The MPLS WG Archive

["Bernstein, Greg" <GregB@ciena.com>]

We started out with the simple term "arbitrary concatenation" a while back
to mean arbitrary in size and in timeslots used.  I'm not sure what was
meant when we added the "contiguous" to this.  Was it:
(1)	Treat this as one big signal within a single SONET Line (SDH MS),
with potentially arbitrary timeslots used.
(2)	Treat this as one big signal within a single SONET line (SDH MS),
with the timeslot numbering lying within a single range, i.e.,  X through Y,
with X < Y.

If (1) then we need a list of time slots. If (2) then only the beginning
time slot is needed.  The problem with (2) is that it is a pretty useless
feature, i.e., doesn't prevent the need for re-grooming and seemed like a
mistake from the rather long gestation period for this specification rather
than something truly intended.

Greg B.
	Dr. Greg M. Bernstein, Senior Scientist, Ciena 
	New phone: (510) 573-2237


		-----Original Message-----
		From:	Mannie, Eric [mailto:Eric.Mannie@ebone.com]
		Sent:	Wednesday, May 16, 2001 12:44 PM
		To:	Bernstein, Greg; ccamp@ops.ietf.org; mpls@UU.NET
		Subject:	RE: Small issue on
draft-ietf-ccamp-gmpls-sdh-00.txt

		Dear All,

		Sorry I was confused, the original text of the draft is
correct:

		With any kind of ***contiguous*** concatenation there is one
big signal, so
		one and only one label (pointer) is needed (otherwise it is
not a contiguous
		concatenation). With any kind of virtual concatenation,
there are several
		VC's, so one label (pointer) per VC is needed. Even if all
the VC's
		virtually concatenated are contiguous (by coincidence) we
still need to
		identify each of them.

		Arbitrary and standard concatenations are orthogonal with
contiguous and
		virtual concatenations.

		Arbitrary means anything that is not standard.

		We use a code to differentiate between standard and
arbitrary contiguous
		concatenation to avoid that a downstream node returns a
timeslot at a
		position not supported by the upstream node. The upstream
node indicates the
		number and types of signals to be concatenated and the
downstream node
		cannot change it (it can just accept or refuse).

		We don't need a code to differentiate between standard
versus arbitrary
		virtual concatenation because there is no restriction anyway
on the timeslot
		positions that can return the downstream node. Again, the
upstream node
		indicates the number and types of signals to be concatenated
and the
		downstream node cannot change that (it can just accept or
refuse). SDH 1996
		restricts the virtual concatenation to some well defined
signals, while SDH
		2000 allows everything that make sense. But for the previous
reasons we
		don't need to differentiate between the two (thing about the
reason why you
		put a signaling element in a signaling message).

		Agreed ?

		Kind regards,

		Eric

		-----Original Message-----
		From: Bernstein, Greg [mailto:GregB@ciena.com]
		Sent: Wednesday, May 16, 2001 5:33 PM
		To: ccamp@ops.ietf.org; mpls@UU.NET
		Subject: Small issue on draft-ietf-ccamp-gmpls-sdh-00.txt


		Hi in the draft draft-ietf-ccamp-gmpls-sdh-00.txt it says:

		   In case of any type of contiguous concatenation (e.g.
standard or
		   arbitrary concatenation), only one label appears in the
Label
		   field. That label is the lowest signal of the
contiguously
		   concatenated signal. By lowest signal we mean the one
having the
		   lowest label when compared as integer values, i.e. the
first
		   component signal of the concatenated signal encountered
when
		   descending the tree.

		   In case of virtual concatenation, the explicit ordered
list of all
		   labels in the concatenation is given. Each label
indicates a
		   component of the virtually concatenated signal.

		This does not reflect the intent of arbitrary concatenation-
arbitrary, size
		and placement of timeslots.  Otherwise the main benefit of
arbitrary
		concatenation, preventing re-grooming is lost.  Corrected
text could read:

		    In the case of standard contiguous, only one label
appears in the Label
		   field. That label is the lowest signal of the standard
contiguously
		   concatenated signal. By lowest signal we mean the one
having the
		   lowest label when compared as integer values, i.e. the
first
		   component signal of the concatenated signal encountered
when
		   descending the tree.

		   In the cases of arbitrary or virtual concatenation, the
explicit ordered
		list of all
		   labels in the concatenation is given. Each label
indicates a
		   component of the arbitrary or virtually concatenated
signal.


		Greg B.
			Dr. Greg M. Bernstein, Senior Scientist, Ciena 
			New phone: (510) 573-2237