Does anyone have some experience to use dwdm monofiber mux/demux ( ex.
fiberstore ) about 68km using a ADFA ? Have I to use a DCM( for chromatic
dispersion ) on this distance? When I have to use a DCM ?

Rodrigo Augusto
Gestor de T.I. Grupo Connectoway
* rodrigo@connectoway.com.br <mailto:rodrigo@connectoway.com.br>
( (81) 3497-6060
( (81) 8184-3646
( INOC-DBA 52965*100

You have to use DCM when the chromatic dispersion caused by your distance exceeds what your receiver optical module can handle.

So the answer is "it depends". If you're using 1GBASE-DWDM optics then you'll be fine, if you use 10GBASE DWDM optics then it depends on the distance they were designed to handle, if you buy the 40km ones then you should have DCM.

Buy 80km sfp+ dwdm modulesŠ c21 and c51.
On this scenario a don¹t have a EDFA, only put these sfp+ and I have link
on other side( 60km) but I have a -19dbm and other side I have -21dbm( ddm
sfp+ output).. I think I have a better signal than thisŠ because I use
80km sfp+ and my distance is 60kmŠ can I have a chromatic dispersion? I
think to use a EDFA, but i¹m not sure thisŠ if I have a chromatic
dispersion I have to use a DCM not a ADFA or a boosterŠ

Rodrigo Augusto
Gestor de T.I. Grupo Connectoway
* rodrigo@connectoway.com.br
( (81) 3497-6060
( (81) 8184-3646
( INOC-DBA 52965*100

First: buy a power meter. They are really cheap and the only way to know
for sure how much signal you got. It will also tell you how much launch
power you have. The fiberstore modules are listed as 0 to +5 dBm launch
power - if you got lucky it might be +5 and if you got a lower end module
it might be close to 0. Obviously this makes a huge difference for how much
power you get on the other end. Also it is said that the laser will lose
power over time.

Second you need to think in terms of power budget, not distance. So you got
68 km and the module is rated for 80 km - but not all fiber is not born
equal. A power meter allows you to measure the true link loss.

Third you did not tell what DWDM multiplexer you are using. A 44 channel
DWDM multiplexer from Fiberstore can have up to 4.5 dB insertion loss. You
might have two of those on your link for a total of 9 dB loss. Your 80 km
module has a 23 dB link budget, so this leaves you with 23-9 = 14 dB
budget. If your fiber has 0.25 dB loss per km, that is only 56 km.



I think the OP is asking about whether it should account for chromatic
dispersion or not. Intramodal dispersion may very well be a limit on your
link even the power budget (as presented before) is fine. As Mikael said,
I would stick to the specs from the manufacturer for that specific module,
or rent an OTDR and make the measurements.

Nothing is wrong with the fiber... Attenuation is good... Gbics specs says -23db as a limit of your sensibility ...i have tried to put bidi sfp+ 80km on this fiber and have -25dbi on other side( not connect) this module have -20dbi sensibility ...
This scenario have a 4 channels... And i use 2 10gb channels... C21 and c22 on side A and c51 and c52 on side B....

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Grupo Connectoway

Remember, distance ratings are just generalizations. It all comes down to
power budget. When fiber is laid there are slack loops for potential
future service and for use if a cable is cut, splice cases -- because it's
hard to work with a fiber spool with more than 5 miles of cable on it,
other connectors, hand holes with slack coils, etc. If the route is 80km
the actual fiber distance could be more like 100 or 120km with all of the
slack. Then you add on DB loss for every splice and connector. As others
have said, the only way to really know is to shoot it with a power meter
and see what the end to end loss is, and then get the correct optics for
the path you have

If you use 80km SFP+ then they should be able to handle the CD (chromatic dispersion) of your 68km fiber stretch, and if you have a power problem, then you can solve that by adding EDFA mid-span.

CD causes "noise" (OSNR) to the receiver, it doesn't cause your power levels to be low. So if you want to solve your power problem, add EDFA mid-span. If you want to be able to use 40km optics (they might be cheaper), add DCM as well if the manufacturer rates them as not being able to electronically compensate for dispersion more than 40km.

Should you find yourself on the edge (or unknowing) of the dispersion tolerance of the 80km modules you would like to use, 120km-tolerant modules are also somewhat readily available these days, including from fiberstore. They don't have the power to shoot 120km without external (generally mid-span) amplification, but they will tolerate the accumulation of ~120km worth of chromatic dispersion. Thus, you can do 120km of fiber (typ.) with EDFAs in the span for power budget reasons but without an accompanying DCM at each hop. Since the commodity DCMs cost almost as much as commodity mid-power EDFAs, these days, that could be a significant cost savings.

As always when buying whitebox/commodity networking goods, careful review of the specifications and testing in your proposed application is in order.

Rule of thumb is you need Dispersion compensation for any single span over 60Km. 10G/STM64 has a CD Tolerance of 1176 ps/nm, 40G/STM256 has a CD tolerance of 73.5ps/nm but you don't want your dispersion number to ever go negative. If it's a single-span only rule of thumb is use the next size smaller than the measured fiber distance maintaining at least 10km on the bottom end, 65km would use a 40km dcm 70km would use a 60km dcm. As long as each site does OEO you can do Dispersion hop-by-hop, if any node on the ring pass a channel through, or is only optically amplified, you need to calculate DC along the entire path, ensuring that the DC number never goes negative.

DC should be inserted between the egress of the combining mux and the post-amp to maximize your launch power. Try to stay away from channel-by-channel DCM, it gets really messy as the system grows. And remember always clean-scope-clean!