White Paper
Andreas Clauser
Hauptsitz
Binzstrasse 31
CH-8622 Wetzikon
Tel
+41 1 933 8375
Fax
+41 1 930 49 41
Internet www.rdm.com
02. Juli 2002
Do you know if your Cat. 6 patch cord has been tested according to standards?
Unfortunately, reality shows that many of the alleged Cat. 6
patch cords do not fulfil the values laid down in standards!
It is common knowledge that today most of the installations
are only measured as permanent links. But will your
installations still yield the required performance, once
the patch cords are connected? Is it enough when the
stranded cable complies with the standard? How can you
make sure yours is a good patch cord?
This article will give you the answers to all these important
questions when choosing patch cords. It also presents today’s
standards of patch cords and stranded cables and discusses
their differences. Furthermore, it clearly describes how to
proceedin order to find guaranteed top-grade patch cords.
Summary
nd
Cat. 6 patch cords are specified in the standards PrEN 50173, ISO/IEC 11801 2 Edition and
ANSI/TIA/EIA-568-B.2.1. They include defined minimum values for near-end crosstalk and return
loss.
Due to its consistent organisation the TIA/EIA-568-B.2.1, Draft 9 should be used as reference for the
nd
assessment of flex cables and patch cords. The draft of ISO/IEC 11801 2 Edition from April 2001
contains mistakes and should not serve as reference in the assessment of flex cables. CENELEC
with PrEN 50173 has not yet defined a required near-end crosstalk value for Cat. 6 patch cords.
There is only one way to make absolutely sure that your patch cord fulfils the standard, namely to ask
the manufacturer for the test record from patch cord production.
Detailed specifications
nd
The Cat. 6 patch cords are specified in the standards PrEN 50173, ISO/IEC 11801 2 Edition and
ANSI/TIA/EIA-568-B.2.1. These standards issue identical required values for return loss. ISO/IEC
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and TIA/EIA issue the same required values for near-end crosstalk, whereas CENELEC has not yet
determined values required for Cat. 6 patch cord near-end crosstalk (as of April 2002).
The new cabling standards specify patch cords of up to 20 metres. The frequency range is specified
from 1 to 250 MHz. The near-end crosstalk values vary depending on the patch cord's length. By
contrast the return loss values were specified independent of the patch cord's length.
.
Table 1: Standards for patch cords and flexible cables
Document Name
Title
ANSI/TIA/EIA-568-B.2.1
Addendum No. 1 to TIA/EIA-568-B.2, "Transmission
Performance Specifications for 4-Pair 100 Category 6
Cabling", November 2001 Draft 10 Preliminary
nd
nd
ISO/IEC 11801 2 edition
2 CD, IT-Cabling for customer premises, April 2001
PrEN 50173
Information technology-generic cabling systems,
August 2001
The standards give identical values for flex cables. There is, however, a small but significant
difference: ISO/IEC 11801 specifies return loss between 4 and 250 MHz whereas ANSI/TIA/EIA set
their frequency range at between 1 and 250 MHz.
In reality, the return loss as specified in ISO/IEC 11801
2nd
leads to the situation where the cable
fulfils the standard for a flexible cable of 100 m, but the patch cords of between 5 and 10 m no longer
fulfil the standard.
Graph 1
Graph 2
RL S-STP flex cable 5m
70.0
60.0
60.0
50.0
50.0
Magnitude [dB]
Magnitude [dB]
RL S-STP flex cable 100m a
70.0
40.0
30.0
40.0
30.0
20.0
20.0
10.0
10.0
0.0
0.0
1
10
100
1
10
Frequency [MHz]
Limit C6 flex cable
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1,2 100m side a
3,6 100m side a
100
Frequency [MHz]
4,5 100m side a
7,8 100m side a
Limite C6 Cord
1,2 5m
3,6 5m
4,5 5m
7,8 5m
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Limit C6 flex cable
Graph 1 shows the measurement of a 100 m flexible cable, which fulfils the specifications according
to ISO/IEC. It only falls short of the limit below 4 MHz. Then, 20 metres of the cable were cut off and
it was tested for the patch cords' limits as specified by ISO/IEC. To exclude any influence from the
connector and the connector's termination the cable was measured separately. The result is shown
below, in Graph 3: the patch cord fails. It is the same with patch cords of 10 metres (Graph 4). The
patch cords of 5 metres only just about fulfil the ISO/IEC requirements again (Graph 2).
Graph 3
Graph 4
RL S-STP flex cable 20m
RL S-STP flex cable 10m
60.0
70.0
60.0
50.0
50.0
Magnitude [dB]
Magnitude [MHz]
40.0
40.0
30.0
30.0
20.0
20.0
10.0
10.0
0.0
0.0
1
10
1
100
10
Frequency [MHz]
Limite Cord
1,2 20m
3,6 20m
4,5 20m
100
Frequency [MHz]
7,8 20m
Limit (dB)
Limite C6 Cord
1,2 10m
3,6 m
4,5 m
7,8 m
Limit flex cable
The results are summarised in Table 2. They show that up to 3.7 dB of reserve can be lost from a
flexible cable to a patch cord of 20 metres due to the fact that ISO/IEC only start measuring cables
from 4 MHz upward.
Table 2: ISO/IEC 11801
2nd
Edition
Standard for 100 m flex cable
Standard for patch cord up to 20 m
Frequency range
4 ... 250 MHz
1 ... 250 MHz
Length
100 m
20 m
10 m
5m
Frequency of
1.4 dB
-2.3 dB
-1.4 dB
0.15 dB
smallest reserve
4.6 MHz
2.0 MHz
4.4 MHz
8.9 MHz
Result
PASS
FAIL
FAIL
PASS
Conclusion:
The draft of ISO/IEC 11801 2
nd
Edition from April 2001 contains mistakes and
should not serve as reference in the assessment of flex cables.
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In a second step the measuring results were compared with the specifications of ANSI/TIA/EIA 568B2.-1 Draft 10 of November 2001. The results are summarised in Table 3.
Table 3: ANSI/TIA/EIA 568-B.2-1 Draft 10
Standard for 100 m flex cable
Standard for patch cord up to 20 m
Frequency range
1 ... 250 MHz
1 ... 250 MHz
Length
100 m
20 m
10 m
5m
Frequency of
-2.0 dB
-2.3 dB
-1.4 dB
0.15 dB
smallest reserve
1.5 MHz
2.0 MHz
4.4
8.9
Result
FAIL
FAIL
FAIL
PASS
In TIA/EIA 568-B.2-1 Draft 10 the return loss specifications for flex cables are consistent with the
limits for patch cords, both starting at 1 MHz. The reserves for the limits of a 100 m flex cable and of
a 20 m patch cord also match. Furthermore, it is shown that the frequency of the worst value with
reference to the limit is doubled when the patch cord's length is cut in half. This effect is caused by
standing waves in the cable.
Conclusion:
Due to its consistent organisation the TIA/EIA-568-B.2.1, Draft 9 should be used
as reference for the assessment of flex cables and patch cords.
Reality has shown that only a few of the alleged Cat. 6 patch
cords actually fulfil the values stipulated by the standards.
How can you make absolutely sure that your patch cord
complies with the TIA/EIA or ISO/IEC standards?
It is only possible if the patch cord production is subject to a
test system. The parameters near-end crosstalk and return
loss must be fulfilled in compliance with ANSI/TIA/EIA-568nd
B.2.1 (as of Draft 9) or ISO/IEC 11801 2 Edition.
How can a customer make sure such a test system was not
only implemented by marketing but also in production? Here
the only way is to ask for the manufacturer's test record of the
patch cord production, which should list the measured values
and the standards applied.
Conclusion:
Ask the manufacturer for the test record of
the patch cord production.
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