Re: Unified PMD vs. Unified PHY
Thanks for the clarification. It appears that you are now in agreement with Mr.
Andreas Bechtolsheim's original statement that the UniPHY proposed by Mr. Howard
Frazier, et. al. affects the transport of Ethernet over SONET to the tune of
only 3% (3.125% to be exact) overhead. I also agree that this is a compromise
with the WAN compatible PHY, which is not LAN compatible.
I have a few additional comments below:
Jonathan, Question for you below.
Roy Bynum wrote:
> A LAN only PHY that is at 10Gbps transfer rate is exactly what I am talking
> about. The proposed "UniPHY" is ~3% less than the original proposal for a
> WAN compatible PHY which, as you pointed out, is less than the original LAN
> PHY to start with.
This appears to be a good compromise. Full 10 Gbps for the LAN and only 3%
penalty for the WAN.
> As far as a unified PHY is concerned, no one has said that the WAN
> compatible PHY could not be used in a privately owned fiber systems, like
> the LAN PHY.
I have absolutely no problem with this.
> The WAN compatible PHY just has ~5% less MAC transfer rate. As far as I
> I know, there has never been a presentation that would only work in the
> WAN, ie. a WAN only PHY. This understanding makes the WAN compatible
> PHY functional as a reduced rate LAN PHY.
The WAN PHY is not compatible with the LAN since it is speaks SONET. The LAN
does not transport SONET. The LAN transports Ethernet (in most cases). Am I
> In other words, the unified PHY that Jonathan Thatcher is wanting is
> already the WAN compatible PHY.
Can you shed any light on this?
> I think that the preferences that came out of the survey that Jonathan
> indicates that the majority of the group would prefer the WAN compatible PHY
> because it will support both the LAN and WAN implimentations at only ~5%
> overhead cost. From what I have been able to determine, the actual
> implementation costs seem to be about the same. The second alternative is
> seperate LAN only and WAN compatible PHYs.
What survey are you referring to? The only survey I know of:
http://grouper.ieee.org/groups/802/3/ae/public/mar00/brown_1_0300.pdf, shows a
WAN PHY in dead last place and a UniPHY in first place.
The second alternative is again a UniPHY with a 10% penalty.
The third alternative endorses separate LAN only and WAN compatible PHYs.
> Thank you,
> Roy Bynum
> > Roy,
> > I believe that you have overhead sources twisted a bit.
> > All proposals for the LAN PHY support a MAC data transfer rate of 10 Gbps.
> > are you referring to when you say ~10% slower? The only thing that's
> > limiting the MAC's accepted 10 Gbps data rate is legacy SONET OC-192c
> > and it's inherent overhead.
> > Best Regards,
> > Rich
> > --
> > Roy Bynum wrote:
> > >
> > > Andreas,
> > >
> > > The real question is, do we need a LAN PHY that is ~10% slower than the
> > > 10.000 Gigbit transfer rate that was so important in June, July,
> > > September, and November of 1999? Did all of that support for 10.000
> > > Gigabit suddenly disappear? It makes me very suspicious. The
> > > additional ~3% loss to the WAN compatable PHY is a seperate issue.
> > >
> > > Thank you,
> > > Roy Bynum
> > >
> > > --
> > > >
> > > > Roy,
> > > >
> > > > the question is do we need to create two separate PHY standards
> > > > because of a 3% difference in transmission efficiency.
> > > >
> > > > If you look at the results of the Albuquerque straw poll,
> > > > the majority of 802.3ae appears to answer this question with "no".
> > > >
> > > > Andy
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