Megger - Alien Crosstalk Testing with a Review of Structured Cabling Parameters

Alien Crosstalk Testingwith iha Review ofStructured CablingParameters

Agenda• Category frequencies & LAN standards• Review of structured cabling parameters• Alien Crosstalk• What is alien crosstalk• Where does alien crosstalk occur in thelink• Standards & guidelines defining aliencrosstalk• Creating a quality plan to addressrequirements• Link performance requirements• Link certification

Cabling FrequenciesFrequency 1 MHz 16 MHz 100 MHz 250 MHz 500 MHzCategory 3Category 5(obsolete)Category5eCategory 6Category6A

Cabling - Ethernet StandardsEthernetStandard10BASE-T100BASE-T1000Base-T10GBASE-TCategory 3Category 5(obsolete)√√Category√ √ √5eCategory 6√ √ √ √*Category6A√ √ √ √*N t d d f i t ll ti*Not recommended for new installations*May not meet extended performance and AXT requirements√

ANSI/TIA-568-C.2 CablingParameters• Wiremap• Delay & Delay Skew• Length• Insertion Loss• Return Loss• NEXT & PSNEXT• ACR-F & PSACR-F(Attenuation to Cross TalkRatio Far, previously calledELFEXT)* Alien Cross Talk• PSANEXT*• Average PSANEXT*• PSAACRF*• Average PSAACRF*

Wiremap• Wiremap determines how the individualconductors are connected from one end ofthe link to the other.

Typical Wiring Possibilities

Delay• Propagation delay determines the time (nS)required for a signal to travel from one endof the link to the other.• The propagation delay of each pair may beslightly different due to differences in thetwist rate and insulation materials of eachpair

(Propagation Delay) Skew• Delay skew calculates the difference in time(nS) between the delay of the shortest pairand that of the other three pairs

Length• The length of each pair may appear slightlydifferent due to differences in the twist rateand insulation materials of each pair

Length Calculation• Length is calculated from the measured delay and thecable NVP (Nominal Velocity of Propagation)• NVP - The speed at which a signal moves through acable, expressed as a percentage or fraction of the speedof light in a vacuum. (NVP < 1)• A incorrect NVP setting will result in an inaccurate lengthcalculationl • It is desirable if the tester has a library of manufacturers’cables including their NVPs, and can calculate the NVP ofunknown cable

Insertion Loss• Insertion loss determines the signalamplitude loss as it travels from one end ofa link to the other• Insertion loss is caused by link componentsthat impede or reflect a transmitted signal

Return Loss• Return loss determines the amount of signal that isreflected when a transmitted signal is applied to a link.Return loss is expressed as a ratio of the reflected totransmitted signal• Signals are reflected by impedance changes in the link• Impedance changes are due to a pair’s twist ratiochanging, distortion ti in the cable and connector impedancemismatch

Return Loss Evaluation• If the insertion loss is less than 3.0 dB at any frequency point,return loss at that frequency point will not be evaluated• If the insertion loss is less than 3.0 dB at all frequency points,return loss will be marked as information and will not beevaluated• *TIA only►

Near-End Crosstalk (NEXT)• NEXT measures the power of a reflected signal on a pairthat coupled from a transmitted tted signal on a different e pair.NEXT is expressed as a ratio of the reflected totransmitted signal• Undesirable coupling occurs if incorrect cable orconnectors are used or connectors are poorly wired• Testers with vector measurement capability canaccurately locate sources of NEXT in a link

Power-Sum Near-End Crosstalk(PSNEXT)• PSNEXT is an extension of pair-to-pairpNEXT• PSNEXT calculates the power summationof individual pair NEXT from threedisturbing pairs on to one victim pair.

Far End Crosstalk (FEXT)• Far End Crosstalk is similar to Near EndCross Talk (NEXT), except that the signal issent from the local end and crosstalk ismeasured at the far end.

Attenuation Crosstalk Ratio-Far End (ACR-F)• ACRF is a calculation of the measured FEXT minus the insertion loss[ ACR-F = FEXT (dB) – Insertion Loss (dB) ]• FEXT measures the power of a received signal at the end of the linkon one pair that coupled from a transmitted signal at the beginning ofthe link on different pair• Simply put, ACR-F is a length-independent method for calculating thesignal power that was transmitted into one end of the link on a pairand arrived at the other end of the link on a different pair

Power-Sum Attenuation CrosstalkRatio-Far End (PSACR-F)• PSACR-F Fis an extension of pair-to-pair i ACR-F• PSACR-F calculates the power summation ofindividual pair ACR-F from three disturbing pairson to one victim pair.

What is AlienCrosstalk

What is Alien Crosstalk• Alien crosstalk (AXT) is a unwanted disturbing signal couplingfrom one balanced twisted-pair component, channel orpermanent link to another• The term “Alien” is used because unlike pair to pair crosstalk,alien crosstalk is a disturbing noise source that originates fromoutside the affected link’s cable and components

History - Alien Crosstalk• In 2006 the IEEE ratified 10GBASE-T and later published IEEE 802.3-2008 defining a version of Ethernet with a nominal data rate of 10Gbit/s, ten times faster than Gigabit Ethernet• Achieving 10GBASE-T over copper required new encoding schemes,500MHz bandwidth and full duplex transmission• Due to these changes alien crosstalk, which h has always been presentin twisted pair copper networks and cannot currently be cancelled,became a significant noise source capable of disrupting 10GBASE-T• In response the industry defined new standards and guidelines foracceptable levels of alien crosstalk and developed test methods formeasuring alien crosstalk

Reflected Mode of AlienCrosstalk Near end alien crosstalk is a reflectedmode that is sourced and received at thesame ends of the disturbing and disturbedlinks

Transmitted Mode of AlienCrosstalk• Far end alien crosstalk is atransmitted mode that is sourcedand received at opposite ends ofthe disturbing and disturbed links

Where Does AlienCrosstalk Occur in theLink

Where Does Alien CrosstalkOccur• Alien crosstalk occurs between the cables and components ofa disturber link and a disturbed (victim) link• Alien crosstalk coupling increases as the components andcables of the two links approach each other• Alien crosstalk is extremely dependent upon installationpractices such as patch cord positioning, cable bundling, useof tie-wraps, pathway fills and component placement• Alien crosstalk is not simply limited to a single disturbing link,multiple disturbing links may add to the total alien crosstalkpresent on a disturbed link

Alien Crosstalk in theHorizontal Link• Alien crosstalk occurs whendifferent cables run in parallel foran extended distance in closeproximity• Long, tightly bound cable bundlespresent an ideal location forsignificant levels of alien crosstalk• A worst case condition existswhen a disturbed (victim) cable issurround by six disturbing cables

Alien Crosstalk in Cords• Alien crosstalk occurs whendifferent equipment and patchcords are routed together inclose proximity• Bound cords present an ideallocation for significant levels ofalien crosstalk in the first fewmeters of the link• Management bar lay andwaterfalls also presentopportunity for alien crosstalk

Alien Crosstalk inComponents• Alien crosstalk occurs wherecomponents of different linkscome into close proximity• Patch panels present an ideallocation for significant levels ofalien crosstalk• A worst case condition existswhen a disturbed port issurrounded on three or foursides by disturber ports

Standards & GuidelinesDefining Alien Crosstalk

Standards Defining AlienCrosstalk• ISO/IEC 11801 Ed 2.0 Amendment 1 provideschannel and alien crosstalk requirements for ClassE A , Class F and Class F A• BS EN 50173-1 A1 provides channel and aliencrosstalk requirements for Class E A , Class F andClass F A• ANSI/TIA-568-C.2 provides channel, permanentlink and alien crosstalk requirements for Category6A

Guidelines Defining AlienCrosstalk• Guidelines provide methods for re-characterizing installedClass E and Category 6 cabling to ensure 10GBASE-Toperation• ISO/IEC TR 24750 and CLC/TR 50173-99-1:2007 bothprovide channel and alien crosstalk recommendations forinstalled Class E• TIA TSB-155 provides channel, permanent link and aliencrosstalk recommendations for installed Category 6• Class E and Category 6 cabling is not recommended fornew installations supporting 10GBASE-T operation

Creating aQuality Plan

Cable Considerations• UTP Class E A and Category 6A cables with improvedalien crosstalk performance may be constructed with aninner separator, a larger outside wall thickness and anincreased cable diameter.• Cable alien crosstalk performance can be compromisedby deforming the outer jacket or inner separator due to tiewraps, excessive conduit/pathway fill or exceedingrecommended bend radius.•• Pathway and conduit fill ratios increase for the samenumber of cables if the cable diameter increases

Cord and ComponentConsiderations• UTP Class E A and dCategory 6A equipment and patchcords typically have a larger outside wall thickness toreduce alien crosstalk• Cord alien crosstalk performance can be compromised bydeforming the outer jacket due to tie wraps and exceedingrecommended bend radius• Compacting cords in management bars and trays bringscords into closer proximity increasing alien crosstalk in thecritical first few meters of the link• UTP Class E A and Category 6A patch panels are typicallylower density than Class E and Category 6

Reducing Alien Crosstalk• Minimize the number of cables in a bundle, reducing thenumber of possible disturbers• Un-bundle the horizontal link in the first 15 meters allowingthe cables to separate• Eliminate cable ties if possible, if not reduce cable tietension and space cable ties farther apart• Randomly lay cable in trays to prevent any two cablesfrom running in close proximity their entire length• Use F/UTP or S/FTP cables and cords to significantlyreduces alien crosstalk• Cont.

Reducing Alien Crosstalk(cont)• Separate equipment and patch cords and eliminate cableties to reduces the alien crosstalk coupling in the first fewmeters of the link• Lay cords randomly in management bars to prevent anytwo cords from running in close proximity their entirelength• Reduce the number of cords in a waterfall and maximizethe radius to reduce cord compaction• Use fully shielded components to significantly reduce aliencrosstalk

Alien Crosstalk Consideration• Alien crosstalk is extremely dependent uponinstallation practices such as patch cord positioning,cable bundling, use of tie-wraps, pathway fills andcomponent placement• Alien crosstalk certification is unique, its a selectiveprocess using statistical data about the installationto identify and certify the links deemed most proneto alien crosstalk interference• Certifying alien crosstalk on each Class E A /F/F A andCategory 6A link or re-certifying i alien crosstalk oneach Class E or Category 6 link may not benecessary nor plausible due to test times• Cont.

Alien Crosstalk Consideration(cont)• Alien crosstalk testing consumes significantly more time thanchannel or link testing• Worst case instrument test time for a single disturbed linktesting PSANEXT and PSAACRF at both ends of the link# of Disturbing Worst Case Instrument TestLinksTime1 1.5 minutes2 3 minutes4 6 minutes8 12 minutes

Additional Guidance• Seek guidance from cable and componentmanufacturers for installing and certifying ClassE A /F/F A or Category 6A links• Seek additional guidance from cable andcomponent manufacturers for identifying andselecting disturbed and disturbing links for aliencrosstalk certification• Consult ISO/IEC TR 24750, CLC/TR 50173-99-1:2007 or TIA TSB-155 for determining the ClassE or Category 6 alien crosstalk environment andalien crosstalk mitigation techniques

Create a Quality Plan• Create a quality plan that considers how theselection and installation of cable and componentsaffects the alien crosstalk environment• The quality plan should identify changes to theinstallation brought on by Class E A /F/F A or Category6A components• The quality plan should address alien crosstalkcertification, including identification & selection oftest links and criteria for obtaining satisfactoryperformance• A Class E and Category 6 quality plan shouldaddress alien crosstalk mitigation practices• Obtain agreement from all parties• Cont.

Create a Quality Plan (cont)• A good quality plan thatconsiders and incorporates theelements in the previous slideswill reduce installation ti andcertification time whileincreasing confidence ininstallation’s ability to meetalien crosstalk requirements

Link PerformanceRequirements

Performance 10GBASE-T Class E& Category 6• Pair measurements– Wiremap– Delay/DelaySkew/Length*– Resistance**• Pair to pair performanceextended to 500MHz– Insertion Loss– Return Loss– NEXT & PSNEXT– ACR-N & PSACR-N**– ACR-F & PSACR-F• Alien crosstalk added 1-500MHz– PSANEXT– Average PSANEXT– PSAACRF– Average PSAACRF– Marginal Computation* Not a recognized Class E measurement** Not a recognized Category 6 measurement

Performance Class E A &Category 6A• Pair measurements– Wiremap– Delay/DelaySkew/Length*– Resistance**• Pair to pair performance 1-500MHz– Insertion Loss– Return Loss– NEXT & PSNEXT– ACR-N & PSACR-N**– ACR-F & PSACR-F• Alien crosstalk 1-500MHz– PSANEXT– Average PSANEXT– PSAACRF– Average PSAACRF* Not a recognized Class E A measurement** Not a recognized Category 6A measurement

Performance Class F• Pair measurements– Wiremap– Delay/Delay Skew– Resistance• Pair to pair performance 1-600MHz– Insertion Loss– Return Loss– NEXT & PSNEXT– ACR-N & PSACR-N– ACR-F & PSACR-F• Alien crosstalk added 1-600MHz– PSANEXT– Average PSANEXT– PSAACRF– Average PSAACRF

Performance Class F A• Pair measurements– Wiremap– Delay/Delay Skew– Resistance• Pair to pair performance 1-1000MHz– Insertion Loss– Return Loss– NEXT & PSNEXT– ACR-N & PSACR-N– ACR-F & PSACR-F• Alien crosstalk 1-1000MHz– PSANEXT– Average PSANEXT– PSAACRF– Average PSAACRF

Power Sum Alien NEXT(PSANEXT)• PSANEXT sums four near end alien crosstalk measurementsfrom each pair of the disturbing link to a single pair of thedisturbed link• Four PSANEXT results are calculated at the end of a disturbedlink for a total of 8 results if both ends are tested

Power Sum Alien ACRF(PSAACRF)• PSAACRF sums four far end alien crosstalk measurementsfrom each pair of the disturbing link to a single pair of thedisturbed link• Four PSACRF results are calculated at the end of a disturbedlink for a total of 8 results if both ends are tested

Average PSANEXT &PSAACRF• Average PSANEXT is the average of the PSANEXTresults on each of the disturbed link pairs• Average PSAACRF is the average of the PSAACRFresults on each of the disturbed link pairs• One Average PSANEXT or PSAACRF result is calculatedgat the end of a disturbed link for a total of 2 results if bothends are tested

Alien Crosstalk MarginComputation• The alien crosstalk margin computation is used if thePSANEXT or the PSAACRF limits are not met on Class Eor Category 6 links• The alien crosstalk margin computation ensures that thetotal combined PSAFEXT and PSANEXT that couples intoa channel is limited in order to maintain the 10GBASE-Tminimum signal to noise ratio• The alien crosstalk margin calculation l is a sufficienti qualification for suitability of Class E or Category 6channels to support 10GBASE-T operation

Link Certification

Certifying Class E A /F/F A &Category 6A• Certify the channel or link performance of every linksaving the Autotest result and graphical data• Using the test plan criteria and result data, identifythe disturbed links deemed most prone to aliencrosstalk interference and their associated disturbinglinks• Per the test plan criteria, select from the identifiedlinks those disturbed and disturbing links that requirealien crosstalk certification• Certify the alien crosstalk of the selected disturbedlinks per the test plan

Re-certifying Class E &Category 6• Re-certify the channel or link performance of every linkdesignated to support 10BASE-T saving the Autotestresult and graphical data• Using the test plan criteria and result data, identify thedisturbed links deemed most prone to alien crosstalkinterference and their associated disturbing links• Re-test the channel or link performance of all identifieddisturbing links saving the Autotest result and graphicaldata*• Certify the alien crosstalk of the selected disturbed linksper the test plan*Links designated only as a disturber do not have to pass channel or link certification

Typical PSANEXT Test Setup

Typical PSAACRF Test Setup

Conclusion• Alien crosstalk is a unwanted disturbing signal couplingfrom one balanced twisted-pair component, channel orpermanent link to another• Alien crosstalk is extremely dependent upon installationpractices and occurs where links come into closeproximity such as in cable bundles and patch panels• ISO/IEC 11801 Ed 2.0 Amendment 1 and BS EN 50173-11A1 provide channel and alien crosstalk performancerequirements for Class E A /F/F A links• ANSI/TIA-568-C.2 provides channel or link and aliencrosstalk performance requirements for Category 6A links• Cont

Conclusion (cont)• ISO/IEC TR 24750 & CLC/TR 50173-99-1:2007provide guidance for supporting 10GBASE-T onClass E channels• TIA TSB-155 provides guidance for supporting10GBASE-T on Category 6 channels and links• Create a quality plan addressing the uniquerequirements for installation, certification and aliencrosstalk mitigation prior to starting• A good quality plan will reduce installation andcertification time while increasing confidence ininstallation’s ability to meet alien crosstalkrequirements