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Hi,

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
all.

The following is an example that worked, from the backbone 3750 it
starts:
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

On 2004-09-10, John Smith <> wrote:
> 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
> all.
>
> The following is an example that worked, from the backbone 3750 it
> starts:
> 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.

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.

(John Smith) writes:
>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
>all.

>The following is an example that worked, from the backbone 3750 it
>starts:
>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?


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
Network Engineer/Jack of All Trades
Vector Internet Services, Inc.

(John Smith) wrote in message news:<. com>...
> Hi,
>
> 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
> all.
>
> The following is an example that worked, from the backbone 3750 it
> starts:
> 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..


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.

http://www.cisco.com/en/US/products/hw/modules/ps5000/
products_data_sheet09186a008014cb62.html

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.

Cheers.