9.7 Range of Equipment for Testing Structured Cabling Projects 9.7.2 Network operation testing Instructor Note The importance of a baseline measurement of network performance is introduced. The baseline is the set of data about your network that you check periodically to ensure the network is still functioning properly. The IEEE and the TIA/EIA have established standards that allow you to test whether your network is operating at an acceptable level. If your network passes this test and is certified as meeting the standards, you can use this measurement as an established baseline. The baseline is a record of your network's starting point or newly installed performance capabilities.Knowing the baseline measurement is important. Testing does not end just because your network installation is certified as meeting the standards. You should continue to test your network on a regular basis in order to ensure that it performs at its peak. You can do this by comparing current measurements with recorded measurements that were taken when the system was known to be operating properly. If there is a significant change from the baseline measurement, it is an indication that there is something wrong with the network. Repeated testing of your network, and comparisons against its baseline, will help you spot specific network problems that may be caused by aging, poor maintenance practices, weather, or other factors. Web Links Cabling Glossary Network Test Equipment 9.7 Range of Equipment for Testing Structured Cabling Projects 9.7.3 Cable testing equipment Instructor Note The importance of dedicated cable testing equipment is emphasized. You might think that testing cable is simply a matter of substituting one cable for another. This does not, however, provide certain proof of anything, since a common problem can effect all cables on a LAN. For this reason, it is recommended that you use a cable tester to measure network performance. A cable tester is a hand held device that can certify that cable meets the required IEEE and TIA/EIA standards. Cable testers vary in the types of testing functions they provide. Some can provide printouts, others can be attached to a PC to create a data file. Little or no special training is required to use the cable testers that are currently available on the market today. Most competent network administrators or installers find that the operating manuals, supplied by the cable tester manufacturers, provide sufficient instruction. Web Links Cabling Glossary Network Test Equipment 9.7 Range of Equipment for Testing Structured Cabling Projects 9.7.4 Tests performed by cable testers Instructor Note Some basic parameters that cable testers measure are introduced. One example is the Fluke 620 Cablemeter (or equivalent), which can determine cable continuity and pinout, perform cable identification, cable distance, locate bad connections, provide wire maps for detecting crossed pairs, detect split pairs, and trace cable behind walls. Cable testers - have a wide range of features and capabilities. The following list is intended to provide you with a general overview of available functions. You must determine which features best meet your needs, and make your selection accordingly. Cable testers can perform tests that measure the overall capability of a cable run. Examples include the following: determine cable distance locate bad connections provide wire maps for detecting crossed pairs measure signal attenuation measure near-end crosstalk detect split pairs perform noise level tests trace cable behind walls Web Links Cabling Glossary Network Test Equipment 9.7 Range of Equipment for Testing Structured Cabling Projects 9.7.5 Cable testers and distance measurements Instructor Note Distance measurements using TDR -- time domain reflectometry -- are described. Using the formula distance = rate x time, and knowing the rate at which signals travel down a particular medium (which can be measured and calculated, is called the nominal velocity of propagation or NVP, and is entered into the meter by the manufacturer), the meter sends out a pulse and waits for the return "echo" reflection. One half of this time is the time of propagation of the pulse down the cable, and when multiplied by the velocity of signal propagation gives the cable distance. You might think of this a cable radar. It is important to measure the overall length of cable runs, because distance can affect the ability of devices on the network to share the networking media. As you have already learned, cable that exceeds the maximum length, specified by TIA/EIA-568-A, causes signal degradation. Cable testers, sometimes referred to as time domain reflectometers (TDRs), measure the distance to open-ended, or shorted, cable. They do it by sending an electrical pulse through the cable. The devices then time the signal's reflection from the end of the cable. This test is called time domain reflectometry, and can provide distance readings that are accurate to within 61 cm. Web Links Cabling Glossary Network Test Equipment 9.7 Range of Equipment for Testing Structured Cabling Projects 9.7.7 Wire maps Instructor Note Crossed pairs, a common wiring error, are introduced. Cable testers use a feature called a wire map to indicate which wire pairs connect to which pins, on lugs and sockets. The test indicates whether the installer properly connected the wires of a plug or jack, or whether he/she connected them in reverse order. When wires are connected in reversed order, they are referred to as crossed pairs. Unique to UTP cable installations, this is a common problem. When crossed pairs are detected in UTP LAN cabling systems, the connections are not good, and must be redone. Web Links Cabling Glossary Network Test Equipment 9.7 Range of Equipment for Testing Structured Cabling Projects 9.7.8 Split pairs Instructor Note Simple wire mapping meters will not detect split wire pairs; a more sophisticated meter is required. A more sophisticated meter -- such as the Fluke 620 -- is required. Visual inspection and crosstalk measurements are the only ways to detect a condition known as split pairs. As you know, the twisting in wire pairs shields them from external interference from signals that pass near other wire pairs. However, this shielding effect can only occur if the wires in the pair are part of the same circuit. When wires split, they are no longer part of the same circuit. Although current can flow in the circuit, making the system appear to work, no shielding is in effect. Consequently, the signals are not protected. Eventually, near-end crosstalk will become a problem. A wire map cannot detect a split pair condition, because in split pairs, a circuit is still present. Web Links Cabling Glossary Network Test Equipment 9.7 Range of Equipment for Testing Structured Cabling Projects 9.7.9 Signal attenuation Instructor Note It generally requires a fairly expensive cable meter (over $1000) to test signal attenuation. These measurements are described. One such device is the Fluke DSP-2000. Various factors can reduce the power of a signal as it passes through the copper wires used in UTP cables. This reduction in the power of a signal is called attenuation. It occurs because a signal loses energy to a cable. A cable tester can measure the reduction in power of a signal received from a device known as a signal injector - a small box, approximately the size of a deck of playing cards, attached to the far end of a cable. Cable testers generally measure attenuation at several frequencies. Cable testers for CAT 5 cable generally measure up to 100 MHz. Check the TIA/EIA-568-A specifications to see what amount of loss is allowed for the type of cable used in your LAN. Web Links Cabling Glossary Network Test Equipment 9.7 Range of Equipment for Testing Structured Cabling Projects 9.7.10 Causes of near-end crosstalk Instructor Note It generally requires a fairly expensive cable meter (over $1000) to test near-end cross talk (NEXT).. These measurements are described. One such device is the Fluke DSP-2000. Several factors can contribute to near-end crosstalk. The most common cause is crossed pairs. As mentioned earlier, you can detect these with the wire map feature of a cable tester. Near-end crosstalk can also be caused by twisted pairs that have become untwisted after being attached to cross-connect devices (e.g. patch panels) that have patch cords that are untwisted, or by cables that have been pulled too tightly around sharp corners, causing pairs to change position inside the cable jacket. If you measure near-end crosstalk, you should do a visual check of the horizontal cabling, in order to rule out any of these possibilities. If you find nothing, then split pairs have most likely caused the problem. A cable tester measures for near-end crosstalk by measuring a series of frequencies up to 100 MHz. High numbers are good; low numbers indicate problems on the network. Web Links Cabling Glossary Network Test Equipment 9.7 Range of Equipment for Testing Structured Cabling Projects 9.7.11 Problems detected by a noise level test Instructor Note Common noise sources are listed. Many outside factors can contribute to interference on the networking media. Some examples of sources that can produce outside signals that can impose themselves on wire pairs in UTP cable include: fluorescent lights heaters radios air cleaners televisions computers motion sensors radar motors switches welders auto ignitions electronic devices of all kinds Fortunately, signals produced by these outside sources often occupy specific frequencies. This enables an electrical noise level test to not only detect such outside interferences, but to narrow the range of possible sources that produced them. Web Links Cabling Glossary Network Test Equipment 9.7 Range of Equipment for Testing Structured Cabling Projects 9.7.13 Cable testing procedures Instructor Note Students should demonstrate the ability to use simple continuity-level cable testers. Instructors should at least demonstrate cable testing to the level of a Fluke 620 Cablemeter or equivalent. If more Fluke meters (or equivalent) are available, then training all students on these meters will give them enhanced professional skills. If available (perhaps on loan from your regional academy or a local cable installation company), demonstrate the use of the higher end cable testers -- they are truly remarkable devices which measure many of the cable parameters discussed throughout the curriculum. Lab Activity In this lab, you will use the Fluke 620 (or equivalent) to perform cable verification experiments on newly installed cable runs. Your instructor will demonstrate some of the tests that can be performed with a cable tester. In some instances, the tests will indicate that problems exist. You will be asked to outline how you would determine what the problems are, and describe how you would fix them. During the second half of the lab, you will be asked to demonstrate your ability to use a star topology to set up a simple Ethernet LAN. Your instructor will evaluate you on your ability to handle the cable correctly, and to lay, and punch down wires, in a jack, and at a patch panel, so that there are good connections. After you complete the connections for your star topology LAN, you will be asked to test it. If tests indicate problems, you will be asked to diagnose and troubleshoot those problems. The goal in this series of lab exercises is be to produce a completely functional star topology LAN that meets TIA/EIA and IEEE specifications. Web Links Cabling Glossary Network Test Equipment Summary In this chapter, you learned that to ensure that cabling is done thoroughly, accurately, and on time, you should create a flowchart that includes each of the tasks that must be completed, and the order in which they should be performed. Additionally, your flowchart should also include a timeline for each of these tasks: installing outlets installing jacks running cables punching cables into patch panels testing cables documenting cables installing NICs installing hubs, switches, bridges, and routers configuring routers installing and configuring PCs Your cabling plan should include the following: building materials suppliers tools date and length of time tools required Lastly, you learned about installing, string, running cable and the basics of wiring closets and patch panels along with testing cable. In the next chapter, you will start to see how routing and addressing operate at the network layer.
