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From: barmar@think.com (Barry Margolin)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: seeking experiences with FDDI interfaces for Sun's
Message-ID: <1991Jun22.080838.6400@Think.COM>
Date: 22 Jun 91 08:08:38 GMT
References: <9106041306.AA09116@msr.EPM.ORNL.GOV> <3384@redstar.dcs.qmw.ac.uk> <3393@redstar.dcs.qmw.ac.uk>
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In article <3393@redstar.dcs.qmw.ac.uk> liam@dcs.qmw.ac.uk (William Roberts;) writes:
>I'm quite prepared to believe that Sun4 machines (I was using a Sun 4/280 and 
>a Sun 4/160) can drive the FDDI network at greater than Ethernet bandwidth: 
>one of the planned experiments was to change the FDDI driver software so that 
>it generated continuous "idle traffic" transmitting strips of a VME 
>framebuffer, sending to another machine which writes such things direct into 
>its display memory.

Someone here did some tests with a program that just sends UDP or TCP data,
not NFS, 4/3xx and 4/4xx machines, over FDDI.  For certain datagram sizes
he was able to get much better than Ethernet bandwidth.  But at other
sizes, it wasn't much better than Ethernet; I suspected that this was due
to kernel buffering strategies optimized for Ethernet's smaller MTU.

>FDDI doesn't make any difference because present machines can't really compute 
>at those speeds (well, Crays and the like perhaps, but nothing that Sun 
>manufacture).

Be aware that the machines you said you tried are not "present machines."
The 4/280 and 4/160 have been around for almost four years.  The current
top-of-the-line Sun-4's are about an order of magnitude faster.
-- 
Barry Margolin, Thinking Machines Corp.

barmar@think.com
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