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 <= 0.22 dB/km for SMF-28 G.652 if you have a nice clean fiber path...possibly even <= 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 = 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. > > 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. > > 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. > > 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. > > jms >
