Re: Local Fault/Remote Fault
Your specific example configuration is a PMD device which interfaces to
its PCS by an XSBI interface, which is a PMA. This configuration is very
similar to a 1000BASE-X PHY where the PMD interface to its 8B/10B PCS
through a TBI PMA (I realize that the TBI is optional, but I believe
that it is employed in 100% of all implementations). Note that the
signal-detect signal runs alongside the PMA (see 802.3 figure 36-10).
The XSBI is an optional interface. The XSBI may generate its own fault
conditions such as Loss_of_Lock. Both the Loss_of_Lock and
Loss_of_Signal conditions, if detectable, should be forwarded to the PCS
and also reported via MDIO. What's left up to the implementation is the
level of integration of the PCS, PMA and PMD. One example of a high
level of integration would have a XAUI interface to a Fiber Optic module
which contains the serial PCS, PMA and PMD. This physical instantiation
of a 10GBASE-R PHY could report LF and RF via XAUI primitives. Other
physical instantiations and levels of integration are possible.
Note that you are touching on one of the deficiencies of simple parallel
interfaces like the XSBI. That is, generally additional signals must be
added to provide additional functionality. This includes: clocking,
fault signaling, error control (e.g. parity), flow control, status, etc.
If the XSBI is used as component level interface, signal-detect would
have to be added as an additional signal, other-wise, it is not possible
to distinguish fault locations across the interface.
> The proposal we adopted in November said we would add a signal. Doing so is
> preferable to requiring adding multiple squelch circuits. Clauses 49, 50,
> and 53 all incorporated a primative for this signal. The direction we chose
> in November works and it isn't the time to be inventing except where needed
> to fix something broken. If pieces necessary to our November decision where
> left out of the draft, we need to add them.
> -----Original Message-----
> From: Stephen.Finch@xxxxxx [mailto:Stephen.Finch@xxxxxx]
> Sent: Tuesday, January 02, 2001 7:03 AM
> To: stds-802-3-hssg@xxxxxxxx
> Subject: RE: Local Fault/Remote Fault
> Okay, we need a signal. Or do we? A PMA/PMD device can attach to a PCS
> device using the XSBI bus. But I don't see a signal called loss of
> signal or loss of lock. So, either we add such a signal, admit that the
> XSBI isn't complete enough to do its job, OR use the bus in a way that
> "signals" these conditions by another means, such as sending all zeros
> or all ones.
> So, I went off and invented something new that works.
> The question is, do we want to add another signal to XSBI? I don't.
> One could add an implementation dependent signal, but then the purpose
> of the standardizing XSBI just bit the dust.
> I suggest we don't add a new signal. I suggest we state that if a
> PMA/PMD "can't say something nice", then "shouldn't say anything at
> all", and define the "all" as "all zeros".
> Steve Finch
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