Subject: [Megaco] H248 Subtract

From: Sankar Raman <[email-masked]>
Date: Thu, 04 Oct 2001 14:54:50 -0400

On a Subtract, the MG is supposed to return 
statistics associated with the termination.
Let's say that there was a problem in ONLY retreiving valid statistics,
and if we go by the command rules, this failure will cause
the subtract command to fail, leaving the termination and
context  and their associated resources.still in the MG.

The MGC would have no way to clear that termination and context as
any subsequent subtract will result in the same error. Also, the there is no
specific way of indicating to the MGC that it was statistcis collection that
resulted in error. This results in stuck resources at MG.

What is the recommendation for this scenario ? Can the MG clean up
its termination and contect even though it reported subtract command
failed ? Or Indicate subtract completed without statistics ??

Thanks

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From: "Raju" <[email-masked]>
Date: Thu, 4 Oct 2001 15:34:43 -0400

Sankar,

Scenario 1 : Going by Command rules
MG will return failure and MGC should resend Subtract with no 'Audit {
Statistics }'. Subtract with
no descriptors should succede!

Scenario 2:
I fell Subtract is like memory free() function call, which should never fail
to free memory.
In this case MG should subtract and return null or invalid Statistics (some
special values like -1).

I favor Scenario 2 as Scenario 1 involves in resending the Subtract but with
no real benefits (i.e no Statistics
can be retrieved anyway).

Hope this helps
Raju

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From: Terry L Anderson <[email-masked]>
Date: Thu, 04 Oct 2001 17:14:05 -0400

> failed ? Or Indicate subtract completed without statistics ??

I believe that the MG should return
    532 Name: Audited Property, Statistic, Event or Signal does not exist
Then the MGC should repeat the Subtract with an empty Statistic descriptor to
avoid requesting even the default statistics.  This would them succeed and clean
up the context.

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From: Terry L Anderson <[email-masked]>
Date: Thu, 04 Oct 2001 17:34:00 -0400

> no descriptors should succede!

Subtract with no descriptors will still attempt to return statistics due to the
statement in 7.2.3 "By default, the Statistics parameter is returned to report
..." (even though the example in Appendix A includes an Audit{Statistics}).
So to suppress the default on must send an empty Audit descriptor Audit{}.

> can be retrieved anyway).

That would be more efficient, but this would make Subtract deviate from the
general rule in 8.0: "If a command fails, the MG shall as far as possible
restore the state that existed prior to the attempted execution of the command
before continuing with command processing."  Clearly MG is supposed to try to
avoid side-effects of failed commands.  Performing the move to NULL is a big
side-effect.  I think its a mistake to start making different commands follow
different rules on errors.  Just how much of a failure in a Subtract should have
the subtract continue and what errors should allow completion??  Presumably this
and similar errors should be very rare and so the extra Subtract is not a big
impact.

--

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From: "Chuong N. Nguyen" <[email-masked]>
Date: Thu, 04 Oct 2001 17:02:46 -0500

If we are voting, I am for an error descriptor in place of  the statistics
descriptor.
A clearly defined Error Code in AnnexL and the expected behavior.

Also statistics is optional to start w/.
It depends on what packages the termination support.
You might ask for it but if termination does not support it, I thought it was
understood that it would return nothing.

No point in sending another subtract.
Think of the customer when do you stop charging on the subtract or after the 100
retries.

Chuong

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