RE: Optical transceiver question

["Jameson, Daniel" <Daniel.Jameson () tdstelecom com>]

There are a bunch of variables that impact actual power needed vs. road-miles, number of cross-connects,  type of 
fiber, amount of slack,  type of connectors,  frequency,  dispersion, etc.  The km notation simplifies the naming 
convention.  As a general rule 40Km budget 20db,  60km budget 24db,  and 80km budget 28db.  Best practice is design and 
deploy to stay a minimum of 4db above the Minimum Input Sensitivity,  and 4db below the Max Receive Level to account 
for the change as the optic and glass as it ages.  If you are engineering a 60km fiber length,  you'd step up to the 
next higher optic to account for other losses.  60KM is just a rough number.

There  is another value to worry about as well.  It's the De-Assert Level;  an optic will run all the way down to its 
minimum input sensitivity,  sometimes a couple db below.  But once it hit's the De-assert level,  the optic will stop 
forwarding what it receives.  So there is a little more fudge in the numbers if you're not playing by the rules.


-----Original Message-----
From: NANOG [mailto:nanog-bounces () nanog org] On Behalf Of Robert Jacobs
Sent: Wednesday, September 07, 2016 3:33 PM
To: Eric Kuhnke; nanog () nanog org list
Subject: RE: Optical transceiver question

Not buying fresh veggies here... All optics have about a 5 db range that the vendor will say it is good.  The better 
venders stamp the output power on the optics but not all do this... What he said is to achieve the 60 Km selling point 
you would have to have all the optic be on the high side of the db TX power... I have never heard of a 60 Km rated 
optics and it would seem they should be saying 40 to 60 not just 60.  It would be nice to say I only want the optics 
that have an output on the high side and will accept only a 1 db variance but have never seen that in reality.  Most 
are in the middle..

Robert Jacobs | Network Director/Architect 

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-----Original Message-----
From: NANOG [mailto:nanog-bounces () nanog org] On Behalf Of Eric Kuhnke
Sent: Wednesday, September 7, 2016 3:51 PM
To: nanog () nanog org list <nanog () nanog org>
Subject: Re: Optical transceiver question

What you're saying is if you purchase ten identical optics with the same SKU, and put them on a few hundred meters of 
coiled SC/UPC to SC/UPC simplex fiber and an optical power meter on the other end, they're showing varying real world 
Tx powers from between +0 to +5dBm?

That's not right at all, they're supposed to be sorted at the factory by their actual optical power output before they 
have labels put on them.

On Wed, Sep 7, 2016 at 1:23 PM, Frank Bulk <frnkblk () iname com> wrote:

> We recently purchased some generic optics from a reputable reseller 
> that were marketed to reach 60 km.
>
> But what we found, based on the spec sheets, is that it could only 
> reach that distance if the optics were transmitting on the high side 
> of the transmit power range.
>
> For example, if the TX range was 0 to +5 dBm and minimum RX power was
> -20 dB, the designed optical budget should be no more than 20 dB (0 - -20).
> Based on the wavelength the appropriate loss would be 0.4 dB/km and 
> results in only 50 km, not 60 km.  To get 60 km it would need 24 dB of 
> link margin, and that would only be attainable if it was transmitting 
> on the high side, at +4 dBm.
>
> Is it an industry practice to market distance based on the hot optics, 
> not on the worst case, which is minimum TX power?
>
> Frank