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From: gaj@hpctdja.HP.COM (Gordon Jensen)
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet collisions
Message-ID: <3260009@hpctdja.HP.COM>
Date: 5 Dec 90 19:37:42 GMT
References: <467@pirates.UUCP>
Organization: Hewlett-Packard CTD, Colo. Spgs.
Lines: 25

>I would like to know what can cause excessive collisions on Ethernet.  I 
>realize that collisions are a fact of life on ethernet.
>My net analyzer shows a large number of local collisions (as high as 20%).
>I can't isolate to just one or two machines.  I also don't have any one
>machine which is completely non functional.  In other words I haven't
>nailed it down to a problem with one machine (bad card or ?).  What other
>things should I look for?  Ground problems?  My cable scanner doesn't show
>any bad segments of cable.

>Bob Fawcett

First thing to check for is grounding problems, especially on your
ThinLAN.  If there are two grounds on a segment, 60 Hz can flow in
the shield.  Enough IR drop can occur to trigger a repeater's carrier
sense circuit.  Since there is no signal to lock to, repeaters that
I've seen just source 10 MHz out all ports.  This is bad.  Extra 
grounds can occur when the T connector isn't covered with it's
prophylactic.  A quick test is to throw an *analog* scope on the
cable and sync to line, with the timebase set to show multiple
cycles of 60 Hz.  


Good luck,

Gordon