Optical transceiver question

Mon Sep 12 03:29:58 UTC 2016

In discussions with the reseller he admitted that they market the distance
based on average TX power and average link loss, so it is possible to
purchase optics that may not be able to attain certain necessary link
budgets and therefore distances.

There are 1270/1310 nm BiDi optics with a worst-case link margin of 19 dB.
Assuming a loss of 0.38 dB/km
(https://www.cisco.com/c/en/us/support/docs/optical-networking/ons-15454-son
et-multiservice-provisioning-platform-mspp/27042-max-att-27042.html) that's
just 50 km.  Of course, with a link margin of 24 dB that would be 61.5 km.
So unless you assume best-cast scenarios, 60 km is a stretch.

Frank

-----Original Message-----
From: Mikael Abrahamsson [mailto:swmike at swm.pp.se] 
Sent: Thursday, September 08, 2016 1:36 PM
To: Frank Bulk <frnkblk at iname.com>
Cc: nanog at nanog.org
Subject: Re: Optical transceiver question

On Wed, 7 Sep 2016, Frank Bulk wrote:

> Is it an industry practice to market distance based on the hot optics, 
> not on the worst case, which is minimum TX power?

No. If this is 1310nm optics with 0.4dB/km budget, the budget figure 
should be end-of-life figure, ie worst case according to the specs.

I don't like the "kilometer" figures, that can be marketed with very 
optimistic figures. However, if the transceiver says 0 to -5 transmit, if 
it doesn't transmit 0 to -5 then it's out of spec.

I treat the kilometer figure as "marketing", and look only at the optical 
specifications. So using your figures, if the device doesn't have 0 to -5 
out, and can receive error free at -20, then it's out of spec and it 
should be replaced free of charge.

However, if they market 1310nm with 15dB link budget at 60km reach, then 
I'd consder that false marketing.

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se