Conference 7.286::fddi

265.0. "Can we stretch the 2 Km limit?" by VAXRIO::ROLF () Mon May 27 1991 13:25

    We need to install an FDDI link over 2.5 Km distance. 
    
    This being 25% OVER the 2 KM limit for MMF, immediatelly the SMF
    solution comes to mind. However, it is impossible to get the
    required FC-PC connectors in Brazil, nor the SMF patch-cables
    for ST-to-FC-PC connections. 
    
    Our fiber subcontractor tells me though, that, if runs of high-quality
    fibers are used over this 2.5 Km span, and the number of splices is
    controlled, regular size (50/125) fiber would possibly do the job.
    
    Knowing DEC I'm sure that the "2 Km maximum" certainly is based on
    worst-case conditions in terms of fiber quality and splices/losses, and
    I think our sub may have a point and I wonder if someone out there would 
    have some concrete specs which we could try to match?
    
    Based on a formula I found in the Fiber Optic Planning & Config Guide,
    we would need a fiber with 625 MHz modal bandwidth at 1300 nm, and that
    would get us to 2.5 Km. Does this make sense? Or is it not practical?
    
    Any help is welcome
    
    Rolf, NWSS Brazil

Losses are only part of the problem.  Dispersion is another.  Also, such
a connection would violate the ANSI standard; no one would want to guarantee
that it works or will continue to work.

Can't you order the cables from here?  

	paul

    Thanks Paul
    
    Just to give u an idea, I just found someone who has the equipment to
    mount FC-PC's onto SMF, but he doesn't have the connectors. 
    
    For us to order anything from the states which is not sourced by DEC
    is a hassle, but it's possible, but I'd have to have all the info
    about the source (catalogs, prices, etc) which I don't...
    
    I guess the way to go would be to buy the adapter cables for FC-PC to
    ST from the states and use local SMF and ST connectors on them.
    
    Rolf