Subject: [midcom] Re: draft-sct-midcom-megaco-01.txt

From: "Joel M. Halpern" <[email-masked]>
Date: Thu, 25 Apr 2002 14:06:36 -0400

As with some of the other analysis, this analysis treats partitioning as a 
solution to the multiple manager problem.  This does not meet the 
requirements as stated.  (It may be a compromise we are willing to accept, 
but should be described as partially met or not met, not claimed to be 
completely met.)
With apologies for appearing to be hammering on this particular author (as 
they are not the only ones to have made this leap), I will quote from their 
document:

  ô2.2.7.

    The Midcom protocol must not preclude multiple authorized agents
    from working on the same policy rule.ö

      In case the Megaco state machine on the Middle Box is decoupled
      from the Middle Box policy rule management, this requirement is
      met with local policies on the Middle Box.

  ô2.1.3.

    The Midcom protocol must allow a middlebox to communicate with more
    than one Midcom agent simultaneously.

    There may be multiple instances of a single application or multiple
    applications desiring service from a single middlebox, and differ-
    ent agents may represent them.  The protocol design must not pre-
    clude the ability to do so.ö

      Megaco has the concept of Virtual Media Gateways (VMG) within a
      single physical MG that allows multiple MGCs communicate
      simultaneously with the same MG, sharing resources in a conflict-
      free manner.

  3. Virtual Media Gateways: A physical MG can be partitioned into
    multiple virtual MG's allowing multiple Controllers to interact with
    disjoint sets of Contexts/Terminations within a single physical
    device.

So we see on the one hand that working with multiple agents is a local 
matter, and on the other that it is to be dealt with by VMGs.  However, if 
it were actually practical to deal with it purely as a local matter, we 
would not have included it as a protocol requirement.  And the description 
of the VMG requires complete partition of scope, while it is clear to me at 
least that the intent of the requirement is to allow overlapping scopes.

Yours,
Joel M. Halpern

PS: There is a reasonable claim that the determinism requirement and the 
overlapping control requirement can not both be met as written.  If that is 
your view, then describe the protocol as partially meeting each requirement 
and we as a working group may decide to accept such.  Noone is being asked 
to claim to do the impossible.  Accurate descriptions are much more helpful.

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