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Re: [EFM] flow control in 802.3




Marc,

What a good question!

This is a problem that we (almost certainly) have to solve in the copper track. We are looking for suggestions, the ones that immediately come to mind are:

MII clock adjustment
IPG stretching
.3x pause frames
half-duplex back pressure (force collision)
new signal for pause/continue

The matter was discussed at length during .3ae - take a look at 10G website...

 http://grouper.ieee.org/groups/802/3/ae/public/jul00/muller_1_0700.pdf

There are various other discussions of this on 10G. It's not clear that the arguments and conclusions are valid for .3ah in the same way as .3ae - but it's always worth taking a look.

Hugh.

PS - Any of the 10G'ers care to comment?


MARC KIMPE wrote:

> All,
>
> Is there a way to transmit flow control information across an MII interface from the PHY direction to the MAC ? If yes could someone point me to the pertaining clause of 802.3 ?
>
> In other words, let's assume that a PHY for some reason or other can only transmit at 3Mbps while information to that PHY flows at 10Mbps. How can the PHY tell the MAC to stop sending ? I saw some presentations related to 10 Gigabit Ethernet that proposed various mechanisms but I do not know if anything was adopted.
>
> Any help would be appreciated.
>
> Thanks,
> Marc Kimpe
> Adtran