[K12OSN] Gigabit headach

Wed Sep 1 00:30:05 UTC 2004

Actually, IEEE 802.3ab does indeed specify 100m, or 328ft, for 
1000BaseT, on Cat5 or above wiring.  This is because of the large 
installed base of Cat5 wiring; the 1000BaseT protocol was specifically 
designed with this in mind.  There are some who *recommend* shorter 
distances than the full 100m when doing Gig-E or even 100BaseTX, and 
personally, I agree, but the IEEE has certified 1000BaseT to that 
distance. 

As for the Bluemax recommendation, here's my guess as to how that came 
about.  When these folks said "82ft", that was very likely a propagated 
typo, combined with another recommendation that these folks had read, 
specifically one that says "allow for patch cables."  See, a lot of 
folks use 2m (7ft) cables from their patch panel to the switch, and from 
the network drop in the wall to their boxes.  The folks at Bluemax 
probably saw the 100m and accidentally translated that mentally into 
"100ft", remembered that most folks use 7ft patch cables, noted that 
82+(7*2)=96 (just under "100ft"), and thus said, "AHA, here's our 
recommendation!"  Oops.

Now mind you, the 100m spec assumes fairly optimal conditions; we know 
that real buildings in the real world are very often far from optimal.  
For example, if your cable runs are snaking right through a bunch of 
fluorescent lights or next to high EMF-emitting electric motors, your 
cable runs will need to be much shorter, and you may wish to revisit 
your cable run placement anyway.  On the other hand, if your cable runs 
are, say, encased in grounded steel conduit, you should be able to get 
the full 100m with little trouble.

That said, if I find that I'm getting close to that 100m limit, or if I 
can see that I'm going through a high EMF area regardless of cable 
length, I'm runnin' some fiber.

--TP

Brock Noland wrote:

>If that is true I was not aware of it, but I am no expert! However I
>found this interesting note yesterday.
>
>
>"Using quality CAT 5 Cabling, good wiring practices and no EMI
>problems, the maximum recommended transmission line length between
>nodes for 10BaseT and 100TX is 100 Meters (about 329 feet).  For
>Gigabit wiring using 1000BaseT operating at 350MHz, the limitation is
>82 feet.."
>
>
>http://www.bluemax.net/techtips/networking/Wiring_Tips/Wiring100TX/alittletheory.htm
>
>On Tue, 31 Aug 2004 19:20:19 -0400, Shane Stafford
><staffords at glenburn.net> wrote:
>  
>
>>oh knowing who did our cabling and the fact we just purchased 5 of these
>>switches, this is not a good thing.
>>
>>ah well, life stays interesting
>>
>>Shane
>>
>>"Support list for opensource software in schools." <k12osn at redhat.com> on
>>
>>
>>Tuesday, August 31, 2004 at 7:12 PM -0500 wrote:
>>    
>>
>>>On Mon, 2004-08-30 at 22:46, Duane Wilson wrote:
>>>      
>>>
>>>>I took everyones advice and bought the amer.com  SR24G2.
>>>>
>>>>Installed it between server and terminals.
>>>>
>>>>Tried to boot terminals all at once - nada!
>>>>    Would not even get DHCP
>>>>
>>>>Tried one terminal.
>>>>    Got DHCP but choked on 'loading vmlinuz'
>>>>
>>>>There is about 230 ft. of cat Ve from the server to the AR24G2.
>>>>
>>>>Is that too far?
>>>>Did I crimp the end wrong?  (It works fine when connected to the old
>>>>        
>>>>
>>>100
>>>      
>>>
>>>>Mbit)
>>>>Is my switch bad?
>>>>
>>>>Anyone???
>>>>
>>>>
>>>>Thanks,
>>>>Duane Wilson
>>>>
>>>>
>>>>        
>>>>
>>>I agree with Terrell.  The tolerances for Gig vs 100mb are substantial.
>>>Just because it works with 100mb does *not* mean it will work with gig.
>>>Take it from a person who has already gone through what you are going
>>>through.  Check your cabling.  It has to be done *perfectly* for gig to
>>>work over copper.
>>>
>>>Jack
>>>
>>>
>>>_______________________________________________
>>>K12OSN mailing list
>>>K12OSN at redhat.com
>>>https://www.redhat.com/mailman/listinfo/k12osn
>>>For more info see <http://www.k12os.org>
>>>      
>>>
>>Shane Stafford, MCSE, MCT
>>Director Information Services Glenburn School and Town
>>Educational System Integrator/Network Engineer
>>S & B Consulting
>>
>>
>>
>>
>>_______________________________________________
>>K12OSN mailing list
>>K12OSN at redhat.com
>>https://www.redhat.com/mailman/listinfo/k12osn
>>For more info see <http://www.k12os.org>
>>
>>    
>>
>
>
>  
>

-- 
_____________________
Do you GNU!? <http://www.gnu.org>
Win freedom from all but 1 of 4000 spams with Mozilla Thunderbird. 
Download it now. <http://www.mozilla.org/thunderbird>