You Can Too #539D

Frank Jerwin carment4y at CANADA.COM
Thu Jul 26 22:40:22 EDT 2001

G'Day Tom,

I do support multiple packages for the play, playcol, playrec
I don't know that we need to introduce a new USES concept for this.
We shall produce an H.248 Annex M.4 for this. It can contain any
headings we like. We can update the annex at any time we like. Also
remember that the syntax is a property value and we can support what
property values we like. ie. a subset of the total. We audit to find out
what values are supported. Packages may also extend the values defined
in other packages.

So what I propose is a structure:
H.248 Annex K
1. Summary
2. References
3. Definitions
4. Introduction
5. Syntax
5.1 Basic
5.2 Extended 1
5.3 Extended 2
6. Package 1  Value: See Syntax Basic 5.1
7. Package 2  Extends: 1  Value: See Syntax 5.1 + Syntax Extended 5.3

(ie. we audit to find out what values are supported). Perhaps we can
define a functional extension with a name. We can then introduce a
property "Syntax Extensions". This way the MGC can find out exactly
which extension it needs to support.

Does this help any?


Tom-PT Taylor wrote:
> I have an interesting situation with the Advanced Audio Server packages
> (H.248 Annex M.1), and I wanted to check out my proposed solution with the
> list.
> The "basic" package currently consists of three functions: play, play and
> collect digits, and play and collect a recording.  It also includes an
> extensive description of a syntax for specifying individual announcements,
> including variable elements.  This syntax appears to the Megaco/H.248
> grammar as a parameter VALUE in quotedString form.
> One "advanced" package defined in the current draft Annex doesn't change any
> of the functions, but extends the announcement-specifying syntax.  Using
> past practice as a guide, the package was modelled as an extension of the
> basic one.  However, note that the new functionality is actually hidden
> below the level that would normally distinguish an extension -- no new
> signals or events are added, and no new parameters are added.  (That last
> wouldn't be legal in any event.)
> However, this approach doesn't really work.  The first sign of trouble was
> when I thought to split up the play, play-and-collect, and play-and-record
> functions, both to clarify the functional definitions and because it would
> provide more flexibility for product implementation.  How would I introduce
> the "advanced" syntax for each function?  Do I need to define an "advanced"
> package for each, so that the two packages become six?
> It becomes worse now that more than one advanced syntax feature has been
> proposed.  I now need a package for the basic announcement syntax, one for
> that plus feature A, one for that plus feature B, and a fourth one for all
> three features together.  You get the idea: an exponential explosion,
> multiplied by the number of functions if we decide to split them.
> I have an answer to this, but I thought it might be a good idea to
> legitimize it.  It could even lead to a v2 formalization of the process if
> accepted (with no change in what goes out over the wire!).  My proposal is
> this:
> 1) We define the announcement specification syntax itself in a package of
> its own.  Note that this package will have none of the usual content -- no
> properties, signals, events, or statistics.
> 2) We define each additional feature of the announcement specification
> syntax in another package which is an extension of the basic syntax package.
> 3) Within the functional packages (play, play-and-collect, etc.) we say
> first that the package USES the syntax of the basic syntax package and
> secondly that if any extension of the basic syntax package is supported the
> functional package also USES that extension.  An implication is that if a
> device supports an advanced syntactical feature (e.g. sets) for one function
> it MUST support that feature for all of the functions it implements.
> Comments?  Is this a legitimate use of packaging?  Should we add the USES
> relationship to our section 12 package description requirements in v2?
> Please copy follow-ups to the Megaco list, now at megaco at
> Tom Taylor
> taylor at
> Ph. +1 613 736 0961 (ESN 396 1490)
> _______________________________________________
> Megaco mailing list
> Megaco at

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