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Twisted Pair Cabling Systems

Twisted Pair Parameters

• Cable Category and Performance• Cabling Distance• Connector Performance• System Performance• Performance Testing

Twisted Pair Category and Transmission Performance

MediaType

Tested (up to)Bandwidth

100 MHz

16 MHz

300 MHz

100Ω CAT 3

100Ω CAT 5

100Ω CAT 5e 100 MHz

TypicalUtilization

Voice

2-pairservices2/4-pairservices

100Ω CAT 6

100Ω CAT 7

150Ω Shielded

250 MHz 2/4-pairservices

2/4-pair services, shielded

600 MHz

2-pair services, shielded

Transmission Parameters

• DC Resistance & DC Resistance Unbalance• Capacitance & Capacitance Unbalance• Attenuation• Characteristic Impedance• Structural Return Loss• NEXT/FEXT/ELFEXT loss

− Pair to Pair− Power Sum (CAT 5e & CAT 6)

• Propagation Delay• Delay Skew (CAT 5e & CAT 6)

Horizontal Cabling Distance

6 m 90 m 3 m

Backbone Cabling Distance

HC/FD 500m

HC/FD 800m90m

IC/BD

300m

MC/CD EP

VoiceData

Cross-connect jumpers/patch cables = 20m

Telecommunications equipment cables = 30m

AttenuationReturn LossDC ResistanceNEXT/ FEXT/ELFEXT

Pair-Pair & Power SumPropagation Delay & Delay SkewLCL

Connecting Hardware

Cabling Practices Affecting Performance• Connector Termination Practices

− Use proper category of cable and matching components− Category 5 = < 13mm (0.5”) amount of untwist− Strip only enough cable jacket as necessary

• Patch Cable and Connector Consistency− Use of pre-terminated patch cables

• Cable Management Practices− Eliminate cable stress caused by tension & cinching− Keep cable bend radii no less than 4 times the cable

diameter− No more than 30 m or (2) 90º bends in a single conduit pull

Field Testing Parameters

• Wire Map• Length

− Propagation Delay

− Delay Skew• Attenuation• NEXT• PSNEXT

• ACR• PSACR• FEXT• ELFEXT• PSELFEXT• Return Loss

Wire Map

12

36

54

78

12

36

54

78

Correct Pairs

12

36

54

78

12

36

54

78

Reversed Pair

12

36

54

78

12

36

54

78

Crossed Pairs

12

36

54

78

12

36

54

78

Split Pairs

Length

• Maximum Link Length− 90 meters

− plus a maximum of 2 meters of test equipment patch cords at each end

• Maximum Channel Length− 100 meters

− including equipment cords and patch cords

Nominal Velocity of Propagation (NVP)

The speed at which a signal travels in a cable, expressed as a percentage of the speed of light in vacuum.

NVP =speed at which pulse travels in cable

speed of light in vacuum X 100%

Speed of light in vacuum is 300,000 km/s or 0.3 m/nsec

Length Calculation

Length =RT_Prop_delay (nsec) x NVP x Speed_of_Light

2Example:

measurement of Prop_delay: 435 nsec

NVP (%) Length (ft)68.5 293.369 295.469.5 297.670 299.7

Propagation Delay and Delay Skew

HUBPair 2

Pair 1

Pair 3

Pair 4

NIC

Frequency Link Channel Link ChannelPropagation Delay Delay Skew

1 MHz2 MHz10 MHz

100 MHz200 MHz

541 ns531 ns518 ns510 ns509 ns

580 ns569 ns555 ns548 ns547 ns

45 ns45 ns45 ns45 ns45 ns

50 ns50 ns50 ns50 ns50 ns

Traveling signals is like electrons following a somewhat rocky path

Electrons travel at approx. constant speed

(≈ 20 cm or 8” per ns,

1 ns = 0.000 000 0001 s

NVP * speed of light)

Propagation delay

(max 555 ns later ..)

SpecificationsEffects of Delay Skew

T2T1

HUB

Fastest

Pair 2

Pair 1

Pair 3

Pair 4

SlowestNIC

• Skew is the difference in propagation delay between the fastest and slowest pairs in a cable.

• Proposed requirement: <45 ns @ 100 MHz (Channel)

But every cable has at least 4 electronic highways

Delay SkewThe length of every electronic

road in a cable is slightly different because of twist rates (max 50 ns

differences ..)

Attenuation

NIC HUB

Transmitted Signal

Attenuated Signal

dB loss

Calculated Link Attenuation is the sum of the attenuation of:

• cable segment• all connecting hardware• 10 m of patch cable for channel• 4 m of patch cable for link

There are potholes in the road….

is represented by the electrons that get stuck

Attenuation

Fewer electrons show up!

heat! heat!

Link AttenuationLink Attenuation

Cat 5 Class D Class D Cat 5E Cat 6 Class ETSB 67 ISO/IEC ISO/IEC TIA/EIA TIA/EIA ISO/IEC

Specification Oct-95 11801: JTC1 4195-A Draft 3 JTC11995(E) SC25 WG3 25-Aug-98 18-Aug-98 SC25 WG3

PDAM 3 (Tokyo 92A)Freq. (MHz)

1.00 2.1 2.5 2.1 2.1 2.1 1.94.00 4.0 4.8 4.1 4.0 3.9 3.58.00 5.7 -- 5.7 5.5 --

10.00 6.3 7.5 6.1 6.3 6.2 5.616.00 8.2 9.4 7.8 8.2 7.8 7.120.00 9.2 10.5 8.7 9.2 8.8 7.925.00 10.3 -- 10.3 9.9 --31.25 11.5 13.1 11 11.5 11.1 1062.50 16.7 18.4 16 16.7 16 14.4100.00 21.6 23.2 20.6 21.6 20.7 18.5125.00 -- -- -- -- 20.9155.52 -- -- -- -- 23.6175.00 -- -- -- -- 25.2200.00 -- -- -- 30.4 27.1250.00 -- -- -- -- 30.7

Channel AttenuationChannel Attenuation



PDAM 3 (Tokyo 92A)Freq. (MHz)

1.00 2.5 -- 2.5 2.5 2.1 2.24.00 4.5 -- 4.5 4.5 4 4.28.00 6.3 -- -- 6.3 5.7 --

10.00 7 -- 7 7 6.3 6.516.00 9.2 -- 9.2 9.2 8 8.320.00 10.3 -- 10.3 10.3 9 9.325.00 11.4 -- -- 11.4 10.1 --31.25 12.8 -- 12.8 12.8 11.4 11.762.50 18.5 -- 18.5 18.5 16.5 16.9100.00 24 -- 24 24 21.2 21.7125.00 -- -- -- -- -- 24.5155.52 -- -- -- -- -- 27.6175.00 -- -- -- -- -- 29.5200.00 -- -- -- -- 32.2 31.7

On top of that: the road is not level and electrons fly off!

Crosstalk!!

A level problem in the electronic road will cause some electrons to fall on an adjacent road

NEXT

HUBNICrx

rxtx

tx

Transmitted Signal

Coupled Noise

• Testing of NEXT shall be performed at both ends• All pair combinations shall be measured

Near End Crosstalk (NEXT)

Near End Crosstalk is by the electrons that return back to the beginning

Link NEXTLink NEXT



(Tokyo 92A)Freq. (MHz)

1.00 60 54.0 61.2 64.2 73.5 72.74.00 51.8 45.0 51.8 54.8 64.1 638.00 47.1 -- -- 50.0 59.4 --

10.00 45.5 39.0 45.5 48.5 57.8 56.616.00 42.3 36.0 42.3 45.2 54.6 53.220.00 40.7 35.0 40.7 43.7 53.1 51.625.00 39.1 -- -- 42.1 51.5 --31.25 37.6 32.0 37.6 40.6 50 48.462.50 32.7 27.0 32.7 35.7 45.2 43.4100.00 29.3 24.0 29.3 32.3 41.9 39.9125.00 -- -- -- -- -- 38.3155.52 -- -- -- -- -- 36.7175.00 -- -- -- -- -- 35.8200.00 -- -- -- -- 36.9 34.8250.00 -- -- -- -- -- 33.1

Channel NEXTChannel NEXT



(Tokyo 92A)Freq. (MHz)

1.00 60.0 -- 60.3 63.3 72.7 72.74.00 50.6 -- 50.6 53.6 63.1 638.00 45.6 -- -- 48.6 58.2 --

10.00 44.0 -- 44 47.0 56.6 56.616.00 40.6 -- 40.6 43.6 53.2 53.220.00 39.0 -- 39 42.0 51.6 51.625.00 37.4 -- -- 40.4 50 --31.25 35.7 -- 35.7 38.7 48.4 48.462.50 30.6 -- 30.6 33.6 43.4 43.4100.00 27.1 -- 27.1 30.1 39.9 39.9125.00 -- -- -- -- -- 38.3155.52 -- -- -- -- -- 36.7175.00 -- -- -- -- -- 35.8200.00 -- -- -- -- 34.8 34.8250.00 -- -- -- -- -- 33.1

FEXT

HUBNICrx

rxtx

tx

Transmitted Signal

Coupled Noise

Attenuated Signal

• Testing of FEXT shall be performed at both ends• All pair combinations shall be measured

Far end crosstalk (FEXT)

Far End Crosstalk is by the electrons that continue to the far end

Return Loss

-12dBm -14dBmtx rx

• Typically attenuation caused by characteristicsinherent in the cable, such as:

• impedance mismatches• kinks in the cable• poor construction

SpecificationsEffects of Return Loss

Reflected Signals

Pair 1

Pair 2

Pair 3

Pair 4

NIC

Transmitted Signals Attenuated Signals

HUBImpedance mismatch or variation

• A measure of the reflected transmit energy caused by impedance mismatches in the cabling systems

• Especially important in applications that use full duplex transmission schemes

There are also bumps and dips in the road: return loss

A bump or dip causes

some electronsto go back

Link Return LossLink Return Loss



(Orlando 39A) (Orlando 39A)Freq. (MHz)

1.00 -- 18.0 17.0 17.0 19.0 19.04.00 -- 18.0 17.0 17.0 19.0 19.08.00 -- 18.0 17.0 17.0 19.0 19.010.00 -- 15.0 17.0 17.0 19.0 19.016.00 -- 15.0 17.0 17.0 19.0 19.020.00 -- 15.0 17.0 17.0 19.0 19.025.00 -- 10.0 16.3 16.3 18.3 18.331.25 -- 10.0 15.6 15.6 17.6 17.662.50 -- 10.0 13.5 13.5 15.5 15.5

100.00 -- 10.0 12.1 12.1 14.1 14.1125.00 -- -- -- -- 13.4 13.4155.52 -- -- -- -- 12.8 12.8175.00 -- -- -- -- 12.4 12.4200.00 -- -- -- -- 12 12250.00 -- -- -- -- 11.3 11.3

Channel Return LossChannel Return Loss



(Orlando 39A) (Orlando 39A)Freq. (MHz)

1.00 -- -- 17 17 19 194.00 -- -- 17 17 19 198.00 -- -- 17 17 19 1910.00 -- -- 17 17 19 1916.00 -- -- 17 17 19 1920.00 -- -- 17 17 19 1925.00 -- -- 16 16 18 1831.25 -- -- 15.1 15.1 17.1 17.162.50 -- -- 12.1 12.1 14.1 14.1

100.00 -- -- 10 10 12 12125.00 -- -- -- -- 11 11155.52 -- -- -- -- 10.1 10.1175.00 -- -- -- -- 9.6 9.6200.00 -- -- -- -- 9 9250.00 -- -- -- -- 8 8

Some electrons may fly into the air and eventually land on earth!

Electromagnetic Interference (EMI)!!

Electrons in the air may be picked up by your radio or TV antenna and cause interference!

Signal-to-noise ratios (3)

• There are three quantities which affect signal-to-noise ratio (SNR):

• Attenuation to Crosstalk Ratio (ACR).• Equal Level Far End Crosstalk

(ELFEXT).• Return Loss.

Signal-to-noise ratio #1: ACR

• Attenuation to Crosstalk Ratio (ACR)• Applicable to 2-wire pair LAN

applications (10BASE-T, 100BASE-TX).

• Each wire pair carries signal in one direction only.

CharacteristicsEffects of ACR

Transmitter Receiver

Receiver Transmitter

NIC HubNIC HUBCoupled NEXT Noise

Attenuated Signal Transmitted

SignalACR

Attenuated Signal NEXT Noise

ACR = the traditional SNR

Desired signal = attenuated signal from other end.

Noise = NEXT + external noise (ignore external noise).

TransmitOutput

TransmitOutput

ReceiveInput

ReceiveInput

Workstation LANequipmentSignal

NEXT

Externalnoise

Signal

(For LAN systems with two wire pairs carrying signalsin one direction each.)

You need more signal (blue,pink) than NEXT (black) electrons!

TransmitOutput

ReceiveInput

Workstation

TransmitOutput

ReceiveInput

LANequipment

NEXT(local)

NEXT(remote)

Signal(from remote to local)

Signal(from local to remote)

Look here and here!

Signal-to-noise ratio (ELFEXT)

• Equal Level Far End Crosstalk (ELFEXT).

• Applicable to applications where 2 or more signals travel in the same direction at the same time (1000BASE-T).

Another S/N = ELFEXT


Noise = FEXT + external noise (ignore external noise).

TransmitOutput

TransmitOutput

ReceiveInput

ReceiveInput

Workstation LANequipmentSignal

FEXT

Externalnoise

Signal

(For LAN systems with two or more wire pairs carrying signals in the same direction at the same time.)

You need more signal (blue,pink) than FEXT (black) electrons!

TransmitOutput

ReceiveInput

Workstation

TransmitOutput

ReceiveInput

LANequipment

Look here!

Signal(from local to remote)

Signal(also from local to remote)

FEXT

FEXT

Yet another S/N = Return Loss


Noise = reflected signal in own wire pair

“hybrid”“hybrid”

TransmitOutput

TransmitOutput

ReceiveInput

ReceiveInput

Workstation LANequipment

Signal

Return loss(bump in

electronic road)

(For LAN systems with a wire pair carrying signals in both directions at the same time.)

Yet another S/N = Return Loss


Noise = reflected signal from own end

“hybrid”

TransmitOutput

TransmitOutput

ReceiveInput

ReceiveInput

Workstation LANequipment

Return loss signal (bump in electronic road)

Signal Signal“hybrid”

(For LAN systems with a wire pair carrying signals in both directions at the same time.)

Power Sum Performance

Pair-to-pair:Single disturberSingle receiver

Power sum:Multiple disturbersSingle receiver

• Power sum performance is the sum of the pair-to-pair performance of the component or system.

• Power sum NEXT performance should meet or exceed the existing TIA pair-to-pair NEXT requirements.

What is “power sum” NEXT and “power sum” ELFEXT?

• Both are computed values from measured pair to pair NEXT or ELFEXT results:− Power Sum NEXT computed from three

pair-to-pair NEXT results− Power Sum ELFEXT is computed from

three pair-to-pair ELFEXT results

• Often required when more than 2 wire pairs are transmitting signals in the same direction (1 Gbps Ethernet).

When are “power sum” NEXT and “power sum” ELFEXT needed?

• Often required when more than 2 wire pairs are transmitting signals in the same direction (1 Gbps Ethernet).

• Significant if 25-pair cables are used (split up in six 4-pair links).

• May also be used to reflect crosstalk between separate 4-pair cables in a cable bundle.

PS ELFEXT

HUBNIC

x

x

x

xx

x

x

xNear End Far End

PS ELFEXT = -10log(10-x1/10 + 10-x2/10 + 10-x3/10) dB

Link PS ELFEXTLink Power Sum ELFEXT



(Tokyo 78A) (Tokyo 92A)Freq. (MHz)

1.00 -- -- 57.0 57.0 62.2 61.24.00 -- -- 45.0 45.0 50.2 49.18.00 -- -- -- 38.9 44.1 --10.00 -- -- 37.0 37.0 42.2 41.216.00 -- -- 32.9 32.9 38.1 37.120.00 -- -- 31.0 31.0 36.2 35.125.00 -- -- -- 29.0 34.2 --31.25 -- -- 27.1 27.1 32.2 31.362.50 -- -- 21.1 21.1 26.3 25.2

100.00 -- -- 17.0 17.0 22.2 21.2125.00 -- -- -- -- -- 19.2155.52 -- -- -- -- -- 17.3175.00 -- -- -- -- -- 16.3200.00 -- -- -- -- 16.2 15.1250.00 -- -- -- -- -- 13.2

Channel PS ELFEXTChannel Power Sum ELFEXT



(Tokyo 78A) (Tokyo 92A)Freq. (MHz)

1.00 -- -- 54.4 54.4 60.2 60.24.00 -- -- 42.4 42.4 48.2 48.28.00 -- -- -- 36.3 42.2 --10.00 -- -- 34.4 34.4 40.2 40.216.00 -- -- 30.3 30.3 36.1 36.120.00 -- -- 28.4 28.4 34.2 34.225.00 -- -- -- 26.4 32.3 --31.25 -- -- 24.5 24.5 30.3 30.362.50 -- -- 18.5 18.5 24.3 24.3

100.00 -- -- 14.4 14.4 20.2 20.2125.00 -- -- -- -- -- 18.3155.52 -- -- -- -- -- 16.4175.00 -- -- -- -- -- 15.4200.00 -- -- -- -- 14.2 14.2250.00 -- -- -- -- -- 12.3

Data Measurement

• Test equipment manufacturer access cords and adapters should be used in link testing

• User cords should be tested in place for channel testing, and be used in that channel only

• Any reconfiguration of components must be re-tested to verify conformance

• Inspect the connecting hardware for wear and tear resulting from multiple mating cycles

Data Administration & Reporting• Pass or Fail result for each parameter should be

determined by comparison with the allowable limits

• Overall Pass is determined by passing all of the individual tests

• Overall Fail is determined by failing at least one of the individual tests

• Whether Pass or Fail, pair, frequency and test limit at the worst-case should be reported

• Pass condition - either the worst-case margin or worse-case data point should be reported

• Fail condition - the worse-case margin should be reported− Multiple Fail - the worse-case at the highest frequency point

Field Testing Parameters Summary

Wire MapLength

AttenuationNEXT

Return LossELFEXT

Propagation DelayDelay Skew

Troubleshooting Common Faults

Length violationEMI sourcesBad quality cableConductor untwistShorts, Opens, Split pairs, Crossed pairsCAT 5 Return Loss and ELFEXT Failures

Twisted Pair Summary

• Twisted Pair Cable Categories and Performance• Cabling Distances

− Horizontal− Backbone

• Connecting Hardware Specifications• Factors Affecting Performance• Field testing requirements of twisted pair cabling

links and channels• Recognizing, troubleshooting and mitigating

common faults

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