Re: [ethmac] Collisions

[Alex Shayda <al_shayda@mail.ru>]

nbase wrote:

> Hi,
>
>    I would be EXTREMLY carefull in changing ANY of the spec definition like
> the collition you suggested as most spec defineition are not coming "out of
> the blue" but rather have some importent aspect behind them, which you
> might not be aware of.
>
> a small exmaple is the prevantion of constat head to head collision, not
> only for any two or more shared port but also what if two of those ports
> are your own design since the random is the same in both port and since
> both will start immidiatly than you will never get out of this collision
> until you reach the 16'th repeteted collision and than both port might want
> to discard the packet and will continue so until one of them don't have any
> more packet to transmite. and this is of course a beahve we would not want
> to happen.
>

  You'll get the same behavior if you have inquality random number generator in
out-of-the-blue design.
  From what place the seed for random numbers come from, and why there isn't link
to random seed on your design? Do you want to get seed from a system clock? From
a packets coming through net? I think now your diagrams misses it.
  At this point, my suggestion is to use both clock and MAC address of the core
as a seed for random number generator.

  Concerning MAC address, where did you store it? Where it is compared to the
recepient's address in the packet? Do you want to leave comparison of recepient's
MAC out of your design?

> and the point of saving slot time is also danger as after collision BY
> DEFINITON each station need to continue transmiting so ALL station will
> "hear" it for at least extra 32BT (jam), and after this there must be an
> IPG and so we get back to the traditional

I need to think about it more. Can you mail me some datasheets you have?

> I would also think that any change from the standard should be (if at all)
> only as an option.
>    Illan

With best regards, Alex Shayda.