when operating gigabit ethernet , local area network data communications systems it is vital to monitor data transmission with an absolute minimum of intrusion or disruption of the data stream . 1000base - t uses a symbol rate of 125 mbaud , but it uses all four pairs for the link and a more sophisticated five - level coding scheme . in addition , 1000base - t sends and receives simultaneously on each pair . combining 5 - level coding and 4 pairs allows 1000base - t to send one byte in parallel at each signal pulse . 4 ( pairs )× 125 msymbols / second × 2 bits / symbol = 1 gbps . the transmission can be simplex or half - duplex mode , or transmission can be in full - duplex mode ( both directions simultaneously , usually using two oppositely - directed simplex channels ). one of the more common families of existing transmission testing apparatus or transmission analyzer ( tas ) has an input impedance of about on hundred ohms . performance criteria for 1000base - t , which is advised to test each link for , includes the return loss and equal - level far end crosstalk ( elfext ) as specified in 1000base - t . return loss is a measure of the reflected energy caused by impedance mismatches in the cabling system . elfext is defined as the measure of the unwanted signal coupling from a transmitter at the near - end into a neighboring pair measured at the far - end relative to the received signal level measured on that same pair . power sum equal level far end cross talk ( pselfext ) is a computation of the unwanted signal coupling from multiple transmitters at the near - end into a pair measured at the far - end relative to the received signal level on that same pair . return loss and elfext have a significantly affect 1000base - t operation . in a local area network , a group of workstations is usually connected to a transmission line or to a digital switch by a circuit called a shared media hub ( smh ), which sends all traffic from one workstation to all the other workstations that it serves in addition to sending that traffic to the switch , if required . unless the smh is connected into the line a - b and left permanently in place , dedicated to testing that transmission line at that node , the transmission must be interrupted and restarted each time that the testing smh is reconnected into the transmission line so that testing can be stared . the transmission would again have to be interrupted to remove the smh for use in a test somewhere else . temporarily taking the transmission line out of service twice whenever the line is to be tested is usually unacceptable to the users of the workstations . leaving the lines untested and letting problems ‘ fester ’ is also sufficiently undesirable as to cause significant task and personal problems ( as any network technician can confirm ). permanently installing smhs at any number of nodes of transmission line for testing purposes only is also unacceptable , when it is considered that each amh can cost about $ 3 , 000 . also , most smhs , as presently available , are for simplex transmission only and would not support the very common full duplex transmissions without addition of a second smh . reasonable cost objectives militate against installing a plurality of paired smhs at strategic locations in a local area network for the sole purpose of facilitating occasional testing of the network at that particular node . the use of impedance - matching coupling transformers is widely known in the digital data communications field , where any transmission is likely to encounter interconnecting devices and media of different impedances . however , for digital data transmission , such coupling transformers are usually designed for use over a limited band of digital transmission speed or rates . it may be theoretically possible to custom design a coupling transformer to meet a very wide frequency bandwidth needed to transmit digital signals at rates of from ten megabaud to significantly over one thousand megabaud . however , it should be highly unlikely that such a custom - made coupling transformer would meet cost objectives ( mentioned above ) in order to permit widespread permanent installation at strategic locations thought a local area network where monitoring and transmission analysis might be desired in the future . impedance matching can also be accomplished using discrete passive electronic devices such as individual capacitors and inductors . however , at such digital transmission speed , design difficulties such as component and conductor placement and orientation pose significant design difficulties , which would be expected to affect adversely upon production yield , and operational time demands . it is theoretically possible to use operational amplifiers to present very high input impedance to a digital transmission line and fairly low output impedance to a transmission analyzer . however , since operation is expected to take place at thousand megabaud speeds , the maximum frequency capability of the operational amplifier must be many times higher than the baud ( bit per second ) of the digital data transmission signal . such high - frequency operational amplifiers exist . however , there are four conductors comprising each simplex transmission line . there must be a separate operational amplifier for each conductor of the transmission line in order to reproduce the positive and negative signals involved . four operational amplifiers connected to the four conductors of a digital data transmission line must have the same maximum frequency capability . otherwise the positive and negative transitions of the amplified digital data signals will lack and thus impair the operation of the digital transmission analyzer . in accordance with one aspect of the present invention , the input terminals of four high - frequency operational amplifiers that are manufactured on a single integrated circuit die are connected to the four conductors of a digital data transmission line serving a local area network . the output terminals of the four operational amplifiers are connected through a suitable impedance match to the input of the digital transmission analyzer . it is an object of the present invention to provide a permanent , inexpensive facility in multiple locations of a local area network to allow monitoring of data transmission traffic without disrupting ongoing data transmission by either interrupting transmission or upsetting its characteristic transmission impedance . it is another object of the present invention to provide an interface or monitor port on a local area data transmission network for use with either simplex and half - duplex transmission or with full duplex transmission . it is still another object of the present invention to provide a monitor port that is sufficiently inexpensive that it can be installed at a plurality of nodes at the initial installation of a local area network transmission system and left in place , permanently . it is another object of the present invention to have an uninterruptible power supply to the tap , in case of power failure , so the potential link signal will not delay any link between the monitored devices , resulting in network data flow interruption . the best embodiment of the present form of the invention uses a passive - link integrity which allows the network communication to flow through the tap even when the power is turned off to either the tap or any of the monitoring devices to which it may be connected . because the network link , to meet 1000 base t standards , will have twinned input and output ports , each of which will have a top and bottom part comprising a impedance - matching coupling transformers , thereby giving the full duplex mode ( both directions simultaneously , using two oppositely - directed simplex channels ). each simplex channel is connected to a splitter , which duplicates the signals flowing over the channel without changing the characteristics otherwise . ( both impedance - matching coupling transformers and splitters are known within the industry .) from the splitter , one line goes back out through the matching impedance - matching coupling transformer , completing that simplex channel through the tap . the other line from the splitter goes through a second splitter where it becomes two lines , which then both through a signal regenerating board , and then through a second pair of splitters where it becomes four lines , each of which now goes to an impedance - matching coupling transformer serving as a monitoring port , to which an analytical or monitoring device can be attached and through which the signal can be monitored and analyzed . it is possible to decrease the number of stages of splitters ( remove the second pair , and only two simultaneous , parallel ports for each simplex channel will exist ) or to increase them , though this will require adding additional signal - regenerating boards . each connection is best thought of as a pair of channels ( a and b ), through which communications flow simultaneously into and then out of the tap . ( in on a , out on b ; and in on b , out on a .) to monitor the communication , the communication flowing on each channel is simultaneously and in parallel duplicated ; where there was a , there is now a and a ′; where there was b , there is now b and b ′. a and b are sent off out of the tap , while the duplicated a ′ and b ′ are now available for monitoring and analysis without affecting the original a or b . for two parallel devices , each of a ′ and b ′ must be duplicated a second time ; for four parallel devices , a ′ and b ′ must be duplicated a second and third time ( 2 * 2 , after all , equals 4 ). these extra steps may require that the signals be regenerated to overcome potential frictional interference and timing delays . in an alternative embodiment of this invention , one of the monitoring ports can become an interactive source for injecting signals into the communications passing through the network link . preferentially , this will be the monitoring port ( 4 d ) closest to the network ports ( 2 a , 2 b ). this port will receive , at the bottom port ( 4 d bottom ) the signal from one simplex channel ( 2 a top ), but not from the second simplex channel ( 2 b top ); instead , the device connected to that now - interactive monitoring port will send out a feedback signal ( through 4 d top ). this interactive signal will be merged with , and override or otherwise interact with , the signal from the second simplex channel ( 2 b , top ) ( which as before will flow through the first splitter ( 10 a - b ) and back towards the other network port ( 2 a )), at a bidirectional splitter ( 25 ) before actually reaching the other the other network port ( 2 a ). while this invention has been described in reference to illustrative embodiments , this description is not to be construed in a limiting sense . various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention will be apparent to those skilled in the art upon referencing this disclosure . it is therefore intended this disclosure encompass any such modifications or embodiments . the scope of this invention includes any combination of the elements from the different embodiments disclosed in this specification , and is not limited to the specifics of the preferred embodiment or any of the alternative embodiments mentioned above . individual user configurations and embodiments of this invention may contain all , or less than all , of the elements disclosed in the specification according to the needs and desires of that user . the claims stated herein should be read as including those elements which are not necessary to the invention yet are in the prior art and are necessary to the overall function of that particular claim , and should be read as including , to the maximum extent permissible by law , known functional equivalents to those elements disclosed in this specification , even though those known functional equivalents are not exhaustively detailed herein . although the present invention has been described chiefly in terms of the presently preferred embodiment , it is to be understood that the disclosure is not to be interpreted as limiting . various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure . such modifications may involve other features which are already known in the design , manufacture and use of network communication taps , and which may be used instead of or in addition to features already described herein . the industry - standard components not specifically detailed herein are not limiting but instructive of the embodiment of the invention , and variations which are readily derived through market or mechanical transformations which are standard or known to the appropriate art are not excluded by omission . accordingly , it is intended that the appended claims are interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention in light of the prior art . additionally , although claims have been formulated in this application to particular combinations of elements , it should be understood that the scope of the disclosure of the present application also includes any single novel element or any novel combination of elements disclosed herein , either explicitly or implicitly , whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention . the applicants hereby give notice that new claims may be formulated to such features and / or combinations of such features during the prosecution of the present application or of any further application derived therefrom .