BIHTEL 2014
X International Symposium on Telecommunications
A Possibility of Using Longitudinal Balance for
Qualification and Troubleshooting of DSL Lines
Namir Škaljo, Alen Begović, Narcis Behlilović
27-29 October 2014, Sarajevo, BiH
CONTENT
I
INTRODUCTION
II A SHORT OVERVIEW OF LONGITUDINAL BALANCE
III THE RECOMMENDED LEVEL OF LONGITUDINAL BALANCE
IV RESULTS OF LONGITUDINAL BALANCE MEASURING
V THE DEPENDENCE OF LONGITUDINAL BALANCE ON THE
INSULATION RESISTANCE
VI CONCLUSION
I INTRODUCTION
• From technical aspects, DSL lines have some significant disadvantages
compared to other types of broadband access (FTTH).
• The biggest drawback of DSL lines is high risk of occurrences of faults and
disturbances.
• It is very important to detect the existence of faults and disturbances in a
reliable and time-efficient way and, also, it is very important to detect the
causes of faults and disturbances.
• By testing the QoS parameters it is determined whether there are problems
with service delivery and by testing the physical layer parameters it is
determined whether occurrences that create problems with service delivery
come from the DSL.
• By measuring the electrical parameters of symmetrical copper pair it is
determined which occurrences on the copper pair (faults or disturbances or
simultaneous activity of both) cause problems in the delivery of services.
I INTRODUCTION
• For testing the QoS and the physical layer parameters highly reliable
mechanisms for centralized testing of these parameters are developed.
• The measurement of the electrical parameters of symmetrical copper pairs is
still performed primarily by using manual measuring instruments.
• Measuring of electrical parameters are very complex and require
considerable consumption of time.
• Are there some electrical parameters that give more information on the
general state of copper pairs than the other parameters?
• Longitudinal balance as more important parameter?
• This paper will in experimental form investigate the actual usability and
importance of longitudinal balance.
II
A SHORT OVERVIEW OF LONGITUDINAL BALANCE
• Good pair balance is the key for its properties in terms of immunity to various
electromagnetic influences.
• One way to verify whether the symmetrical copper pair is in a good balance
should be measuring the level of the longitudinal balance.
Figure 1
Principal way of measuring
longitudinal balance
III THE RECOMMENDED LEVEL OF LONGITUDINAL BALANCE
• „The measurement of the longitudinal balance is extremely useful for
identifying lines that are exposed to interference that comes from other lines
in the cable that transmits broadband signals“
• „The longitudinal balance of a pair in the cable measures the uniformity of
electrical characteristics of the two conductors in a single pair“
• „A pair with good longitudinal balance will transmit signals without errors“.
•
The recommended levels of longitudinal balance:
< 50 dB - unacceptable pairs,
50 – 60 dB - marginal pairs,
> 60 dB - acceptable pairs.
IV
RESULTS OF LONGITUDINAL BALANCE MEASURING
• We shall show results of measurement of longitudinal balance values on the
copper pairs without any faults and on the same pairs when there are some
different types of highly expressed faults.
Figure 2: Pairs without any
faults
LB =
> 100 dB
Some basic electrical parameters of pair without any faults are:
- Insulation resistance: > 20 GΩ (a-b), > 20 GΩ (a-g), > 20 GΩ (b-g) - both pairs,
- Loop resistance: 70.5 Ω (pair 1) and 71.5 Ω (pair 2)
- Capacity: 8.61 nF (a-b), 270.2 pF (a-g), 269.9 pF (b-g) - pair 1
8.82 nF (a-b), 270.9 pF (a-g), 278.9 pF (b-g) - pair 2.
IV RESULTS OF LONGITUDINAL BALANCE MEASURING – HIGHLY
EXPRESSED FAULTS
Split pairs – very significant
and often faults, It occurs
exclusively due to the
human factor
LB =
> 100 dB
Figure 3
Pair with longitudinal
resistive fault - occurs quite
frequently, caused by badly
done contacts, or corrosion
Figure 4
LB =
> 100 dB
IV RESULTS OF LONGITUDINAL BALANCE MEASURING – HIGHLY
EXPRESSED FAULTS
Pair with shunt resistive fault
between wires – quite often
fault, occurs mostly because of
poorly executed connections or
the humidity that may remain in
the cable in the closure, or in
telecommunication patch boxes.
Figure 5
LB =
Figure 6
LB =
< 28 dB
> 100 dB
Pair with shunt resistive fault
to ground – very often fault, It
occurs on the connection points
of conductors mostly due to the
influence of moisture, or by
touching one of the wires with a
grounded sheath of cable
V
THE DEPENDENCE OF LONGITUDINAL BALANCE ON THE INSULATION RESISTANCE
-
Longitudinal balance does not depend on the
value of the insulation resistance between two
wires – according LB for figure 5. and column
„a-b“ from table 1.
-
Longitudinal balance depends on the
difference of levels of insulation resistance of
individual wires to a grounded sheath of cable.
-
All obtained results, in fact, are in accordance
with the definition and principle scheme of
measuring the longitudinal balance.
VI CONCLUSION
• By measuring value of longitudinal balance we cannot detect very significant
faults, such as: split pair, longitudinal and shunt resistive faults between two
wires of one pair.
• High value of longitudinal balance does not mean that copper pair is without
any faults.
• Only the low value of longitudinal balance indicate that there is probably
some significant fault to ground on this line.
• For complete knowledge of symmetrical copper pairs from the standpoint of
electrical parameters, it is often necessary to measure a large number of
electrical parameters, and it takes a very long time.
• The only "problem" regarding this parameter is that it is often given greater
importance than what it really has, especially by manufacturers of test
instruments.
THANK YOU!