Date: Sat, 20 Oct 2007 13:56:18 -0700 From: Julian Elischer <julian@elischer.org> To: Len Gross <sandiegobiker@gmail.com> Cc: freebsd-net@freebsd.org, Harti Brandt <harti@freebsd.org> Subject: Re: Disable Exponential Backoff (retry) on Ethernet? Message-ID: <471A6B72.2030305@elischer.org> In-Reply-To: <27cb3ada0710201108l5e717fdbhc9fab610cb2a047c@mail.gmail.com> References: <27cb3ada0710172051t536a4d11pfdfdb079ebd98932@mail.gmail.com> <20071019224155.GI20308@server.vk2pj.dyndns.org> <20071020183000.E8153@knop-beagle.kn.op.dlr.de> <27cb3ada0710201108l5e717fdbhc9fab610cb2a047c@mail.gmail.com>
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Len Gross wrote: > If I have to, I will employ some form of simulation of collisions, but that > will have to be done carefully in order to get the effect of collsions > beteen multiple stations without messing up timing. > > I REALLY wanted to have the PHY handle it. Usng half duplex and some old > hubs (if I can find one) would get collisions, but the retry would create > other problems. > > So, looks like "simulated" collisions will be the way to go. > > BTW: I'm using Netgraph - very cool stuff. > > --Len > thankyou :-) > > > > On 10/20/07, Harti Brandt <hartmut.brandt@dlr.de> wrote: >> On Sat, 20 Oct 2007, Peter Jeremy wrote: >> >> PJ>On Wed, Oct 17, 2007 at 08:51:34PM -0700, Len Gross wrote: >> PJ>>I'm doing some protocol development and it is convenient to start it >> on >> PJ>>Ethernet. I will need to send a packet to the Ethernet device and >> only have >> PJ>>it be sent once, even if there is a colision. >> PJ> >> PJ>I know we've still got some hubs lying around in a backroom at work >> PJ>but I don't know of anything that will let you disable the retry-on-CD. >> PJ> >> PJ>Have you considered simulating the network at a slightly higher lever: >> PJ>Use ipfw pipes or similar to simulate packet loss (either set a queue >> PJ>length of 1 or probabilistically). This could be done either as a >> PJ>bridge or by tunneling your protocol over IP or UDP. >> >> Some years ago I wrote a netgraph node that connected to ethernet nodes >> and simulated a wireless broadcast channel including collisions, >> timevariable delay, loss and shaping. Can be done in a couple of hundreds >> of lines and easily allows >100MBit/sec with gigabit ethernet. The >> ethernet is just the physical transport medium for the packets and does >> not take part in the emulation. All that was controlled by bsnmpd and a >> remote command line tool and/or Java-GUI. Unfortunately I cannot release >> this (yet) due to licensing... >> >> harti >> > _______________________________________________ > freebsd-net@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"
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