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[802.3ae] Re: Clarification of the 10GBASE-W ELTE function

On Thu, 17 Jan 2002, Roy Bynum wrote:
> There is a single point of failure that prevents a WIS as defined
> by IEEE from ever being an interface on SONET ADM.  The client
> interface on a SONET ADM requires clock synchronization either
> through "loop timing" or "PRS".  Neither of these are available in
> the WIS.  This lack of synchronization to a transmission network
> prevents the ADM from being able to multiplex the WIS signal into
> a SONET signal.

That conclusion is false.  It is is possible to multiplex the WIS
SPE into a higher-order SONET signal because the WIS transmit clock
is required to meet the SONET minimum clock frequency accurracy of
+/- 20 ppm.  That is good enough to ensure that pointer justifications
can absorb the timing differences between the WIS clock and the
stratum clock used by a SONET ADM.  It is not necessary that the WIS
be loop timed or synchronized to a stratum clock in order to do that.
All this is spelled out in Section 2.4 of the T1X1.5 contribution.

> As defined, the WIS can never be a client of a SONET or SDH system.
> It can be a "peer" on an optical network only.  The T1X1.5 proposal
> provides for a "peering" between a WIS and a SONET managed optical
> network.  It does not provide for the WIS to be an interface on a
> SONET system.

I don't think that the authors of T1X1.5/2002-027 would necessarily
agree, since that contribution explicitly states that "[ ... ] the
ELTE function is intended to be realized within a SONET/SDH NE
(potentially on a line card)."


Mike Heard