As an OTDR trace it looks really good, but your problem might be at event 18
and/or 19. I don’t know how much you wanted to know so I apologize if I’m
starting too far towards the beginning.
#18 is around 100m from the end and has reflectance of -21.36. That’s crappy.
The -15 below it is even crappier.
A UPC connector should be -40 to -50 dB
An APC connector should be better than -55 or -60 depending on who you believe.
If the distance is correct then maybe #18 is a cross connect panel? #19 should
be your Arista. Start with re-cleaning those connectors. One-click cleaners
are fast and cheap. They only shot this in one direction, so we don’t know
about the connectors on the other end. I’d clean it on both sides.
The line graph is showing you attenuation over distance. You’re averaging
under 0.2dB per Km so that’s really good. The table below is showing you 19
events. An event is any point along the graph where attenuation suddenly
increased. Events are either “reflective” or “non-reflective”. In the first
column of the table they’re showing you a /R or /N for reflective or
non-reflective. You can also tell that in the line graph because reflective
events will have a spike before the dip. You don’t want reflections.
Reflections are given in a -dB and you want it farther from zero (i.e.: -55
reflectance is better than -40 reflectance).
(And side comment: reflectance is the same thing as return loss, but in optics
people seem to prefer the term “reflectance”. The only difference is return
loss should be indicated with a positive number and reflectance is negative.
Return Loss = 10*log(incident power/reflected power) in +dB
Reflectance = 10*log(reflected power/incident power) in -dB
)
Non-reflective events are things adding attenuation but not adding reflectance.
Those would be fusion splices, coils, and bends.
Reflective events mean there’s an exposed face of glass. Those would be
mechanical splices or connectors. Reflective events could also be a fault in
the fiber like a bubbled fusion splice.
All that noise at the end of the line shows where the dead end is.
On that test result the only event I don’t like along the middle of the run is
#9. 4dB is a lot for one event. It might be a less than perfect splice, a
tight bend in a splice tray, a slack coil that’s too tight, or whatever. It’s
not enough to ruin this link, and it’s probably ok if it stays at 4dB forever.
There are some underground cases where I’ve seen the same high attenuation
events for years, but they’re not hurting us and it’s too much trouble to
access the case to fix something that isn’t currently a problem.
If nobody ever said this before: you should clean connectors every time they
are handled. No matter what anybody tells you, the caps they come with are not
“dust caps” and they won’t keep it clean; the caps are there so the glass face
doesn’t get scratched. When I’m plugging things in I clean the jack, clean the
plug, and then treat it like I’m playing the old Operation game: If the
ferrule touches anything before it goes into the hole then it’s “Bzzzzzt!” and
reclean it.
The dispersion thing is a new concept for me, and I don’t think you could
diagnose it from this one trace. From what I’m gathering in this thread, I
think you’d have to shoot it on multiple wavelengths and compare the
differences. This trace is only at 1550nm.
-Adam
From: AF <[email protected]> On Behalf Of Zach Underwood
Sent: Wednesday, January 24, 2024 7:41 PM
To: AnimalFarm Microwave Users Group <[email protected]>
Subject: Re: [AFMUG] optical TX power levels
Ok we got the report back from the fiber supplier. This is new to me so anyone
can offer insight into it?
PDF
https://drive.google.com/file/d/1KeIuWHFsiKZHxcmpPiY8PX_-PABl55Sz/view?usp=sharing
On Wed, Jan 24, 2024 at 6:00 PM Daniel Pautz via AF <[email protected]
<mailto:[email protected]> > wrote:
Dispersion compensation module - https://www.fs.com/products/65783.html
From: AF <[email protected] <mailto:[email protected]> > On Behalf
Of Ken Hohhof
Sent: Wednesday, January 24, 2024 3:53 PM
To: 'AnimalFarm Microwave Users Group' <[email protected]
<mailto:[email protected]> >
Subject: Re: [AFMUG] optical TX power levels
I spent a few minutes searching on the term DCM and came up with “chirped fiber
Bragg grating”.
https://en.wikipedia.org/wiki/Fiber_Bragg_grating
OK, I’m out of my depth now.
From: AF <[email protected] <mailto:[email protected]> > On Behalf
Of Daniel Pautz via AF
Sent: Wednesday, January 24, 2024 4:40 PM
To: AnimalFarm Microwave Users Group <[email protected] <mailto:[email protected]> >
Cc: Daniel Pautz <[email protected] <mailto:[email protected]> >
Subject: Re: [AFMUG] optical TX power levels
Perhaps pick up a used cheap DCM and see if it helps, adjustable preferred if
not as close to the fiber distance. Our newest 100G dwdm build (dozen 100G
optics) very much needed a DCM on it.
From: AF <[email protected] <mailto:[email protected]> > On Behalf
Of Chuck McCown via AF
Sent: Wednesday, January 24, 2024 3:36 PM
To: 'AnimalFarm Microwave Users Group' <[email protected]
<mailto:[email protected]> >
Cc: [email protected] <mailto:[email protected]>
Subject: Re: [AFMUG] optical TX power levels
Gotta think of the Fourier series of the pulse. Yes group velocities or group
delay of the whole enchalada. It is all kinda the same thing. They were doing
some kind of soliton fiber development. Haven’t heard much for some time about
that. No idea how frequency pure/coherent the tx is. I imagine phase
coherency is a big deal.
From: Ken Hohhof
Sent: Wednesday, January 24, 2024 4:12 PM
To: 'AnimalFarm Microwave Users Group'
Subject: Re: [AFMUG] optical TX power levels
Looks like different wavelengths have different group velocities, so
compensation is possible (but probably not cheap?).
Is this because the transmitter doesn’t generate literally a single wavelength?
Or is this a WDM issue? Chuck says the pulses get smeared out in time, that
sounds like the first one.
From: AF <[email protected] <mailto:[email protected]> > On Behalf
Of Chuck McCown via AF
Sent: Wednesday, January 24, 2024 3:56 PM
To: AnimalFarm Microwave Users Group <[email protected] <mailto:[email protected]> >
Cc: [email protected] <mailto:[email protected]>
Subject: Re: [AFMUG] optical TX power levels
Yeah, the pulses tend to get smeared out in time if there is too much
dispersion. Similar to trying to use too high level of QAM with SNR issues.
From: Josh Luthman
Sent: Wednesday, January 24, 2024 12:26 PM
To: AnimalFarm Microwave Users Group
Subject: Re: [AFMUG] optical TX power levels
Even if the RX level is good?
> rx was within 0.3dBm on all 4 lanes on both sides
On Wed, Jan 24, 2024 at 1:22 PM Daniel Pautz via AF <[email protected]
<mailto:[email protected]> > wrote:
Yeah makes me think the two paths have different loss. We have had that on
mirrored paths, or even single paths with crappy splices on one of the
strands.
From: AF <[email protected] <mailto:[email protected]> > On Behalf
Of Chuck McCown via AF
Sent: Wednesday, January 24, 2024 11:12 AM
To: AnimalFarm Microwave Users Group <[email protected] <mailto:[email protected]> >
Cc: [email protected] <mailto:[email protected]>
Subject: Re: [AFMUG] optical TX power levels
Did anyone do dispersion testing on the fiber?
Chuck McCown
McCown Technology Corporation
8401 N Commerce Dr
Lake Point, Utah 84074
801-250-9503
435-830-4306 cell
www.mccowntech.com <http://www.mccowntech.com>
www.microtrench-blades.com <http://www.microtrench-blades.com>
www.terabitnetworks.com <http://www.terabitnetworks.com>
From: Zach Underwood
Sent: Wednesday, January 24, 2024 12:07 PM
To: AnimalFarm Microwave Users Group
Subject: Re: [AFMUG] optical TX power levels
tired again this morning and still no link. rx was within 0.3dBm on all 4 lanes
on both sides. We got 10gb 80km to link up. This will do for now. We will be
looking at getting 40gb 80km single lane optics or adding another site to fiber
loop to shorten the footage to under 40km.
On Wed, Jan 24, 2024 at 11:14 AM Colin Stanners <[email protected]
<mailto:[email protected]> > wrote:
So both of those SFPs are within the tx power range.
100G may not work on a link that long unless you have dispersion compensation
fiber on the path or in a huge loop in a box style at one end.
You likely cannot change tx power levels on those SFPs, they will run at the
max they can do for that specific unit.
On Wed, Jan 24, 2024, 7:46 a.m. Zach Underwood <[email protected]
<mailto:[email protected]> > wrote:
TX Power 2~6.5dBm
I am struggling to get this 100gb link up. In the field this link is quoted at
31 miles. The rx levels are -22 and -20 on both sides but I can't get it to
link. I take the same optics to the lab and add 20dbm of attenuator to get
almost the same rx levels as the field and it will link up.
I have added error-correction encoding reed-solomon per the user guide for
links over 40km.
So far I have not found a way to change the TX levels in arista, the options
are in the CLI but they dont seem to change the outcome. For me this is the
first time dealing with 80km optics or 100gb optics over 10km.
switch is Arista DCS-7060SX2-48YC6-R
https://resource.fs.com/mall/doc/20230531114903y4ljxw.pdf
https://www.fs.com/products/115818.html?attribute=29032
<https://www.fs.com/products/115818.html?attribute=29032&id=3462585> &id=3462585
On Wed, Jan 24, 2024 at 8:35 AM Colin Stanners <[email protected]
<mailto:[email protected]> > wrote:
There should be. What does their datasheey indicate for tx power range?
On Wed, Jan 24, 2024, 7:31 a.m. Zach Underwood <[email protected]
<mailto:[email protected]> > wrote:
Yep labels identical but there is a difference in default power levels.
On Wed, Jan 24, 2024, 8:13 AM Mike Hammett <[email protected]
<mailto:[email protected]> > wrote:
Oh, meaning the variance between the two, otherwise identical models?
-----
Mike Hammett
<http://www.ics-il.com/> Intelligent Computing Solutions
<https://www.facebook.com/ICSIL>
Midwest Internet Exchange
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<https://www.facebook.com/ICSIL> From: "Zach Underwood" <[email protected]>
To: "AnimalFarm Microwave Users Group" <[email protected]>
Sent: Tuesday, January 23, 2024 12:51:39 PM
Subject: [AFMUG] optical TX power levels
<https://www.facebook.com/ICSIL> I got 2x 100gb 80km optics from FS that run
difficult default TX power levels one is 3.81dBm and the other 2.63dBm, the
config on the arista devices hosting the optics is the same.
<https://www.facebook.com/ICSIL>
<https://www.facebook.com/ICSIL> Has anyone seen much difference between optic
like this? My sample size is small due to the optices costing $4k each
<https://www.facebook.com/ICSIL>
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