Abstract:
A communication system having first and second states for use with a shared transmission line composed of at least two conductors and composed of first and second transmission line segments connected to each other at a single connection point. In the first state, a termination is coupled to the single connection point and is operative to at least attenuate a signal propagated between the first and second segments. In the second state, a driver is coupled to the connection point and is operative to conduct a signal over the first and second segments.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of U.S. application Ser. No. 12/724,952, filed on Mar. 16, 2010, which is a continuation of U.S. application Ser. No. 12/252,025, filed Oct. 15, 2008, now allowed, which is a continuation of U.S. application Ser. No. 12/026,321, filed Feb. 5, 2008, now U.S. Pat. No. 7,453,284, issued on Nov. 18, 2008, which is a continuation of U.S. application Ser. No. 11/346,396, filed on Feb. 3, 2006, now U.S. Pat. No. 7,336,096, issued on Feb. 26, 2008, which is a division of U.S. application Ser. No. 11/100,453, filed on Apr. 7, 2005, now U.S. Pat. No. 7,068,066, issued on Jun. 27, 2006, which is a continuation of U.S. application Ser. No. 10/380,538, filed on Sep. 12, 2001, now U.S. Pat. No. 6,937,056, issued on Aug. 30, 2005, which is a national stage of PCT/IL01/00863, filed on Sep. 17, 2000, the disclosures of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of electrically-wired communication, and, in particular, to communication lines employing termination. 
       BACKGROUND OF THE INVENTION 
       [0003]    The term “data unit” herein denotes any data processing device, such as a computer or a personal computer, including workstations or other data terminal equipment (DTE) with an interface for connection to any wired communication network, such as a Local Area Network (LAN). 
         [0004]    Transmission lines over which digital signals are transmitted must be properly terminated in order to prevent overshoot, undershoot and reflections. These effects, when caused by impedance mismatch, become more pronounced as the length of the conductor increases, and limit the rate at which data can be transmitted over a transmission line. The transmission line can be a trace on an integrated circuit, a trace on a board, or a wire in a cable. The impedance of both the source and load should be matched to the characteristic impedance of the transmission line. Since the output impedance of a transmitter and the input impedance of a receiver generally differ from the characteristic impedance of a transmission line interconnecting the transmitter and the receiver in a point-to-point configuration, it is necessary to alter the existing impedance differently at the source and load ends of the transmission line. 
         [0005]    Wire-based communication networks commonly employ terminations in order to avoid reflections. An example of termination within a network is shown in  FIG. 1 . A shared wired network  10  is based on a two-wire transmission line having wires  15   a  and  15   b . In the following description, reference will be made to “transmission line  15   a  and  15   b ”, it being understood that the reference numerals actually refer to the wires forming the transmission line. For example, network  10  may be an EIA/TIA-485 standard type, wherein transmission line  15   a  and  15   b  consists of a single twisted pair, or an Ethernet IEEE802.3 standard 10Base2 or 10Base5, wherein transmission line  15   a  and  15   b  is a coaxial cable. In general, the term ‘transmission line’ herein denotes any electrically-conductive media capable of carrying electrical current and voltages, and transporting electromagnetic signals, including without limitation wires, cables, and PCB traces. Differential line drivers  11   a  and  11   b  are used in order to transmit signals to the transmission line, while line-receivers  12   a  and  12   b  are used to receive signals carried over transmission line  15   a  and  15   b . Data unit  16   a  is a “transmit only” unit, which transmits data to the transmission line via line driver  11   a , and data unit  16   b  is a “receive only” unit that receives data from the transmission line via line receiver  12   a . Data unit  16   c  can both receive data from and transmit data to the transmission line  15   a  and  15   b  via line diver  11   b  and line receiver  12   b , forming a transceiver  14 . Of course, additional units can be connected to shared transmission lines, each such units employing a line receiver, a line driver, or both. In order to allow for proper operation of network  10 , terminators  13   a  and  13   b  are commonly installed and connected to both ends of transmission line  15   a  and  15   b . In order to function properly, terminators  13   a  and  13   b  should be equal in impedance to the characteristic impedance of transmission line  15   a  and  15   b . Similarly, such terminations are employed in both ends of a point-to-point connection. 
         [0006]    The need for termination is a major drawback in building a network. First, the transmission line ends must be identified and accessed, which may not be simple in the case of existing wiring. Additionally, terminator installation requires both labor and materials, and there is also the issue of additional equipment required to configure a network. Furthermore, for proper operation, the termination type, topology and values are mainly based on the transmission line characteristics, which may be unknown and/or inconsistent, and may vary from cable to cable or from location to location. 
         [0007]    An additional drawback of network  10  relates to being a multi-point shared transmission line network. In a Time Domain Multiplexing (TDM) scheme, only a single driver can transmit over the transmission line during any time interval, rendering other units as receive-only during that time interval. This limits the total volume of data that can be transported over a specified period. In order to allow multiple data transport over this shared transmission line, it is necessary to allow multiple transmitters and receiver to use the transmission line simultaneously. 
         [0008]    One common method for such multiple transmissions over shared transmission line employs the Frequency Domain Multiplexing (FDM) scheme, wherein each transmitter uses a different dedicated portion of the transmission line&#39;s available spectrum. Such a solution, however, requires complex and expensive circuitry. 
         [0009]    Another method for enabling multiple transmissions is shown in  FIG. 2 , and involves splitting the transmission line into distinct segments. A network  20  is shown in part, wherein the transmission line is split into two distinct portions, one of which is identified as transmission line segment  15   a  and  15   b  (as in  FIG. 1 ), while the other portion is identified as a transmission line segment  15   c  and  15   d . Transmission line segment  15   a  and  15   b  is used for full duplex communication using line drivers  11   a   2  and  11   b   1 , located at respective ends of transmission line segment  15   a  and  15   b . Similarly, line receivers  12   b  and  12   a   2  as well as terminators (not shown) are installed at the respective ends of transmission line segment  15   a  and  15   b . Line driver  11   a   2  and line receiver  12   a   2  are both part of a unit  21   a , which is connected at one end of transmission line segment  15   a  and  15   b . Similarly, transmission line segment  15   c  and  15   d  is coupled to line drivers  11   c   1  and  11   b   2 , as well as to line receivers  12   c   1  and  12   b   2 . Line driver  11   c   1  and line receiver  12   c   1  are both part of a unit  21   c , connected at one end of transmission line segment  15   c  and  15   d . Line drivers  11   b   2  and  11   b   1 , as well as line receivers  12   b   1  and  12   b   2  are all part of a unit  21   b , connected to transmission line segment  15   a  and  15   b , and to transmission line segment  15   c  and  15   d . These two distinct transmission line segments as well as their related drivers/receivers are coupled by a logic block  22 , which is part of unit  21   b . In certain prior art configurations, the logic block is either omitted or acts as transparent connection. In such case, unit  21   b  serves as a repeater. In other configurations, logic block  22  processes the data streams flowing through unit  21   b.    
         [0010]    Network  20  offers two major advantages over network  10  as shown in  FIG. 1 . First, each transmission line segment of network  20  is independent, allowing two communication links to operate simultaneously. Hence, line driver  11   a   2  of unit  21   a  can transmit data over transmission line segment  15   a  and  15   b , to be received by line receiver  12   b   1  of unit  21   b . Simultaneously, and without any interference, line driver  11   c   1  of unit  21   c  can transmit data over transmission line segment  15   c  and  15   d  to be received by line receiver  12   b   2  of unit  21   b.    
         [0011]    Yet another advantage of network  20  is that of having point-to-point communication segments. As is well known in the art, point-to-point topology is a highly favored configuration in wired communication, enabling robust, high bandwidth communications with low-cost, simple circuitry. 
         [0012]    Principles of the above description are demonstrated by the evolution of the Ethernet Local Area Network (LAN) as specified in the IEEE802.3 standard, wherein shared transmission line systems based on coaxial cable 10Base2 and 10Base5 were upgraded towards 10BaseT and 10BaseTX based networks, both built around point-to-point segments. 
         [0013]    However, network  20  also exhibits a major disadvantage in comparison to network  10 . As shown in  FIG. 1 , network  10  uses a continuous uninterrupted transmission line. In contrast, the wiring of network  20  must be cut at several points throughout the network, wherein units  21  are simply connected. In the case of existing transmission lines (such as in-wall telephone wiring), cutting into the network may be complex, expensive, and labor-intensive. 
         [0014]    There is thus a widely recognized need for, and it would be highly advantageous to have, a means for implementing a generic termination that is not transmission line-dependent, and which therefore would not need to be changed when the transmission line characteristics change. There is also a widely recognized need for a means for simultaneous multiple use of a single wiring infrastructure, and for employing a point-to-point connection scheme, without modifying such existing wiring. These goals are addressed by the present invention. 
       SUMMARY OF THE INVENTION 
       [0015]    The invention relates to a system and method for signal termination, based on a two-port unit, denoted herein as a Signal Canceling Unit (SCU). The SCU senses the signal present over its terminal, and operates to absorb and cancel this signal. When connected at an end of a transmission line, such as a wire transmission line used for communication, the SCU functions as a terminator by absorbing the signal energy. When connected in the middle of such wiring transmission line, the SCU terminates any signal sensed over its terminals, and thus can be used for noise isolation, or to emulate a network end in the connected points. In this functional mode, the SCU effectively splits the wires, allowing for different independent networks operation at each side of the SCU connection, without interfering or interacting with each other, even though the continuity of the wiring is not affected. 
         [0016]    In another embodiment, the SCU is upgraded to include line receiver functionality, denoted herein as a Signal Canceling and Receiving Unit (SCRU). In addition to having full SCU functionality, the SCRU also operates as a line receiver, and hence can be used as an active receiver in the network, in addition to serving in termination and signal canceling roles. 
         [0017]    In yet another embodiment, the SCRU is upgraded to include line driver functionality, denoted herein as a Signal Canceling, Receiving, and Transmitting Unit (SCRTU). In addition having full SCRU functionality, the SCRTU also performs as a line driver, and hence can be used as an active transmitter in the network, in addition to serving in termination, signal canceling, and receiving roles. Multiple SCRTU&#39;s connected to wired transmission lines can communicate for construction of a full network. In such a network, every pair of adjacent-connected SCRTUs can communicate in a point-to-point fashion, in a terminated and independent transmission line segment. 
         [0018]    Therefore, according to a broad aspect of the present invention there is provided a device for actively terminating and isolating a continuously conducting transmission line, said device comprising: 
         [0019]    a sensor operative to sensing a first signal on the transmission line; 
         [0020]    a first driver operative to placing a second signal on the transmission line for canceling the first signal; and 
         [0021]    a processing unit operative to receiving input from said sensor and providing input to said first driver. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
           [0023]      FIG. 1  shows a common prior art shared wired Local Area Network configuration; 
           [0024]      FIG. 2  shows a prior art repeater based communication network; 
           [0025]      FIG. 3  shows a Signal Canceling Unit (SCU) functional block diagram according to a first embodiment of the present invention; 
           [0026]      FIG. 4  shows a shared wiring based network, wherein an SCU is used as an end terminator according to the present invention; 
           [0027]      FIG. 5  shows a shared wiring based network, wherein an SCU is used as a parallel connected terminator according to the present invention; 
           [0028]      FIG. 6  shows a shared wiring based network, wherein an SCU is used for noise isolating according to the present invention; 
           [0029]      FIG. 7  shows a shared wiring based network, wherein an SCU is used for bridge-tap isolating according to the present invention; 
           [0030]      FIG. 8  shows a shared wiring based network, wherein an SCU is used for allowing multiple independent communication segments over continuous wiring according to the present invention; 
           [0031]      FIG. 9  shows a Signal Canceling and Receiving Unit (SCRU) functional block diagram according to a second embodiment of the present invention; 
           [0032]      FIG. 10  shows a shared wiring based network, wherein an SCRU is used for allowing multiple independent communication segments over continuous wiring according to the present invention; 
           [0033]      FIG. 11  shows a Signal Canceling, Receiving and Transmitting Unit (SCRTU) functional block diagram according to a third embodiment of the present invention; 
           [0034]      FIG. 12  shows an alternative Signal Canceling, Receiving and Transmitting Unit (SCRTU) functional block diagram according to a fourth embodiment of the present invention; and 
           [0035]      FIG. 13  shows a shared wiring based network, wherein multiple SCRTU&#39;s are used for allowing multiple independent communication segments over continuous wiring according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    The principles and operation of a network according to the present invention may be understood with reference to the drawings and the accompanying description. The drawings and descriptions are conceptual only. In actual practice, a single component can implement one or more functions; alternatively, each function can be implemented by a plurality of components and circuits. In the drawings and descriptions, identical reference numerals indicate those components that are common to different embodiments or configurations. 
         [0037]      FIG. 3  illustrates a Signal Canceling Unit (SCU)  30 , which includes two external terminal connections, a terminal  34   a  (A) and a terminal  34   b  (B). Coupled to these terminals is a sensor  31 , which measures the differential voltage (constituting a “first signal”) between terminal  34   a  and terminal  34   b . The value measured by sensor  31  is input into a processing unit  33 , which in turn provides input to a differential driver  32  (constituting a “first driver”), whose outputs are coupled to the terminal  34   a  and terminal  34   b . Driver  32  can sink or source enough current (constituting a “second signal”) to cancel the first signal at the terminals. Processing unit  33  along with sensor  31  and driver  32  forms a closed negative feedback loop, which attenuates and cancels any signal sensed over terminal  34   a  and terminal  34   b.    
         [0038]      FIG. 4  illustrates a network  40 , with SCU  30  used as a terminator. Network  40  is based on network  10  ( FIG. 1 ), but modified to use SCU  30  as a terminator in place of terminator  13   b . Signals transmitted to transmission line  15   a  and  15   b  (by line driver  11   a , for example) propagate along the transmission line. Upon reaching the end of the transmission line, where terminals  51   a  and  51   b  of SCU  30  are connected, SCU  30  senses and acts to cancel the signals. As a result, the signal energy is absorbed by SCU  30 , and neither reflection nor any other mismatch occurs. Hence, SCU  30  acts as a termination device. However, since the structure of SCU  30  is generic and is not tailored to the specific transmission line (e.g., characteristic impedance), this same SCU can be used for many types of transmission line, such as twisted pair wiring, coaxial cables, etc., obviating the need to match a specific termination to a specific transmission line. This, of course, provides simple installation and easy logistics, due to the employment of common components for various different applications. 
         [0039]    A further advantage of using an SCU as a terminator stems from the fact that the SCU performs the termination function even when not connected at the ends of the transmission line, but at any point throughout the transmission line run, as illustrated in  FIG. 5  for a network  50 , which is based on transmission line  15   a ,  15   b ,  15   c , and  15   d . As with network  10  ( FIG. 1 ), terminator  13  is located at one end (left side of the figure), and line driver  11   a  and line receivers  12   a  and  12   b  are coupled to the transmission line. Data units  16   a ,  16   b , and  16   d  are coupled to line units  11   a ,  12   a , and  12   b , respectively. If SCU  30  were not present in network  50 , network  10  of  FIG. 1  would be obtained, wherein data unit  16   a  can transmit data to the entire transmission line via line driver  11   a . The transmitting signals would then propagate in the transmission line and would be received by data units  16   b  and  16   d  via line receivers  12   a  and  12   b , respectively. In this case, however, where SCU  30  is connected to the transmission line at connection points  51   a  and  51   b , the network  50  is modified such that signals transmitted to line driver  11   a , are propagated in the transmission line in two directions. Part of the signal energy is propagated towards terminator  13  (towards the left side of the figure), where they are absorbed. The other part of the signal energy propagates towards points  51   c  and  51   d , representing the other end of the wiring. When the signal reaches points  51   a  and  51   b  (connected to the terminals of SCU  30 ), SCU  30  operates to attenuate, cancel, and absorb the signal energy. Thus, little or no signal will propagate from the points  51   a  and  51   b  towards the end points  51   c  and  51   d . In such case, while line receiver  12   a  will receive the transmitted signals, line receiver  12   b  will not sense any such signals, which are attenuated by SCU  30 . Thus, SCU  30  functions as a terminator for the network segment  15   a  and  15   b , extending from terminator  13  to points  51   a  and  51   b , helping to avoid reflections in this part of the transmission line. As a result, SCU  30  modifies the functionality of the continuous transmission line to be virtually separated into two distinct segments, one using the transmission line from terminator  13  to points  51   a  and  51   b , while the other uses the transmission line from points  51   a  and  51   b  to the end-points  51   c  and  51   d . The two network segments are isolated in the sense that signals in one segment cannot pass to the other, even though electrical continuity of the transmission line is fully retained. 
         [0040]    One application of such virtual networks separation is for noise isolation, as illustrated in  FIG. 6  with a network  60 . Network  60  is similar to network  50  ( FIG. 5 ), except that a noise source  61  appears in place of data unit  16   d  and line receiver  12   b . The noise generated by noise source  61  propagates (in the left direction) towards SCU  30 . Upon reaching SCU terminals  51   a  and  51   b , SCU  30  operates to attenuate the noise signal, and prevents the noise from reaching transmission line  15   a  and  15   b  and thereby degrading communication over that network segment. While noise source  61  is described and illustrated as a distinct unit connected at a single point to transmission line  15   c  and  15   d , the same noise cancellation function is performed where noise is generated by inductive means from external sources. For example, transmission line  15   c  and  15   d  may extend over an area near sources of electromagnetic interference. The SCU can thus help in isolating the induced noise from a specific portion of the conductive transmission line. 
         [0041]    Bridge-taps are known to cause impedance mismatch and reflections in transmission lines and other wired communication environments.  FIG. 7  illustrates a network  70 , which is similar to network  60  ( FIG. 6 ), but with added transmission line  15   e  and  15   f , connected to terminals  51   a  and  51   b  respectively, forming a bridge tap at terminals  51   a  and  51   b . Without SCU  30 , the bridge tap at these points would create an impedance mismatch and cause signal reflections in the communications over transmission line  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f . The presence of SCU  30  at the bridge-tap junction, however, cancels and absorbs the signals at terminals  51   a  and  51   b , and eliminates such reflections. In doing so, three isolated communication segments are formed, one segment consisting of transmission line  15   a  and  15   b , a second segment consisting of transmission line  15   c  and  15   d , and a third segment consisting of transmission line  15   e  and  15   f.    
         [0042]    The capability of an SCU to isolate electrically connected transmission line enables the formation of multiple distinct communication networks over continuous electrical conducting transmission line, as shown in  FIG. 8 . A network  80  is based on transmission line  15   a ,  15   b ,  15   c , and  15   d . SCU  30  connects to the transmission line at terminals  51   a  and  51   b , and isolates the transmission line into two communication segments. One segment is based on transmission line  15   a  and  15   b , and extends from terminals  51   a  and  51   b  towards the left in  FIG. 8 . The other segment is based on transmission line  15   c  and  15   d , and extends toward the right. Data unit  16   a  transmits across transmission line  15   a  and  15   b  via line driver  11   a , and provides the signal received by data unit  16   b  via line receiver  12   a . Similarly, data unit  16   e  transmits across transmission line  15   c  and  15   d  via line driver  11   b , with the signal received by data unit  16   d  via line receiver  12   b . Being isolated by SCU  30 , both transmissions can occur simultaneously, without interfering with each other. Additional line drivers, line receivers and transceivers can be added to each communication segment. Similarly, adding additional SCU&#39;s can split electrically-connected transmission line into more segments, wherein an isolated segment is formed between adjacent SCU pairs, or between the SCU and the ends or terminators of transmission lines. 
         [0043]    The function of the SCU has been so far been described only as a terminator, but an SCU can also be modified to perform a line receiving function, as shown in  FIG. 9 , which illustrates a Signal Canceling and Receiving Unit (SCRU)  90 . SCRU  90  is based on the structure of SCU  30 , ( FIG. 3 ), but the processing unit  33  is modified to a processing unit  91 , which provides additional output via a terminal  34   c  (C). The output on terminal  34   c  uses sensing function  31 , and together with part of processing unit  91  serves as a line receiver, similar to line receiver  12   a  or  12   b . Thus, SCRU  90  simultaneously performs two functions: signal cancellation as does SCU  30 , and line receiver functionality, as do line receivers  12   a  and  12   b , thus allowing the sensed signal or any function thereof to be output on the terminal  34   c  and placed on the transmission line. 
         [0044]    An example of an application using SCRU  90  is shown in  FIG. 10 , for a network  100 . Network  100  is based on network  80  ( FIG. 8 ), but SCU  30  is replaced by SCRU  90 , whose terminal C is connected to a data unit  16   f  via a connection  102 . SCRU  90  further is connected to transmission line  15   a ,  15   b ,  15   c , and  15   d  at junctions  101   a  and  101   b . In a manner similar to that of network  80  ( FIG. 8 ), this configuration allows two isolated communication segments to use the transmission line simultaneously without interfering with each other. One segment transports data over transmission line  15   a  and  15   b , while the other segment transports data over transmission line  15   c  and  15   d . In addition, by utilizing the line-receiving functionality of SCRU  90 , data unit  16   f  can receive signals from both networks. 
         [0045]    In yet another embodiment of the invention, a line-driving capability is also integrated into the SCRU.  FIG. 11  illustrates an SCRTU (Signal Canceling, Receive and Transmit unit)  110 . SCRTU  110  includes all components of SCRU  90 , but also includes a line driver  111  (constituting a “second driver”), which is fed from an additional SCRTU terminal  34   d  (D) and feeds a third signal to the transmission line. SCRTU  110  has two states of operation, denoted as “receive” and “transmit”. In “receive” state, the functionality of SCRU  90  is fully retained, and SCRTU  110  performs signal cancellation and reception. In “transmit” state, line terminals  34   a  (A) and  34   b  (B) are connected to line driver  111  output terminals as shown, so that SCRTU  110  can transmit data received at terminal  34   d  to terminals  34   a  and  34   b . Shifting between the states is performed by two SPDT (single pole double throw) switches  112  and  113 . Switches  113  and  112  are connected to terminals  34   a  and  34   b , respectively. In the ‘receive’ state, both switches  112  and  113  are in state ‘1’, thus connecting terminal  34   a  and terminal  34   b  terminals to sensor  31  and driver  32 , and thereby performing the function of SCRU  90 . In the ‘transmit’ state, both switches  112  and  113  are in state ‘2’, thus connecting terminal  34   a  and terminal  34   b  to the outputs of line driver  111 , and thereby performing as a line driver. Switches  112  and  113  are controlled by a logic unit  114 , which changes switches  113  and  112  as required to select the desired state. 
         [0046]      FIG. 12  illustrates an alternative implementation of an SCRTU  120 . In this alternative configuration, driver  32  is also used as the line driver. An SPST switch  121  is used to route the input into driver  32 . In state ‘1’, driver  32  is connected to the output of processing  91 , and thereby performing the function of SCRU  90 . In state ‘2’, driver  32  is coupled to terminal  34   d , and thereby functions as a line driver. A logic block (not shown in  FIG. 12 ) is used to control switch  121 , shifting it from state to state as required. 
         [0047]      FIG. 13  illustrates a network  130  using such SCRTU&#39;s. Network  130  uses network transmission line  15   a ,  15   b ,  15   c ,  15   d ,  15   e ,  15   f ,  15   g , and  15   h , and has a bridge-tap at points  51   a  and  51   b . Data units  16   f ,  16   g ,  16   h ,  16   i , and  16   j  are coupled to the transmission line via SCRTU&#39;s  110   a ,  110   b ,  110   c ,  110   d , and  110   e , respectively. As explained above, although the wiring is electrically continuous, the communication segments formed are of point-to-point type between any SCRTU pair. SCRTU  110   a  communicates in a point-to-point topology with SCRTU  11   b , over transmission line segment  15   a  and  15   b . Similarly, SCRTU&#39;s  110   b  and  110   e  communicate over transmission line segment  15   e  and  15   f , SCRTU&#39;s  110   b  and  110   c  communicate over transmission line segment  15   c  and  15   d , and SCRTU&#39;s  110   c  and  110   d  communicate over transmission line segment  15   g  and  15   h . In addition to the benefit of point-to-point, the network also allows for multiple independent communication segments to operate independently, as long as there are not any two SCRTU&#39;s transmitting to the same segment. For example, SCRTU  110   a  can transmit to SCRTU  110   b  over transmission line segment  15   a  and  15   b , while SCRTU  110   d  can simultaneously transmit to SCRTU  110   c  over transmission line segment  15   g  and  15   h.    
         [0048]    Network  130  demonstrates the SCRTU based network capability of point-to-point communications and multiple transmissions over continuous wiring. These capabilities can be useful for existing wiring having unknown topology, and having ‘bus’ type connection points. For example, in-wall existing telephone wiring, in-wall existing power lines or CATV cabling which are not used for their original purpose. Continuity is common to all of these types of wiring, where outlets are provided for connecting to the wiring. Hence, coupling SCRTU&#39;s to each outlet allows for reliable high bandwidth communication between data units connected to the SCRTU&#39;s. 
         [0049]    While the invention has been described with respect to a digital communication application, it will be appreciated that the invention is equally applicable to analog communication as well, such as video, audio or any other type of communication. In such configurations, data units  16  are replaced by suitable analog units, and the SCU&#39;s, SCRU&#39;s, and SCRTU&#39;s are modified accordingly to support such communication. 
         [0050]    While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.