# Performance Testing of Twisted Pair Cables

Authors: Ahmed F. Mahmoud; Mahmoud I. Abdallah
Journal: Journal of Computer Systems, Networks, and Communications
 (2008-02-04)

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## Abstract

This work introduces characteristics of twisted pair cables which play           an important role in transferring data. In this paper, category 5 enhanced as         a type of unshielded twisted pair cables was selected to verify all tests on it according to ISO/IEC 11801 as  one of international standard specifications. Random samples were selected from cables market. All tests were done on these samples to make sure of using validity and complying with the international standard. After testing the selected samples, it is found that4% are not satisfying the international standard specification while as 96% are satisfying the international standard specification.


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## Body

## 1. Introduction

Today, communication enters our daily lives in so many
different ways that it is very easy to overlook the multitude of its facets
[1]. In the recent years, most of us realized the crucial impact of the
telecommunication systems in our modern life that destroyed the geographical
boundaries between people everywhere in the world.High-speed data transmission over twisted pair cables is indeed a challenging proposition
and currently of great interest [2–5]. Twisted pair
cables used for transport of telecommunication services consist of bundles of
copper wire pairs connecting a wire center to customers [6]. Twisted pair
cables also are commonly used for the connections between the different parts
of the system in the telecom field [7]. Twisted pair cables are well known for
computer networks designers and installers.The cables after their production should meet
some hard tests in the plant to verify their validation for usage. Main part in
this paper is about these tests and comparing the characteristics of twisted
pair cables in the cables market with the international standard specification.The paper is organized as follows. Following
this introduction, the international standard specification ISO/IEC 11801 used for twisted pair cable manufacturing
is given in Section2. Performance test parameters are given in
Section 3. Experimental results and discussion are introduced in Section 4. Conclusion
is presented in Section 5.


## 2. International Standard Specification ISO/IEC 11801

In a real manufacturing environment, it's very
sophisticated to obtain finished cables with the required performance which meets
both the international standards recommendations and customer requests with
minimum costs. This is the problem which the researchers are still doing their
best to solve. International specification unified the developing,
manufacturing, testing, and maintaining high quality of the products.Standards
make an enormous contribution to most aspects of our lives, although that
contribution is invisible. People are usually unaware of the role played by
standards in raising levels of quality, safety, reliability, efficiency, and
interchangeability as well as in providing such benefits at an economical cost
[8].The international organizations that produce international standards are the International Electrotechnical Commission
(IEC), the International Organization for Standardization (ISO), and the
International Telecommunication Union (ITU).One of the international standard specifications
the used in testing twisted pair cables is (ISO/IEC 11801), which is selected as an example to make tests according to it.The ISO/IEC 11801 standard defines a generic cabling system which is application
independent and supports an open market for cabling components. It is designed
to provide users with a flexible cabling scheme such that changes are both easy and economical to
implement. In addition, it provides the industry with a cabling system which
will support current active equipment and provides a basis for future
developments [9].


## 3. Performance Test Parameters

### 3.1. Length

Length is defined as the physical or sheath length of the cable. It
should correspond to the length derived from the length marking commonly
found on the outside jacket of the cable. Physical length is in contrast to
electrical or helical length, which is the length ofthe
copper conductors. Physical length will always be slightly less than electrical
length, due to the twisting of the conductors [10].In the test, there is a limit which must not be exceeded. This limit is equal to 361 ft.


### 3.2. Propagation Delay

Propagation delay, or delay, is a measure of the time required for a signal to propagate from one end of
the circuit to the other. This measurement is to be performed for each of the
four wire pairs. Delay is measured in nanoseconds (ns). Typical delay for
category 5e is a bit less than 5 nanoseconds per meter (worst case
allowed is 5.8 ns/m as illustrated in ISO/IEC 11801). A 100 meter cable might
have delay equal to 500 ns (worst case allowed is 580 ns/m).


### 3.3. Delay Skew

Propagation delay skew is the difference
between the propagation delay on the fastest and slowest pairs in a UTP cable. A cable should have a skew less than 50 nanoseconds over a 100-meter link according to ISO/IEC 11801. Lower skew is better. Anything under 25 nanoseconds is
excellent. Skew between 45 and 50 nanoseconds is marginally acceptable.


### 3.4. Attenuation

Electrical signals transmitted by a link lose some of their energy as they travel along
the link as shown in Figure1. Attenuation measures the amount of energy that is
lost as the signal arrives at the receiving end of the cabling link. The
attenuation measurement quantifies the effect of the resistance the cabling
link offers to the transmission of the electrical signals.Figure 1
Electrical signals transmitted by a link.According to ISO/IEC 11801, attenuation at frequencies that correspond to calculated
values of less than 4.0 dB will revert to a maximum requirement of 4.0 dB and
attenuation of each pair in category 5e will meet the requirements derived by
the following formula [9]:
(1)1.05×(1.9108f+0.022×f+0.2f)+4×0.04×f.


### 3.5. Near-End Crosstalk (NEXT)

When a current flows through a wire, an
electromagnetic field is created which can interfere with signals on adjacent
wires. As frequency increases, this effect becomes stronger. Each pair is
twisted because this allows opposing fields in the wire pair to cancel each
other. The tighter the twist, the more effective the cancellation and the higher the data
rate supported by the cable.According to
ISO/IEC 11801, NEXT of each pair will meet the requirements
derived by the  following formula [9]:
(2)−20log(10(65.3−15log(f))/−20+2×10(83−20log(f))/−20).


### 3.6. Power Sum NEXT (PSNEXT)

Power sum NEXT (PSNEXT) is a calculation, not a measurement. PSNEXT is
derived from the summation of the individual NEXT effects on each pair by the
other three pairs.According to ISO/IEC 11801, PSNEXT of each pair will meet the
requirements derived by the following formula [9]:(3)−20log(10(62.3−15log(f))/−20+2×10(80−20log(f))/−20).PSNEXT of pairk, PSNEXT (k), is computed from pair-to-pair NEXT (i,k) of the adjacent pairsi, j=1,…,n, as follows:(4)PSNEXTk=−10log∑i=1,i≠kn10−NEXTik/10,
where, i is the number of the disturbing pair, k is the number of
the disturbed pair, n is the total number of pairs, and NEXTik is the near end
crosstalk loss coupled from pair iinto
pair k.


### 3.7. Equal Level Far End Crosstalk (ELFEXT)

ELFEXT is a calculated result rather
than a measurement. It is derived by subtracting the attenuation of the
disturbing pair from the far end crosstalk (FEXT) this pair induces inan
adjacent pair. This normalizes the results for length.According to ISO/IEC 11801, ELFEXT of each pair will meet the requirements derived by the following
formula [9]:(5)−20log(10(63.8−20log(f))/−20+4×10(75.1−20log(f))/−20).ELFEXTik of pairs i and k is
computed as follows:(6)ELFEXTik=FEXTik−ILk,
where, i is the number of the
disturbed pair, k is the number of the
disturbing pair, FEXTik is the far end crosstalk loss coupled
from pair iinto pair k, and ILk is the insertion loss
of pair k.


### 3.8. Power Sum Equal Level Far End Crosstalk (PSELFEXT)

Power sum ELFEXT (PSELFEXT) is actually a
calculation, not a measurement. PSELFEXT is derived from an
algebraic summation of the individual ELFEXT effects on each pair by
the other three pairs. There are four PSELFEXT results for each end.According to ISO/IEC 11801, PSNEXT of each
pair will meet the requirements derived by the following formula [9]:
(7)−20log(10(60.8−20log(f))/−20+4×10(72.1−20log(f))/−20).


### 3.9. Return Loss (RL)

The impact of incorrect characteristic impedance is more accurately measured and represented by the quantity return
loss.Return loss (RL) is a measure of all reflections that are caused by the
impedance mismatches at all locations along the link and is expressed in
decibel (dB).According to ISO/IEC 11801, return loss will meet the requirements
derived by the following formula [9]:(8)30−10log(f).


## 3.1. Length

Length is defined as the physical or sheath length of the cable. It
should correspond to the length derived from the length marking commonly
found on the outside jacket of the cable. Physical length is in contrast to
electrical or helical length, which is the length ofthe
copper conductors. Physical length will always be slightly less than electrical
length, due to the twisting of the conductors [10].In the test, there is a limit which must not be exceeded. This limit is equal to 361 ft.


## 3.2. Propagation Delay

Propagation delay, or delay, is a measure of the time required for a signal to propagate from one end of
the circuit to the other. This measurement is to be performed for each of the
four wire pairs. Delay is measured in nanoseconds (ns). Typical delay for
category 5e is a bit less than 5 nanoseconds per meter (worst case
allowed is 5.8 ns/m as illustrated in ISO/IEC 11801). A 100 meter cable might
have delay equal to 500 ns (worst case allowed is 580 ns/m).


## 3.3. Delay Skew

Propagation delay skew is the difference
between the propagation delay on the fastest and slowest pairs in a UTP cable. A cable should have a skew less than 50 nanoseconds over a 100-meter link according to ISO/IEC 11801. Lower skew is better. Anything under 25 nanoseconds is
excellent. Skew between 45 and 50 nanoseconds is marginally acceptable.


## 3.4. Attenuation

Electrical signals transmitted by a link lose some of their energy as they travel along
the link as shown in Figure1. Attenuation measures the amount of energy that is
lost as the signal arrives at the receiving end of the cabling link. The
attenuation measurement quantifies the effect of the resistance the cabling
link offers to the transmission of the electrical signals.Figure 1
Electrical signals transmitted by a link.According to ISO/IEC 11801, attenuation at frequencies that correspond to calculated
values of less than 4.0 dB will revert to a maximum requirement of 4.0 dB and
attenuation of each pair in category 5e will meet the requirements derived by
the following formula [9]:
(1)1.05×(1.9108f+0.022×f+0.2f)+4×0.04×f.


## 3.5. Near-End Crosstalk (NEXT)

When a current flows through a wire, an
electromagnetic field is created which can interfere with signals on adjacent
wires. As frequency increases, this effect becomes stronger. Each pair is
twisted because this allows opposing fields in the wire pair to cancel each
other. The tighter the twist, the more effective the cancellation and the higher the data
rate supported by the cable.According to
ISO/IEC 11801, NEXT of each pair will meet the requirements
derived by the  following formula [9]:
(2)−20log(10(65.3−15log(f))/−20+2×10(83−20log(f))/−20).


## 3.6. Power Sum NEXT (PSNEXT)

Power sum NEXT (PSNEXT) is a calculation, not a measurement. PSNEXT is
derived from the summation of the individual NEXT effects on each pair by the
other three pairs.According to ISO/IEC 11801, PSNEXT of each pair will meet the
requirements derived by the following formula [9]:(3)−20log(10(62.3−15log(f))/−20+2×10(80−20log(f))/−20).PSNEXT of pairk, PSNEXT (k), is computed from pair-to-pair NEXT (i,k) of the adjacent pairsi, j=1,…,n, as follows:(4)PSNEXTk=−10log∑i=1,i≠kn10−NEXTik/10,
where, i is the number of the disturbing pair, k is the number of
the disturbed pair, n is the total number of pairs, and NEXTik is the near end
crosstalk loss coupled from pair iinto
pair k.


## 3.7. Equal Level Far End Crosstalk (ELFEXT)

ELFEXT is a calculated result rather
than a measurement. It is derived by subtracting the attenuation of the
disturbing pair from the far end crosstalk (FEXT) this pair induces inan
adjacent pair. This normalizes the results for length.According to ISO/IEC 11801, ELFEXT of each pair will meet the requirements derived by the following
formula [9]:(5)−20log(10(63.8−20log(f))/−20+4×10(75.1−20log(f))/−20).ELFEXTik of pairs i and k is
computed as follows:(6)ELFEXTik=FEXTik−ILk,
where, i is the number of the
disturbed pair, k is the number of the
disturbing pair, FEXTik is the far end crosstalk loss coupled
from pair iinto pair k, and ILk is the insertion loss
of pair k.


## 3.8. Power Sum Equal Level Far End Crosstalk (PSELFEXT)

Power sum ELFEXT (PSELFEXT) is actually a
calculation, not a measurement. PSELFEXT is derived from an
algebraic summation of the individual ELFEXT effects on each pair by
the other three pairs. There are four PSELFEXT results for each end.According to ISO/IEC 11801, PSNEXT of each
pair will meet the requirements derived by the following formula [9]:
(7)−20log(10(60.8−20log(f))/−20+4×10(72.1−20log(f))/−20).


## 3.9. Return Loss (RL)

The impact of incorrect characteristic impedance is more accurately measured and represented by the quantity return
loss.Return loss (RL) is a measure of all reflections that are caused by the
impedance mismatches at all locations along the link and is expressed in
decibel (dB).According to ISO/IEC 11801, return loss will meet the requirements
derived by the following formula [9]:(8)30−10log(f).


## 4. Experimental Results

To obtain the optimum performance for
the twisted pair cable, it must realize the characteristics of the cabling
systems. To get closer to the cables manufacturing process, simply the raw
copper is drawn to different rod diameters that will be later drawn to the
required conductor diameters.After that, it is insulated with a suitable insulation material to
produce a single wire.The first requirement is to provide
electrical isolation of the wires from each other by insulating the individual wires
[10]. Without proper insulation and the use of protection materials, wires and
cables would not function properly or safeley, and they would not last very long
[11].These insulation wires will be assembled to create pairs which in turn
are assembled together and then covered with a suitable sheath to produce a
final cable.The cable sheath will prevent any
damage to the cable core due to the effects of external mechanical stress and,
depending on the type of material used, it can also play a very considerable
part in protecting the cable core from external electrical interference [12].Figure2 shows Fluke Networks DSP-SPOOL cable spool test interface adapters
used for testing twisted pair cables [13].Figure 2
Testing cable spools with the cable spool interface adapter.The performance test parameters for Cat 5e
are defined in ISO/IEC 11801. The test of each sample should contain all of the
parameters as discussed before. In order to pass the test, all measurements (at
each frequency in the range from 1 MHz to 100 MHz) must meet or exceed the
limit value determined in the above-mentioned standard, otherwise the sample is
failed.When dealing with the cables market, it is found that a lot of samples of
twisted pair cables were manufactured in many countries. After testing these selected samples, it is found that 96% are passed
and satisfying the international standard specification while  4% are failed
and not satisfying the international standard specification.Passed sample of twisted pair cables is the sample in which all measurements (at each
frequency in the range from 1 MHz through 100 MHz) must meet or exceed the
limit value determined in ISO/IEC 11801.The analysis of the passed sample is given from Figure3 to Figure 11. There isa
limit which must not be exceeded. All performance test parameters discussed
before do not exceed that limit.Figure 3
The length of passed sample does not exceed the limit.As shown in Figure3, there is a limit that equals 361 ft, and the
passed samples does not exceed that limit.As shown in Figure4, although propagation
delay of passed samples has the worst values of pairs 12 and 78 that equal
432 nanoseconds, but these values of the propagation delay do not exceed 580 nanoseconds.Figure 4
The propagation delay of the passed sample does not exceed 580 ns.As shown in Figure5, although delay skew of
passed samples has the worst values of pairs 12 and 78 that equal 14 nanoseconds, but these values of the delay skew are
excellent results as they do  not exceed 25 nanoseconds.Figure 5
The delay skew of passed sample does not exceed 50 ns.As shown in Figure6, attenuation of passed samples of pair 1,2, pair 3,6,
pair 4,5, and pair 7,8, not exceed does the limit.Figure 6
The attenuation of passed sample does not exceed the limit.As shown in Figure7, although the NEXT between pair 3,6 and pair 7,8 has the worst value that
equals 38.3 dB at 85.6 MHz, but it does not exceed the limit. NEXT of passed samples
between each pair and the others does not exceed the limit.Figure 7
The NEXT of passed does sample not exceed the limit.As shown in Figure8, although the PSNEXT of
pair 36 has the worst value that equals 37.9 dB at 85.6 MHz, but it does not exceed
the limit. PSNEXT of passed samples of pairs 12, 36, 45, and 78 does not exceeds the
limit.Figure 8
The PSNEXT of passed sample does not exceed the limit.As shown in Figure9, although the ELFEXT
between pairs 45 and 36 has the worst value that equals 31.7 dB
at 67 MHz, but it does not exceed the limit.Figure 9
The ELFEXT of passed sample does not exceed the limit.As shown in Figure10, although the PSELFEXT
of pair 36 has the worst value that equals 31.7 dB at 67 MHz, but it does not exceed
the limit. PSELFEXT of passed samples of pairs 12, 36, 45, and 78 does not exceeds
the limit.Figure 10
The PSELFEXT of passed sample does not exceed the limit.Figure 11
The return loss of passed sample does not exceed the limit.As shown in Figure11, although return loss of
pair 36 has the worst value that equals to 21.9 dB at 86.8 MHz, but it does not exceed
the limit. Return loss of passed samples of pairs 12, 36, 45, and 78 does not exceed
the limit.On the other hand, failed sample of twisted
pair cables is the sample which some of measurements (frequency in the range
from 1 MHz to 100 MHz) to don't have within the limit value determined in ISO/IEC
11801.The analysis of failed sample is given from Figure12 to Figure 20. There is a limit
which must not be exceeded. Although propagation
delay, delay skew, ELFEXT, and PSELFEXT do not exceed that limit, but the problem is in
attenuation, NEXT, PSNEXT, and RL which exceed that limit, and of course that has an
effect on transferring data.Figure 12
The length of failed sample does not exceed the limit.As shown in Figure12, there is a limit that equals 361 ft,
and the failed samples do not exceed that limit.As shown in Figure13, although propagation delay of failed samples has
the worst values of pair 45 that equals 520 nanoseconds, but this value of the
propagation delay does not exceeds the worst case allowed that equals to 580 nanoseconds.Figure 13
The propagation delay of the failed sample does not exceeds 580 ns.As shown in Figure14, although the delay skew of
failed samples has the worst value of pair 45 that equals 23 nanoseconds, but this
value of the delay skew does not exceed the limit.Figure 14
The delay skew of failed sample does not exceed 50 ns.As shown in Figure15, although the
attenuation of pair 12 does not exceed the limit, but attenuation of pairs 36, 45,
and 78 exceeds the limit.Figure 15
The attenuation of failed sample does exceed the limit.As shown in Figure16, although the NEXT between pairs 36–45 and 36–78
does not exceed the limit, but the NEXT of failed samples between pairs 12-36, 12–45, 12–78 and 45–78 exceeds the limit,
and the worst value of pairs 12–45 equals to 29 dB at 47.6 MHz.Figure 16
The NEXT of failed sample exceeds the limit.As shown in Figure17, although the PSNEXT of
pair 36 does not exceed the limit, but the PSNEXT of failed samples between pairs
12, 45, and 78 exceeds the limit, and the worst value of pair 45 equals 29 dB
at 47.6 MHz.Figure 17
The PSNEXT of failed sample exceeds the limit.As shown in Figure18, the ELFEXT of failed samples between each pair and others does not
exceed the limit.Figure 18
The ELFEXT of failed sample does not exceed the limit.As shown in Figure19, the PSELFEXT of failed
samples of each pair does not exceed the limit.Figure 19
The PSELFEXT of failed sample does not exceed the limit.Figure 20
The return loss of failed sample exceeds the limit.As shown in Figure20, although return loss of pair 45 does not exceed the limit,
but the return loss of failed samples between pairs 12, 36, and 78 exceeds the limit,
and the worst value of pair 36 equals 17.7 dB at 89.2 MHz.There are other primary tests which can be done
on each single wire of twisted pair cable as continuity, resistance, and
elongation.About
continuity, to make sure that there's no short between wires, simply, that test
can be done by using any device for short/continuity tester such as a multimeter. The cables selected
for testing have continuity, and without continuity, there are no parameters for
cables.About resistance, all single wires of passed sample have resistance in
the range from 81.76Ω/km to 81.88 Ω/km. The maximum resistance allowed for each conductor
is 84 Ω/km according to the international, standard and over
that, the sample is failed.About elongation percentage, all insulated materials of conductors of
passed sample have values range from 550% to 690%. The minimum elongation
percentage allowed for insulated materials of conductors is 400% according to
international standard.About tension force, all insulated materials of conductors of passed
sample have values range from 24 N/mm2 to 27 N/mm2. The
minimum tension force allowed for insulated materials of conductors is 22.1 N/mm2 according to the international standard.The primary test that every cable should
pass is the dielectric strength test, where the cable is exposed to a higher
voltage than that of the real operating voltage for a certain period. The
purpose of that test is to insure the perfection of the insulation. If there's
a weak point in the insulation, it should fail the test.The main difference between types of twisted
pair cables is the cable performance at higher frequency that means the higher
category. With the greatest development in manufacturing
cables, it appears that new types of twisted pair cables that have a
higher category number than Category 5 enhanced. This implies that for
performance improvement in twisted pair cables applications, all tests were
done on them to make sure of using validity and complying with the
international standard specification.


## 5. Conclusion

This paper presents Category 5 enhanced as a type of unshielded twisted pair
cables and makes all the  testing on it according to ISO/IEC 11801 as one of
the international standard specifications.The parameters used for performance test are propagation delay, delay
skew, attenuation, near-end crosstalk loss
(NEXT), powersum NEXT (PSNEXT), equal level far end crosstalk
(ELFEXT), power sum equal level far end crosstalk (PSELFEXT), and return
loss.When dealing with random samples of twisted
pair cables selected from the cables market, it is found that 96% of
these samples have been passed and complied with the international standard. On
the other hand, 4% of these samples have been failed and not complied with the
international standard.Quality pass samples should be acceptable at all tests
according to the international standard specification.Customer should review these tests according
to the international standard specification.



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*Source: 586427-2008-03-12.xml*