Subject: Re: 1394 packet size and IP

From: Ran Atkinson <[email-masked]>
Date: Thu, 1 Oct 1998 17:25:54 -0700

Colin,

        The packet size breakpoint of (4096 user bytes + sizeof(NFS header)
+ sizeof(UDP header) + sizeof(IP header)) is a big deal.  Its a big deal
because a whole lot of systems can gain big performance wins at that MTU
size via an operating systems technique known as "page flipping".  This win
is especially big with applications such as NFS or Microsoft's proprietary
filesystem (misnamed CIFS), but benefits all network applications.

        More generically put, much of today's deployed Internet has a "Path
MTU" equal to the FDDI MTU.  Even the Ethernet crowd, which have
traditionally used an MTU ~~= 1500 bytes, are working on "Ethernet
Jumbograms" that will be at least the size of the FDDI MTU.  There
is a proposal in IEEE to add Jumbogram support into the Gigabit
Ethernet standards, for example.

        I hope this helps explain the concern.

Regards,

Ran
[email-masked]