Question about SONET Transparency

[David Wang <david.wang@metro-optix.com>]

[ post by non-subscriber ]

Dear Experts,

In draft document "GMPLS extension for SONET and SDH Control",  one of the
SONET/SDH parameter is the "Transparency" field. Two values has been defined
for this field. 

Flag 1 (bit 1): section/regenerator transparency, which means all overhead
bytes will be unchanged in the intermediate device.
Flag 1 (bit 2): Line/multiplex transparency, which means LOH/MSON cannot be
changed in the intermediate device.

By definition, in SONET network the SOH will be read and re-written at the
end of each section span and LOH will be read and re-written at the end of
each line span. Where this "transparency" come from? Is it for Digital
Wrapper? Can somebody give me some background information or point to me
some Bell Core or ITU-T document or some technical document I can find the
answer to this "Transparency" SONET/SDH.

Thanks very much
David