1. Testing

2. Maximum Length - 90 Meters
Permanent Link
Definition
Horizontal cabling extending from the wall plate to the cross connect
WORK AREA
Wall Outlet
Maximum Length - 90 Meters
Horizontal
Cross-connect
TELECOMMUNICATIONS CLOSET

3. Channel
Definition
The end-to-end transmission path connecting any two points at which application specific equipment is connected. Equipment and work area cables are included in the channel

4. Channel WORK AREA TELECOMMUNICATIONS CLOSET Wall Outlet Horizontal
Equipment
Cable
Maximum Length 100 Meters
Horizontal
Concentration
Point
Cross-connect
Patch
Cable
TELECOMMUNICATIONS CLOSET

5. Permanent Link Test Configuration WORK AREA TELECOMMUNICATIONS CLOSET
Wall Outlet
Test Set
Test Set Connection Cable (2 meters)
Horizontal
Maximum Length 94 meters
Cross-connect
Test Set
TELECOMMUNICATIONS CLOSET

6. Channel Test Configuration WORK AREA TELECOMMUNICATIONS CLOSET
Equipment
Cable
Test Set
Maximum Length 100 Meters
Wall Outlet
Cross-connect
Horizontal
Test Set
TELECOMMUNICATIONS CLOSET
Patch
Cable
Concentration
Point

7. Before we look at each of the basic tests we need to review the
Twisted Pair
Before we look at each of the basic tests we need to review the
Physical
Electrical characteristics of a wire pair

8. Anatomy of a Wire Pair
What we think of when we envision a wire pair.

9. Anatomy of a Wire Pair However, to a signal it looks like:
Resistors
Capacitors
Inductors
The cable is not made up of discrete components but has the characteristics of these components
Resistance
Capacitance
Inductance

10. Damaging the cable The characteristics are changed when a cable is:
Stretched (pulling / laying)
Kinked (handling / storage / tight corners)
Distorted (cable ties / stood upon / Heavy cable bundles)

11. Physical Layer Tests Test Parameter TIA-568-B ISO 11801:2002 Wiremap
Pass/Fail
Propagation Delay
Delay Skew
Cable Length
Information only
Insertion Loss (IL)
Return Loss (RL)
Pass/Fail (except Cat3)
Near-End Crosstalk (NEXT)
Power Sum NEXT (PSNEXT)
Equal-Level Far-End Crosstalk (ELFEXT)
Power Sum ELFEXT (PSELFEXT)
Attenuation-to-Crosstalk Ratio (ACR)
Pass/Fail (except Class C)
Power sum ACR (PSACR)
DC Loop Resistance

12. Wire Map
Verification of the physical connection at each end of the cable
Checks for
Opens
Shorts
Crosses
Reverses and any other misfiring
Splits
Difficult to identify with a DC wire map tester
Must use an advanced tester
Will fail on crosstalk

13. Length Physical Calculated based on the length markings on the cable
Maximum physical length of a permanent link is 90 meters
Maximum physical length of a channel is 100 meters

14. Length
Electrical
Based on the propagation delay of a signal over the cable pair
Accomplished using a TDR (Time Domain Reflectometer)
Calculation base on the Nominal Velocity of Propagation (NVP) of the signal over the pair being tested

15. DATA DATA DATA DATA DATA DATA DATA DATA DATA
Attenuation
An analogy is friction
Some of the signal is lost over distance
Energy is dissipated in the form of heat
Message may become to weak to be understood
DATA DATA DATA DATA DATA DATA DATA DATA DATA

16. Before we go any further we must talk a little about decibels (dB’s)

17. Signal Path Decibels dB’s
The deciBel is a convenient means of expressing the ratio of two values
it is commonly used for example to express the Gain or Attenuation of a signal path:
Signal Path
Electrical/ Optical Signal Input
Electrical/ Optical Signal Output
Gain or Attenuation = Output Signal ÷ Input Signal
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18. Decibels dB’s
deciBel expressions for the power and voltage level of a signal are slightly different:
Voltage Gain/Attenuation =
Power Gain/Attenuation =
Note: For Optical Fibre only the Power expression is relevant
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19. Example 1
A NEXT reading is -40 dB for Pair 1 to Pair2. What percentage of the Pair 1 input voltage appears at the input of Pair 2 ?
ANSWER
This result says that 1% of whatever is injected into Pair 1 will appear at the input of Pair 2
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20. Example 2
A FEXT reading is -50 dB from Pair 3 to Pair2. What percentage of the Pair 3 input voltage appears at the output of Pair 2 ?
ANSWER
This result says that 0.3% of whatever is injected into Pair 3 will appear at the output of Pair 2
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21. Example 3
Pair 4 has an Attenuation reading of 20 dB. What percentage of the Pair 4 input voltage appears at the output of Pair 4 ?
ANSWER
This result says that 10% of whatever is injected into Pair 4 will appear at the output of Pair 4
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22. Back To Attenuation
The loss of signal strength over the cable pair, measured in dB
Increases as the carrier frequency increases
Pass/fail based on the worst case attenuation of all pairs

23. Attenuation

24. Crosstalk
Defined as the induction of a portion of the signal from one pair into the adjacent pairs
Measured in dB

25. Cross Talk Types NEXT ELFEXT PSNEXT PSELFEXT NEAR END CROSS TALK
EQUAL LEVEL FAR END CROSS TALK
PSNEXT
POWER SUM NEAR END CROSS TALK
PSELFEXT
POWER SUM EQUAL LEVEL FAR END CROSS TALK

26. NEXT and ELFEXT
A final point is that ELFEXT depends greatly on the length of cable being examined, whereas the NEXT is much less dependent

27. Crosstalk Components
Inductive and Capacitive Relationships:

28. Cross Talk DATA DATA DDATA DATA DATA DATTA DATA DATA
SPILL OVER
ELECTRONS ARE LOST TO THE ADJACENT CABLE PAIRS
THE MESSAGE IS CORRUPTED
DATA DATA DDATA DATA DATA DATTA DATA DATA
DATA DATA ATA DATA DATA DATA DAA DATA DATA

29. NEXT
NEXT MEASURES THE CROSSTALK EFFECT ONE PAIR HAS UPON THE OTHER WITH RESPECT TO THE NEAR END OF THE CABLE

30. Near-End Crosstalk (NEXT)

31. Power Sum Use of the TIA Algorithm for Calculating Power Sum
Calculation is derived from the conventional NEXT measurement.
Only one pair is energized at a time; formula “sums” the crosstalk effect of three energized pairs on the remaining fourth pair.

32. PSNEXT
POWER SUM NEXT IS THE COMPUTED EFFECT OF THREE PAIRS UPON THE FOURTH WITH RESPECT TO THE NEAR END OF THE CABLE

33. ELFEXT
ELFEXT MEASURES THE CROSSTALK EFFECT ONE PAIR HAS UPON THE OTHER WITH RESPECT TO THE FAR END OF THE CABLE

34. PSELFEXT
POWER SUM ELFEXT IS THE COMPUTED EFFECT OF THREE PAIRS UPON THE FOURTH WITH RESPECT TO THE FAR END OF THE CABLE

35. NEXT and ELFEXT
NEXT and ELFEXT (and crosstalk in general) depend very much on the frequency at which they are measured
they increase as the frequency increases
on average they may be described as follows:

36. NEXT and ELFEXT
In practise this means as the Cat6 specification includes frequencies up to 250 MHz, that both the NEXT and ELFEXT measurements will increase dramatically
For example the NEXT at 250 MHz should be about 4 times higher than the NEXT at 100MHz for any given combination of pairs
Even worse the ELFEXT at 250 MHz should be over 6 times higher than the value at 100 MHz for any given combination of pairs
For these reasons (and more) cable that passes Cat 5/5e quite easily may still fail the Cat 6 standard

37. NEXT dB Calculations CAT 5 to CAT 7 NEXT values at 100 MHz
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38. Attenuation to Crosstalk Ratio
Definition:
A ratio comparing the received signal with the near-end crosstalk on a cable
It is not a direct test
It is a comparison of the attenuation test and NEXT test
Used to give an indication of how problem-free the cable line will be
Attenuation-to-Crosstalk ratio (ACR) is the difference between the signal attenuation produced and NEXT and is measured in decibels (dB). The ACR indicates how much stronger the attenuated signal is than the crosstalk at the destination (receiving) end of a communications circuit. The ACR figure must be at least several decibels for proper performance. If the ACR is not large enough, errors will be frequent. In many cases, even a small improvement in ACR can cause a dramatic reduction in the bit error rate. Sometimes it may be necessary to switch from un-shielded twisted pair (UTP) cable to shielded twisted pair (STP) in order to increase the ACR.

39. Attenuation to Crosstalk Ratio (ACR)

40. Propagation Delay Propagation Delay
The time needed for the signal to travel from the transmitter to the receiver over a 100 Ohm 4-pair cable.

41. Delay
THE TRANSMISSION TIME T1 T2

42. Delay Skew THE DIFFERENCE IN TIME BETWEEN THE FASTEST AND SLOWEST PAIR
Delay Skew = Difference between T2 and T3

43. Delay / Delay skew X DELAY THE TRANSMISSION TIME DELAY SKEW (X)
THE DIFFERENCE IN TIME BETWEEN THE FASTEST AND SLOWEST PAIR X

44. Propagation Delay

45. DC Loop Resistance
DC Loop Resistance measures the total resistance through one wire pair looped at one end of the connection. This will increase with the length of the cable. DC resistance usually has less effect on a signal than insertion loss, but plays a major role if you require power over Ethernet. Also measured in ohms is the characteristic impedance of the cable, which is independent of the cable length

46. Return Loss
It measures the difference between test signal’s amplitude and the amplitude of signal reflections returned by the cable.
Information Provided:
Indicates how well the cable’s characteristic impedance matches its rated impedance
Return Loss is the measurement (in dB) of the amount of signal that is reflected back toward the transmitter. The reflection of the signal is caused by the variations of impedance in the connectors and cable and is usually attributed to a poorly terminated wire. The greater the variation in impedance, the greater the return loss reading. If 3 pairs of wire pass by a substantial amount, but the 4 pair barely passes, it usually is an indication of a bad crimp or bad connection at the RJ45 plug.

47. Return Loss