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Testing. Permanent Link Definition –Horizontal cabling extending from the wall plate to the cross connect WORK AREA TELECOMMUNICATIONS CLOSET Horizontal.

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Presentation on theme: "Testing. Permanent Link Definition –Horizontal cabling extending from the wall plate to the cross connect WORK AREA TELECOMMUNICATIONS CLOSET Horizontal."— Presentation transcript:

1 Testing

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

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 Horizontal Cross-connect Wall Outlet Concentration Point Equipment Cable Patch Cable Maximum Length 100 Meters

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

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

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

11 Physical Layer Tests Test ParameterTIA-568-BISO 11801:2002 WiremapPass/Fail Propagation DelayPass/Fail Delay SkewPass/Fail Cable LengthPass/FailInformation only Insertion Loss (IL)Pass/Fail Return Loss (RL)Pass/Fail (except Cat3) Pass/Fail Near-End Crosstalk (NEXT)Pass/Fail Power Sum NEXT (PSNEXT)Pass/Fail Equal-Level Far-End Crosstalk (ELFEXT) Pass/Fail Power Sum ELFEXT (PSELFEXT)Pass/Fail Attenuation-to-Crosstalk Ratio (ACR)Information onlyPass/Fail (except Class C) Power sum ACR (PSACR)Information onlyPass/Fail (except Class C) DC Loop ResistancePass/Fail

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 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 Attenuation

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

17 Copyright of the Applied Optoelectronics Centre DIT 19/08/99 Photocopying strictly prohibited17 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 Decibels dB’s

18 Copyright of the Applied Optoelectronics Centre DIT 19/08/99 Photocopying strictly prohibited18 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 Decibels dB’s

19 Copyright of the Applied Optoelectronics Centre DIT 19/08/99 Photocopying strictly prohibited19 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 Example 1

20 Copyright of the Applied Optoelectronics Centre DIT 19/08/99 Photocopying strictly prohibited20 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 Example 2

21 Copyright of the Applied Optoelectronics Centre DIT 19/08/99 Photocopying strictly prohibited21 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 Example 3

22 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 Back To Attenuation

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

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

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

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

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

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

35 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: NEXT and ELFEXT

36 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 Copyright of the Applied Optoelectronics Centre DIT 19/08/99 Photocopying strictly prohibited37 CAT 5 to CAT 7 NEXT values at 100 MHz NEXT dB Calculations

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

41 THE TRANSMISSION TIME T1T1 T2T2 Delay

42 THE DIFFERENCE IN TIME BETWEEN THE FASTEST AND SLOWEST PAIR T2T2 T1T1 T3T3 Delay Skew = Difference between T 2 and T 3 Delay Skew

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


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