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Too Many Testing Standards Create Confusion

By Jim Hayes | Apr 26, 2023
fiber optic testing diagrams
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I’ve written many articles about standards for ELECTRICAL CONTRACTOR. It’s usually about trying to explain the meaning of some obscure standard written in what I call “standardese,” the language that seems to be created by combining the gibberish of techies and lawyers.

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I’ve written many articles about standards for ELECTRICAL CONTRACTOR. It’s usually about trying to explain the meaning of some obscure standard written in what I call “standardese,” the language that seems to be created by combining the gibberish of techies and lawyers. Occasionally, it is about how someone twisted meanings to suit their products, like how with decibel loss, a negative number like -10 dB became a positive number, +10 dB, which looks better on a meter display but defies hundreds of years of scientific convention.

I once sat on a panel discussing the internet, back it its early days, with Bob Metcalfe, the co-inventor of ethernet at Xerox’s Palo Alto Research Labs. When the topic of internet standards came up, he said, “The wonderful thing about standards is we have so many to choose from.” Sarcastically, of course, but much too true to be funny.

 Which brings us to the topic here: the lack of consistency in fiber optic testing standards. All this came up recently in a TIA standards subcommittee meeting trying to make sense of references to testing in TIA 568.3.E, the primary fiber optic standard for fiber optic cabling at TIA.

TIA 568.3.E is the latest revision of the document, published in 2022. It is the collaborative effort of about 40 participants in the TR42.11 standards committee over about 5 years of meetings to update the standard. As with any standard developed by committee, it involves a lot of negotiation, compromise and rewrites.

Almost half of this standard is devoted to polarity—how fibers connect in cables—practically all related to multifiber connectors like the MPO. It’s full of complicated drawings that try to explain the 9 billion ways that multifiber connectors can be used. (Just kidding, it’s probably not more than a million ways!) 

There are many sections in this standard that refer to fiber optic testing requirements. Many of these refer to other standards, either other TIA standards or ISO/IEC standards and maybe some others. Over the last few years, TIA has followed a policy of adopting the IEC or ISO standards, of which there are many, to replace TIA-written standards.

For example, the latest standard for testing multimode fiber optic cabling—originally known as OFSTP-14, but now officially TIA-526-14—is an adoption of IEC 61280-4-1, with a four-page introduction that essentially says “TIA has adopted this standard but we take exception to certain sections and still do it our way.”

As you can guess, a process like this sometimes creates glitches.

 In the current discussions, the topic is primarily focused on two terms adopted about a decade ago, “Tier 1 testing,” which refers to insertion loss testing with a light source and power meter, and “Tier 2 testing,” which refers to optical time-domain reflectometer (OTDR) testing. These two terms were adopted to satisfy OTDR manufacturers who wanted OTDR testing included in TIA standards that cover fiber optic testing.

 If you are familiar with fiber optic testing, you know there are two distinct ways to test the loss of a fiber optic cable plant: insertion loss and OTDR testing. Insertion loss testing uses a light source and power meter, although it is sometimes called “LSPM” or “OLTS” for optical loss test set.

You calibrate the output of the light source with the power meter, couple it to the fiber to test and measure the output from the far end with the power meter. The difference between the two measurements is the loss of the fiber. Since an insertion loss test measures in a manner similar to the way a system works, this is generally considered the correct way to measure loss. That’s why it is the required Tier 1 test. 

OTDR testing uses an indirect method of testing, shooting a pulse down the fiber and looking at the light scattered back towards the instrument, creating a “snapshot” of the fiber. Since it doesn’t work the same way as the network itself, it may not give the same results as an insertion loss test, so insertion loss is the preferred method. But OTDRs give more information than loss—they tell you how long the fiber is and where it is joined, and can locate problems for troubleshooting.

The original TIA-526-14 was written to require insertion loss testing with a light source and power meter. I helped write the original in the 1980s. When the IEC decided to write their own standards, their equivalent standard included both insertion loss and OTDR testing. When the IEC version was adopted by TIA in place of the original TIA standard, the new document included both insertion loss testing and OTDR testing mixed together in some very confusing text about what were acceptable test procedures. 

So how do you test according to the standards?

That’s the problem. The TIA standard covers so much material, has been edited so many times by so many contributors and mixed up with IEC standards that the language has become ambiguous in places. TIA 568.3.E says that Tier 1 (LSPM) testing is required and Tier 2 (OTDR) testing is supplemental and refers to TIA-526-14. But TIA-526-14 for multimode fiber and TIA-526-7 for single-mode fiber, which was adopted from IEC standards, now include options for both insertion loss and OTDR testing without specifically saying which is required or preferred.

Then there are all the other standards that cover testing topics. All are written individually, often by different groups and lacking in coordination. And that’s the conundrum. They seem to be in conflict. Or maybe it just means, like Bob Metcalfe said, “The wonderful thing about standards is we have so many to choose from.”

About The Author

HAYES is a VDV writer and educator and the president of the Fiber Optic Association. Find him at www.JimHayes.com.

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