Re: [802.3ae] Unclosed TR comments
"Rahn, Juergen (Juergen)" wrote:
> Hi,
> There are still some unclosed TR comments against 802.3 where technical
> discussion is required versus some procedural assessment in the response to
> this comment. One important comment against the Serial WAN Phy was the
> required clock tolerance rate at the receiver. In the arguments rejecting
> this was stated that this primarily concerns clause 51. This assessment is
> difficult to be followed, as a +/- 20ppm serial clock of the PHY will always
> lie within a +/- 100ppm XSBI requirement (where one can argue for, as this
> <snip>
This issue was documented as comment #661 from draft 3.0. At the May
interim in St. Louis, the joint session voted in favour of adopting 20ppm for
the transmitter only (90% in favour). The argument for changing the transmitter
only was that Ethernet has a history of being conservative in transmission but
liberal in what it will accept. With additional comments to the effect that
because we can't see an application for it now, doesn't mean it won't
exist in the future.
Juergen is correct. There is no way that the existing SONET infrastructure
can provide a clock with 100ppm tolerance. Furthermore, if two 10GBase-W devices
were interconnected, the max clock deviation would also be 20ppm.
Conceptually, it could be possible to generate a WIS compatible signal with greater
than 20ppm tolerance when dropping a 10GBase-W signal out of a higher order
tributary (such as OTN-3). One would have to design a system which deliberately
took advantage of the receive clock tolerance range of the 10GBase-W to save some
functionality. Arguably, this would appear as low frequency jitter. Changing the
Rx tolerance, closes this loop hole.
I'm not speaking in favour or against your point Juergen, I am merely providing
an alternative view for consideration.
--
Tim Warland P. Eng.
Applications Engineer
Quake Technologies (613)270-8113 ext 2311
Tough Times don't last, tough people do