[Beowulf] Jury rigged ethernet?

Reuti reuti at staff.uni-marburg.de
Mon Jun 27 10:22:50 PDT 2005


point to mention is the most likely unknown wave resistance of the 
existing wires. You have

150 Ohm for IBM Type 1
100 (sometimes 105?) Ohm for CAT3/5 twisted pair
50 Ohm for coax 10Base2 (RG58)
93 Ohm for coax of the IBM 3278 Terminal connection (RG59)

There are adapters (called baluns) around, to convert it at both ends of 
the wire.

I would first try to get it working without any balun using 10BaseT 
connections. At this distance it might work already. If not, there are 
long distance adapters from e.g. Allied Telesyn around which will 
convert 10BaseT to a CAT 1/2/3 connection with RJ11 connectors.

If you must use coax because it's on the machines, you can try a balun 
first, or convert 10Base2 to 10BaseT by using an used hub with these 
type of connecters (or another type of converter from the above 
mentioned company).

Cheers - Reuti

Ed Karns wrote:
> Not a good idea, although it may actually work. ... not necessarily  
> doomed to failure, but not industry standard practice.
> Test before you commit.
> Ed
> FireWireStuff.com
> On Sunday, June 26, 2005, at 12:04  PM, beowulf-request at beowulf.org  wrote:
>> Today's Topics:
>>    1. (Huntress Gary B NPRI)
>>  .....
>> ----------------------------------------------------------------------
>> Message: 1
>> Date: Wed, 22 Jun 2005 22:37:29 -0400
>> From: Huntress Gary B NPRI <HuntressGB at Npt.NUWC.Navy.Mil>
>> Subject: [Beowulf] Jury rigged ethernet?
>> To: "'beowulf at beowulf.org'" <beowulf at beowulf.org>
>> Message-ID:
>> <A506359028CAD21191C10008C75D895C0C6D5248 at NPRI54EXC14.NPT.NUWC.NAVY.MIL >
>> Content-Type: text/plain
>> This is more than a little off topic but if the answer is encouraging  
>> it will strengthen my case to purchase a small-ish cluster  
>> significantly.
>> Basically I am exploring the idea of placing a cluster in a dedicated  
>> "non-traditional" physical location where space is at a dramatic  
>> premium.  This particular space has existing cabling that I cannot  
>> change and it is my only electrical access.  A single existing cable  
>> provides 3 phase power, a few DC discrete signal pairs, and a few  
>> twisted shielded pairs that were used for serial communication.   The  
>> cable is approximately 30 feet long.  I would like to adapt two  
>> twisted pairs for ethernet.
>> What are the chances that I can coax 10Mbps out of this connection  
>> with modern (hopefully tolerant) ethernet cards at either end?  Is  
>> this doomed to failure?
>> Thanks,
>> Gary H.
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