SC Fibre Problem??

Discussion in 'Cisco' started by John Smith, Sep 10, 2004.

  1. John Smith

    John Smith Guest


    I am currently trying to upgrade a site from old hubs to new switches,
    there is interconnecting sc and st fibre between the different
    buildings. The backbone switch I installed was a 3750 with 4 LC SFP's.
    The buildings that had ST interpatching worked fine on the new switch
    but the buildings that had SC fibre interpatching wouldn't work at

    The following is an example that worked, from the backbone 3750 it
    LC - ST, then to the local 2950sx switch the fibre is ST - MTRJ
    ....worked fine...

    The following is an example that didn't work, from backbone 3750 it
    starts: LC - SC, then to the local 2950 sx switch the fibre is SC - MT
    RJ..wouldn't work..

    Is there something I'm not doing?

    I really do apprecitate any help on this.

    Thanks in advance
    John Smith, Sep 10, 2004
    1. Advertisements

  2. John Smith

    Blaz Zupan Guest

    The connectors are not so important, more important is what kind of fiber you
    have. What kind of GBIC/SFP is on the switches? Multimode or singlemode? What
    kind of fiber is the one that has ST plugs and the one that has SC plugs? In my
    experience, ST connectors are often used for multimode while SC for single mode.
    Blaz Zupan, Sep 10, 2004
    1. Advertisements

  3. Connectors shouldn't matter at all, as long as you have the same type
    of fiber (ie. multimode vs. singlemode), and the same size
    (ie. 50 vs 62.5 for multimode) thoughout.

    I'd imagine that you either are mixing in some single mode into your
    multimode network, or possibly running into some issues mixing sizes.

    I've done things in the past simular to you, although I pretty much
    spec out SC connectors on the patchpanels everywhere.
    Doug McIntyre, Sep 10, 2004
  4. John Smith

    AnyBody43 Guest

    Have you considered that the Transmitter on one end must connect to the
    Receiver at the other?

    With the ST you must, however some SC patch leads come with the
    connectors in a carrier. Most fiber optic patch leads that come
    with the end as a pair are crossover so that if you use two of
    them in the path you get Tx connected to Tx and rx.....

    You can break the end connectors out of their housing quite easily.
    I suspect that such violence may not be necesary but I have never
    had the patience to worry about it.

    Other issues. Fo cable comes in many different types. The main
    classifications are:-

    Single mode 9/125 (or 8 or 8.5)
    Multimode 50/125
    " 62.5/125

    The size is usually printed on the cable along its length every few
    feet in a very small type face.

    These various types are incompatible so you must use matching
    patch leads.

    Single mode 9/125 Won't work
    Multimode 50/125 500m
    " 62.5/125 220m

    With ideal cable. you may get slightly longer distances.

    You can get a piece of equipment that will tell you how long the
    cable is with access only to one end. It's called a Time Domain
    Reflectometer and you probably need an operator for it too.
    The same piece of equipment can test the cable for various
    problems too.
    AnyBody43, Sep 10, 2004
  5. John Smith

    Mario Guest

    From your description nothing shouts problem.

    I'm assuming this is multi-mode fibre, as it's within a building.
    Fibre is fibre, the ends are just different. Things to check:

    1. Make sure your sfp and gbics are all MM 850nm end to end.

    2. Have you swapped the sfp's with the connections that are working
    with the one thats not? You might have a bad sfp. This can sometimes
    happen with new equipment.

    3. Check that TX to RX connected at each link.

    4. If you have access to an optical power meter, make sure, there's
    light where you expect. And also make sure that you are receiving and
    transmitting at the correct levels. Check the specs on the equipment.

    Usually thats all thats needed. Check your layer 1, if thats ok move
    on to layer 2.

    Mario, Sep 10, 2004
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.