[166385] in North American Network Operators' Group
Re: Pad 1310nm cross-connects?
daemon@ATHENA.MIT.EDU (Leo Bicknell)
Sun Oct 20 16:15:17 2013
Date: Sun, 20 Oct 2013 13:14:59 -0700
From: Leo Bicknell <bicknell@ufp.org>
To: nanog@nanog.org
In-Reply-To: <CAN8DL0XVDUV20-Wk6LYuuuufq22VnNznOVRvwL=_aYt90bagkg@mail.gmail.com>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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In a message written on Sat, Oct 19, 2013 at 07:33:19PM -0700, Chris Costa =
wrote:
> What are the opinions/views on attenuating short, 1310nm LR cross-connect=
s.
> Assume < 20m cable length and utilizing the same vendor optics on each
> side of the link. Considering the LR transmit spec doesn't exceed the
> receiver's high threshold value do you pad the receiver closer to the
> median RX range to avoid potential receiver burnout over time, or just
> leave it un-padded?
With any optics, you need to go to the specifications.
I assume here you mean 10GbaseLR, although I will point out that "LR" is
ambiguous as there is also for instance OC192-LR.
I'm going to pick on Juniper specs, just because they were the easiest
to find with Google:
http://www.juniper.net/techpubs/en_US/release-independent/junos/topics/refe=
rence/specifications/transceiver-m-mx-t-series-10-gigabit-optical-specifica=
tions.html
And similar for 1000baseLX, the similar technology for GigE:
http://www.juniper.net/techpubs/en_US/release-independent/junos/topics/refe=
rence/specifications/transceiver-m-mx-t-series-1000base-optical-specificati=
ons.html
Note that for both 10GbaseLR and 1000baseLX the transmitter power range
is entirely inside the allowed receiver range. They were designed this
way on purpose, to never need a pad. An in-spec optic can never over
drive the receiver, even with zero loss.
Answering your question, I would never pad them.
Compare with for instance a 10Gbase-ER or 1000baseEX, 40km over
single mode optics. In both cases an in-spec can exceed a receiver.
10Gbase-ER can transmit up to +4.0dBm, while the receiver needs
-1.0dBm or below. When connecting them "back to back" a 5dB
attenuator is required to keep the receiver in-spec. For any real
connections (over a fiber path more trivial than a jumper) a light
meter should be used, the value checked, and an attenuator that
places the circuit 1-2dB inside of the safe zone of the receiver
should be used.
--=20
Leo Bicknell - bicknell@ufp.org - CCIE 3440
PGP keys at http://www.ufp.org/~bicknell/
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