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From: tucker@ccvaxa.UUCP
Newsgroups: net.lan
Subject: Re: Problems with IP/UDP speed on Vax75
Message-ID: <7300005@ccvaxa>
Date: Wed, 12-Feb-86 12:43:00 EST
Article-I.D.: ccvaxa.7300005
Posted: Wed Feb 12 12:43:00 1986
Date-Received: Fri, 14-Feb-86 07:42:56 EST
References: <776@duvan.UUCP>
Lines: 25
Nf-ID: #R:duvan.UUCP:776:ccvaxa:7300005:000:1063
Nf-From: ccvaxa.UUCP!tucker    Feb 12 11:43:00 1986


The main reason rawIP packets are SO MUCH FASTER than UDP/IP is
that the UDP layer does a big checksum on the entire data section.
This can easily be turned off (even if you have binary only) by
changing the value of a variable in the kernel called:

     "udpcksum"  (1 for checksum, 0 for no checksum)

This should increase the speed of UDP/IP to that of rawIP.  Note
that as long as you are running on ethernet the UDP checksum isn't
really needed.  Ethernet does a full packet checksum for you.

I would suggest using bigger packets to get higher speeds in
general.  You should be able to send UDP/IP packets in the 2k-8k
range (depends on the socket space limit set in udp_usrreq.c on
you VAX UNIx).  Your micro graphics station must also support IP
fragmentation to handle this.  If you can change your kernel
you can increase the UDP socket space limit even higher if you
want.  Take care when doing this.  The maximum possible with
IP fragmentation is 64k at a shot.

Tim Tucker
Gould Electronics
tucker@gswd-vms.ARPA
..ucbvax!ihnp4!uiucdcs!ccvaxa!tucker