Subject: (IPng 6469) Re: Host Fragmentation

From: David Borman <[email-masked]>
Date: Tue, 15 Sep 1998 10:46:32 -0500 (CDT)

> From: [email-masked]
> Date: Mon, 14 Sep 1998 22:08:05 EDT
> Subject: Re: (IPng 6448) Re: Host Fragmentation
> ...
> Here are the most important data of the announcement.
>
>   Microsoft officials said they achieved 920Mbps throughput on a server
>   using the AceNIC 180, a Gigabit Ethernet network interface card from
>   Alteon, which also supplied the proprietary jumbo-frame technology.

Ok, does anyone know how big were these jumbo-frames were?  4K?

> ...
>   The tests were conducted using a single-processor Intel 400-MHz
>   Xeon-based server and four 333-MHz Pentium II clients. An Alteon
>   Gigabit Ethernet server switch connected the servers and clients.

This says to me that the jumbo-frames were going from the server to the
clients without fragmentation.  That's great.

Yes, you can get better performance with bigger packets.  I don't think
anyone argues with that, and this test supports it.  I've shown the same
thing many times over the years when I worked at Cray Research.

Now, as for the "IPv6 won't let me fragment" complaint, I'll offer an
alternative view (that I don't necessarily agree with...).  Since the
high-speed fragmenting router sits close to the server, draw a circle
around both of them and call that your "host".  Then, rather than doing
IP level fragmentation, do TCP level splitting of the packet.  It's easy
to take one large TCP packet and split it down into multiple TCP packets.
The hard part is that you'd have to recalculate the TCP checksum over
each piece.

I'm not really interested in discussing this alternate solution, because
I don't especially like it myself; it's too easy to argue about what is
wrong with it.  I'm just presenting it as a different way of looking at
the issue.  It is actually better than the IP level fragmentation
arguement, because 1) lost segments don't invalidate the whole original
packet and 2) the client doesn't have the added latency of waiting for
all the IP fragments to show up before passing anything up the stack to
TCP.

		-David Borman, [email-masked]
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