Smart Buildings

OLTS or OTDR: Which Test Is Acceptable for Fiber Certification?

Molly Hunter
There are two big problems with using OTDR results instead of OLTS results to certify fiber systems: OTDR tests aren’t accurate, and TIA doesn’t recognize them.


Fiber is the backbone of today’s mission-critical infrastructure—and that’s no exaggeration.


It supports life-saving robotic surgeries. It enables high-speed trading. It creates the foundation for interactive fan experiences. But it must be installed properly to function in these capacities.


Proper fiber deployment begins with the people who install it: They should be certified technicians and installers who are trained in the latest design standards and installation best practices and understand the products they’re installing. Because they’re certified, they make fewer installation errors and know the most efficient ways to achieve reliability.


Once their work is complete, the installation itself should be certified, too, conducting proper testing with certified fiber testers.


The Advantage of Having a Certified Fiber System

If you want a warranty, then this level of certification testing is required.


Certification not only proves that mission-critical infrastructure works, but also gives installers a way to differentiate their services and connects owners to valuable warranties that protect their fiber investments.


Belden’s certified fiber systems are designed and installed by certified installers according to specific standards. This gives customers peace of mind that the system will perform as expected.


Belden certified systems are also supported by outstanding performance warranties:

  • 25-Year Product Warranty
  • Lifetime Application Assurance


This combination ensures that the installed system will meet or exceed industry standards for 25 years, as well as support future standards and protocols. Once the cabling is put in place, you’ll be able to support whatever technology or applications you need to deploy down the road.


Why OTDR Test Results Won’t Lead to Certification

There are two types of fiber tests that can be conducted: OTDR (optical time domain reflectometer) and OLTS (optical loss test set).


OLTS is the most accurate test to verify total insertion loss along a fiber link. OLTS devices are also easy to use. To test, you simply choose your application (100GBASE-SR4, for example) and go. Instead of generating a complex report, an OLTS device provides a simple “pass” or “fail” status based on results.


Lately, however, we’ve noticed that more installers are conducting OTDR tests and submitting those results in an effort to certify their fiber installations.


While an OTDR test can help you see whether a long link works or how signals react across long distances (think broadband applications)—or can be helpful for engineers who need to report on conditions like end-to-end distance or specific performance issues to evaluate system design—it’s not the right test for fiber certification.


There are two problems with using OTDR test results to certify fiber systems:

  • OTDR is not a very accurate test. The algorithms that use pulses of light to measure returned light and evaluate link loss are not always precise, especially with shorter links. To make up for this, the test must be conducted in both directions on the same run.

  • It doesn’t comply with standards. TIA and IEC don’t recognize OTDR as a valid way to certify fiber performance.


What the Standards Say About Fiber Testing

details two testing tiers to certify fiber optic system performance:

  • Basic tests (Tier 1). These simple tests use OLTS devices to check link attenuation, continuity/length and polarity. TIA identifies Tier 1 tests as required in the standards.

  • Extended tests (Tier 2). These tests use OTDR devices for troubleshooting or to check for splice and connector loss, optical return loss, etc. TIA identifies Tier 2 tests as optional in the standards. Tier 1 is required as a complementary evaluation to Tier 2.

Currently, OTDR tests are not accepted by TIA. What this means: Submitting OTDR test results for certification negatively impacts installers (creating the need for rework if they want to certify the fiber system they installed) and end-users (they can’t get access to the warranty they were promised). When installers submit OTDR results for Belden certification, those results cannot be used.


This isn’t just a Belden rule. Contact any manufacturer or Belden competitor, and they’ll tell you the same thing: OLTS is the only acceptable test result for certifying fiber system performance.


We even discussed this topic at a recent Fiber Optic Tech Consortium, posing the question: “Does anyone here accept OTDR test results without the accompanying OLTS test results?” The answer was a resounding “no” from everyone in the room.


Don’t Forget to Use Certified Testing Devices

There are different types of tests that can be conducted on fiber systems. Thus, there are different types of testers. Some are designed to test for connectivity and nothing more. Others are designed to verify the speed of a link.


OLTS tests must be conducted with certified fiber testers. Certified testers are designed to test all parameters through a rigorous testing regime so you can be confident in the results.


To be certified, testers must offer a certain level of accuracy and be recalibrated regularly (according to manufacturer specifications).


How to Get Your Belden Warranty

Remember: Per TIA and IEC standards, OLTS testing is a requirement for fiber system certification. If you want your Belden warranty, then you must use an OLTS device to conduct Tier 1 testing.


Installers will be able to pass along the promised Belden warranty to the owner and get paid for their work faster so they can move on to the next project.



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