cohen_1_0103

IEEE802.3 Interim January 200310GBASE-T

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Alien Crosstalk MeasurementsAlien Crosstalk Measurements

Larry CohenSolarflare Communications


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Alien Crosstalk OverviewAlien Crosstalk Overview

How does installation practice affect alien NEXT?

Measurement method and test setup NEXT Measurement results Summary


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Alien Crosstalk Cable Test BedAlien Crosstalk Cable Test Bed

Unbundled cable

Bundled cable


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Alien NEXT Measurement SetupAlien NEXT Measurement Setup

Network Analyzer

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6 dB Splitter

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R A

Cat 5e/6 test cable bundle(horizontal cable)

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50Attenuator

Attenuator matched to lineinterface matching pads

50:100 Interface

Matchingpad

Matchingpad

50:100Interface

100 OhmTerminations

100 OhmTerminations

Cat 5e/6 RJ45patch panels

40 meters

Isolated interconnect span(2 meters patch cord)

1 meterpatch cords

1 meterpatch cords

Six disturber cables

Victimcable

Cable ties

10 cm 10 cm

VictimDisturber

Tight bundle cross-section


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Figure of MeritFigure of Merit

Figure of merit used to compare effects independent of twist pitch

Measure coupling between same wire pairs of victim and disturber cable (i.e. pair 1 disturber cable into pair 1 victim cable, etc) Same twist pitch pair coupling is dominant Reduces number of measurements (96 measurements become 24)

Calibrate out insertion loss from balun (test fixture) and interconnect patch cord (between balun and patch panel).

Calculate power sum of all same pair coupling measurements between the victim cable and six (surrounding) disturber cables

Power sum result is integrated from DC to 500 MHz to obtain total power coupling figure of merit

Figure of merit allows meaningful comparison of visually indistinguishable data plots.


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Effects of Bundling and Cable TypeEffects of Bundling and Cable Type

0 50 100 150 200 250 300 350 400 450 500-70

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Measured Power Sum Alien NEXT Coupling - 6 Disturber Cables

Frequency (MHz)

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Cat 5e bundle = -30.66 dBCat 5e unbundled = -34.41 dBCat 6 bundle = -33.08 dBCat 6 unbundled = -36.51 dBCat 5e PTP NEXT limit = -28.79 dB

All test cases are six disturber cables; two disturbers in adjacent patch panel ports

Unbundling reduces coupling about 4 dB

Cat 6 has 2-3 dB advantage over Cat 5e.

Variation in bundling may be more important than cable category.


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Effect of Bundling ProximityEffect of Bundling Proximity

0 50 100 150 200 250 300 350 400 450 500-80

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-20Measured Power Sum Alien NEXT - Three Disturber Cables

Frequency (MHz)

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Adjacent pairs = -35.08 dBOpposite pairs = -39.83 dBCat 5e PTP NEXT limit

No victim/disturbers in adjacent patch panel ports.

Opposite cables separated by width of one (center) cable over entire span.

Separation reduces coupling 4-5 dB; correlates with unbundled test case.

Disturber cable Victim cableDisturber cables

Victim cable

Opposite pairs Adjacent pairs


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Effects of Patch Panel Port PlacementEffects of Patch Panel Port Placement

0 50 100 150 200 250 300 350 400 450 500-80

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-20Measured Power Sum Alien NEXT Coupling into Victim Cable 4

Frequency (MHz)

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Cable 1 = -44.83 dBCable 2 = -44.61 dBCable 3 = -38.75 dBCable 5 = -39.38 dBCable 6 = -46.17 dBCable 7 = -46.58 dB

Test case is unbundled Cat 5e

Cables on adjacent plug ports of patch panel (cables 3 and 5) are dominant disturbers (> 5 dB)

7 6 5 4 3 2 1

Cat 5e/Cat6 Patch panel

Victim cableDisturber cables Disturber cables


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Adjacent vs. Separated Patch Panel PortsAdjacent vs. Separated Patch Panel Ports

7 6 5 4 3 2 1

Cat 5e/Cat6 Patch panel

Victimport

Separated ports

Adjacent ports

Test Configuration Measured Power Sum Alien NEXT Coupling(2 disturber cables)

Adjacent ports Non-adjacent portsCat 5e bundled/Cat 5e patch panel -34.07 dB -36.13 dBCat 5e unbundled/Cat 5e patch panel -36.07 dB -42.62 dBCat 5e unbundled/Cat 5e Keystone panel -37.05 dB -44.28 dBCat 6 bundled/Cat 6 patch panel -37.13 dB -38.23 dBCat 6 unbundled/Cat 6 patch panel -39.53 dB -43.41 dBCat 6 unbundled/Cat 6 Keystone panel -44.49 dB -45.10 dB

Patch panel coupling becomes very significant (> 4 dB) for unbundled cable; less significant (< 2 dB) for tightly bundled cable.

Patch panel coupling depends on proximity, terminal layout geometry, and quality of installation.

Keystone jacks in panel frames produce less coupling for Cat 5e installations.

Alien NEXT effects from wiring installation may not be detected by cable analyzers.


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Effect of NearEffect of Near--end Cable Isolationend Cable Isolation

Add extra physical isolation (> 10 cm separation) between disturber and victim cables on short span between equipment and patch panel.

Produces attenuated NEXT behavior

Reduction better than 1 dB attenuation per meter isolated span length. 0 50 100 150 200 250 300 350 400 450 500-70

-65

-60

-55

-50

-45

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-20Measured Power Sum Alien NEXT Coupling - Six Disturber Cables

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Cat 5e unbundled, no near-end isolation = -34.53 dBCat 5e unbundled, 2m isolated span = -37.17 dBCat 6 unbundled, no near-end isolation = -36.81 dBCat 6 unbundled, 2m isolated span = -39.46 dB

Cat 5e PTP NEXT limit = -28.79 dB


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Summary of All NEXT Coupling EffectsSummary of All NEXT Coupling Effects

Test Configuration(Six disturber cables)

Power Sum Alien NEXTCoupling

Cat 5e Cat 6Bundled with adjacent patch panel ports -30.68 dB -33.22 dBBundled, no adjacent patch panel ports -31.67 dB -33.83 dBBundled, no adjacent patch panel ports, 2 meterisolated near-end span

-33.28 dB -35.92 dB

Unbundled with adjacent patch panel ports -34.53 dB -36.81 dBUnbundled, no adjacent patch panel ports -38.08 dB -38.47 dBUnbundled, no adjacent patch panel ports, with 2 meterisolated near-end span

-40.34 dB -41.16 dB

Unbundled with adjacent Keystone ports -35.61 dB -40.13 dBUnbundled, no adjacent Keystone ports -39.28 dB -40.22 dB

Unbundling provides 3-4 dB reductionNot using adjacent patch panel ports provides 2-4 dB reductionIsolating the first two meters of the channel provides 2.5 dB reductionSpecific reductions are greater for Cat 5e installations than Cat 6 installationsKeystone jack panels provide 1 dB improvement for Cat 5e, 3-4 dB improvement for Cat 6 (no adjacency coupling with Cat 6 Keystone jacks)


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Alien Crosstalk SummaryAlien Crosstalk Summary Worst-case alien crosstalk power sum may be as bad as Cat 5e

pair-to-pair NEXT Alien NEXT variations from installation practice

Affected by cable bundling, cable type (category), patch panel coupling, and near-end cable separation

Patch panel coupling may be dominant effect for unbundled cables(> 4 dB degradation)

Alien NEXT effects from wiring installation may not be detected by cable analyzers

Different installation practices will cause significant variations in observed alien NEXT energy.

Alien Crosstalk MeasurementsAlien Crosstalk OverviewAlien Crosstalk Cable Test BedAlien NEXT Measurement SetupFigure of MeritEffects of Bundling and Cable TypeEffect of Bundling ProximityEffects of Patch Panel Port PlacementAdjacent vs. Separated Patch Panel PortsEffect of Near-end Cable IsolationSummary of All NEXT Coupling EffectsAlien Crosstalk Summary

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cohen_1_0103