Disable Exponential Backoff (retry) on Ethernet?

[Julian Elischer]

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 at 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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