Date: Sat, 20 Oct 2007 18:35:17 +0200 (CEST) From: Harti Brandt <hartmut.brandt@dlr.de> To: Len Gross <sandiegobiker@gmail.com> Cc: freebsd-net@freebsd.org Subject: Re: Disable Exponential Backoff (retry) on Ethernet? Message-ID: <20071020183000.E8153@knop-beagle.kn.op.dlr.de> In-Reply-To: <20071019224155.GI20308@server.vk2pj.dyndns.org> References: <27cb3ada0710172051t536a4d11pfdfdb079ebd98932@mail.gmail.com> <20071019224155.GI20308@server.vk2pj.dyndns.org>
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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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