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Re: Proposal for accomodating 10.0000 and 9.58464 line rates


The reason I suggested a PHY based control was that the issue is based
on the PHY's transmit FIFO overflowing, not the adjacent node's receive FIFO
or some other upstream blocking. Different problems often require
different remedies.

If the OC-192 PHY is receiving at full line rate, there will be no way
for a PHY to insert a flow-control frame into its receive stream without
dropping data, and this would be a much more complicated implementation.

If you are suggesting that the MAC residing at the other end of the OC-192
link should assert a flow-control frame, what criteria would
there be to drive this action? The MAC would be receiving less than
its maximum rate and if there was no upstream blocking, it would be
very happy as the PHY on the other end of the link overflowed.

I believe that this matter is best solved with a PHY based signal.

Was your assertion of the Sun patent intended to suggest that there may
the IP may not be available for us to use in the standard if this method 
achieves concensus?

Dan Dove

___________     _________________________________________________________
_________    _/    ___________  Daniel Dove         Principal Engineer __
_______     _/        ________     LAN PHY Technology __
_____      _/           ______  Hewlett-Packard Company                __
____      _/_/_/ _/_/_/  _____  Workgroup Networks Division            __
____     _/  _/ _/  _/   _____  8000 Foothills Blvd. MS 5555           __
_____   _/  _/ _/_/_/   ______  Roseville, CA 95747-5555               __
______        _/      ________  Phone: 916 785 4187                    __
_______      _/      _________  Fax  : 916 785 1815                    __
__________  _/ __________________________________________________________ wrote:
> Not only did Shimon and I present the CRS deferral flow control
> mechanism to the 802.3x Task Force 4 years ago, we were granted a patent
> on it.  US Pat No 5,784,559 Full Duplex Flow Control was assigned to
> Sun Microsystems, Inc, and issued on July 21, 1998.
> After much careful consideration, 802.3x rejected CRS deferral flow
> control in favor of the frame based flow control which was eventually
> incorporated into the standard.  One of the points of general agreement
> was that CRS based flow control offered no performance advantage over
> frame based flow control, while frame based flow control could be
> applied over a variety of media, and at a variety of speeds.
> The idea of using frame based flow control as a solution to the problem
> of adapting a 10 Gbps MAC to a 9.?????? PHY has been previously
> suggested in this debate.  As Rich Taborek mentioned earlier today,
> there have been no counter arguments to this proposal offered.
> I contend that, rather than creating a new flow control mechanism for
> 10 Gigabit Ethernet, it would be preferable to make use of the flow
> control mechanism that we have already defined. We don't need another
> flow control mechanism in Ethernet, and we certainly don't need to
> rehash old debates.
> Howard Frazier