3c905 full duplex with netboot prom?

[Henrik Olsen]

On Tue, 16 Mar 1999, Donald Becker wrote:
> Subject: Re: 3c905 full duplex with netboot prom?
> 
> On Tue, 16 Mar 1999, Hans-Peter Jansen wrote:
> 
> > I'm running a couple of diskless ws with the 3c905(!b) 
> > card and a netboot bootprom at a 24 port 10/100 intel 
> > 510T switch. Because the packetdriver forces the card
> > to half duplex (according to it's messages), I had
> > to switch off NWAY auto negotation on the cards to
> > prevent netboot failures (50% chance).
> 
> > Is there a way
> > to reestablish full duplex mode again? (Or does anybody 
> > know of a FD enabled packet driver for this card?) 
<Don Beckers technical answer snipped>
<Soapbox mode> 
With a switch you really really want to use Half Duplex anyway, since full
duplex has no congestion control, so will grind to uselessness once your
load increases.

To see why, consider that the switch has to buffer the packets, and simple
queue theory will tell you that those buffers will run out. When they do,
the switch can force collisions (half duplex) or silently drop the
packets (full duplex).

Retransmissions after collisions are handled by the cards, and is very
fast compared to the end-to-end retransmission by the protocol stacks,
resulting in a very much slower network.
</Soapbox mode>

Full Duplex is for marketing droids and management, not for tech staff.

-- 
Henrik Olsen,  Dawn Solutions I/S
URL=http://www.iaeste.dk/~henrik/
Get the rest there.