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Re: exchange point media (was: Re: MAE-EAST Moving? ...)
From: Wayne Bouchard <web () typo org>
Date: Wed, 14 Jun 2000 23:11:00 -0700 (MST)


On Wed, 14 Jun 2000, Brandon Ross wrote:

While there are certainly shortcomings to using GbE as a public exchange
infrastructure, I fail to see how a 1500 byte MTU has anything to do with
it.  In every network I have ever seen, there have very, very rarely been
any packets larger than 1500 bytes.

One of the major arguments against gigE I've heard is the lower MTU. Yes,
currently there are not much packets that are larger than 1500 due to
endsystems, but if we limit the infrastructure then there'll never be a
larger MTU here. ATM/FDDI/POS and even Token Ring (to mix apples with
oranges) all support larger MTUs and future standards will probably will
as well. Therefore I believe that any shared medium used for exchanging
traffic should also have the same capabilities. Larger packets mean fewer
forwarding/routing decisions per second for the same megabit rate of
traffic. 

This was one of my concerns when GE was released. It is likely that
many desktop users will be connected by fastethernet now and probably
ge later on. Many web servers are already connected by ge. So there
are instances where there COULD have been a continous path at 4k but
instead, there is 1.5. My motiviation in wanting a higher MTU is in
efficiency. One of the concerns that customers were bringing to me on
occassion was not necessarily bandwidth OR latency, but rather, the
composit.. data per unit of latency. They wanted to get be able to
send larger amounts of data without having it fragmented.
(particularly important in the multiplayer real-time gaiming bit.)

As a side effect (albeit, neglibible), if there were retransmissions
of a packet, there might be 1 instead of 3 with the current 1500
mtu. Some gain there as well. (Of course, given that the average
packet size on the net today is less than 75K, the relative benifit of
increasing the size breaks off quickly.)

The utility of a higher MTU is still dubious in the practicle realm,
but I agree that I would like to see the infrastructure move to 4 or
9k.

----------------------------------------------------------------------
Wayne Bouchard                                    [Immagine Your    ]
web () typo org                                      [Company Name Here]
Network Engineer
http://www.typo.org/~web/resume.html
----------------------------------------------------------------------



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