===== Original Message From "adrian.wells"
===== Hi Paul, This does sound strange!
I know that d-link are cheap but... (I'd recommend Lantech MaxSwitches - easy after the event.)
Are the units doing a full reset. i.e they go through a POST or are
resetting the tables only?
I think it is the power cables as I just had a look (see the message to Mark) and tere are power cables all over the data cables.
Do all of the units reset at the same time?
I assume that you are happy with the mains supply. Have you tried fitting a UPS to filler out staffroom kettles etc. :-)
There are no UPS at present which could well solve a lot of it.
Another big problem in school is the need to have everything up at
I think that, unless the reseller/manufacturer have suggested the systems
have some sort of bizarre surge protection/voltage on interface function
that causes the switch to reset, then none of these sorts of problems
could/should have an effect.
Mains voltage, flourescent lights etc. near data cables will not cause
significantly high voltage to run in the data cable; however it can degrade
data quality to the point of uselessness, e.g. 80%+ packet loss - easily
tested with ping. Even if high voltage was to reach the switch interface (is
that an ethernet socket or an ISDN one - oops, it was ISDN...) it would at
worst kill the switch (permanently) and at best damage the particular
interface it was applied to; this would similarly effect the devices at the
other end of the cable.
The switch configuration should be stored in flash ram, where some (more
expensive!) switches may have three stored - default, startup and running -
some older switch OSes like CatOS only have default and running, which is
scary in a complex network (change settings only when you have a console
cable available and physical access to the switches...).
Resetting to default is normally through actuation of a concealed button
(like the manual release for CD drives), or via user intervention during the
boot up sequence (console lead time again...). Again, high voltage causing
this reset would be much more likely to damage the switch and other
connected devices.
Presumably you could test how the current switches store configs by making a
change and powering them off and seeing if the change is still there on
power-on. A switch that loses settings during power off is not suitable for
use in mission critical network (like any school one!) and should be
returned for a full refund on that basis. Realistically, switches installed
on large(r) sites should also have layer 3 functionality and significant
switching fabric capacity to allow for future capacity demands.
The current best value solution for education is HP - if you want more
advice on specs for these, let me know.
Cheers
Chris
-----Original Message-----
From: adrian.wells
To: SuSE for Schools
Sent: 10/10/03 3:51 PM
Subject: Re: [suse-linux-uk-schools] Switched off
Hi Paul,
I missed the bit about the mains & data sharing the same conduit. This
is
against regs. and you should get the installer to make good. There is a
recommended minimum distance for mains & data running in a parallel
course,
even in separate conduits and they should not run in the same conduit.
Tis
Friday and I cant remember the details. Note that 3 part trunking should
be
screened, but little that is installed today is because users get away
with
it working!
Same thing goes for avoiding fluorescent lamps, give a wide birth - I
think
that's 0.5m.. Crossing mains at 90deg is okay but looks bad (hey, lets
keep
those walls neat!)
The problem is that there's a lot of 'professional installers' out there
that would be better suited to house bashing and have learned their
trade
from a mate, having never read the CAT5 regs let alone the electrical
regs.
If you have induced voltages on the cat5 then the UPS will not help, you
could try surge protectors on the CAT5 but you'd do better to get the
cabling sorted first. If the manufactures send a rep to your site
they'll be
looking for any 'let-out' rather than admit fault.
As Mark says, it's okay to mix lo voltages in the same conduit.
including
telephones that can have 120V on the ringer! although 50V is more common
on
conventional switches - rambling now!
Not sure how much this helps
Have a good weekend
Adrian
----- Original Message -----
From: Paul Taylor
time, but have you tried connecting one segment at a time.
Sorry, but all obvious stuff really :-(
Adrian
Thanks Adrian,
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