Subject: [Megaco] Specifying values in AuditCapabilities responses

From: Nigel Williams <[email-masked]>
Date: Fri, 19 Jul 2002 14:47:00 +0100

Hello List,

When auditing capabilities it is possible that the MG supports multiple
values for a property or parameter.  The RFC says the following on this.

  7.2.6 AuditCapabilities

   [...] Descriptors may be repeated where there are multiple possible
values. 

If the AuditCapabilities reply only includes a single property or parameter
with a value then this is practical.  For example, it would be possible to
return one Media Descriptor with Echo Cancellation (from the TDM Circuit
Package) set to "On" and another with it set to "Off".  However, if there
are many possible values or many properties and parameters then there seem
to be two issues.

1. If the value type is a number then an unfeasibly large number of
descriptors would be required.

2. If there is more than one property or parameter that takes a value then
it would be necessary to enumerate the different combinations of the
supported values.  This could lead to an even larger number of descriptors
being required.

The obvious solution to this is to use ranges or lists of values.  However,
the RFC says the following on this.

   Values assigned to Properties may be simple values 
   (integer/string/enumeration) or may be underspecified, where more 
   than one value is supplied and the MG may make a choice: [...]

This does not mention AuditCapablities.  Does anyone have an opinion on
whether using lists and/or ranges for AuditCapabilities should be considered
valid?

Another possible solution would be to use the CHOOSE wildcard ("$") in cases
where all values are valid.  This could save sending a long list of
enumerated type values or a range such as [0:4294967295].  Does anyone have
any comments on whether this should be considered valid?

Thanks in advance
Nigel

Nigel Williams
Voice Networking Group
Data Connection Ltd
Tel: +44 20 8366 1177
Fax: +44 20 8363 1039
Email: [email-masked]
Web: http://www.dataconnection.com

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---

From: Nigel Williams <[email-masked]>
Date: Wed, 24 Jul 2002 12:05:01 +0100

Christian, List,

Thank you for the advice, this is very helpful.  I have a couple of
follow-up questions.

- Is "$" (CHOOSE) (or even "*" (ALL)) valid as a value in an
AuditCapabilities reply?  This would save sending [0:18446744073709551616]
for properties that are defined as being of type double.  A wildcard would
be even more useful in a case where a property takes a string value.

- I'm not sure what you mean by "7.2.6 is only relevant in the case that you
audit different descriptors in the one audit".  This seems to imply that
auditing multiple descriptors could/would make it necessary to repeat single
descriptors.  Am I interpreting this correctly?  It would be great if you
(or anyone else) could expand on this.

Thanks in advance
Nigel

Nigel Williams
Network Protocols Group
Data Connection Ltd
Tel: +44 20 8366 1177
Fax: +44 20 8363 1039

-----Original Message-----
From: Christian Groves [mailto:[email-masked]]
Sent: 22 July 2002 08:12
To: Nigel Williams
Cc: [email-masked]'
Subject: Re: [Megaco] Specifying values in AuditCapabilities responses

G'Day Nigel,

I don't recall any text forbidding you to use ranges in this respect, so
thus I
would consider this valid. The text you refer to in 7.2.6 is only relevant
in
the case that you audit different descriptors in the one audit.

Regards, Christian

---

From: Nigel Williams <[email-masked]>
Date: Fri, 26 Jul 2002 14:24:51 +0100

Christian, List,

Thank you for clarifying the use of wildcards in Audit responses.

I agree that there should only be one instance of each descriptor in an
AuditValue reply.  However, Section 7.2.6 _AuditCapabilities_ of RFC 3015
(and draft-ietf-megaco-3015corr-01.txt) refers to the AuditCapabilities
command.  Is it also the case that there should only be one instance of each
type of descriptor in AuditCapabilities replies?

If this is the case then it seems as though the sentence "Descriptors may be
repeated where there are multiple possible values." could be considered
misleading.  This is because a "repeated" descriptor could be taken to be
another instance of the same thing (for example, another Media descriptor).
This contrasts with the reply containing more than one descriptor of
different types, but only at most one of each.

As a (slightly contrived) concrete example, suppose that a gateway can only
handle a minimum flashhook duration of under 100ms if the maximum is under
1000ms.  In this case my reading of Section 7.2.6 indicates that the
following is valid.

MEGACO/1 [127.0.0.1]:55555
Reply = 1 { Context = - { AuditCapability = Term1 {
 Events {al/fl(mindur = [0:100], maxdur = [0:1000])},
 Events {al/fl(mindur = [101:2147483647], maxdur = [1001:2147483647])
}}}}

Any clarification that you (or anyone else) is able to provide would be
greatly appreciated.

Thanks in advance
Nigel

> Sent: 25 July 2002 01:49
> Hello Nigel,
> As Madhu has stated a wildcard return is not allowed. 
> 
> On the second point I meant that if you send an AuditValue 
> (localDescriptor,
> remoteDescriptor, LocalControl) then the response would have the
> localDescriptor, RemoteDescriptor and LocalControl 
> descriptor. Thus the reply
> would need multiple descriptors in answer to the auditvalue. 
> I believe that the
> text in 7.2.6 describes this situation not the case where you 
> use multiple
> instances of a single descriptor, which would be an error case.
> 
> Regards, Christian
> 
> Nigel Williams wrote:
> > 
> > Christian, List,
> > 
> > > Another possible solution would be to use the CHOOSE 
> wildcard ("$") in
> > cases
> > > enumerated type values or a range such as [0:4294967295]. 
>  Does anyone
> > have