Abstract:
A method and apparatus for monitoring telecommunication lines. A switch is disposed between the telecommunication lines to be monitored and a jack which is connectable to a signal monitoring device. The switch is positionable into a neutral position for permitting connection of the signal monitoring device to the jack and at least a second position where the signal monitoring device may monitor the signals of the telecommunication lines.

Description:
FIELD OF THE INVENTION 
     The present invention relates to electrical test equipment and more particularly to telecommunications test equipment. 
     BACKGROUND OF THE INVENTION 
     When troubleshooting telephone lines, it is desirable to monitor the signal on the line of interest without introducing noise or other spurious signals onto the line being monitored. Such monitoring has been performed in the past by placing a high impedance signal monitoring device across the line. This required gaining access to the line by, for example, electrically connecting some form of monitoring connector, such as a jack, across the line. The very act of inserting a monitor plug or similar connector into the jack, however, can diminish the accuracy of the monitoring process. 
     SUMMARY OF THE INVENTION 
     The present invention relates to apparatus for monitoring telecommunication signals on at least two telecommunication lines. The apparatus includes a jack having at least two terminals which are electrically connectable to a signal monitoring device. A switch having a neutral position and at least one operative position enables selective switching of the terminals of the jack from an electrically disconnected position with respect to the telecommunication lines to a position which electrically connects the terminals of the jack across selected ones of the telecommunication lines. The signal monitoring device is connected to the jack while the switch is in neutral position. Thereafter, the switch is moved to an operative position electrically linking the signal monitoring device to the telecommunication lines. The apparatus reduces spurious signals, spikes, noise and other distortion which occurs when a signal monitoring device is directly connected to a telecommunication line monitoring jack without an intervening switch mechanism. In addition, the apparatus permits signal monitoring of both incoming and outgoing telecommunications lines. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an electrical schematic of a prior art telecommunications monitoring apparatus; 
     FIG. 2 is an electrical schematic of an embodiment of a telecommunications monitoring apparatus in accordance with the present invention; 
     FIG. 3 is a schematic diagram of a system employing the apparatus depicted in FIG. 2 connected to two network elements; and 
     FIG. 4 is a schematic diagram of a further system employing a cross-connected pair of the apparatus depicted in FIG. 2 also connected to two network elements. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As depicted schematically in FIG. 1, there is shown a typical arrangement for monitoring the output signal of telephone lines. An input signal may be applied to telecommunications input signal lines  100  at an input jack  102  or to input terminals  104  which are electrically connected to the input signal lines  100 . The output signal appears at output jack  106  or at output terminals  108 . 
     The output signal is normally monitored by inserting a plug, which is electrically connected to a signal monitoring device, not shown, into a monitor jack  110  . The terminals of the monitoring jack  110  are electrically connected to telecommunications output signal lines  112  through a pair of resistors  114 . Thus, in order to monitor the signal, a plug, which is electrically connected to the terminals of the monitoring device, is inserted into the jack which is electrically connected across the line. However, insertion of the plug into the jack can itself cause perturbations in the signal being monitored even though an attempt has been made to minimize such perturbations by use of the resistors  114 . 
     Referring to FIG. 2, there is shown an electrical schematic of an apparatus according to the present invention for monitoring telecommunications signals, generally designated  200 . The apparatus  200  includes an input jack  202  which is electrically connected to a pair of input signal lines  204 . Input terminals  206  are also electrically connected to the input signal lines  204  through contacts  208  of the input jack  202 . An output jack  210  is electrically connected to a pair of output signal lines  212 . Output terminals  214  are also electrically connected to the output signal lines  212  through contacts  216  of the output jack  210 . The terminals  217  of a monitor jack  218  are electrically connected to the poles of a double pole, double throw, DPDT, switch  220 . The DPDT switch  220  has a neutral position as shown in FIG. 2. A first set of contacts  222  of the DPDT switch  220  are electrically connected to the input signal lines  204  through resistors  224 . A second set of contacts  226  of the DPDT switch  220  are electrically connected to the output signal lines  212  through resistors  228 . 
     An input signal is applied to input signal lines  204  by either inserting an input signal plug which is electrically connected to a signal source, not shown, into the input jack  202  or by applying the input signal to input terminals  206 . These two different modes of applying the input signal are mutually exclusive since, as shown in FIG. 2, inserting the input signal plug into the input jack  202  will cause the contacts  208  to open thereby disconnecting the input terminals  206  from the input signal lines  204 . The input signal is coupled to a network element, not shown, by the input signal lines  204 . An output signal is coupled from the network element to the output jack  210  and the output terminals  214  by the output signal lines  212 . The output signal is accessed at either the output terminals  214  or by an output signal plug, not shown, inserted into the output signal jack  210 . These two different modes of accessing the output signal are mutually exclusive since, as shown in FIG. 2, inserting the output signal plug into the output jack  210  will cause the contacts  216  to open thereby disconnecting the output terminals  214  from the output signal lines  212 . 
     The apparatus  200  operates as follows. A telecommunications signal is applied to the input signal lines  204  by either applying the signal directly to the input terminals  206  or by inserting a plug, which is electrically connected to the telecommunications signal source, into the input signal jack  202 . The signal is coupled to a network element, not shown, by the input signal lines  204 . An output signal from the network element is coupled to the output jack  210  and the output terminals  214  by the output signal lines  212 . Either or both of the input signal and the output signal is monitored by inserting a plug, which is electrically connected to a signal monitoring device, not shown, into the monitor jack  218 , preferably when the DPDT switch  220  is in the neutral position shown in FIG.  2 . 
     To monitor the input signal, the DPDT switch  220  is switched to a first position whereby the terminals  217  of the monitor jack  218  are electrically connected to the input signal lines  204  through resistors  224 . The resistors  224  minimize the effect on the input signal caused by connecting the monitoring device across the input signal lines  204  when the DPDT switch  220  is switched to the first switch position. To monitor the output signal, the DPDT switch  220  is switched to a second position whereby the terminals  217  of the monitor jack  218  are electrically connected to the output signal lines  212  through resistors  228 . The resistors  228  minimize the effect on the output signal caused by connecting the monitoring device across the output signal lines  212  when the DPDT switch  220  is switched to the second switch position. 
     Thus, in order to monitor either the input signal or the output signal, the signal monitor plug, which is electrically connected to the monitoring device, is inserted into the monitor jack  218 , and the DPDT switch  220 , which is initially in the neutral position when the monitor plug is inserted into the monitor jack  218 , is switched to either the first position, which electrically connects the terminals  217  of the monitor jack  218  across the input signal lines  204  through resistors  224 , or the second position, which electrically connects the terminals  217  of the monitor jack  218  across the output signal lines  212  through resistors  228 . Because the DPDT switch  220  is in the neutral position initially, insertion of the monitor plug into the monitor jack  218  will have no effect on either the input signal or the output signal. 
     Referring to FIG. 3, there is shown a telecommunications system  300  comprising a monitoring apparatus  302  linked to a first network element  304  and a second network element  306 . Monitoring apparatus  302  is constructed substantially similar to apparatus  200  described above, and the first and second network elements  304 , 306  may include, without limitation, MUX (a multiplexer that combines several digital signals, for example, 28 DS1 signals, into a high bit-rate signal; for example, one DS3 signal, and vice versa), fiber terminal, (DACS) and the like. DACS is an electronic digital crossconnect system manufactured by Lucent Technologies Network Systems that has the capability to rearrange the digital signal components of a particular transmission rate. For example, the DACS I and II systems can rearrange the DSO components of DS1 signals, and the DACS IV-2000 can rearrange the DS1 components of a DS3 signal. The DACS III-2000 cross connects DS3 signals with no component rearrangement. 
     Monitoring apparatus  302  is powered and grounded by power and ground lines  308 . Apparatus  302  connects the network elements  304 ,  306  such that the output signal of one network element ( 304  or  306 ) serves as the input signal of the other network element ( 304  or  306 ) wherein “T” and “R” respectively represent the tip and ring lines of the input and output signal lines. Additionally, monitoring apparatus  302  preferably includes a tracing lamp  310 . The tracing lamp  310  may be a lamp or light-emitting diode (LED) located on the front or rear of the module that aids the craft in locating the two ends of a cross-connect or interconnect circuit. 
     By disposing the DPDT switch  312  from neutral position “2” to active positions “1”or “3”, one may selectively monitor the coupled input and output signals of the first and second network elements  304 ,  306 . 
     FIG. 4 illustrates a telecommunications system  400  comprising a pair of cross-connected monitoring apparatus  402 . Apparatus  402  are constructed substantially similar for apparatus  200  and are serially linked to a first network element  404  and a second network element  406 . Similar to system  300 , the output signal of one network element ( 404  or  406 ) serves as the input signal of the other network element ( 404  or  406 ). Each network element  404 ,  406  is powered and grounded by power and ground lines  408  and each preferably includes a tracing lamp  410 . Among the relative advantages provided by the architectures of systems  300  and  400  is that system  300 , an “interconnect” system of termination, requires no additional wires and only one module to complete a circuit. The “cross-connect” system  400  requires that two modules be used to complete a circuit. However, a cross-connect system, unlike an interconnect system, allows identification of, and connection to, new and/or other types of equipment. 
     It should be understood that various changes in the details, materials and arrangement of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the principle and scope of the invention as described in the following claims.