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P b C d C bl dPruebas en Campo de CableadoEstructurado Desde TSB‐67 a la ISO‐
61935
Field Certification Procedures
and
How to Interpret Resultsp
Presented byPresented byJim Davis
AgendaAgenda
• Certification of Structured CablingCertification of Structured Cabling– How to read Certification reports
Parameters to measure– Parameters to measure
• Certification for Cat 6a and Class Fa– fun with Alien Next
– 600 MHz or 1000 MHz
• Recommendations for the future
Why Certify?Why Certify?Be sure that the installed cabling meets the performance you are paying forare paying for.
Cat 6 jack + Cat 6 cable + Cat 6 installer ≠ Cat 6
Ask your integrator for test results from previous jobs to showAsk your integrator for test results from previous jobs to show their competency
Experience has shown that Certified networks run faster
CRC/FCS errors lead to re‐transmissions
Less expensive components can be considered – if they meet your performance requirementsyour performance requirements
Beware of those who offer to save $ on the installation by not certifying
Don’t be this guy (see next)
Avoid this:
Use the least expensive cable that meets f t tiyour performance expectations…
The cable was bad –The cable was bad who knew – but the
f dcustomer found out in time
Certification is for the Field not the Lab
Return Loss in Near EndReturn Loss in Near End
PVC jacketed CM cable outdoors?
How to Read Test Results
How to Read Test Results
How to Read Test Results – Class FHow to Read Test Results Class F
How to Read Test Results – Class FHow to Read Test Results Class F
Propagation DelayPropagation Delay
Traveling signals is like electrons following a h k h
Propagation delay
somewhat rocky path
Electrons travel at approx. constant speed
(≈ 20 cm or 8” per ns,
1 ns = 0.000 000 0001 s
(max 555 ns later ..)
NVP * speed of light)
Insertion Loss on Test ReportInsertion Loss on Test Report
Existen baches en el caminoExisten baches en el camino….
Atenuación
(Perdida de inserción)(Perdida de inserción) Menos electrones!
Calor! Calor!
Attenuation/Insertion Loss increases h dwith Distance and Frequency
Atten ation on a shorter (25Mtr) linkAttenuation on a shorter (25Mtr) link
Attenuation/Insertion Loss increases h dwith Distance and Frequency
l ( ) l kAttenuation on a longer (60 Mtr) link
Attenuation/Insertion Loss increases h dwith Distance and Frequency
Attenuation at 550 MHz
NEXT on Test ResultsNEXT on Test Results
On top of that: the road is not level and l fl ff!
Crosstalk!!
electrons fly off!
Crosstalk!!
A level problem in the electronic road will cause some electrons to fall on an adjacent road
Near End Crosstalk (NEXT)
Near End Crosstalk is by the electrons thatNear End Crosstalk is by the electrons that return back to the beginning
ELFEXT on Certification ReportELFEXT on Certification Report
Far end crosstalk (FEXT)
Far End Crosstalk is by the electrons that continue to ythe far end
NEXT and FEXT increase with FrequencyNEXT and FEXT increase with Frequency
NEXT can be reduced with Shielded CablingNEXT can be reduced with Shielded Cabling
But the shield has to be properly terminated f h k f ll lfor this to work up to its full potential
• We have seen shielded systems fail in the FIELDy
Shielded cable does not need to be dtested?
• The shield may not be connected correctly, as in this example
ACR on Test Results – Bigger Gap BetterACR on Test Results Bigger Gap Better
Combine two effects: attenuation and NEXT: S/N = ACR
Look here!
At a receiver input you need more signal electrons than stray electrons
Poor ACR (and NEXT problems)can lead to d d !FCS and CRC errors and – Retransmissions!
FCS/ACR Errors Lead to Slow NetworksBelow is a an example of a typical TCP conversation
HTTP “Get” data I want
ACK – I see your request
H i d ( i h B d FCS)Here is your data (with Bad FCS)Yuck, bad FCS!I’ll just discard at Physical Layer Where’s my ACK?
ReTransmit – Here is your Data ‐ again
Time goes by
ReTransmit Here is your Data again
ACK – I received the data
Bad Cabling = Slow NetworkBad Cabling Slow Network
Sender waited 2.6 seconds prior to retransmissionSender waited 2.6 seconds prior to retransmission
Cat 6a and Class FaCat 6a and Class Fa
Welcome to Alien Next
Why to test for Alien Next?Why to test for Alien Next?
• ANEXT has always existedANEXT has always existed
• Higher Frequencies, more attenuation, signals that are more susceptible to interferencethat are more susceptible to interference
• Data Errors in the Core of a Network (D ) h l i ll(Datacenter) have a larger impact on all users
• Assure the Field Installation meets the performance expectations
When to Test for Alien Cross TalkWhen to Test for Alien Cross Talk
• High Frequency ApplicationsHigh Frequency Applications
• 10GBaseT
C 6• Cat 6a
• Class F and Class Fa
• Datacenter cabling
• Shielded CablingShielded Cabling
• Unshielded Cabling
Alien NEXT Test ResultsAlien NEXT Test Results
Alien NEXT Test Results
Alien CrosstalkAlien crosstalk occurs between cables
Cat 6a/Class F and Fa TestingCat 6a/Class F and Fa Testing
• Two steps
• Step 1 – Regular Field Testing– Make the Permanent Link/Channel MeasurementMake the Permanent Link/Channel Measurement– Make sure you are storing plot/graphical data
• Step 2 – Alien TestingFind your longest link– Find your longest link
– Select a disturbed cable– Energize the cables around it one at a time
• Taking into account Insertion Loss Power Backoff• Taking into account Insertion Loss – Power Backoff– Do PS ANEXT (Power Sum Alien Near‐End Crosstalk– Do PS AACR‐F (Power Sum Alien Attenuation Far End Crosstalk
Special Requirement for Class FaCat 7 patch cords/Permanent Link Adapters
ANEXT – Picking DisturbersThis could be clearer
• 6.2.1.4 Alien (exogenous) crosstalk testing
• Where the installation specification requires acceptance testing of alien (exogenous) crosstalk transmission parameters... against the requirements of permanent link or channel Classes EA or FA of ISO/IEC 11801, the sample level for disturbed permanent links or channels shall be determined according to ISO 2859 series. …The selected sample quantity shall be subject to the selection as specified in IEC 61935‐1.
• ISO 2859 is a generic standard for statistical sampling procedures applied to quality control in many industries (very similar to MIL‐STD 105E and ANSI/ASQ Z1.4). Default recommendations in the same section of 14763‐2 ll f i i i f 32 li k f ll i ll i i h l h2 call for testing a minimum of 32 links for all installations with less than 500,000 links. The same selection criteria (based on IL) and margin allowance (5dB) shall be applied from 61935‐1
ANEXT – Picking Disturbed and b blDisturbing cables
• Will be Statistical – a function of all cablesWill be Statistical a function of all cables– 12 – 20 disturbed links for locations with 150 –3000 cables installed
• Disturbing cables will be based on proximity– In Patch Panel– In Bundle – keep bundles small– Use a mix of long, medium and short links
• If good margin on these links, other links will be good
All the Cables in the Bundle are b k h b dl llDisturbers – keep those bundles small
/Selecting a disturbed/victim cable• Bad choice
• There are no adjacent connectors
/Selecting a disturbed/victim cable• Good choice
• There are adjacent connectors
Selecting the disturbers (cables to )energize)
• Good choice
• Select the cables in that bundle
Selecting the disturbers (cables to energize)
• Correct choice
• Connectors produce most of the alien crosstalk, so you need to select all of the connectors located next to the disturbed/victim link
PS ANEXTPS ANEXT
• Power Sum Alien Near End CrosstalkPower Sum Alien Near End Crosstalk
PS AACR‐F• Power Sum Alien Attenuation Crosstalk Ratio Far end
Example PS ANEXT measurementExample PS ANEXT measurement
600MHz vs 1000 MHz for Class Fa600MHz vs 1000 MHz for Class Fa
• Class Fa links have a performance limitsClass Fa links have a performance limits specified out to 1000 MHz
• Field testers today do not have sufficient• Field testers today do not have sufficient accuracy to provide useful data at these high frequenciesfrequencies
• The standard requires testing for Class Fa to 600MH b d hi f l600MHz, beyond this frequency, test results are ‘informative’
Field Test of Cat 7/ClassFaField Test of Cat 7/ClassFa
• In IEC 61935‐1 we see the following text:In IEC 61935 1 we see the following text:
• 6.7 Accuracy performance requirements for Level IV field testers over 600 MHzIV field testers over 600 MHz The Level IV requirements shall apply to measurements of class FA cabling up to 600 MHzmeasurements of class FA cabling up to 600 MHz and pass/fail evaluation criteria shall apply. Measurement data over 600 MHz shall be provided for information only. Detailed requirements over 600 MHz are for further study.
Tester Accuracy Deteriorates at Higher Frequencies
Here we see +/‐ 2.75 dB @600MHz( / )(Level IV accuracy @600MHz is >+/‐5dB)
ConclusionsConclusions
• Certification is the best way to assure thatCertification is the best way to assure that installed links meet your performance requirementsrequirements
• Class Fa links should be tested to 600 MHz
Ali NEXT i h ld b ll d• Alien NEXT testing should be called out on both Cat 6a and Class Fa links to assure best
fperformance