stinct methods for evaluating the cable;
- Link Analysis
- Time Domain Reflectometry (TDR)
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2 Cable Analysis
Link analysis evaluates the cable while the link is active. Link analysis can detect faults that are not
detectable using TDR analysis; these include pair swaps, polarity reversals and cable quality. Link
analysis can also estimate the cable length, link quality and cable quality. The specifications for the link
analysis functions are detailed in Table 1.
TDR analysis can detect cable faults such as open circuits and short circuits, which pair the fault is on,
distance to the fault, pair skew, excessive crosstalk and split pairs. TDR can estimate the cable length for
a terminated cable where the link partner not powered. TDR analysis can also be used to detect the
presence of an unpowered IP Phone. The specifications for TDR functions are detailed in Table 2.

Link Analysis
Feature Description
10
100
1000
Detect Pair Swap
Pair swaps
X
X
X
3

Detect Polarity Reversal Polarity
X 4
X
Good Cable with Link
Indicate length

± 5 m
± 5 m
Pair Skew with Link
Detect skew >50 ns


X
5

Link Quality
Indicate link and cable
quality
6

X X
Table 1: Link Analysis

TDR Analysis
Feature Description
Term
Unterm
Cable open
X
Cable short
X
Detection of cable fault
on any pair
Indicate distance to fault
± 2 m
± 2 m

Good Cable without Link Indicate length
± 5 m
1

± 2 m
Pair Skew without Link
Detect skew >50 ns
X
1

Excessive Crosstalk
Cable quality or split pairs
X
IP Phone Detection
Detect unpowered IP Phone
X
2

Table 2: TDR Analysis

1
If return loss is less than 20 dB (20 MHz 100 MHz).
2
If transfer function between pairs A and B sufficiently different from a straight loopback cable.
3
Pair swaps on C and D as well as pairs A and B are reported.
4
Polarity reversal in 100Base-Tx is not detected, as MLT-3 signaling is polarity insensitive.
5
Pair skew measured with a link active is only available for 1000Base-T.
6
Link and cable quality reports SNR, echo, NEXT, frequency offset and channel response.
Echo and NEXT are not available at 100Base-TX.
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2.1 Line Probing Module
The ET1081 contains a line probing module that greatly reduces the software task of capturing and
processing TDR samples. The line probe module contains two important features that are used for TDR.
The first feature is the pulse generator, which allows a digital pulse to be transmitted on one of the four
cable pairs. The second feature is the thresholder, which extracts key features of the TDR signal on one
of the four cable pairs without the additional software burden and memory resources associated with
capturing and processing all of the TDR samples. Software algorithms developed by Agere Systems uses
these two features to determine the cable characteristics. The TDR analysis has an execution time of less
than 1 second.
3 Cable Analysis Software
The cable analysis software consists of two main libraries:
-
Silicon Debug Features Support Library (SDF)
-
IntelliSupport Library (INL)

SDF is a low-level library that contains API functions for reading and writing the proprietary registers of
the PHY. INL is a high-level library that makes use of SDF to control these registers and process them in
order to perform cable analysis. The API functions for these two libraries are discussed in detail in the
Cable Analysis API application note.
The top-level INL routine, which is the main entry point for cable analysis used by
TruePHY
Evaluation
System software, performs the processing shown in
Figure 1
.

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Start
Forced IP Phone
Detection?
Yes
Perform IP Phone
Detection
No
Forced TDR analysis?
Perform TDR Analysis
Yes
No
End
Link is up?
Yes
No
Perform Link Analysis

Figure 1: Processing for ET1081 top-level INL routine
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3.1 Link Analysis
Link Analysis acquires the following cable analysis information: Basic link information: Link speed, master/slave setting, and MDI/MDI-X setting Wire map: crossover and polarity inversion detection Signal-to-noise ratio (SNR) Frequency offset error Coarse cable length estimation Coarse pair skew estimation

The link speed, master/slave setting, and MDI/MDI-X setting are retrieved using MI registers in the PHY.
The master/slave setting is only applicable for a 1000Base-T link.
The wire map is deduced based on the MDI/MDI-X setting and proprietary PHY registers. Polarity
inversion cannot be determined for a 100Base-TX link since 100Base-TX is polarity insensitive.
The SNR is a measure of the quality of the receive signal. It is determined using an internal diagnostics
block called the Diagnostic ALU, which allows simple operations to be performed on internal signals of
the PHY. The SNR is calculated using the energy at the input and output of the slicer. The SNR can only
be determined for a 1000Base-T and 100Base-TX link.
The frequency offset error indicates the difference in frequency between the master and slave clocks for a
1000Base-T link. For the master PHY, the offset will always be zero since the master PHY provides the
timing for the slave PHY. For a 100Base-TX link, the frequency offset error indicates the difference in
frequency between the clocks of the remote and local PHYs. Frequency offset error is determined using
proprietary PHY registers and is not applicable for a 10Base-T link.
Coarse cable length estimation indicates the overall length of the cable and the length of each individual
pair. The length estimation accuracy is ± 5 m with a 1000Base-T or 100Base-TX link. The cable length
cannot be determined for a 10Base-T link. The length estimate is calculated based on equalizer
coefficients and proprietary PHY registers.
Coarse pair skew indicates the time difference between the shortest length pair and the other pairs with
8ns resolution. Coarse pair skew is only applicable for a 1000Base-T link.

3.2 TDR Analysis
TDR Analysis acquires the following cable analysis information: Cable length estimation Distance to cable faults Pair
skew
estimation

TDR analysis is accomplished using the line probing module. This module transmits one or more pulses
on each cable pair. These pulses are reflected (echo) or coupled back (NeXT) to a receiver on each cable
pair. The thresholder extracts the key features of the TDR signals for each transmit/receive combination.
The software reads the thresholder and performs an analysis to estimate cable length, distance to fault (if
any), and pair skew.

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The cable length is based on time difference between the transmitted pulse and the peak reflection in the
echo signal. The distance to cable faults is based on the time difference between the transmitted pulse
and significant reflections in the echo signals or coupling in the NeXT signals. The type of faults is based
on the amplitude and polarity of the significant reflections in the echo signals or the amplitude and polarity
of the coupling in the NeXT signals. The pair skew estimations are calculated based on the cable length
of the shortest pair and all other pairs.
The cable length and distance to cable fault accuracy is ± 2 m for an unterminated link (i.e., the cable has
been disconnected from the remote device), and ± 5 m for a terminated link (i.e., the remote device has
been powered down) provided that the return loss is less than 20 dB (20 MHz 100 MHz).

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4 Screen Shots
This section contains screen shots taken from the
TruePHY
Evaluation System software. It is used to
illustrate the capabilities of the Cable Analysis software for both Link Analysis and TDR Analysis.
4.1 Link Analysis
Link analysis consists of the following pages: Summary, Echo, NeXT, and Channel Response. These
pages are discussed in detail in subsequent sections.

4.1.1 Summary
Figure 2 (a) illustrates the link analysis information provided for a 1000Base-T master link.
Figure 2
(b)
illustrates the link analysis information provided for a 1000Base-T slave link.





(a)




(b)
Figure 2: Link Analysis for 1000Base-T Link

The Cable Length category indicates the overall length of the cable and the length of each individual pair.
The Cable Configuration/Quality category shows the wire map, signal quality, and pair skew condition.
The wire map indicates pair swaps (crossovers) and polarity reversals in the cable. The signal quality
indicates the condition of the receive signal. The pair skew indicates whether or not the time difference
between the shortest length pair and the other pairs is within 50nSec. The ET1081 can automatically
compensate for pair swaps, polarity reversals, and pair skew.
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The Frequency Offset Error category indicates the percent difference in clock frequencies between the
local and remote PHY.
The Advertisement/Link Control settings indicate the link speeds that the local PHY supports and the link