[Gllug] Bank Holiday Monday type question

[Ian Norton]

On Mon, May 30, 2005 at 06:38:35PM +0100, Ian Norton wrote:
> if my brain is working, you will get better efficiancy by setting your mtu to
> be about 1483 bytes (or maybe 1531).
> 
> See:-
> http://support.metronet.co.uk/adsl/general-opt.xhtml1

It wasnt working perfectly,

quote...

"We get presented with a PPP header (4 bytes), a L2TP header (6 bytes), a UDP
header (8 bytes), an ATM VPI/VCI header and an ATM AAL5-SNAP header (8 bytes).
We also have currently a fragmentation issue where if packets arrive off the
155Mbps pipe larger than 1500 bytes they have to be fragmented and reassembled
later on, this adds a small extra bit of latency and load on some of our
servers. We can avoid this but due to hardware and driver restrictions its not
possible at the time. We would love to play with this but we would probably
wipe out everyones ADSL connection for an hour or two which probably would not
be apprieated; this is something for when we install a brand new spanking
155Mbps pipe which is on order."

so, thats 4 + 6 + 8 + 8 = 26 bytes of overhead for every packet from an adsl 
line.

basically, they say, best latency is with a mtu of 1428, best thruput is 
a mtu of 1476.


-- 
Ian Norton-Badrul

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