connected to the personal computer to an arbitrary wall outlet 50.

FIG. 9 illustrates another example of the network in a building according to the present invention. In the network shown in FIG. 9, devices are connected in series along the telephone cable. Particularly, a plurality of users can connect their computers to the network in order to use the LAN. If the plurality of computers are to be connected to the network as such, computers except the last one are connected to the telephone cable by use of the serial expansion module 70 of FIG. 7. As described above with reference to FIG. 7, the serial expansion module 70 multiplexes the uplink LAN data signal from the cable behind the module 70 and that from the data terminal connection port to transmit the multiplexed signal to the center module, and demultiplexes the downlink LAN data signal to transmit the demultiplexed signal to the cable behind the module 70 or to the computer connected to the data terminal connection port.

FIG. 10 illustrates yet another example of the network in a building according to the present invention. In the network shown in FIG. 10, the telephone cable is routed in a parallel pattern, and a

plurality of users can connect their computers to the network in order to use the LAN. When the plurality of computers are to be connected to the telephone cable routed in the parallel pattern, computers can be connected to the telephone cable at each branch if the parallel expansion module 60 is installed at the node.

Although the present invention has been described in detail above, it should be understood that the foregoing description is illustrative and not restrictive. Those of ordinary skill in the art will appreciate that many obvious modifications can be made to the invention without departing from its spirit or essential characteristics.

For example, the voice signal is carried through the first wire pairs of the telephone cable through which the uplink data signal is transmitted in the preferred embodiments, the voice signal may be carried alternatively through the second wire pairs of the telephone cable through which the downlink data signal is transmitted. In such an alternative, the data signal is frequency-division-multiplexed or demultiplexed with the voice signal by the highpass-filtering of the downlink signal instead of the uplink signal. The transmission of the voice signal along with the uplink data signal is preferable for a usual user whose uplink data traffic is less than the downlink data traffic, while the transmission of the voice signal along with the downlink data signal is preferable for a user whose downlink data traffic is less than the uplink data traffic.

Also, two-port hub 62 and 72 are employed in the parallel expansion module 60 and the serial expansion module 70, respectively, in the above-described embodiments, multiple-port hub having more than two ports may be used as well. Of course, the parallel expansion module 60 and the serial expansion module 70 may be used simultaneously in the network.

In another alternative embodiment, the voice signal may be transmitted through both the first and the second wire pairs. Such an embodiment may be implemented easily by adding LPFs to the second wire pair in the network described above. In such a case, the first wire pair carries a voice channel of a first channel and the downlink data signal, and the second wire pair carries a voice channel of a second channel and the uplink data signal. Thus, it is possible to simultaneously set up a bidirectional data channel and two voice channel by use of one four-wiring telephone cable.

On the other hand, the data communication network was described in terms of accessing Internet at home, the network of the present invention may be employed in office buildings or factories as well. Further, the data communication network according to the present invention may be used for implementing an office LAN or a home automation system rather than accessing Internet. In the specification including the appended claims, the phrase"an in-building system"is to be construed as being descriptive of a general class of system including all the applications above.

Having described and illustrated the principles of the invention in preferred embodiments and alternatives thereof, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications and variation coming within the spirit and scope of the following claims.

Industrial Applicability The present invention facilitates the implementation of a high- speed Ethernet of 10 MHz level in an office building, an apartment house, a shopping center, or an hotel by use of the telephone wiring

already installed. In particular, the network is advantageous in that it operates in full-duplex.

Also, since the number of LAN ports for connecting customer premises can be increased by using the serial expansion module or the parallel expansion module, plural users can simultaneously use the data communication service, e. g., Internet service.