link capacity and reservable

["Lai, Wai S (Waisum), ALABS" <wlai@att.com>]

This is in response to the discussion of maximum reservable
bandwidth in
http://ops.ietf.org/lists/te-wg/te-wg.2003/msg00264.html
http://ops.ietf.org/lists/te-wg/te-wg.2003/msg00265.html
As the issue is not restricted solely to MAM, and has impact on
RDM and in fact all BC models, I am talking about it in a more
general context.

Current TE extension in IGP deals with aggregate traffic.
There is thus a simple average-overall relationship:
max link bandwidth = max reservable bandwidth/overbooking.
As a result, whether "max link bandwidth" is supported or
commonly used or not is immaterial.

In DS-TE, there is per-CT bandwidth contstraint and per-CT
overbooking.  Max reservable bandwidth should accordingly be
treated as a vector quantity.  Reflecting this view, the
following definition for MAM in <tewg-diff-te-reqts> is
adequate:
  for each value of b in the range 0 <= b <= 7:
    Reserved (CTb) <= BCb
(with some clarification in MAM spec regarding overbooking)

Also, the following additional condition for MAM definition as
proposed in the second message quoted above is both unneccsary
and incorrect:
  SUM (Reserved (CTc)) <= Max Reservable Bandwidth
    for all "c" in the range 0 <= c <= (MaxCT-1)

This is like when I have 15 dollars and 10 euros in my pocket,
then my max reserve is 25 (of what unit).

The "max link bandwidth," being a normalized quantity, is more
meaningful.  For admission control under MAM, in addition to
the observing the bandwidth constraints as specified in the
above deinition, something like the following may be used:
  SUM (Reserved (CTc)/overbooking(CTc)) <= Max Link Bandwidth
    for all "c" in the range 0 <= c <= (MaxCT-1)
(with some tweaks to account for priorities)

Thanks, Wai Sum