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.Signals that enter the cable at the same time willprobably be slightly out-of-sync when they get to the far end.This is referred to as delay skew.Sloppy termination canmagnify this problem if the cables are asymmetric withrespect to the connector pins.A difference in propagationdelay between the wires in a cable pair can also cause delayskew.80 - 129 CCNA 1: Networking Basics v3.1 Structured Cabling Supplement Copyright © 2004, Cisco Systems, Inc. 6.3.3 Link and channel testingFigure 1 Permanent Link TestThe two methods used when testing are the channel test and the linktest.The channel test goes end-to-end from the workstation ortelephone to the device in the TR.The channel test measures all ofthe cable and patch cords, including the line cord from the jack to theuser equipment and the patch cord from the patch panel to thecommunications equipment.The link test only tests the cable fromthe wall back to the patch panel in the TR.There are two types of linktests.The basic link test measurement starts at the field tester andends at the field tester remote unit at the other end of the link.Thepermanent link test excludes the cable portions of the field test units,but includes the mated connection where the cable is connected to theadapter cable at each end, as shown in Figure 1.The permanent linktest also allows for a consolidation point.This is desirable for openoffice cabling installations and is therefore more practical.The only accepted test is the permanent link test.The channel test hasbeen officially eliminated by TIA/EIA-568-B.1.6.3.4 Certification tipsThe interpretation of test results is just as important as the detectionof problems.Installers can learn how to interpret test results by usingtest equipment on known good wires and circuits.This will provide aknowledge base of how to properly use test equipment and how thetest results should appear when the circuits function properly.To gain experience with troubleshooting and problem identification,create cables with specific problems.Observe how testers react tothese problems.Practice identifying these problems based on testresults for randomly chosen cables.The time invested in educationwill help the installer identify and fix future problems quickly.81 - 129 CCNA 1: Networking Basics v3.1 Structured Cabling Supplement Copyright © 2004, Cisco Systems, Inc. 6.3.5 Professional certification documentationFigure 1 Cable Certification DocumentationMany cable certification tools can export results in a database format.This can be used in a personal computer to produce high-qualitydocuments, as shown in Figure 1.Installation software is generally provided with sophisticatedcertification testers.The software will allow the contractor to presentthe test result to the customer in an orderly manner.The softwareeliminates the need to manually enter the results in a spreadsheet.Software packages store test results as either pass or fail.Whendeficiencies are found and corrected, items are retested and presentedto the customer.Customers generally want both an electronic copyand a paper copy of the test results.Documentation must be accessible to be useful.Electronic deliveryensures that the results are always available when needed.A paper setof both the as-built documents and the certification results should beprovided to the customer.Installers should retain a copy in theirpermanent records.Certification documentation becomes very important when there is aquestion about the quality or accuracy of the wiring job.It shows thaton a specific date, the wires existed in a particular order and couldcarry signals at a specified level of quality.Changes in the ability ofthe cable to move signals over time can be determined by comparingcurrent tests to previous results.Unexpected obstacles, change orders, and last minute equipmentupgrades can affect the documentation.Therefore, the documentationthat was used to construct a network wiring system may not berepresentative of the system that was actually constructed.Anytime amodification is made to the wiring system, it is important to knowwhat is happening in the system.Otherwise, the changes could haveunpredictable effects.As-built documents can help avoid this kind oftrouble.Always create change documents before any changes aremade.82 - 129 CCNA 1: Networking Basics v3.1 Structured Cabling Supplement Copyright © 2004, Cisco Systems, Inc. 6.4 Cutting overCutting over is the term used for the transfer of existing services to anew cable system.It is also used for the installation of new equipmenton a newly installed cable system.6.4.1 Cutover guidelinesSuccessful cutovers require careful planning, organization, andattention to detail.When cutting over, use the following guidelines toensure success:" Keep detailed records of the installation.These records willverify that all cables have been installed in the correctlocations." Test every cable that is installed." Develop accurate cut sheets.Cut sheets are a chart of circuitsand the cables on which they operate.The installationsupervisor normally develops cut sheets with informationreceived from the customer." Schedule the cutover when it is most convenient for thecustomer.Since cutovers usually require taking some systemsoffline, they are often scheduled late at night or on weekends.6.4.2 Removing abandoned cableAccording to the National Electrical Code, edition 2002, allabandoned cables must be removed when certain criteria definedwithin the code are met.Currently, the customer and cableinstallation contractor decide whether or not the cost involved inremoving cables is justified.The customer and contractor must besure to adhere to the local code.Always check with the localauthority and discuss the details with the customer before beginningthe retrofit.Before removing any abandoned cable, first verify that there are nolive circuits on the cable by using a multimeter or a telephone test set.Remove the abandoned cable carefully to avoid damaging ceilingtiles or dropped ceiling support members.83 - 129 CCNA 1: Networking Basics v3.1 Structured Cabling Supplement Copyright © 2004, Cisco Systems, Inc. 7 The Cabling BusinessAs with most jobs, the appearance and demeanor of cable installerscan affect how customers, bosses, and fellow employees perceivethem.The choices a cable installer makes on the job may result inpromotions or terminations.As an employee, the cable installerbecomes a representative of a company.Therefore, a professionalappearance and demeanor should always be maintained.When working on a job, use the following guidelines:" Respect the job site.Be careful to avoid causing damage.Clean up all messes immediately if they affect other workersor clean them up at the end of the day." Wear clean and neat work clothes to the job site." Arrive at an agreed upon time.Punctuality is important." Determine the acceptable noise level.Avoid playing music,whistling, singing, or shouting if working on a retrofit projectwhile business is being conducted." Treat customers, building occupants, coworkers, and bosseswith respect.7.1 Site SurveyThe site survey, or project walk through, is one of the most importantsteps before preparing a cost estimate for a project
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