RE: XAUI and 64b/66b
I'm hoping that I can make a couple of statements here that might set people
straight and help them with their presentations:
1) P802.3ae will document a PCS Service Interface that will exist
between the PCS and the Reconciliation Sublayer (RS).
2) This PCS Service Interface is not XAUI, Hari, XGMII or anything else
electrical. It is a conceptual means by which data flows between the PCS
3) Given past experience, the XGMII will closely resemble the PCS
Service Interface and will be documented as an instantiation of the service
interface. Given that there is currently only one proposal for XGMII and no
apparent opposition, it would be fair to assume that this will be documented
as an instantiation for the service interface.
4) The XGXS and XAUI are currently proposed as an extension to the
XGMII. In fact, the XGXS is a proposed sublayer to permit the extension of
a physical instantiation (XGMII) of the PCS Service Interface. The XGXS
uses a PCS Service Interface on one side and an XGXS Service Interface on
5) Like with the PCS Service Interface, the XGXS Service Interface is a
conceptual means of passing data between two XGXSs.
6) A possible instantiation of the XGXS Service Interface is XAUI.
If you're doing a presentation, you have a few choices. You can document
your presentation based upon Service Interfaces (i.e. PCS Service Interface,
XGXS Service Interface, etc.), or you can document based upon an
instantiation (i.e. XGMII, XAUI, OIF, etc.). Considering that most people
will wish to document their proposals based upon implementations, and
therefore instantiations of service interfaces, the proposals should take
care in representing all the sublayers and service interfaces required.
For example, a PHY proposal that documents from the XAUI down to the MDI
should cover the XGXS service interface, the XGXS, the PCS Service
Interface, the PCS, the PMA Service Interface, the PMA, the PMD Service
Interface and the PMD. A PMD proposal should at least cover the PMD Service
Interface and the PMD. I would highly recommend that proposals reference
previous work (don't re-invent XAUI if you just plan to say that you're
going to use it), or call out whether the sublayer and its service interface
are required (a WDM PMD may not require a PMA or PMA Service Interface).
As we move to creating Draft 1.0, proposals that are not complete will come
under tighter scrutiny.