The MPLS WG Archive

["Amir Hermelin" <amir@cwnt.com>]

Kireeti,

A few comments regarding your proposal:

1) it seems there is a typo in your draft, section 7.3. The last two
lines in the section read:
       reserved[p] := reserved[p] + B'
       unreserved[q] := unreserved[q] - B' for q >= p
and they should read:
       reserved[p] := reserved[p] - B'
       unreserved[q] := unreserved[q] + B' for q >= p

2) The current approach supports configuration changes without "losing
the math". However, in your proposal, if the administrator changes the
subscription factor after some LSPs were set up at that priority, it
would mean that when one of these LSPs were removed you can't properly
calculate which B' to use in the math. If you were to correct this by
adjusting unreserved[p] and reserved[p] when the configuration of
subscr[p] takes place, you'd still have a problem of what to do in the
lower priorities (q > p), since their values could be a mixture of other
priorities as well.

3) With your proposal, it is possible to model the current approach with
over-subscription (with necessary modifications to TE extensions and
CSPF code). However, under-subscription can't be modeled (due to the
restriction in 7.1). What are the reasons for this decision?

4) It seems that this proposal (as well as others before it) doesn't
fully address considerations for (Diffserv) inter-class(type)
pre-emption. Since B' is computed using subscr[p], and is used at lower
priorities (q > p) for pre-emption, IMHO an explanation of how this is
sensible for pre-empting between classes should be accompanied.

5) Your "Current Approach" explanation is IMO the clearest and most
concise out there.


Regards,
	Amir.

--
Amir Hermelin                    <mailto:amir@cwnt.com>
Charlotte's Web Networks Inc.     <http://www.cwnt.com>