Trouble with B2B fiber connection

I have a fiber link between 2 buildings (distance approx. 500 meters)

3com superstack II 3000 on one side and HP2424M on the other. Problem is I can't get 100 mb half or full duplex to work properly. Roadkil's Comtest
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shows an 9000 kb/s out but the bytes in's stay below 50? I tried to set both sides manually of course, but I get the best results by setting it to 10mb half duplex 468/1144.

If I run the same test in one building (so without using the fiber) I get 8000/8000, 10000/5000, 9000/9000, etc.

Thing is that I need to copy a 6 GIG Oracle dump file nightly between the two buildings and I need the speed 8-)

Anyone can shine a light on my prob?

Thanks in advance,


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Id call up the contractor who put the link in and describe what is happening. Could be a bad connector on end. Maybe a bad patch cord? replace the patch cords before calling the contractor. Maybe the connector isnt fully inserted into the switch on your receive end. Or it could be the any of the splice points between the buildings.

Check both connector ends in each building. I cant how many times I had customers complain about a fiber link not working where I went out there and it ended up being THEIR bad patch cords. I billed them for the call and sold them their patch cords.

Good Luck

Joe Perkowski

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Get some alcohol swabs and a can of compressed air and clean all the fiber connectors. Sometimes all it is is dirt. Then switch the fibers at each end to see if the trouble stays with the fiber or with the port. Switch patch cords to see if you have a bad patch cord. Also be sure the patch cords are the matching diameter as the interbuilding link fiber. Then it's time to bring in an OTDR and someone who knows how to use it to troubleshoot.


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Dale Farmer

Thank you all for your suggestions, I've found the solution thanks to a Arie Goldberg:

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I hyperterminaled into the 3com 3000 and the HP2424 and changed the settings for the fiber port. They were all on default and that means 100mb Half Duplex. The stats showed millions of CRC align errors and late events not to mention the collisions... I used to have ping -l 65500's with timeouts and 140 ms response time and now they' re as steady as a heartbeat and no timeouts!

Imagine the problems we had and the costs we've made tuning the backoffice of every application we run (ERP, WMS). All due to a misconfiguration of the hardware... sniff...

Thanks again and I hope this posting will help another poor soul!



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