Date: Thu, 18 Oct 2007 18:42:10 -0700 From: "Len Gross" <sandiegobiker@gmail.com> To: "John-Mark Gurney" <gurney_j@resnet.uoregon.edu>, "Len Gross" <sandiegobiker@gmail.com>, freebsd-net@freebsd.org Subject: Re: Disable Exponential Backoff (retry) on Ethernet? Message-ID: <27cb3ada0710181842x4d214d31ob4f474ff790355b8@mail.gmail.com> In-Reply-To: <20071018082056.GW39759@funkthat.com> References: <27cb3ada0710172051t536a4d11pfdfdb079ebd98932@mail.gmail.com> <20071018082056.GW39759@funkthat.com>
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Thanks so much for the response. Here is some additional information. I'm trying to emulate an RF network where there are colisions (e.g. "Aloha" type protocol) so I actually need collisions! I had forgotten that modern hardware essentially eliminated them. So, lets say I can find/use an "old hub", can I control the number of retries? Maybe I have to find some old NICs and old drivers? -- Len On 10/18/07, John-Mark Gurney <gurney_j@resnet.uoregon.edu> wrote: > > Len Gross wrote this message on Wed, Oct 17, 2007 at 20:51 -0700: > > I'm doing some protocol development and it is convenient to start it on > > Ethernet. I will need to send a packet to the Ethernet device and only > have > > it be sent once, even if there is a colision. (Higher levels in the > > protocol will detect the failure.) I've searched quite a bit, and > haven't > > found any place that talks about this. Are there any hardware cards, > or > > drivers, that let me turn off the backoff/retry behavior? > > Are you even using hardware that does collisions? Collisions pretty > much went out w/ 10Mbit ethernet... Not completely as there are older > 10/100mbit "switches" that only switched between the two segments (and > each of 10/100 segments was hubbed)... All modern switches are > full-duplex and don't suffer from the old CD part of CDMA that was part > of the original ethernet specification.. > > For Gige, you can't even do half-duplex, as each side is transmitting > on all four pairs at the same time... The physical layer handles the > fact that both sides may transmit at the same time, and knows how to > cancel their own interference out so they can hear the other side... > > -- > John-Mark Gurney Voice: +1 415 225 5579 > > "All that I will do, has been done, All that I have, has not." >
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