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 <af-boun...@af.afmug.com> On Behalf Of Zach Underwood
Sent: Wednesday, January 24, 2024 7:41 PM
To: AnimalFarm Microwave Users Group <af@af.afmug.com>
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 <af@af.afmug.com 
<mailto:af@af.afmug.com> > wrote:

Dispersion compensation module - https://www.fs.com/products/65783.html

 

From: AF <af-boun...@af.afmug.com <mailto:af-boun...@af.afmug.com> > On Behalf 
Of Ken Hohhof
Sent: Wednesday, January 24, 2024 3:53 PM
To: 'AnimalFarm Microwave Users Group' <af@af.afmug.com 
<mailto:af@af.afmug.com> >
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 <af-boun...@af.afmug.com <mailto:af-boun...@af.afmug.com> > On Behalf 
Of Daniel Pautz via AF
Sent: Wednesday, January 24, 2024 4:40 PM
To: AnimalFarm Microwave Users Group <af@af.afmug.com <mailto:af@af.afmug.com> >
Cc: Daniel Pautz <d...@webnx.com <mailto:d...@webnx.com> >
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 <af-boun...@af.afmug.com <mailto:af-boun...@af.afmug.com> > On Behalf 
Of Chuck McCown via AF
Sent: Wednesday, January 24, 2024 3:36 PM
To: 'AnimalFarm Microwave Users Group' <af@af.afmug.com 
<mailto:af@af.afmug.com> >
Cc: ch...@go-mtc.com <mailto:ch...@go-mtc.com> 
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 <af-boun...@af.afmug.com <mailto:af-boun...@af.afmug.com> > On Behalf 
Of Chuck McCown via AF
Sent: Wednesday, January 24, 2024 3:56 PM
To: AnimalFarm Microwave Users Group <af@af.afmug.com <mailto:af@af.afmug.com> >
Cc: ch...@go-mtc.com <mailto:ch...@go-mtc.com> 
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 <af@af.afmug.com 
<mailto:af@af.afmug.com> > 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 <af-boun...@af.afmug.com <mailto:af-boun...@af.afmug.com> > On Behalf 
Of Chuck McCown via AF
Sent: Wednesday, January 24, 2024 11:12 AM
To: AnimalFarm Microwave Users Group <af@af.afmug.com <mailto:af@af.afmug.com> >
Cc: ch...@go-mtc.com <mailto:ch...@go-mtc.com> 
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 <cstann...@gmail.com 
<mailto:cstann...@gmail.com> > 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 <zunder1...@gmail.com 
<mailto:zunder1...@gmail.com> > 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 <cstann...@gmail.com 
<mailto:cstann...@gmail.com> > wrote:

There should be. What does their datasheey indicate for tx power range?

 

On Wed, Jan 24, 2024, 7:31 a.m. Zach Underwood <zunder1...@gmail.com 
<mailto:zunder1...@gmail.com> > wrote:

Yep labels identical but there is a difference in default power levels.

 

On Wed, Jan 24, 2024, 8:13 AM Mike Hammett <af...@ics-il.net 
<mailto:af...@ics-il.net> > 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

The Brothers WISP






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 <https://www.facebook.com/ICSIL> 
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 <https://www.facebook.com/ICSIL> From: "Zach Underwood" <zunder1...@gmail.com>
To: "AnimalFarm Microwave Users Group" <af@af.afmug.com>
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>  

 <https://www.facebook.com/ICSIL> -- 

 <https://www.facebook.com/ICSIL> Zach Underwood (RHCE,RHCSA,RHCT,UACA) 

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