Okay.
So we are still on the subject of testing.
And in this lesson, we're going to have a look at the differences between Tier one and Tier two testing.
Now, this is going to make sense to you in just a moment as we go through this actually very important
subject, because some customers will ask you for a tier one test and some will ask you for a tier one
and a tier two test.
So you need to know what the differences are between these two testing methodologies.
Okay.
So unlike copper cabling, where only one level of testing is defined by standards, there are two levels
or tiers available when testing and certifying fiber optic cable.
Now the different tiers specify which type of tests are performed during testing and therefore define
the test equipment to be used.
And it is rare, but not impossible for a customer to ask for a Tier two testing on a network.
And it's becoming less and less rare.
I have to say, and we are going to have a look in the next lesson between the difference between certification,
verification and qualification, because that's actually some very important distinctions there as well.
Okay.
So tier one is traditionally a simple test for attenuation continuity and polarity.
Now, most times this testing can be achieved with a basic power meter and light source set, also known
as an optical loss test test or an OTS.
And we had a look at the RTS sets and obviously the what power means for your fiber optic networks.
ET cetera.
So Tier two is a bit more comprehensive and normally more expensive for your customers.
It involves an optical time domain.
Reflectometer.
Remember our beloved otdr that we spend so much time on?
And in addition to measuring attenuation, it can measure back reflection, optical return, loss or
l and give a pass fail status for each event, whether reflective or non-reflective on the cable.
This is what would need to be done to certify a network.
And again, we're going to have a look at network certifications in the next lesson.
So the outdoor the ability to characterize events and faults on the cable with several connections and
shorter jumper connection patch panels.
It will also certify the length of the cable allowing you to formulate a loss budget.
So first of all, and this is important.
That's why I said, you know, it's important.
It's important to acknowledge that Tier two testing does not replace the total insertion loss measurements
taken during Tier one testing.
Tier two testing requires Tier one and is used as a complementary evaluation.
Using both methods provides the most complete picture of the fiber installation.
In other words, just because Tier two, Tier two testing may be required doesn't mean you can skip
Tier one.
You still need to measure the total fiber losses of the link.
However, Tier two testing does something.
Tier two cannot and otdr characterization of the link and this is obviously something that your power
meter cannot do.
So saying all of this, the question arises Tier one, Tier two, or do you need to do both?
Well, one of the most commonly asked questions regarding the types of certification is which type of
test should be used and whether performing Tier two certification meets the requirements of Tier one
certification.
To.
Ultimately, the required testing is an agreement between the cabling contractor and the customer.
However, when certification is required, certification specifically, it is a good practice to always
perform a Tier one test and optionally do a tier two test.
Tier two Certification Supplements.
Tier one Certification.
It is not a replacement for it.
This is very, very important.
And again, our next lesson is going to be about certification, what exactly that means.
So this is often this often confuses people because in addition to the losses for each component in
the link an it will also show the total link loss like an RTS does.
So why then does an Otdr not satisfy the requirement for Tier one certification?
Well, interestingly enough, there is a subtle nuance between the total link loss reported by an RTS
and an Otdr.
And is measures the true optical loss of the link while an outdoor calculates the total loss of the
link.
This is the difference the one measures the true optical loss of the link.
While an outdoor calculates the total loss of the link, it calculates it does not measure it as such.
Now, although may both may provide similar results when testing the same cable, the S is always the
most accurate way to determine the end to end loss of a link.
So absolute accuracy is especially important with high bandwidth multi-mode applications such as 100
gigabit Ethernet, where the total allowable insertion loss can be as low as 1.5dB.
And I'm talking here about the total allowable insertion loss for the whole fiber plant with the connectors
with everything intact.
So that's really, really low.
So you need to plan these cables very, very carefully and loss can make that your bandwidth is not
what it's supposed to be.
And that can be quite a crisis.
I'm sure you can agree with that.
So let's look at each tier testing and in a little bit more detail.
And let's start with Tier one.
So Tier one certification uses an optical light source and optical power meter to measure the total
insertion loss across the cabling under test so that the tester will provide one number.
That is the sum loss of all the events in the cabling connected to the tester.
Events are components of the optical cabling link that either lose or reflect light as it passes through.
Events include the cable itself connectors, bulkheads, splices, splitters and bends or kinks.
Tier one is a simple and accurate way of determining whether a fiber optic link will support an application
or not.
And it's also not as expensive as your Tier two testing because the testing equipment is not that expensive.
The resulting insertion loss measurement can be compared to a specification or standard to provide a
pass fail status of each link for its intended use.
So as I mentioned above, in 100 GB s SR ten Ethernet allows a maximum channel loss of 1.5dB across
the whole channel.
So a channel that exceeds 1.5dB of loss will fail the test and a channel with 1.5dB loss or less will,
in other words, pass.
It's a simple, quick go no go test and is the most common method of certifying fiber optic cable.
So this may vary a bit from manufacturer to manufacturer, but most of your tests are performed in this
way that we are going to explain now.
So to perform Tier one certification, the test codes used for testing with the Pmls are first referenced
or calibrated out so that the loss is not included in the test results.
Now, this is normally done by the equipment itself if you have high end equipment.
Now there are different reference methods available using either one or 2 or 3 test codes.
Now the method used depends on several factors, including the type of pmls used for testing.
In this article, the single test score or one jumper method will be referred to because it's recommended
by both Ansi Tia and ISO IEC standards organizations.
So we do it that way because this is the standard.
Now, as we've mentioned before, the primary reason that testing is the preferred method of testing
insertion loss is that it is very accurate.
Direct measurement of power loss in the link.
So with Tier two certification insertion loss is calculated not directly measured by the Otdr, leading
to potential differences in the reported insertion loss between the two instruments and your CTA and
ISO IEC.
Recognize this as a potential issue where if you are measuring loss.
So the AC is always the most accurate method of measuring insertion loss of a link, even though an
RTS can cost significantly less than an Otdr.
So there is a lesson in here for us.
If you are starting out in the cabling world, in the fiber optic cabling world and you need to start
buying equipment, what kind of testing equipment do you buy first?
And I think this kind of answers.
It does.
It, does it not?
Okay.
So.
A novelty is, is a simple measurement where a known level that is basically a brightness of light is
injected into one end of the link and the level leaving the link at the other end is measured.
It's really as simple as that.
The difference between the two values is the link loss.
They have quickly measured the standards.
So let's talk about the standards for Tier one testing and specifically the Tia standards.
So Ansi Tia 568C dot zero Annex E provides guidelines for field testing length loss and polarity of
optical fiber cabling.
Now, Section E 2.2 describes Tier one testing now.
Tier one testing requires the following link attenuation measurement, fiber length verification and
polarity verification.
And so link attenuation measurement must be performed with an olts according to the standards.
Fiber length verification may be obtained by using an RTS that has length measurement capability and
they are out there and they are slightly more expensive than your normal RTS.
And the last thing is polarity verification.
Now that is performed to ensure the optical path from the transmit port of one device is routed to the
receive port of another device.
The polarity may be verified using an RTS or a VFL or a simple continuity tester.
You just need to see that transmit goes to receive on the other end and receive on the one end go to
transmit on the other end.
It's really as simple as that.
Okay.
So documentation needed for testing.
And this is also described in some of the standards, if I'm not mistaken.
So as you test the cable plant with the IELTS, you need to properly document the results of the test.
Now, the documentation should include, at a minimum, the following the date of the test.
Test personnel that did the test.
Field Test.
Instrument Manufacturer.
Field Test.
Instrument.
Serial number.
Field Test Instrument.
Calibration Date.
Test Jumper type.
Test.
Jumper.
Length.
Number of IDs of fiber or cable tested test procedure method used wavelength directions and the link
loss results.
Obviously and this you can actually set up just like a little spreadsheet or something in Excel.
And this can be a standard document within your company for doing these testing.
So let's look at tier two testing.
While Tier two certification is not a substitute for Tier one certification but is performed in addition
to Tier one certification, when further information about the link is desired about your specifically
from your customer.
So Tier two certification uses an otdr to characterize the link under test by measuring each of the
individual components that make up the entire cabling as we've seen in our section on Otdr.
But an otdr creates a visual representation of the link, allowing the operator to see the contribution
of each component to the Link's total loss, making it a perfect tool for troubleshooting by certifying
new cabling with an otdr.
A snapshot is created documenting the location and performance of every component at the time of installation.
So should an issue arise later?
A current Otdr test can be compared with the initial test to immediately identify what is changed in
the cabling and the location of that fault.
So it's actually quite useful, especially if there is an issue of the cable later on and can be much
later on.
And if you've got this paperwork ready, then it makes life much, much easier.
So before diving into the operation of an HDR, one should understand the measurements it performs during
a test.
And we've had a look at this as well.
So an HDR classifies everything it sees as one of two categories of events attenuation or non reflective
events or the other category is reflective events.
Attenuation events are those where power is lost going through the event and none is reflected back
to the HDR.
Events that fall into this category are.
Fusion splices, micro bands, macro bands and the fiber optic cable itself.
So reflective events are those where power is lost.
Going through the event and power is reflected back to the events that fall into this category.
Are connections or bulkheads, mechanical splices, breaks in the fiber and the end of the fiber optic
cable that we should not forget about.
So we've had a look at what the outdoor cable looks like.
Yes, just another cool picture.
And I'm going to add to this lesson if you want it.
If I forget, please remind me that I add this as well, because this is actually also a nice, um,
diagram of what your outdoor test looks like or your outdoor trace.
So as with Tier one testing, there are Tia standards with regards to Tier two testing.
Now Tier two testing as defined in NCT, A568-C.0 Annex E is optional.
Interestingly enough, it can be used to supplement tier one testing with the addition of an outdoor
trace of the link.
However, it is not a replacement for the tier one link attenuation measurement performed with an RTS.
I've said this quite a lot now in this lesson, haven't I?
So tier two testing with the AAC and characterize the elements of a link including fiber, segment length,
attenuation uniformity and attenuation rate, interconnection, location and insertion loss splice location
and insertion loss and macro bends.
Macro bends the direct.
The dreaded macro bends.
Okay.
And as with your tier one documentation and TTS documentation, you can standardize and you should standardize
your outdoor testing documentation.
So as you test the cable plant with the Otdr, you need to properly document the results of the test.
The documentation should include, at a minimum, the following the date of the testing, the test personnel,
the number or identification of cable or fiber or cable tested.
Test procedure number Otdr.
Make model serial number and calibration dates because an outdoor needs to be calibrated at least once
a year.
Boulsworth range and resolution number of averages tested wavelengths, type and length of launch cable.
And again, this can be a standard document that you create for your company and you can just pull it
up and use it as needed.
And that is it for this lesson.
So I think the most important thing, as I've said so many times now already, is to remember that a
tier two test will never replace a Tier one test.
And even with the standards standards, it is seen as a supplemental test and not a replacement for
a good old test.
And that is it for this lesson.