Slowing down Ethernet

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I mean really slowing ethernet down.

I have a requirement to slow down ethernet so the clock speed is running at
about 100kHz. Everything else should work as is, ie all the usual TCP/IP
protocol stuff.

There will no more than about 8  hosts on this slow network.

The purpose is to remove as much RF interference as possible, bandwidth is
not a problem - small infrequent packets.

The server will have a NIC, the hosts will terminate in PiC devices
emulating ethernet

My initial thought would be to have a modified server NIC and then a
hardwired hub.

Has anyone done this before? I have googled but been singularly unsuccesful
with this.

Regards

Martyn



--
===========================
Martyn Kinder G0CZD

Open-Xchange 0.8b5

http://www.czd.org.uk



Re: Slowing down Ethernet


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An unusual requirement, but I can see how it might be useful in
some situations.

Would it perhaps be practical in the situation to use multidrop
RS422 (serial) instead of ethernet?

Re: Slowing down Ethernet


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What kind of RF environment are you dealing with?

How do you know  your network problems are RF-related?

What king of hub/switch do you have?  What distances?

--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

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I think someone else suggested multi-drop - or, you could just run a
bunch of plain pt-pt PPP links between the systems, and run an IP
routing protocol to deal with occasional link failures.  You could use
heavily shielded serial cables and run them just about as slow as you
please.

Are you worried about RF from the wire, or from the NIC itself?  If
not from the NIC itself, why not just run ethernet over fibre and
stick with COTS kit?

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Not entirely sure if that nixes the idea of fibre or not.

rick jones
--
oxymoron n, commuter in a gas-guzzling luxury SUV with an American flag
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

Re: Slowing down Ethernet


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It's not the clock speed that causes the interference, it's the
rise-time of the signals.

IMHO, this is going to be really difficult to do, as all of your
backoff, retry, and other timing algorythms are going to have to be
redone.  You are going to need to engineer, build, and maintain your
own NICs, hubs/switches, and client devices.

Why not use Rick's suggestion of fiber?

Re: Slowing down Ethernet



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Why not just use fibre?

best regards
  Patrick

Re: Slowing down Ethernet


Hi all,

thanks for the comments so far.

I have to admit, I hadn't considered fibre, but this would probably be too
expensive. The function that we have in mind is to collect data from a Radio
Telescope.  Hence it has to very RF quiet.

We have considered RS423, but the attraction of ethernet is that we can use
established protocols (like SNMP) etc for data acquisition and communication
for control.

We are looking at a number of local modules, each with its own IP address.

But as this an amateur venture (hopefully will hit schools etc) we really
need to keep the costs down. Hence the remote controller will be PiC based
and as data rates will be low we could use a hardwired hub. Ideally the only
thing we would need to change would be the NIC.

Distances - I guess less that 100m.

Regards

Martyn
--
===========================
Martyn Kinder G0CZD

Open-Xchange 0.8b5

http://www.czd.org.uk



Re: Slowing down Ethernet


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Shielded twisted pair?  I believe that you can get shielded cat 5 cable
and shielded modular plugs and jacks.


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--
Tom Schulz
schulz@adi.com

Re: Slowing down Ethernet


Thomas Schulz wrote:
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Hi Thomas,

I think that would be an option and OK for longer runs, but it still can be
RF leaky and would not help with noise suppression from hubs or switches or
from short patch leads

KM

--
===========================
Martyn Kinder G0CZD

Open-Xchange 0.8b5

http://www.czd.org.uk



Re: Slowing down Ethernet


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Won't one need to put the hubs/switches into Farraday (terminology?)
cages anyway?  

rick jones
--
Process shall set you free from the need for rational thought.
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

Re: Slowing down Ethernet



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Maybe you want to go with 10base2 coax. Then you really only have to
make sure you shield the data collection points well.

Well something else is finding 10base2 hubs might be hard unless you
find some in someones storage closet. :)


Re: Slowing down Ethernet


Thomas Schulz wrote:

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Fiber isn't necessarily all that expensive if it doesn't have to be new and
shiny.

For this kind of venture ebay is your friend.

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

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Might be worth checking eBay for second-hand 100 Mbit/s fibre kit.
That stuff has been around long enough that it may not be all that
expensive.

rick jones
--
firebug n, the idiot who tosses a lit cigarette out his car window
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

Re: Slowing down Ethernet


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It would be a PITA but if you get a phone line and a DSL account
for each machine you'll have a network.  

If you've got two serial ports in each machine you can set up a PPP
(point-to-point protocol) connection on each interface, daisychain
machines together and and get 100Kbits/sec, maybe.  It's been ages
since I did PPP.

Then there's this;

http://www.faqs.org/rfcs/rfc1149.html






--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

Re: Slowing down Ethernet


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But he's going to get a LOT of noise with this setup. If I recall, he's
listening for signals that are weaker than the noise on almost any
unshielded wire. He hasn't said what he's using for collection devices
but he might want to look at some micro controllers that have tiny basic
and such for programming. They are very small, very low power, and can
be sealed in a box with coax coming out back to a remote data collection
computer.

Re: Slowing down Ethernet


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Yeah, but he's looking in a band that's about the 100th harmonic
removed from the frequencies involved in serial comms, and the
risetimes of RS232 signals are slow that there aren't any harmonics,
anyway.


--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

Re: Slowing down Ethernet


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Try the residental IP-over-powerline stuff.  No URL. I see it for sale
in the big computer stores.

Have you actually measured/heard noise comming from ethernet cable?  

ISTM that CAT5e or CAT6, done right, is so carefully balanced as to
not radiate much.  Nail the interfaces at 10Mb just to make the
harmonics that much weaker.

If you are getting noise try wrapping the hub/switch in aluminum foil
and grounding it.  

What band are you listening in ?  






--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

Re: Slowing down Ethernet


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Yes.  Light snow on NTSC TV ch2 from pushing 100baseT over Cat3
about 10ft away from antenna.  Snow droped from objectionable
to barely noticeable when cable replaced by Cat5e.  But totally
absent when link depowered.

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10 made it go away.  IMHO, Cat3 is reasonably balanced but the
slower twists give less room for slewing twists so there is more
crosstalk.  Cat5/6 is certainly better, but more in XT than EMI.

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I would worry about the PC or whatever is at the radio-telescope
generating the signal.  Digital equipment is noisy.

-- Robert








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Agreed. With these issues about CAT5, I'm suprised he's got a computer
or a TV set anywhere in the area.    

Based on what he's just said, above, why isn't 10MB on CAT6 wired to
the highest spec quiet enough.

In another post I suggested ethernet over house power wiring (bought
at retail computer stores) or getting each PC a POTS phone line and a
DSL subscription and making an IP network out of that.

Neither of these solutions  have any ethernet signaling.




--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

Re: Slowing down Ethernet


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It possibly is, depending on his frequencies of interest.
Digitial signalling has sharp edges which generate a
wide frequency range.

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And by being analog signalling (digital data) they probably
produce much less interference, or at least it's confined
to well-known frequencies rather than scattered.

-- Robert




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