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