Abstract:
An Ethernet cable used with an Ethernet test-set allows a single connection to an Ethernet port of a network element while maintaining individual connections to separate ports on the test-set. The far-end of the signal path is a single Ethernet cable port having its transmit and receive pins interconnected. The far-end port interconnections cause a test signal which has traveled to the far-end port to be returned to the test-set and to be receive in a test-set port other than the originating port Two signal paths can be simultaneously tested with the same test-kit. Interconnections between the test-set ports by way of the cable maintain a “no-signal”alarm disabled, which otherwise would be energized because there is no signal being received in the port from which the test signal originated.

Description:
BACKGROUND 
     Ethernet cables and the familiar RJ-45 Ethernet plugs and jacks that terminate these cables are standard communication links for computer systems, telecommunications systems, etc. These links need to be tested, particularly, in telecommunications applications, where they can be made over very long distances, e.g., spanning the United States and beyond, when they are interspersed with non-Ethernet links, such as, e.g., optical links. Therefore, Ethernet cable testing is critical to pre-determine that all Ethernet cable connections are good in a given communication path through one or more networks. 
     After that determination is made, a suite of tests can be run, such as those in accordance with International Telecommunications Union Request for Comments 2544 (ITU-RFC-2544). These tests can determine various parameters for that total communication path including its Ethernet cable connections, such as throughput (to determine the quantity of traffic that can be handled), latency (to determine how long it takes to send a signal round-trip), frame loss (to determine if buffers can handle the traffic load without dropping frames), etc. 
     To this end, Ethernet test-sets, which can be configured as hand-held devices, are commercially available. To determine if the Ethernet connections are good, test signals are sent out from one Ethernet port in the test-set and make a round trip back to the test-set. But, in accordance with the design of these test-sets, the returned test signal cannot be received or accepted in the same test-set port from which the signal was sent. A second Ethernet port is available on the test-set to accept the return signal. Therefore, a dedicated return path connecting to this second Ethernet port must be provided, if that is possible to do under the particular testing constraints involved in a particular test. When the distances involved are great, a separate, dedicated Ethernet cable return path is usually not feasible. 
     Moreover, if there is only one Ethernet port in the network node/element at the far-end of the test path available for test purposes, a separate, dedicated return path would then be unavailable. If a technician jumpers the test signal within the pins of that one available Ethernet port (from transmit pins to receive pins) to return the test signal to the test-set along a path similar to that from which it came, the test fails because the signal ultimately returns to the same Ethernet port on the test-set from which it was sent which is not accepted by the test-sets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A ,  1 B and  1 C are schematic diagrams of a commercially-available Ethernet straight through cable as it would appear disassembled in  FIGS. 1A and 1B , and assembled in  FIG. 1C  with standard straight through RJ-45 connectors on each end; 
         FIGS. 2A ,  2 B and  2 C are schematic diagrams of a commercially-available Ethernet crossover cable as it would appear disassembled in  FIGS. 2A and 2B , and assembled in  FIG. 2C  with standard crossover RJ-45 connectors on each end; 
         FIG. 3  is a schematic diagram of an exemplary arrangement of network elements under test in relation to an Ethernet test-set; 
         FIG. 4  is a schematic diagram of detailed wiring interconnections in a novel Ethernet cable of the type used in the arrangement of  FIG. 3 ; 
         FIG. 5  is a schematic diagram of detailed wiring interconnections in a cable as shown in  FIG. 4  but with additional inter-connections between ports of an Ethernet cable tester to disengage a no-signal alarm; 
         FIG. 6  is a schematic diagram of another exemplary arrangement of network elements under test in relation to an Ethernet test-set and with which another exemplary embodiment; and 
         FIG. 7  is a schematic diagram of detailed wiring interconnections in a novel Ethernet cable of the type used in the arrangement of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In this description, unless otherwise noted, if the same reference numeral is used in different Figs. it refers to the same entity. Otherwise, reference numerals of each Fig. start with the same number as the number of that Fig. For example,  FIG. 3  has reference numerals in the “ 300 ” category and  FIG. 4  has reference numerals in the “ 400 ” category, etc. Also, when the term “signal” is used, it is intended to include the plural “signals” if there is more than one electrical conductor involved in transmitting or receiving signals. Similarly when the term “path” is used, it is intended to include the plural “paths” if there is more than one signal, such as a positive polarity signal and a negative polarity signal, being transmitted and received along such path or paths. 
     In overview, exemplary embodiments of the claimed subject matter relate to Ethernet test-set cables or methods for testing Ethernet cables and their connections. In a first exemplary embodiment, a method is provided for testing Ethernet cables and their connections. The method comprises connecting one end of an Ethernet cable to an Ethernet port of a first network element which is connected to other network elements over a network and connecting two other ends of the Ethernet cable to two Ethernet ports, respectively, of an Ethernet test-set which controls the testing. Thereafter, a test signal is sent from one of the two Ethernet ports over the cable to the Ethernet port of the first network element; and a return test signal is received from the Ethernet port of the first network element over the cable in the other of the two Ethernet ports in the Ethernet test-set. 
     In a second exemplary embodiment, the cable includes first mutually-insulated conductive paths interconnecting a first Ethernet port of an Ethernet test-set and a first Ethernet port of a first network element. There are also second mutually-insulated conductive paths, sheathed together with the first mutually-insulated conductive paths within the cable, interconnecting the first Ethernet port of the first network element to a second Ethernet port of the Ethernet test-set. In a further feature, the transmit pins in the second Ethernet port in the Ethernet test-set can be connected, within the cable, to the receive pins in the first Ethernet port in the Ethernet test-set to prevent the energizing of a no-signal alarm which otherwise would be triggered by the test-set. 
     In a third exemplary embodiment, the cable also includes third mutually-insulated conductive paths interconnecting the second Ethernet port of the Ethernet test-set and a second Ethernet port of the first network element. In addition there are also fourth mutually-insulated conductive paths interconnecting the second Ethernet port of the first network element to the first Ethernet port of the Ethernet test-set. In addition, the first conductive paths, the second conductive paths, the third conductive paths and the fourth conductive paths are sheathed together within the protective exterior of the cable for the entire length of the cable connecting the two ports of the first network element to the two ports of the Ethernet test-set, except for a branching of the cable into two cables at both ends of the cable for connecting to the two ports of the network element and the two ports of the Ethernet test-set. 
     In a fourth exemplary embodiment, the testing method includes transmitting a first test signal from a first Ethernet port of an Ethernet test-set to a first Ethernet port of a first network element within an Ethernet cable over first mutually insulated conductive paths. Then, the first test signal is transmitted from the first network element to a second network element along a first test signal path, the second network element including a far-end Ethernet port with jumpered transmit to receive pins, the far-end port returning the first test signal to the first network element along a second test signal path, where the first and second paths together include Ethernet cables and connections. Then, the method includes returning the first test signal from the first Ethernet port of the first network element to a second Ethernet port of the Ethernet test-set over second mutually insulated conductive paths that are bundled together with the first mutually insulated conductive paths within the cable for the entire length of the cable except for an end of the cable which is unbundled into two cables at the location of the Ethernet test-set. 
     Ethernet ports using RJ-45 connectors can be so-called “straight through cable” connectors or “crossover” connectors. Standard straight-through cable wiring must be used between certain pairs of network entities such as, e.g., between a personal computer (PC) and a network hub or switch. Likewise, standard crossover cable wiring must be used between other certain pairs of network entities such as, e.g., between a first PC and a second PC or between a first hub and a second hub or between a first switch and a second switch. 
       FIGS. 1A ,  1 B and  1 C are schematic diagrams of a commercially-available Ethernet straight through cable as it would appear disassembled and assembled with standard straight through Ethernet RJ-45 connectors on each end. In  FIG. 1A , only the straight-through cable is depicted. The solid lines  101 ,  102 ,  103  and  104  represent conductive paths that connect from pins in Ethernet connector plug  105  at the top of the sketch to other pins in Ethernet connector plug  106  at the bottom of the sketch. The dotted lines represent possible connections between other pins in both connector plugs but which are not being used, at least in this application. 
     In  FIG. 1B , two Ethernet ports  107  and  108  are shown, each including an Ethernet jack having eight mutually-insulated and conductive pins labeled a, b, c, d, e, f, g and h respectively. Alternatively, they could be labeled by the numbers “1” through “8” consecutively. In port  107  at the upper area of  FIG. 1B , the pins are labeled from left to right but in port  108  at the lower area of  FIG. 1B  they are shown as being labeled from right to left where the direction of the labeling is immaterial. In port  107 , pin “a” is associated with the Tx+ signal standing for positive polarity signal transmission; pin “b” is associated with the Tx− signal standing for negative polarity signal transmission; pin “c” is associated with the Rx+ signal standing for positive polarity signal reception; and pin “f” is associated with the Rx− signal standing for negative polarity signal reception. But, the Ethernet jack associated with Ethernet port  108  has a complementary association between signals and pin labels compared with those in port  107 ; for port  108 , pin “a” goes with Rx+, pin “b” goes with Rx−, pin “c” goes with Tx+ and pin “f” goes with Tx−, thereby enabling a “straight through” connection between like-designated pins, as explained in the next paragraph. 
     In  FIG. 1C , the cable from  FIG. 1A  is shown assembled with the ports from  FIG. 1B . As can be seen in  FIG. 1C , in one direction, conductive path  101  connects a positive polarity signal transmitted (Tx+) from pin “a” of port  107  to pin “a” of port  108  where it is received (Rx+). Conductive path  102  connects a negative polarity signal transmitted (Tx−) from pin “b” of port  107  to pin “b” of port  108  where it is received (Rx−). In the reverse direction, conductive path  103  connects a positive polarity signal transmitted (Tx+) from pin “c” of port  108  to pin “c” of port  107  where it is received (Rx+). And, conductive path  104  connects a negative polarity signal transmitted (Tx−) from pin “f” of port  108  to pin “f” of port  107  where it is received (Rx−). Because all of these connections are between the same pin designations in the two connectors (“a” to “a”, “b” to “b” etc.) this is known as a “straight through” Ethernet cable and RJ-45 connector. It matters not if the wiring actually twists within the cable, as shown, or if the cable itself twists, as long as the pin connections for each of the wires within that cable are from pin “a” to pin “a” etc., as explained herein. 
       FIGS. 2A ,  2 B and  2 C are schematic diagrams of a commercially-available Ethernet crossover cable as it would appear disassembled and assembled with standard crossover RJ-45 connectors on each end. In  FIG. 2A , only the crossover cable is depicted. The solid lines  201 ,  202 ,  203  and  204  represent conductive paths that connect from pins in Ethernet connector plug  205  at the top of the sketch to other pins in Ethernet connector plug  206  at the bottom of the sketch. The dotted lines represent possible connections between other pins in both connector plugs but which are not being used, at least in this application. 
     In  FIG. 2B , two Ethernet ports  207  and  208  are shown, each including an Ethernet jack having eight mutually-insulated and conductive pins labeled a, b, c, d, e, f, g and h respectively. Alternatively, they could be labeled by the numbers “1” through “8” consecutively. In port  207  at the upper area of  FIG. 2B , the pins are labeled from left to right but in port  208  at the lower area of  FIG. 2B  they are shown as being labeled from right to left where the direction of the labeling is immaterial. In port  207 , pin “a” is associated with the Rx+ signal standing for positive polarity signal reception; pin “b” is associated with the Rx− signal standing for negative polarity signal reception; pin “c” is associated with the Tx+ signal standing for positive polarity signal transmission; and pin “f” is associated with the Tx− signal standing for negative polarity signal transmission. In this crossover cable instance, the Ethernet jack associated with Ethernet port  208  has an association between signals and pin labels identical to that in port  207 , where its pin “a” also goes with Rx+, pin “b” also goes with Rx−, pin “c” also goes with Tx+ and pin “d” also goes with Tx−. This represents a different usage of pins from that used in the straight-through thereby enabling a crossover connection between unlike-labeled pins, as explained in the next paragraph 
     In  FIG. 2C , the cable from  FIG. 2A  is shown assembled with the ports from  FIG. 2B . As can be seen in  FIG. 2C , in one direction, conductive path  201  connects a positive polarity signal transmitted (Tx+) from pin “c” of port  208  to pin “a” of port  207  where it is received (Rx+). Conductive path  202  connects a negative polarity signal transmitted (Tx−) from pin “f” of port  208  to pin “b” of port  207  where it is received (Rx−). In the reverse direction, conductive path  203  connects a positive polarity signal transmitted (Tx+) from pin “c” of port  207  to pin “a” of port  208  where it is received (Rx+). And, conductive path  204  connects a negative polarity signal transmitted (Tx−) from pin “f” of port  207  to pin “b” of port  208  where it is received (Rx−). Because all of these connections are between different pin designations i.e., from “a” to “c” and from “b” to “1” regardless of which direction the signal is moving, this is known as a “crossover” Ethernet cable and RJ-45 connector. It matters not if the wiring actually twists within the cable as shown, or if the cable itself twists, as long as the pin connections at the ends of the wires within that cable are pins “a” and “c” or pins “b” and “f” as explained above. 
       FIG. 3  is a schematic diagram of an exemplary arrangement  300  of Ethernet connections that are under test, those connections being to, through, and/or between network elements in a network, the arrangement. Ethernet test-set  301  includes at least two Ethernet ports  302  and  303 . Network element  304 , which can be, e.g., a network gateway, hub, switch or router, or can include, but not be limited to, an Add/Drop Multiplexer (ADM), a Reconfigurable Optical Add/Drop Multiplexer (ROADM), a Multi-Service Provisioning Platform (MSPP), or a Digital Cross Connect, etc. can include multiple Ethernet ports, one of which is port  307 . Communication path  305  represents a test signal transmission path from port  302  in test-set  301  to port  307  in network element  304 . Communication path  306  represents a test signal return path from port  307  in network element  304  to port  303  in test-set  301 . These test signal transmission and return paths are part of the complete signal path including all Ethernet connections that are under test, those connections being to and through network element  304 , and between network element  304  and other network elements in a network. (The complete signal path is included, but not shown, in  FIG. 3 .) 
     For example, first network element  304  communicates with second network element  309  by way of transport network  308  which can include, for example, a synchronous optical network (SONET) and/or an optical network transmission (ONT) network or other network. It is possible for transport network to include further Ethernet links, (not shown). Network element  309  can also be, e.g., a network gateway, hub, switch or router, or can include, but not be limited to, an Add/Drop Multiplexer (ADM), a Reconfigurable Optical Add/Drop Multiplexer (ROADM), a Multi-Service Provisioning Platform (MSPP), or a Digital Cross Connect, etc. Network layer one port  312  in network element  304  and network layer one port  313  in network element  309  both interface with transport network  308 , thereby establishing a link  314  through network  308  which would be a link between both layer one ports unless the path were changed to conform with other transmission protocol within cloud  308 . Link  314  is shown as a straight line solely for ease of illustration but it should be understood that this link can be connected through different networks and network connections/elements and can span many thousands of miles across the United States and beyond. Network element  309  also includes multiple Ethernet ports, one of which is located at the far-end of the test signal path and is shown as port  310  with loop  311  inter-connecting its positive polarity Tx+ and Rx+ pins (not shown) as well as its negative polarity Tx− and Rx− pins (not shown) enabling the transmitted test signal to loop-back, essentially transmitting to itself. (The Tx+, Rx+, Tx− and Rx− pins of port  310  are arranged similarly, or identical, to those in any of the ports shown in  FIG. 4 .) 
       FIG. 4  is a schematic diagram of detailed wiring interconnections in a novel Ethernet cable  400  of the type used in the arrangement of  FIG. 3 . This cable is a crossover cable which is required in order to connect between an Ethernet test-set and a network gateway, hub, switch or router, or an Add/Drop Multiplexer (ADM), a Reconfigurable Optical Add/Drop Multiplexer (ROADM), a Multi-Service Provisioning Platform (MSPP), or a Digital Cross Connect, etc. The cable contains a first set of mutually-insulated conductive paths  401  and  402  which interconnect, respectively, Tx+ on pin “c” and Tx− on pin “f” in first Ethernet test-set port  302  with Rx+ on pin “a” and Rx− on pin “b,” respectively, in Ethernet port  307  in first network element  304 . The cable also contains a second set of mutually insulated conductive paths  403  and  404  which interconnect, respectively, Tx+ on pin “c” and Tx− on pin “f” in Ethernet port  307  with Rx+ on pin “a” and Rx− on pin “b,” respectively, in second Ethernet test-set port  303 . The first and second sets of mutually insulated conductive paths are commonly sheathed in cable  400  for the entire length  405  of the cable connecting first network element  304  to Ethernet test-set  301 , but for a branching of the cable into two cables  406  at one end of the cable located at Ethernet test-set  301 . 
     In operation, referring to  FIGS. 3 and 4  together, a test signal is sent from test-set  301  in communication path  305  via wires  401  and  402 . That signal is conducted through the internals of network element  304 , which may include additional Ethernet connections, and by which a corresponding network level one signal, such as an optical signal, is obtained and provided to network level one port  312 . The network level one signal is then transmitted from port  312  over transport network  308  and eventually to network layer one port  313  located in second network element  309 . In second network element  309  the level one signal is converted to an Ethernet signal which is routed within network element  309  to Ethernet port  310  located at the far-end of the test signal path. In port  310 , the signal is looped-back because the pins of port  310  are interconnected so that its Tx+pin (not shown) is connected to its Rx+ pin (not shown) and its Tx− pin (not shown) connected to its Rx− pin (not shown). This interconnection causes the Ethernet signal to begin a return trip with the return signal&#39;s destination being the Ethernet test-set  301 . 
     The return signal is first converted back to a network level three signal in second network element  309  for transmission from level three port  313  over transport network  308  to be received eventually in level three port  312  in first network element  304 . The second, return path through transport network  308  need not be the same as the first, forward path through the network and, indeed, can be substantially different in length and character, and, as noted, the first and second paths can even contain other Ethernet links. But, solid line  314  is provided to show that first and second communication paths, wherever they go, ultimately exist between ports  312  and  313 . In first network element  304 , the return signal is again changed from a level one signal to an Ethernet signal and transmitted through pins “c” and “f” in port  307  and via wires  403  and  404 , respectively, to pins “a” and “b,” respectively, in second Ethernet test-set port  303 . 
       FIG. 5  is a schematic diagram of detailed wiring interconnections in a cable  500  as shown in  FIG. 4  but with additional inter-connections between ports of an Ethernet cable tester to disengage a no-signal alarm All connections in Fig,  5  are identical to those in  FIG. 4  except that connections  501  and  502  of Fig,  5  are added to those in  FIG. 4 . Connection  501  conductively interconnects the Tx+pin “c” of second Ethernet port  303  in Ethernet test-set  301  with the Rx+pin “a” of first Ethernet port  302  in Ethernet test-set  301 . Connection  502  conductively interconnects the Tx+pin “f” of second Ethernet port  303  in Ethernet test-set  301  with the Rx+pin “V of first Ethernet port  302  in Ethernet test-set  301 . The purpose of making these connections with these two jumper wires is to provide a connection to the two receive pins of port  302  which would otherwise appear open to test-set  301 . These jumper connections over-ride a “no signal received” alarm which otherwise would be energized by test-set  301 . This avoids an annoying false alarm while conducting the test. These two jumper wires interconnect pins on both ports  302  and  303  which are otherwise not used in this test procedure and on which there is no signal being transmitted or received, but the connection itself is sufficient to quell the alarm at least for certain kinds of testers. A tester with which this alarm disable is particularly useful is an 1XIA Corporation model 400T or model 1600T tester. 
       FIG. 6  is a schematic diagram of another exemplary arrangement  600  of network elements under test in relation to an Ethernet test-set and with which another exemplary embodiment. In general, in this arrangement both Ethernet test-set ports  302  and  303  receive return test signals on all of their receive (Rx+ and Rx−) pins, so the pin-jumper feature of the embodiment of  FIG. 5  is not needed to quell the no-signal alarm. Advantageously, two network elements, each at the terminus of their respective test signal paths, can be simultaneously tested with the same Ethernet test-set. 
     In particular, Ethernet test-set  301  is again connected to first network element  304  which, in turn, is again connected to second network element  309 , similarly to its connection of  FIG. 3 . This portion of  FIG. 6  involves communication paths  305  and  306 , and link  314  through transport network  308 , which is identical to what is depicted in  FIG. 3 , and operates exactly as described above for operation of  FIG. 3 . Simultaneously with this  FIG. 3  related operation, a “mirror-image” operation can take place between Ethernet test-set  301 , first network element  304  and third network element  604 . Third network element  604  is shown interfacing with transport network  308  which involves a separate test path from that used in  FIG. 3 . 
     Communication path  601  represents a third test signal transmission path from port  303  in test-set  301  to port  603  in first network element  304 . Communication path  602  represents a fourth test signal return path from port  603  in network element  304  to port  302  in test-set  301 . These test signal transmission and return paths are part of the complete second signal path including all Ethernet connections that are under test in that second signal path, those connections being to and through network element  304 , and between network element  304  and third network element  604 . (The complete second signal path is included, but not shown, in  FIG. 6 .) 
     First network element  304  communicates with third network element  604  by way of transport network  308 , which can be, for example, a synchronous optical network (SONET) and/or an optical network transmission (ONT) network or other network. Network element  604  can also be, e.g., a network gateway, hub, switch or router, or can include, but not be limited to, an Add/Drop Multiplexer (ADM), a Reconfigurable Optical Add/Drop Multiplexer (ROADM), a Multi-Service Provisioning Platform (MSPP), or a Digital Cross Connect, etc. Network layer one port  605  in network element  304  and network layer one port  609  in network element  604  both interface with transport network  308 , thereby establishing a link  608  through network  308  between both layer one ports. Link  608  is shown as a straight line solely for ease of illustration but it should be understood that this link can be connected through different networks and network connections/elements and can span many thousands of miles across the United States and beyond. Network element  604  also includes multiple Ethernet ports, one of which is located at the far-end of the signal path and is shown as port  606  with loop  607  inter-connecting its positive polarity Tx+ and Rx+pins (not shown) as well as its negative polarity Tx− and Rx−pins (not shown). (The Tx+, Rx+, Tx− and Rx− pins of port  606  are arranged similarly, or identical, to those in any of the ports shown in  FIG. 7 .) 
       FIG. 7  is a schematic diagram of detailed wiring interconnections in a novel Ethernet cable  700  of the type used in the arrangement of  FIG. 6 . This cable is also a crossover cable which is required in order to connect between an Ethernet test-set and a network gateway, hub, switch or router, or can include, but not be limited to, an Add/Drop Multiplexer (ADM), a Reconfigurable Optical Add/Drop Multiplexer (ROADM), a Multi-Service Provisioning Platform (MSPP), or a Digital Cross Connect, etc. All of the connections in  FIG. 6  that are identical to those in  FIG. 3  were previously described in connection with  FIG. 3  and won&#39;t be repeated. The new connections are as follows. 
     The cable contains a first set of mutually-insulated conductive paths  701  and  702  which interconnect, respectively, Tx+ on pin “c” and Tx− on pin “f” in second Ethernet test-set port  303  with Rx+ on pin “a” and Rx− on pin “b,” respectively, in Ethernet port  707  in first network element  304 . The cable also contains a second set of mutually insulated conductive paths  703  and  704  which interconnect, respectively, Tx+ on pin “c” and Tx− on pin “f” in Ethernet port  707  with Rx+ on pin “a” and Rx− on pin “b,” respectively, in first Ethernet test-set port  302 . The third and fourth sets of mutually insulated conductive paths are commonly sheathed in cable  700  for the entire length  705  or  706  of the cable connecting first network element  304  to Ethernet test-set  301 , but for a branching of the cable into two cables, namely cable-pair  708  located at Ethernet test-set  301  and cable-pair  709  located at network element  304 . 
     In operation, referring to  FIGS. 6 and 7  together, in addition to that operation described above with respect to  FIGS. 3 and 4 , a test signal is sent from test-set  301  in communication path  601  via wires  701  and  702 . That signal is conducted through the internals of network element  304 , which may include additional Ethernet connections, and by which a corresponding network level one signal, such as an optical signal, is obtained and provided to network level one port  605 . The network level one signal is then transmitted from port  605  over transport network  308  to network layer one port  609  located in third network element  604 . In third network element  604  the level one signal is converted to an Ethernet signal which is routed within network element  604  to Ethernet port  606  located at the far-end of this test signal path which is different from the test signal path associated with network element  309 . In port  606 , the signal is looped-back because the pins of port  606  are interconnected so that its Tx+ pin (not shown) is connected to its Rx+ pin (not shown) and its Tx− pin (not shown) is connected to its Rx− pin (not shown). This interconnection causes the Ethernet signal to begin a return trip with the return signal&#39;s destination being the Ethernet test-set  301 . 
     The return signal is first converted back to a network level three signal in third network element  604  for transmission from level three port  609  over transport network  308  to be received in level three port  605  in first network element  304 . The fourth, return path through transport network  308  need not be the same as the third, forward path through the network and, indeed, can be substantially different in length and character, but solid line  608  is provided to show that first and second communication paths exist between ports  605  and  609 . In first network element  304 , the return signal is again changed from a level one signal to an Ethernet signal and transmitted through pins “c” and “f” in port  603  and via wires  703  and  704 , respectively, to pins “a” and “b,” respectively, in first Ethernet test-set port  302 . 
     For ease of reference with respect to reading the claims, the following information is a summary of an association between certain terms recited in the claims and reference numbers in the Figs: Support for these terms is not limited to this association. Ethernet test-set first port may be  302 ; second port may be  303 . First mutually insulated conductive paths may be  305 ; second mutually insulated conductive paths may be  306 ; third mutually insulated conductive paths may be  601 ; fourth mutually insulated conductive paths may be  602 . First network element may be  304 . First network element first port may be  307 , second port may be  603 . Second network element may be  309 . Third network element may be  604 . First and second test signal paths may include paths  314 . Third and fourth test signal paths may include paths  608 . 
     In the preceding specification, various preferred embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. Accordingly, the specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.