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You're on the right track. The 63 fixed stuff columns are used in conjunction with
the single POH column for interworking with 'virtual concatenation' in SDH. The
-64c signal ('contiguously concatenated') is split up into 64x STM-1s. The original
POH column maps to STM-1#1, with the other 63 fixed stuff columns becoming
the POH columns for STM-1#2 thru 64. Special OH is inserted so the STM-1s
can be consolidated at the rx end back into a contiguously concatenated VC-4-64c.
The reason for this deviousness is that many transport vendors did not support
handling of concatenated payloads with their first (perhaps later versions too)
releases of SDH equipment (i.e. concatenation flag interpretation by the pointer
processor wasn't built in). With the emergence of POS ports, the way around this
was to split up a concatenated signal into its lowest common denominator.
Note that Nortel equipment has always supported contiguously concatenated
From: Louis Lin [mailto:louislin@xxxxxxxx]
Sent: Wednesday, October 25, 2000 8:29 PM
Subject: Question on WIS(clause50).
At page 183, Figure 50-4 : Structure of SPE
My question is : There are 63 columns of fixed stuff in the SPE and
I don't know what's the purpose of that. My guess it's for compatibility
with SDH VC-4-64c. I am not familier with SDH, but does VC-4-64c
need 64 POH columns?