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WIS Loopbacks

With respect to the proposed loopback mode for the WIS, it
is currently defined that the WIS shall loop data received from
the PCS layer through the WIS transmitter back to the WIS
receiver to the PCS.  The question in today's WG was what
to send over to the PMD.

To clarify my suggestion, the PCS data received by the WIS would
by forwarded to the PMD using the (one and only) WIS transmitter
block.  However, some signalling would have to be imposed to
ensure the far end was aware of a local loopback condition (likely
the reason for the loopback and it is also probable that there would
not be a far end in this condition).  I suggested the WIS could
set an AIS condition in the SONET overhead which would
signal the far end to ignore the data in the SPE. It may however be
a requirement for the PCS layer or higher which called for the
loopback to signal the far end for this condition.

This is in contrast to the suggestion that the (one and only)
block be configured to send all ones or all zeros to the PMA for
it to figure out during a loopback condition.

In addition (to throw it on the reflector) as far as I know, there is
no test pattern available to test the WIS in osolation.  This nullifies
the requirement to develop a WIS test pattern.

Tim Warland
Nortel Networks.