Re: Pointer processing issue
The qustion about setting the pointer to 522 is the function of the
originating SONET/SDH Path terminating equipment.
PTE sets the pointer to some default value and never changes it. 522 is
a comforting choice that puts the payload envelope in alignment
with the Transport Frame, but that has no particular significance from
the bigger network-wide picture. At STS-192c, there is at
present no SONET or SDH equipment that can process the pointer, but when
there is, it will be necessary for the receiving end
to be able to deal with different incoming pointer values and also for
changes in the position of the pointer as encoded by pointer
justifications. The general purpose de-mapping of the 64:66 code will
need to be able to handle arriving pointer justifications.
In my opinion, we ought to make using the capacity those 63 Fixed Stuff
columns an Option that can be provisioned as required by the users
of the equipment and/or services. The only reason to squander those 63
columns is to support Virtual Concatenation which might or might
not be important to any specific application. Virtual Concatenation is
used by some carriers to transport big pipes as integer multiples of
the VC-4/(STS-3c SPE). It is the SONET/SDH equivalent of Inverse
Multiplexing where the big pipe payload is eqally divided among the
VC-4 components and sent across the network to be switched and processed
by VC-4/AU-4 crossconnects and the like. At the receiving
end, the constituent VC-4s will arrive with different delays and hence
different pointer values. Like BONDING for 64kb/s circuits, delay is
added to the different VC-4 parts to get them all into alignment so that
the big pipe service can be recreated.
The liklihood is very high that this Virtual Concatentaion service
delivery will be less important than point-to-point delivery over
wavelengths.
When Virtual Concatentation is used, then we must have the means to
generate those Fixed Stuff colums. But when the service is P-P over
a wavelength, there is no need whatsoever to support Fixed Stuff.
The WIS mapping makes no mention of the complex mechanism of handling 64
separate pointers to do Virtual Concatenation, so it looks
as if we are assuming that point to point delivery will be the norm. If
so, make the fixed stuff columns Required, but make turning off that
feature Optional. That will improve the overall value of the standards
we are defining.
--
Dr. Gary A. Nelson
Zynrgy Group Inc
20708 Deerpath Road
Barrington, IL 60010-3787
USA
+1.847.304.0000
+1.847.304.1929 fax
gnelson@xxxxxxxxxx