Abstract:
A method and associated detecting circuitss for detecting and correcting a connection polarity of a network transmission line include two network clients and a network transmission line. One network client utilizes a detecting circuit to count and compare the number of signal pulses at the receiving and transmitting ports to determine if the connection polarity is correct or inverted. The detecting circuit can switch the connection polarity if required to correct it.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method and associated detecting circuits for detecting connection polarity of network transmission lines, and more particularly, to a method and associated detection circuits for detecting and correcting the connection polarity of network transmission lines by counting the number of signal pulses.  
           [0003]    2. Description of the Prior Art  
           [0004]    In a modern, information based society, computer networks allow people to exchange information. Hence, the manufacture and maintenance of these computer networks is an important issue.  
           [0005]    Please refer to FIG. 1A. FIG. 1A is a schematic diagram of a connection between two network clients  12 A and  12 B via a network transmission line  14 . The clients  12 A and  12 B can be a switch, a router, a terminal of a network system, or other types of network clients. The transmission media between these two clients can be an Ethernet, in which the network transmission line  14  is typical Ethernet transmission cable. The connection port of each client has two ports, a transmitting port and a receiving port, for exchanging information via the network transmission line  14 . A transmitting port Tx 0  and a receiving port Rx 0  are provided in the client  12 A, whereas a transmitting port Tx 1  and a receiving port Rx 1  are provided in the client  12 B. Each port transmits or receives, for example, a differential signal by a pair of wires inside the network transmission line  14 . Under a correct connection, the transmitting port Tx 0  of the client  12 A connects to the receiving port Rx 1  of the client  12 B and the receiving port Rx 0  of the client  12 A connects to the transmitting port Tx 1  of the client  12 B via the network transmission line  14 , as shown in FIG. 1A, so as to provide a correct connection polarity. If the connection polarity is correct then the two clients  12 A and  12 B can communicate properly.  
           [0006]    In practical situations, it happens that the connection polarity of the network transmission line  14  connected between the clients  12 A and  12 B is inverted. Please refer to FIG. 1B. FIG. 1B is a schematic diagram of the network system shown in FIG. 1A but with inverted connection polarity. That is, the transmitting port Tx 1  of the client  12 B connects to the transmitting port Tx 0  of the client  12 A instead of the receiving port Rx 0 . Similarly, the receiving port Rx 1  of the client  12 B does not correctly connect to the corresponding transmitting port Tx 0  of the client  12 A instead of the receiving port Rx 0 . Thus, the receiving ports Rx 0  and Rx 1  of the clients  12 A and  12 B will not receive any meaningful signals, since the network system malfunctions.  
         SUMMARY OF INVENTION  
         [0007]    It is therefore a primary object of the invention to provide a method and associated detecting circuits for detecting and correcting the connection polarity of network transmission lines so as to guarantee that a network system functions normally.  
           [0008]    According to the invention, a method for detecting a connection polarity of a network transmission line comprises a connection port counting a first number of signals transmitted via a first transmission line during a predetermined interval and counting a second number of signals transmitted via a second transmission line during a predetermined interval. The connection port determines that the connection polarity of the network transmission line is correct when a difference between the first number and the second number is less than a threshold value. Conversely, the connection port determines that the connection polarity of the network transmission line is inverted when a difference between the first number and the second number is greater than a threshold value.  
           [0009]    It is an advantage of the claimed invention that the above method and the associated detecting circuitss can detect and correct the connection polarity of a network transmission line to guarantee that information can be shared on the network.  
           [0010]    These and other objects of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]    [0011]FIG. 1A is a schematic diagram of a connection between two clients via a network transmission line.  
         [0012]    [0012]FIG. 1B is a schematic diagram of the network system shown in FIG. 1A wherein the connection polarity is inverted.  
         [0013]    [0013]FIG. 2 shows waveforms of signal pulses triggered by transmission signals on a network transmission line when the network transmission line is connected in different ways.  
         [0014]    [0014]FIG. 3 is a circuit schematic diagram for detecting and correcting the polarity of a network transmission line according to a preferred embodiment of the present invention.  
         [0015]    [0015]FIG. 4 is a schematic diagram of another embodiment according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]    Several kinds of encoded digital signals, with different voltage levels, can be used to transmit signals across a network. Consider an Ethernet 100 Base-T MLT-3 signal as an example. A high voltage level signal A represents a digital “1”, a middle voltage level signal A represents a digital “0”, and a low voltage level signal A represents a digital “−1”. A reference voltage level is set at first. A signal pulse is triggered at a client if the voltage level of a signal on a network transmission line is higher than the reference voltage level. For example, if the reference voltage level is set as the high voltage level reference, each high voltage level signal will correspondingly trigger a signal pulse. A number of signal pulses triggered by a digital signal associates to a flow rate of the digital signal.  
         [0017]    The present invention determines and corrects the connection polarity of a network transmission line by utilizing the quantity and the frequency of signal pulses. Shown in FIG. 2 are three waveforms of signal pulses triggered by transmission signals on a network transmission line. The horizontal-axis of each waveform represents time and the vertical-axis is the amplitude of signal. If clients  12 A and  12 B of a network system are correctly connected, as shown in FIG. 1A, the waveform of signal pulses triggered by transmission signals on each line of the network transmission line will appear approximately like the waveform  16 . Typically, the transmitting port of each client transmits nearly the same flow rate of digital signals to the corresponding receiving port of the other client.  
         [0018]    On the contrary, when the connection polarity of the network transmission line is inverted as shown in FIG. 1B, a measurable difference appears in the number of signal pulses triggered. Because the connection polarity of the network transmission line is inverted, the waveform of signal pulses appearing on the line connected between the two receiving ports looks like the waveform  18  shown in FIG. 2. The frequency of the triggered signal pulses on the line is very low because both ends of the line are receiving ports that will not transmit any signal. The only signals actually seen on the line are generated by noise or interference, such as lightening. On the other hand, the line connecting the two transmitting ports is filled with signals as both transmitting ports are attempting to transmit, illustrated as the waveform  20  in FIG. 2. In other words, when the connection polarity of a network system is inverted, the number of signal pulses on the line connected between two transmitting ports is very large, and the number of signal pulses on the line connected between two receiving ports is very small. When the connection polarity of a network system is correct, the number of signal pulses on each line lies between these previous two numbers.  
         [0019]    Please refer to FIG. 3. FIG. 3 is a circuit schematic diagram of a preferred embodiment according to the present invention for detecting and correcting the connection polarity of a network system. Two clients  21  and  22  connected by the transmission line  19  form a typical network system. A detecting circuit is installed in the client  22 . The clients can be a switch, a router, a terminal, or other types of network clients. The network system formed by the network transmission line  19  can be an Ethernet system. The client  21  comprises two ports C 1  and C 2  each connected to a line (a pair of wires as shown in FIG. 3) of the network transmission line  19  for transmission of mutually counter-phased differential-form transmission signals. The client  22  also comprises two ports; one being a transmitting port Tx 2  and the other being a receiving port Rx 2 . A detecting circuit  24 , installed in the client  22 , comprises a counter  26  and a multiplexer  28 . The counter  26 , connects to one line (two wires) of the network transmission line  19 , receives differential-form transmission signals on the line and counts a number of signal pulses. The counter  26  also sends a control signal to the multiplexer  28  via a control end  30  of the multiplexer  28 . The multiplexer  28  comprises two differential input ports,  32 A and  32 B (a first differential input pair) and  34 A and  34 B (a second differential input pair). The multiplexer also comprises two differential output ports,  36 A and  36 B (a first differential output pair) and  38 A and  38 B (a second differential output pair). The multiplexer  28  can switch the differential input pairs to connect with different differential output pairs based on the control signal generated by the counter  26 .  
         [0020]    [0020]FIG. 3 also shows that the input ports  32 A and  32 B of the multiplexer  28  connect to the port Cl of the client  21  whereas the output ports  36 A and  36 B connect to the transmitting port Tx 2 . The other input ports  34 A and  34 B connect to the port C 2  of the client  21  via the network transmission line  19  whereas the output ports  38 A and  38 B connect to the receiving port Rx 2 . The present invention can detect and correct the connection polarity of a network system using the detecting circuit  24  installed on one client  22  regardless of if the port C 1  or C 2  of the other client  21  is a transmitting port or a receiving port.  
         [0021]    The operation of the detecting circuit  24  of the preferred embodiment of the present invention is described as follows. The multiplexer  28  connects the first and second input pairs respectively to the first and second output pairs such that, the port C 1  connects to the transmitting port Tx 2  and the port C 2  connects to the receiving port Rx 2 . The counter  26  then counts the number of signal pulses on the line connected between the port C 2  and the receiving port Rx 2 . Practically, the counter  26  comprises a comparator for comparing a voltage level of transmission signals with a predetermined voltage level and a Schmitt trigger for generating signal pulses. For example, if the voltage level of transmission signal exceeds the predetermined voltage level, the Schmitt trigger will trigger a signal pulse. The Schmitt trigger can suppress the glitch interference.  
         [0022]    The counter  26  determines the connection polarity of the network transmission line according to the quantity and the frequency of signal pulses. As discussed previously, a very small number of signal pulses, less than a threshold value, received by the counter  26 , shown as waveform  18  in FIG. 2, indicates that the port C 2  of the client  21  does not transmit any meaningful signal and is in fact a receiving port. In other words, the two receiving ports C 2  and Rx 2  are connected. Therefore the counter  26  generates a control signal to the control end  30  of the multiplexer  28  causing the multiplexer  28  to switch the connection polarity for input pairs and output pairs. As a result, the port C 2  of the client  21  connects correctly to the transmitting port Tx 2  of the client  22  and the port Cl of the client  21  also correctly connects to the receiving port Rx 2  of the client  22 .  
         [0023]    If the connection polarity is correct then the number of signal pulses received by the counter  26  will exceed the threshold value. The counter  26  thus determines that the connection polarity of the network transmission line  19  is correct. Of course, the counter  26  will not assert a control signal to the multiplexer  28  to switch the connection polarity of the first and the second input and output pairs. Generally, if the number of signal pulses received by the counter  26  is smaller than a predetermined threshold value, set according to a flow rate of digital signals of normal transmission signals, the connection polarity of the network transmission line  19  is determined to be inverted.  
         [0024]    Please refer to FIG. 4. FIG. 4 is a schematic diagram of another embodiment  44  according to the present invention. Similar to the network system shown in FIG. 3, the client  21  connects to the client  22  via the network transmission line  19 . The client  21  comprises two ports C 1  and C 2  whereas the other client  22  comprises a detecting circuit  44 , transmitting port Tx 2 , and a receiving port Rx 2 . The detecting circuit  44  comprises a counter  50  and a multiplexer  48 . The multiplexer  48 , similar to the first embodiment, is connected between the network transmission line  19 , and the transmitting port Tx 2  and receiving port Rx 2 . The multiplexer  48  has a first differential input pair (input port  52 A and  52 B), a second differential input pair (input port  54 A and  54 B), a first differential output pair (output port  56 A and  56 B), and a second differential output pair (output port  58 A and  58 B). The two pairs of input and output ports can be switched in response to a control signal, transmitted from the counter  50 , of a control end  60 . The counter  50  comprises two counting units  46 A and  46 B. The counting unit  46 A counts the number of signal pulses on the first differential input pair whereas the counting unit  46 B counts the number of signal pulses on the second differential input pair. The counter  50  determines the connection polarity of the network transmission line  19  in response to a counting result of the counting units  46 A and thus controls the multiplexer  48  via the control end  60  to properly connect the network transmission line  19  with the transmitting port Tx 2  and receiving port Rx 2 .  
         [0025]    The present invention can detect and further correct the connection polarity of network transmission line  19  by the detecting circuit  44  installed in the client  22  regardless of if the port C 1  or C 2  of the other client  21  is a transmitting port or a receiving port. Suppose that initially the ports C 1  and C 2  of client  21  are connected through the multiplexer  48  to transmitting port Tx 2  and receiving port Rx 2  respectively. The counting units  46 A and  46 B count the number of signal pulses on the lines between the port Cl and the transmitting port Tx 2 , and the port C 2  and the receiving port Rx 2  respectively. The counter  50  compares the transition numbers of signals of the counting units  46 A and  46 B, and any significant difference between these numbers of signals, as illustrated by the waveforms  18  and  20  in FIG. 2, means that the port C 1  is a transmitting port and the port C 2  is a receiving port, so the connection polarity is inverted. A relative too large transition numbers of signals at a counting unit than the other transition number represents that the two ports connected at both ends of the line are transmitting ports, while the other two ports connected at both ends of the line are receiving ports. After determining an incorrect connection polarity, the counter  50  will control the multiplexer  48  to switch the connection polarity between the input pairs and the output pairs. That is, the input ports  52 A and  52 B will be connected to the output ports  58 A and  58 B, and the input ports  54 A and  54 B will be connected to the outputs port  56 A and  56 B. Thus, the determined transmitting port C 1  will be correctly connected to the receiving port Rx 2  and the determined receiving port C 2  will likewise be correctly connected to the transmitting port Tx 2 .  
         [0026]    On the other hand, if the numbers of signals at counting units  46 A and  46 B are almost equal, then the connection polarity of the network transmission lines  19  will be taken as correct. That is, port C 1  is the receiving port and the port C 2  is the transmitting port of the client  21 . According to this comparison result for the two counting units, the counter  50  determines that the connection polarity of the network transmission line  19  is correct and, of course, needs not to switch the connection state of the multiplexer  48 .  
         [0027]    Practically, if the difference between the totals counted by the two counting units  46 A and  46 B exceeds a predetermined value, set according to the characteristic of the network signals, the connection polarity is inverted. If the difference between these two totals is not large enough to exceed the predetermined value, the connection polarity is correct. Each counting unit ( 46 A and  46 B) can comprise a comparator for comparing voltage levels of transmission signals with a predetermined voltage level, and a Schmitt trigger for generating signal pulses. According to the comparison, the Schmitt trigger can further prevent glitches.  
         [0028]    In contrast to the prior art, the present invention provides a method and related apparatus for detecting the connection polarity of a network transmission line so that an inverted connection polarity of the transmission line can be corrected.  
         [0029]    Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.