[rescue] The Practical Guide to FDDI

[Chris Hedemark]

On Thursday, March 27, 2003, at 06:01 PM, jwbirdsa at picarefy.com wrote:

> what technical mistakes have I made?

"Even though it has the same speed as Fast Ethernet (100Mbps), FDDI is 
more efficient because it has a much larger MTU. Ethernet is limited to 
a packet size of 1536 bytes."

Not so.  That's just the default setting.  Unless you have a Sun 
ethernet card (at least the gigabit ones, anyway, I'm not sure about 
the HME's) you can bump the MTU size effectively to 9000 bytes or so.  
9000 bytes is a good size because NFS frames are 8K and the extra 
accounts for the packet overhead.

I know nothing about FDDI so I can't comment on the max MTU size for 
FDDI.  If the FDDI MTU size you give is as big as it gets, though, the 
edge that you are citing needs to be taken out because most quality 
ethernet devices can go up to 9000 byte MTU "jumbo frames".

The small default MTU on ethernet is just there for backwards 
compatibility.  And actually, it is up to 1540 bytes now (an extra 4 
bytes was added at some point).

Thanks for writing this, though.  I've always been curious about FDDI 
but there was never anything out there (that I saw anyway) that applied 
well to scroungers to familiarize them with the technology.  Since I'm 
renovating my new place now and have yet to wire it, this is definitely 
something to consider (though I have a lot of ethernet hardware and 
several hundred meters of CAT-5 cable that I scrounged).

Chris Hedemark
PGP/GnuPG Public Key at http://yonderway.com/chris/hedemark.gpg
"They that can give up essential liberty to obtain a little temporary 
safety deserve neither liberty nor safety." - Benjamin Franklin