Subject: [Megaco] Omitted property and parameter specification

From: Terry L Anderson <[email-masked]>
Date: Thu, 07 Feb 2002 16:50:59 -0500

More discussions from the ITU SG16 meeting in Geneva.

We are trying to clean up some of the more ambiguous aspects of
MEGACO/H.248 to make V2 clearer.  One aspect that seems to cause a lot
of discussion and confusion is the exact behavior when a property is
omitted from a Descriptor, either in an initial Add or in a subsequent
Modify.  Does the property take on a default value? revert to a default
value? or (as the current spec says) be "removed" (and if so what does
that mean).  We believe that we have come up with new wording that
removes the ambiguity and yet supports all of the current behavior of
existing packages.  We believe that in some cases properties should
return to a default value and in other cases packages intend for certain
processing associated with the propery be suspended or the function to
"be removed".  We believe that both behaviors should be supported and
that a package should specify the interpretation.  If not stated
otherwise an omitted property should reset to a default value, but any
package could define any other desired behavior such as, for example,
that a specified process or feature is deactivated.  With most current
packages the choice is commonly understood, but the text should be
modified to document the choice.  To accomplish this we propose changing
the modification in IG 6.51 to read:

In general, if a Descriptor is completely omitted from one of the
aforementioned Commands, the properties in that Descriptor retain their
prior values for the Termination(s) the Command acts on. On the other
hand, if some read/write properties are omitted from a Descriptor in a
Command – i.e., the Descriptor is only partially specified – those
properties will be reset to their default values for the Termination(s)
the Command acts on unless the package specifies other behavior. For
more details, see section 7.1 dealing with the individual Descriptors.

The change occurs after the second '-' which previous read:
– those properties will be removed/reset for the Termination(s) the
Command acts on. For more details, see section 7.1 dealing with the
individual Descriptors.

Then in section 12 defining how packages are specified we propose to
alter 12.1.2 by adding a description for "possible values" (previously
blank):

Possible Values:
A package MUST specify either a specific set of values or a description
of how values are determined.  A package MUST also specify a default
value or the default behavior when the value is omitted from its
descriptor.  For example, a package may specify that procedures related
to the property are suspended when it value is omitted.  A default value
(but not procedures) may be specified as provisionable.

and nearly identical description in 12.2 for parameters (replacing
"property" with "parameter").

--

------------------------------------------------------------
Terry L Anderson              mailto:[email-masked]
Tel:908.582.7013   Fax:908.582.6729
Lucent Technologies/INS/Voice Over IP Access Networks
Rm 2B-121, 600 Mountain Av, Murray Hill, NJ 07974
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