On Wed, 6 Jan 1999, Yann Bizeul wrote:
> The NICs are plugged to a Extreme Summit 48 ports, 10/100 FD switch
> When a make a direct connection with a cross cable, I got about 6M/s while
> u/l
> and about 10 K/s while d/l
>
> >Yann Bizeul wrote:
> >>
> >> Hi all
> >>
> >> I've got a collision problem :
> >> My NIC is a 3Com 905C or an Asante fast ethernet
> >>
> >> When 100BaseTx Full Duplex:
> >> Transferts are very slow
> >> lot of collisions
> >>
> >> When 100 BaseTx Half Duplex :
> >> Transferts are slow
> >> collisions
> >>
> >> Wgen 10BaseTx :
> >> It's about Okay...
> >> some collisions
This is a problem cause by using full duplex in a situation where it's not
appropriate.
It's fundamentally broken for anything but point to point with a crossover
cable.
It's caused by the inherent lack of flow/congestion control build in to
full duplex which cause buffer exhaustion in the switch.
Note that the brand of switch and the amount of memory in it doesn't
matter, as it's a matter of the fast links being able to feed the switch
at 10 times the rate where it can deliver.
With half duplex, this out of buffer situation is handled by reporting
extra packets as collisions, with full duplex, the packet is simply lost.
This results in retransmission delays that are orders of magniture longer,
since they're handled by the protocol stack instead of the nic.
Unless the switch can reliably tell the fast link to stop sending you'll
get these congestion situations and it can't with full duplex, so my
advice is to use half duplex on all the 100BaseTx lines, don't trust auto
negotiations, get them nailed down tight.
--
Henrik Olsen, Dawn Solutions I/S
URL=http://www.iaeste.dk/~henrik/
Get the rest there.
-
To unsubscribe from this list: send the line "unsubscribe linux-net" in
the body of a message to [EMAIL PROTECTED]
