Post on 26-Mar-2018
Dubai 2008.May
10 Gigabit EthernetTesting of installed fiber optic links –A foundation for today’s and future
high performance applications
10 Gigabit EthernetTesting of installed fiber optic links –A foundation for today’s and future
high performance applications
Mike KazemianSynergix
Dubai 2008.May
SummaryLong awaited guidelines for fiber testing clarify details about how to certify fiber links to be ready for 10G. This presentation covers what we can expect from ISO/IEC 14763-3 and how the use of simple light sources and power meters can be complemented by the use of an OTDR, ensuring optimized margins and consistent installation quality.
Dubai 2008.May
Agenda• Standards Update: What is new in ISO/IEC
14763-3– Short Review of legacy methods– What is new and which questions are
answered– Which questions are new or remain
unanswered• Significance of Launch Conditions• A clarification of the referencing method
ending an ongoing confusion• Advantages of an extended test regime
– Example for a combined field measurement with LSPM and OTDR
• Significance of accuracy in Data Center applications
Dubai 2008.May
10 Gb Ethernet
• Approved by TIA in June 2002• A trend finds it’s continuation
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Smaller loss budgetsSmaller loss budgets
Dubai 2008.May
Relevant International Standards
• ISO/IEC 11801:2002 (EN 50173-1:2002):– Define Links and Channels limits– Relevant parameters are Length and Insertion Loss
• ISO/IEC 14763-3 (EN 50346):– defines details about the test set up (Has been recently
reworked)
• IEC 61280-4-1: (2003)– Defines more details about Referencing Methods for Link &
Channel and launch condition of the light source. (CPR = Coupling Power Ratios)
Dubai 2008.May
The choice of light source is essential
1st 850nm
Std Dev2nd 850nm
Std Dev
VCSELLED w/mandral
LED0.00
0.20
0.40
0.60
0.80
1.00
1.20
dB
50 m 50/125 um 850 nm Test Comparison
VCSELLED w/mandralLED
VCSEL 0.40 0.08 0.65 0.10LED w/mandral 1.08 0.01 0.97 0.04LED 1.10 0.05 1.02 0.08
1st 850 nm Std Dev 2nd 850 nm Std Dev
• OTDR‘s always use a laser• Legacy Standards define
CPR= Category 1 (Overfilled Launch = LED)
• Future standards will be even more specific
Dubai 2008.May
Why the overfilled LED always had been the right light for testing links….
ISO/IEC 11801: 2002Technical Report ISO/IEC TR 14763-3
MM: Method 2 of IEC 61280-4-1SM: Method A1 of IEC 61280-4-2
>> The modal launch conditions from the light source shall be characterized as one of categories 1 through 5 following the procedure in annex A. If not otherwise specified in a reference document, light sources from category 1 shall be used and noted in the test report (see 7.1). Category 1 sources result in the highest measured cable plant loss.
Dubai 2008.May
Review of common test methods
• 5 foils show historically used methods• Some common methods were not correct• Methods were based on partially invalid
assumptions
Dubai 2008.May
Method B – one jumper reference
Setting referenceSetting reference
dBdB
AddedAdded
dBdB
includes link includes link + + ALLALL connectorsconnectors
Supports a Permanent Link Measurement
Dubai 2008.May
Method A – „Two Jumper Reference“
Unfortunately is the most often intuitively used method is not correct
dBdB
Setting ReferenceSetting Reference
includes Link includes Link + + only oneonly one EndEnd--
ConnectorConnector
dBdB
Dubai 2008.May
Method 3 – „Three Jumper Reference“
ReferencingReferencing
Includes Link/Channel Includes Link/Channel BUT NOBUT NO
End ConnectorsEnd Connectors
dBdB
The connector can be The connector can be a different type then a different type then the one on the OLTSthe one on the OLTS
dBdB
Supports a Channel
Measurement
Dubai 2008.May
3.2 dB noted for Gigabit in 568-BTest Example
Source Meter
850 nm1300 nm
62.5/125 µm cabling100m backbone cable6m patch cord106m to the wall outlet
Method A =3 Connections @ 0.7 dB plus0.6 dB for fiber = 2.8 dB
Method B =4 Connections @ 0.7 dB plus0.6 dB for fiber = 3.4 dB
Method C =2 Connections @ 0.7 dB plus0.6 dB for fiber = 2.0 dB
Method AA =3 Connections @ 0.7 dB plus0.6 dB for fiber = 2.8 dB
Method BB =4 Connections @ 0.7 dB plus0.6 dB for fiber = 3.4 dB
Method CC =2 Connections @ 0.7 dB plus0.6 dB for fiber = 2.0 dB
Method BB results in a correct FAILHorizontal Cables
Backbone Cables
TR
TR
MCX
XX X
Dubai 2008.May
Inconsistent nomenclature caused additional confusion
Similar methods used very different and often misleading names
Standard Mode NameEIA/TIA-526-14A-98 Multi
SingleMulti
Single
Method A Method B Method CEIA/TIA-526-7-98 Method B.1 Method A.1 Method C.1IEC 61280-4-1 Method 1
2 jumper reference
Method 21 jumper reference
Method 33 jumper reference
IEC 61280-4-2 Method 1bTwo jumper cable measurement
Method 1aOne jumper cable measurement
Method 1cThree jumper cable measurement
ChannelPermanent Link
Dubai 2008.May
Let’s refresh what is Method 3 - „Three Jumper Reference“
includesLinkincludesLink/Channel /Channel BUT NOBUT NO
End ConnectorsEnd Connectors
dBdBdBdB
Supports a Channel
Measurement
Dubai 2008.May
The test leads decide about the relevance of test results
Source
Analysis of two extreme cases using the „3 Cord Referenz Methode“Case 1:
The test leads show a „typical“ value for the „Mated IL“x2▫y1 = x2▫d1 AND y2▫z1 = d2▫z1…. The measured IL is that of the cable without connecting hardwareNOTE: There is no foundation for assuming a „typical“ value
Case 2:The test leads showing an ideal IL close to 0dB x2▫y1 = 0dB und y2▫z1 = 0dB…. The measured IL is that of the link including* the connecting hardware
NOTE: *) measured mated IL that of a “perfect” cord mated with a random cord
Meter
Source Meter
x y zx2▫y1 y2▫z1
Referencing
dx zx2▫d1 d2▫z1
Measurement
Case 1
Case 2
Dubai 2008.May
Finding leading to parts of ISO/IEC 14763-3A. All Methods for referencing assume that the mated IL of test
leads is the same as randomly mated connectors1) This can not be assumed2) The performance of test leads is significantly affecting the
measured values3) „1 Jumper Method“ is least affected by this incorrect assumption.
B. The distribution of power amongst modes has a significant affect on the measured IL
1) The lack of HOMP (Higher order mode power) will lead to optimistic results
2) Mandrels only represent a partial solution and need to be combined with a well defined launch condition
3) VCSEL light sources suffer HOMP and a mandrel would if anything make it worse
Dubai 2008.May
What is new and different in ISO/IEC 14763-3
ISO/IEC TR 14763-3 (2000) NEW ISO/IEC 14763-3 (2006)
Technical Recommendation International Standard
12 pages 62 Pages
Refers to 1 of 3 methods for referencing in IEC 61280-4-1 (MM) & 61280-4-2 (SM)
Two Reference methods defined“3 jumper reference” …(primary)“1 jumper reference” …(secondary)
Specifies Light source has to have a of Category 1 CPR (coupling power ratio)
Defines MPD of light source (Modal Power Distribution)CPR as a secondary definition
Inspection of fiber end faces
Defines 2 test regimesBASIC: LSPM (Light source & Power Meter)EXTENDED: OTDR (Reflektometer)Method for (re) qualification of test leads
Dubai 2008.May
The NEW “The Three Jumper Reference”• Similar in process to the old method which assumed that the mated IL of a test
lead is similar to when mated with the link• The new method assumes test leads with connectors of „reference quality“
– Max. 0.1 dB Reference Plug ↔ Reference Plug– Max. 0.3 (0.5) dB Reference Plug ↔ Random Plug (SM)– Max. 0.75 dB Random Plug ↔ Random Plug
• The reference quality needs to be verified periodically
– Max. 0.1 dB Reference Plug ↔ Reference Plug
• This results in a new budget when testing PL Example: for MM 850nm 100m link
– OLD: 2 x 0.75dB + 3.5dB/km(2 x 0.75) + 0.35 = 1.85dB
– NEW: 2 x 0.3 dB + 3.5dB/km(2 x 0.3) + 0.35 = 0.95dB …. -50% in this example !!!
Dubai 2008.May
How do the new “1 jumper – “ and new “3 jumper –”reference method compare
Assumption 1 Jumper Method 3 Jumper MethodRegular patch cords as test cords Accuracy Poor Accuracy Very
PoorHigh Quality Test Cord Excellent Good
Meter without interchangeable connectors
works if link has matching connectors
works
Meter withinterchangeable connector
Works: SC, ST, FC (Soon LC, E2000)
Don’t bother
SFF: MTRJ, Volition, etc. Not possible Works. Accuracy will be good if cord in reference quality can be obtained
Dubai 2008.May
2-tier testing per ISO 14763-3Defines BASIC / EXTENDED Test regime similar to Tier 1 & Tier 2
Concept in TIA TSB-140
• BASIC Test Group (…Tier 1) LSPM (Light Source & Power Meter)
• EXTENDED Test Group (…Tier 2) OTDR–… “The tests in the extended test group supplement those of the basic test group”…. “Where measured results do not comply with the applicable limits it is recommended that the channel or permanent link be subjected to investigation using the extended test group”
Dubai 2008.May
OTDR Limits• Standard define limits (calculation) for Tier 1 (OLTS) Tests• The standard defines no limits for Tier 2 (OTDR) Tests
WHY ?!?!• Poor correlation with OLTS results for multimode• Factor 1 – 2.5 (MM)• Die OTDR measurements „Qualitative“ rather then „Quantitative“
• How to choose limits for Tier-2 in a project?• Sometimes Tier-1 limits are used• Often in project limits more demanding
then Tier-1 limits are used• With new OTDR the use specify
project specific/related limits• The test then shows a PASS or a FAIL
against a chosen limit
Dubai 2008.May
Reasons for using a OTDR?1. Single ended test of a link 2. The total length can be detected3. The quality of installation can be verified and
improved• Each individual segment can be evaluated
4. A trace represents the entire links• Build knowledge base for a installed plant• Complete Documentation• A source of later variation/degradation can be identified
5. The only way to efficiently troubleshoot a installed link or channel
Dubai 2008.May
Tier 1 Test Example
Source Meter
850 nm1300 nm
62.5/125 µm cabling100m backbone cable6m patch cord106m to the wall outlet
Horizontal Cables
Backbone Cables
TR
TR
MC X
XXX
Result: 3.05 dB
3.2 dB noted for Gigabit in 568-B.1, Annex E
Dubai 2008.May
Tier 2: The OTDR
TRTR
MCX
XX X
100m 6m 106m
Ooops!
Dubai 2008.May
Tier 1: Retest:1.92dB !!!
TRTR
MC X
XX X
850 nm1300 nm
Source Meter
100 m 6 m 106 m
OoopsEradicated!
The reduced insertion loss results in a more reliable system with a safety margin !
The reduced insertion loss results in a The reduced insertion loss results in a more reliable system with a safety margin !more reliable system with a safety margin !
Dubai 2008.May
Certification with a multifunctional tool
OLTSOTDRInspectionDocumentation
Optical Loss Test System:
uses the “correct light”and provides a standards conformant certification
Optical Loss Test System:
uses the “correct light”and provides a standards conformant certification
Automatic PASS/FAIL Analysis for each segment
Automatic PASS/FAIL Analysis for each segmentLocates events of
incorrect installation
Locates events of incorrect installation
Dubai 2008.May
Further additions in ISO/IEC 14763
• Clarification of bidirectional measurement• Usage of launch and receive fibers• Recommendation for use of EXTENDED
testing regime• Inspection of fiber
end faces
Dubai 2008.May
OTDR
ISO/IEC 14763-3: Launch fiber
Launch fiber
Insertion loss of first connector
Dubai 2008.May
ISO/IEC 14763-3:Launch & Receive Fiber
OTDR
Receive Fiber
IL of last connector
LaunchFiber
?
Dubai 2008.May
Launch and Receive Fiber Compensation
CursorEnd of launchfiber
Event Information relativ to end of launchfiber
Zero Position
Begin of receivefiber
Dubai 2008.May
ISO 14763-3 is calling for a Multifunctional tool
End face inspection
Channel MapOTDR
Traces & Analysis OLTS/LSPM
based certification
Documentation
Dubai 2008.May
ISO/IEC 14763-3 Some questions remain openAnswers are expected for Amendment #1 in Summer 2007
Q: Should the limit calculation for 1 and 3 jumper method be differentA: YES: 0.3dB “Reference <-> Random” should only be valid for “1 Jumper
Method” and 0.2 – 0.25dB for “3 Jumper Method”
Q: Are correction for the channel measurement necessary ?A: Open
Q: Should the more accurate 1 jumper method be titled the primary methodA: YES
Q: What is the effect of using degraded test leads and the the 3 jumper methode
A: BAD NEWS: The contractor will be rewarded with optimistic results
Dubai 2008.May
Special requirements in DatacentersThe Challenge:1. Required are often multiple secure zones, which calls for „Multiple
Patched Channels“
2. The final channel construction is not know during certification
3. The total budget for insertion loss is limitede.g.: IEEE 802.3: 10GBASE-SR/SW 2.6dB (OM3)
Link #2 Link #3Link #1
Channel
Dubai 2008.May
IEEE 802.3ae Allocates the total power budget
Einfüge-dämpfung
„Dispersion-Equivalent“
Dubai 2008.May
Reduced Channel Length ► Increased Loss Budget• A simplified view of a new concept
• Looking at this example– The total loss budget was increased by 120– Using good quality cord and connectors 13 connection should
be possible
Assumption Max. Length 1/3 of max. length
Max. Channel length 300 m 300 * 1/3 = 100 m
Allocation f. Dispersion 4.7 dB 4.7 * 1/3 = 1.6
Loss Budget 2.6 dB 2.6 + (4.7 – 1.6) = 5.7 dB
Max # of connections: Assuming 0.4 dB / Connection
(2.6 – (300 x 003.5)) / 0.4 = <4
(5.7 – (100 x 0.0035)) / 0.4 = > 13
Dubai 2008.May
Datacenter Standards use similar approaches
EN 50173-5Generic cabling systems -Part 5: Data centers
ISO/IEC 24764
TIA 942
Dubai 2008.May
Increased loss budget for short channels: …. Consequences for field testing
1. Limits:No consequence because permanent links will be certifiedUnfortunately Channel or Application Limits are frequently used to certify permanent links …. A fatal mistake
2. Accuracy:Significant consequences:
Very short links are measured with high % in uncertaintyExample: 30m Link + „ non perfect 0.3dB Test Leads“ + “3 Jumper Method” result in a uncertainty of up to 0.6dBLink budget: 0.3 + 0.3 + 0.105 = 0.705 dBUncertainty can be in the range of > 90%The measurement error due to poor test leads is systematic rather then random and typically „optimistic“Often heard: „If I use poor test leads, I test for worst case“…. Is „Top-Non-Sense“
Dubai 2008.May
Conclusion
1. The choice of the right method for referencing is essential2. The quality of test cords decides about the relevance of
test method3. The choice of the right light source has major impact on the
measure results4. The role of a OTDR is that of a complimentary tool for
optimizing and verifying the quality of an installation5. Multiple patched channels in data centers will suffer from
„casual“ test methods