[rescue] u2 drive trays

Dave McGuire mcguire at neurotica.com
Tue Aug 19 12:12:23 CDT 2003

On Tuesday, August 19, 2003, at 12:43 PM, Curtis H. Wilbar Jr. wrote:
>>> If the equipment supports 100baseTX full duplex though that would
>>> eliminate
>>> collisions between the two points.  no ???
>>   Well not exactly.  Yes, the collisions would be gone, but there's
>> still a shared medium in the middle: the switching fabric.  There can
>> be a lot of contention there.  Visualize nodes A, B, and C connected 
>> to
>> switched ports running full-duplex.  Nodes A and B both try to send a
>> packet to node C at the same time.  Many (most?) switches will use a
>> store-and-forward approach to address this issue.
> OK.... but how is this different from FDDI.... if I have two FDDI
> clients trying to throttle one FDDI server... that is still only
> 100Mbit of bandwidth at the server, and aggregated 200Mbit of 
> clients...
> So how does it differ ?

   At that level (in terms of media arbitration) it doesn't.  But to GET 
to that level, you've had to modify a basic aspect of Ethernet's design.

   And then there's still the performance gain of the much larger MTU, 
and the reliability aspects.

> Other than MTU, I don't see a big difference between 100baseTX switched
> and FDDI...  in the example you cite, how is FDDI going to do any 
> better
> than switched 100baseTX (other than an improved MTU) ?

   Aside from the reliability and the MTU, no.  But FDDI's larger MTU 
makes for a big (read: visible) difference in performance.  Set up a 
FDDI ring and drop the MTU to 1500 bytes and see.

   The fact that you have to modify Ethernet to make it work well is 
kludgy, and that alone is enough to make me try to avoid it.


Dave McGuire                 "You don't have Vaseline in Canada?"
St. Petersburg, FL                     -Bill Bradford

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