Date: Sat, 20 Oct 2007 11:08:08 -0700 From: "Len Gross" <sandiegobiker@gmail.com> To: "Harti Brandt" <harti@freebsd.org> Cc: freebsd-net@freebsd.org Subject: Re: Disable Exponential Backoff (retry) on Ethernet? Message-ID: <27cb3ada0710201108l5e717fdbhc9fab610cb2a047c@mail.gmail.com> In-Reply-To: <20071020183000.E8153@knop-beagle.kn.op.dlr.de> References: <27cb3ada0710172051t536a4d11pfdfdb079ebd98932@mail.gmail.com> <20071019224155.GI20308@server.vk2pj.dyndns.org> <20071020183000.E8153@knop-beagle.kn.op.dlr.de>
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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 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 >
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