[123373] in North American Network Operators' Group
Re: 1G/10G options over 130 km of fiber
daemon@ATHENA.MIT.EDU (Chris Tracy)
Fri Mar 5 16:01:08 2010
From: Chris Tracy <ctracy@es.net>
In-Reply-To: <Pine.LNX.4.64.1003051523270.27073@whammy.cluebyfour.org>
Date: Fri, 5 Mar 2010 15:58:53 -0500
To: "Justin M. Streiner" <streiner@cluebyfour.org>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
It would be helpful to know what type of fiber you are working =
with...SMF-28(e) G.652, NZDSF G.655, ...?
You not only need to account for dB loss over the span, but also =
chromatic dispersion.
At 1550nm, you can expect <=3D 0.22 dB/km for SMF-28 G.652 if you have a =
nice clean fiber path...possibly even <=3D 0.20 dB/km. (Got any OTDR or =
CD test results? Your provider might be able to give them to you...)
80km DWDM XFPs typically launch between -1 to +3 dBm, and are only =
sensitive down to about -24 to -25 dBm. Unfortunately, I don't have any =
data sheets on the 120km versions handy, but I suspect you will be close =
to the edge. :-)
As Dale mentioned, long-reach optics typically have something like "path =
penalty at 1450 ps/nm =3D 2.5dB" in the optical characteristics, so you =
need to factor that into your budget as well. The amount of chromatic =
dispersion can either be measured or estimated -- but it will greatly =
depend on which type of fiber you are using. In general, find out what =
the maximum amount of chromatic dispersion the receiver can handle for =
whatever optics you are considering. Then look at a datasheet for the =
fiber you have (or actually measure it) to see if you are within the =
spec given in the transceiver datasheet.
Cheers,
-Chris
On Mar 5, 2010, at 3:36 PM, Justin M. Streiner wrote:
> A dark fiber path was recently ordered to a remote location on our =
network, and to my surprise, the engineering report on the path is =
coming back at around 130 km, which is substantially longer than I =
expected the span to be.
>=20
> While I am researching gear that will drive a signal this far without =
a mid-span regen, I'm also inquiring with the carrier to see if there is =
any way to shorten the span, but I also have to be prepared for the =
chance that a shorter span is not possible.
>=20
> I've seen some pieces from MRV and Transition that might be up to the =
job, though most of the options I've seen are rated to 120 km, tops.
>=20
> That said, I'd be interested in hearing about what people who are =
driving similar spans. I don't think I'm going to have the budget to go =
out and buy Ciena/Infinera/Cisco ONS kit just for this, since I don't =
have any at the present time. The link is still being built, so I =
haven't gotten an engineering report yet. My gut tells me that the =
2-point loss on the span at 1550nm will be somewhere around 30-35 dB.
>=20
> jms
>=20
