Alien Crosstalk Measurements
Larry Cohen
Solarflare Communications
IEEE802.3 Interim January 2003
10GBASE-T
1
Alien 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 Bed
Bundled cable
Unbundled cable
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Alien NEXT Measurement Setup
Tight bundle cross-section
Network Analyzer
S
R
50Ω
Six disturber cables
A
50Ω
Victim
cable
50Ω
Attenuator matched to line
interface matching pads
Matching
pad
50Ω
Attenuator
50:100Ω Interface
Cable ties
50:100Ω
Interface
Matching
pad
6 dB Splitter
10 cm
Disturber
Victim
Isolated interconnect span
(2 meters patch cord)
Cat 5e/6 test cable bundle
(horizontal cable)
100 Ohm
Terminations
40 meters
1 meter
patch cords
10 cm
Cat 5e/6 RJ45
patch panels
IEEE802.3 Interim January 2003
10GBASE-T
100 Ohm
Terminations
1 meter
patch cords
4
Figure 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 Type
Measured Power Sum Alien NEXT Coupling - 6 Disturber Cables
-20
•All test cases are six
disturber cables; two
disturbers in adjacent
patch panel ports
-25
Insertion gain (dB)
-30
-35
•Unbundling reduces
coupling about 4 dB
-40
-45
-50
•Cat 6 has 2-3 dB
advantage over Cat 5e.
Cat 5e bundle = -30.66 dB
Cat 5e unbundled = -34.41 dB
Cat 6 bundle = -33.08 dB
Cat 6 unbundled = -36.51 dB
Cat 5e PTP NEXT limit = -28.79 dB
-55
-60
•Variation in bundling
may be more important
than cable category.
-65
-70
0
50
100
150
200
250
300
350
400
450
500
Frequency (MHz)
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Effect of Bundling Proximity
Opposite pairs
Measured Power Sum Alien NEXT - Three Disturber Cables
Adjacent pairs
-20
Victim cable
-30
Insertion gain (dB)
Disturber cable
Victim cable
Disturber cables
-40
•No victim/disturbers in
adjacent patch panel ports.
-50
•Opposite cables separated
by width of one (center)
cable over entire span.
-60
Adjacent pairs = -35.08 dB
Opposite pairs = -39.83 dB
Cat 5e PTP NEXT limit
-70
-80
0
50
100
150
200
250
300
350
400
450
500
•Separation reduces
coupling 4-5 dB; correlates
with unbundled test case.
Frequency (MHz)
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Effects of Patch Panel Port Placement
Measured Power Sum Alien NEXT Coupling into Victim Cable 4
Cat 5e/Cat6 Patch panel
-20
7
6
5
4
3
2
1
Insertion gain (dB)
-30
Disturber cables
Victim cable
Disturber cables
-40
•Test case is
unbundled Cat 5e
-50
-60
-70
-80
•Cables on adjacent
plug ports of patch
panel (cables 3 and 5)
are dominant disturbers
(> 5 dB)
Cable 1 = -44.83 dB
Cable 2 = -44.61 dB
Cable 3 = -38.75 dB
Cable 5 = -39.38 dB
Cable 6 = -46.17 dB
Cable 7 = -46.58 dB
0
50
100
150
200
250
300
350
400
450
500
Frequency (MHz)
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Adjacent vs. Separated Patch Panel Ports
Test Configuration
Cat 5e bundled/Cat 5e patch panel
Cat 5e unbundled/Cat 5e patch panel
Cat 5e unbundled/Cat 5e Keystone panel
Cat 6 bundled/Cat 6 patch panel
Cat 6 unbundled/Cat 6 patch panel
Cat 6 unbundled/Cat 6 Keystone panel
Measured Power Sum Alien NEXT Coupling
(2 disturber cables)
Adjacent ports
Non-adjacent ports
-34.07 dB
-36.13 dB
-36.07 dB
-42.62 dB
-37.05 dB
-44.28 dB
-37.13 dB
-38.23 dB
-39.53 dB
-43.41 dB
-44.49 dB
-45.10 dB
Cat 5e/Cat6 Patch panel
Separated ports
7
6
5
4
3
2
Victim
port
Adjacent ports
•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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1
Effect of Near-end Cable Isolation
Measured Power Sum Alien NEXT Coupling - Six Disturber Cables
-20
•Add extra physical
isolation (> 10 cm
separation) between
disturber and victim
cables on short span
between equipment and
patch panel.
-25
Insertion gain (dB)
-30
-35
-40
-45
•Produces attenuated
NEXT behavior
-50
-55
Cat 5e unbundled, no near-end isolation = -34.53 dB
Cat 5e unbundled, 2m isolated span = -37.17 dB
Cat 6 unbundled, no near-end isolation = -36.81 dB
Cat 6 unbundled, 2m isolated span = -39.46 dB
Cat 5e PTP NEXT limit = -28.79 dB
-60
-65
-70
0
50
100
150
200
250
300
350
400
450
500
•Reduction better than 1
dB attenuation per
meter isolated span
length.
Frequency (MHz)
IEEE802.3 Interim January 2003
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Summary of All NEXT Coupling Effects
Test Configuration
(Six disturber cables)
Bundled with adjacent patch panel ports
Bundled, no adjacent patch panel ports
Bundled, no adjacent patch panel ports, 2 meter
isolated near-end span
Unbundled with adjacent patch panel ports
Unbundled, no adjacent patch panel ports
Unbundled, no adjacent patch panel ports, with 2 meter
isolated near-end span
Unbundled with adjacent Keystone ports
Unbundled, no adjacent Keystone ports
Power Sum Alien NEXT
Coupling
Cat 5e
Cat 6
-30.68 dB
-33.22 dB
-31.67 dB
-33.83 dB
-33.28 dB
-35.92 dB
-34.53 dB
-38.08 dB
-40.34 dB
-36.81 dB
-38.47 dB
-41.16 dB
-35.61 dB
-39.28 dB
-40.13 dB
-40.22 dB
•Unbundling provides 3-4 dB reduction
•Not using adjacent patch panel ports provides 2-4 dB reduction
•Isolating the first two meters of the channel provides 2.5 dB reduction
•Specific reductions are greater for Cat 5e installations than Cat 6 installations
•Keystone jack panels provide 1 dB improvement for Cat 5e, 3-4 dB improvement
for Cat 6 (no adjacency coupling with Cat 6 Keystone jacks)
IEEE802.3 Interim January 2003
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Alien 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.
IEEE802.3 Interim January 2003
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