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By David Green, P.Eng.Convergedcommunications demandnew troubleshooting skillsFigure 1Figure 2Photo © Fluke NetworksWith the escalating move toward voice, data and video(VDV) convergence, today’s cabling installations arebecoming increasingly sophisticated. These newer,high-performance Cat 5e and Cat 6 cabling systems must supportfaster data communication rates and more precise timingof the delivery of VDV information. As a result, professionalsmust know how to test installations to the more complex performancespecifications that have been developed to addresshigher bandwidth requirements.Testing and certification for newer cabling systems entails newtest parameter and link definitions, more data points, higherbandwidth, a higher level of performance and new connectortypes—as well as patch cord requirements. After all, propercertification is the guarantee that the installer left the job ingood working order, and that the installation will perform at thenecessary levels to support a customer-approved SLA (servicelevel agreement).What follows is a brief overview of what you need to knowabout certifying cabling for today’s VDV triple-play installations.There are, in fact, three key areas that you need to considerin the certification process:• The link model: choosing the proper test setupand eliminating a common source of measurement error.• The measurements: what is tested and reportedduring certification.• The diagnostics: when errors are found, how they canbe fixed as rapidly as possible.Link modelsThe term ‘link model’ refers to the configuration of the cabling linkunder test and the manner in which the test equipment is connectedto it. It is important to ensure you are using the correct link modelstandard with the appropriate tester interface hardware.The majority of all certification tests in the field should usethe Permanent Link model, which consists of the cable and thepermanent connectors in the wall outlet or patch panel. Theconnection from the test instrument to the Permanent Link ismade via a Permanent Link Adapter (Figure 1).Keep in mind that the channel link model defines the performanceof the completed end-to-end link as it is used by theoperating network. Therefore, the patch cords that are used toconnect the PC or network device must remain in the link andplugged into the channel adapter of the test instrument.(This is why channel measurements are typically done whenrestoring service, or for verifying cabling for application support. Itis uncommon to perform channel tests during initial installation,since the patch cords are rarely available at that time. See Figure 2.)From a practical standpoint, installers need more sophisticatedfield testers, because they must to be able to measure theperformance of the link without any of the effects of the testcords with which they are connected to the link-under-test.(The reference point for the measurements is not at the testinstrument but at the far end of the test cord.)If the effect of the adapter is not totally transparent, a goodlink can produce a failing test result. The probability of this happeningincreases with the performance requirements. In otherwords, Cat 6 is more likely to produce these false Fail results.So, when performing Permanent Link tests for Cat 6/Class Elinks, it is important to take special care to ensure you are usingadapters that are appropriate for the cabling under test.Certification measurementsLink certification requires a number of complex measurements,which change in degree of precision depending on the categoryof the installed link. For Cat 5e and Cat 6 links, a certificationtool needs to measure or calculate:• Wire map• Propagation delay (delay skew and link length)• Insertion loss• NEXT (Near-End Crosstalk)• Power sum NEXT• ELFEXT (Equal Level Far-End Crosstalk)• Power sum ELFEXT• Return lossThe accuracy level of the certification tool determines its abilityto make these measurements at an appropriate level for the typeof link. For Cat 5e installations, Level IIe defines the minimumrequired accuracy. For Cat 6, a certification tool needs to meetLevel III accuracy. Level IV defines a higher level of accuracy overa wider frequency range to certify the ISO Class F (Cat 7) links.The certification tool must perform the measurements of allrequired test parameters over the prescribed frequency rangefor the category of cabling and with the number of frequencypoints defined in the standards. The test results can be inspectedon the tester or they can be stored in full detail to be inspected▼22 • NOVEMBER/DECEMBER 2007 • www. mag.com
CALENDARNetworking LuncheonOntario Energy Network (OEN)January 16, 2008Toronto, Ont.Visit www.ontarioenergynetwork.organd click OEN EventsNetworking LuncheonOntario Energy Network (OEN)February 13, 2008Toronto, Ont.Visit www.ontarioenergynetwork.organd click OEN EventsUniversity of Industrial Distribution(In Cooperation with Purdue University)March 2-5, 2008Indianapolis, Ind.Visit www.univid.orgPowerTest 2008InterNational ElectricalTesting Association (NETA)March 17-20, 2008New Orleans, La.Visit www.powertest.orgAccubid User ConferenceApril 24-26, 2008Toronto, Ont.Visit www.accubiduserconference.comAnnual Electrical Industry ConferenceOntario Electrical League (OEL)April 30-May 3, 2008Huntsville, Ont.Visit www.oel.orgBC Industrial ExpoAbbotsford, B.C.April 30-May 1, 2008Visit www.bcindustrialexpo.caWILL BETHERE!14th Canadian Skills CompetitionSkills/Compétences Canada (S/CC)May 25-28, 2008Calgary, Alta.Visit www.skillscanada.comLightfair 2008May 26-30, 2008Las Vegas, Nev.Visit www.lightfair.comWILL BE THERE!WILL BETHERE!Annual ConferenceSupply & Distribution (S&D) Council, EFCJune 4-7, 2008Victoria, B.C.Visit www.electrofed.comand click Events, then EFC EventsWILL BETHERE!Annual General MeetingIndependent Electrical Distributors (IED)June 18-20, 2008St. Andrews, N.B.WILL BETHERE!Visit www.ied.ca/events.htmlIndustry ConferenceElectrical Contractors Association ofOntario (ECAO)September 6-13, 2008Costa del Sol, SpainVisit www.ecao.orgWILL BE THERE!WILL BE THERE!CSA_box_EB_Nov07.indd 1Fire Safety Research for Better Building DesignNRC-IRC (National Research Council of Canada, Institute forResearch in Construction)January 15, 2008, Fredericton (English with simultaneous translation)January 24, 2008, Ottawa (English with simultaneous translation)February 5, 2008, Calgary (English)February 7, 2008, Toronto (English)February 19, 2008, Quebec City (French)February 21, 2008, Montreal (French with simultaneous translation)Visit www.bsi.gc.caWILL BE THERE!INFO NO. 2511/28/07 2:26:57 PMMEET (Mechanical ElectricalElectronic Technology)May 7-8, 2008Moncton, N.B.WILL BETHERE!Check EBMag.com and E-Line for updates.WILL BE THERE!▲later on a computer. (Figures 3 and 4 show detailedresults from the NEXT tests across all four pairs, andthe values-by-frequency for a single pair.)Figure 3 Figure 4Advanced troubleshooting diagnosticsKnowing that a test failed is only the first step.Installers must also know how to repair the link so itwill perform as intended. Where performance issuesdo occur, they tend to fall into two distinct categories:connection and/or transmission performance problems.Having expert diagnostics tools on-hand givesyou a more informed starting point from which tobegin the repair process—a far faster and more productiveapproach than the usual trial-and-error.Many tools can provide information regarding theconnection problems, such as an open, a break, ashort, etc. The user should select a tester that can properlylocate a break or a short in the cabling, as well asidentify problems caused by improper wire pairing. Inaddition, certification testers should include advancedtroubleshooting diagnostics that identify and locatetransmission defects.With the growing demand for converged communications,structured cabling represents a growing opportunityfor the professional installer. Advanced testingand certification skills are essential to assure appropriateperformance levels and guarantee the infrastructure willsupport bandwidth requirements. With the right combinationof tools and procedures, you can make the testingphase fast, effective and, ultimately, more profitable.David Green, P.Eng., is director of marketing for Fluke NetworksCanada, and has been involved in technical support, salesand marketing of various technologies for communications,automation, testing and troubleshooting of industrial and commercialsystems for over 30 years. He is also the education programmanager for Fluke, working with educational institutionsglobally to develop industry-education partnerships.INFO NO. 26Hubbell_EB_Sept07.indd 18/29/07 12:57:35 PMwww. mag.com • NOVEMBER/DECEMBER 2007 • 23
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