2011/12/14 Justin M. Streiner <strei...@cluebyfour.org> > On Wed, 14 Dec 2011, Keegan Holley wrote: > > inappropriate. We are attempting to use Juniper single-mode SFPs (LX >>>> variety) across multi-mode fiber. Standard listed distance is always >>>> for SFPs using the appropriate type of fiber. Does anyone out there >>>> know how much distance we are likely to get? Thanks for your help in >>>> advance. >>>> >>> Single mode just has a smaller core size for the smaller "beam" emitted >> by >> laser vs. LED. it works although I've never done it outside of a lab (MM >> is cheaper). As for the distance it theory that should come down to the >> optics and your transmit power. Hopefully this is just a cable connecting >> the router to a long line. I've never heard of a 10K MM fiber run since >> SX >> optics can't shoot that far. You should be able to get through the 500m >> or >> so that MM optics are rated for, but YMMV (errors, light levels, bounces, >> etc etc) >> > > In a nutshell, don't do it if at all possible. This issue gets > significantly > worse at 10G. If there's any way to get SMF in place for this link, do it. > > +1 probably should have added that. I guess I just assumed.
> In practice, you will likely get something less than the rated distance, > particularly if the MM fiber in question is an older type, such as OM1. If > you're using OM1, mode-conditioning jumpers at both ends are pretty much a > must. > > The problems with shooting an LX/LH beam over MMF are threefold: > 1. Attenuation on some flavors of MMF can be significantly higher than an > equivalent run of SMF. > +1 Assumed again.. > 2. Modal dispersion on MMF will scatter and distort the LX beam, likely > resulting in link errors because the receiver can't recover the data > correctly. > Not that I'm advocating this, but it's fine over short distances. I did this for a few lab routers where I wasn't concerned with link quality, but I was able to fill a 10G pipe with no errors/retransmit over about 10M. > 3. Shooting a 9 micron beam into a 50 (or worse, 62.5) micron core, and > getting enough of the beam to reach the 9 micron target at the other end to > result in a recoverable signal is problematic. Again for short distances it's doable. I agree not to even try over 62.5 though.
