[MEGACO] descriptors order and error descriptors

Hi Christian, Kevin,
 
I was looking for information on the order of descriptors in H.248
replies and found the email exchange below. Looking to the latest
H.248.1 version, it seems that nothing was added about this issue since
then. Is there any reason for that? Are there any plans to address this
in an Implementors Guide?
 
Best Regards
Bruno
 
 
 
 

________________________________



*	To: Kevin Boyle <kboyle at nortelnetworks.com
<mailto:[email protected]> > 
*	Subject: Re: [Megaco] descriptor order and error descriptors 
*	From: Christian Groves <christian.groves at ericsson.com
<mailto:[email protected]> > 
*	Date: Fri, 03 Dec 2004 11:31:00 +1100 
*	Cc: megaco at ietf.org <mailto:[email protected]> , Troy
Cauble <troy at bell-labs.com <mailto:[email protected]> > 
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________________________________

Hello Troy and Kevin,

I had always assumed that you would reply back in the same descriptor
order as what had been requested. I believe this is what we intended. As
has been pointed out the ErrorDescriptor concept doesn't work without
this assumption.

It seems this is another one of those "undocumented" working assumptions
in H.248. I guess we should add something explicitely to Section 7.1 and
fix the examples.


Regards, Christian

Kevin Boyle wrote:


	Wouldn't the command processing stop at the first error?

	I believe the intent is to enforce order, since that is how the
sender can
	align where errors occurred with the command.  Christian may be
able to
	provide more detail on the history of how this was intended to
work...

	Whatever we decide, we should document the fix into the
Implementors' Guides
	for V1 and V2, and fix the text in V3.

	Kevin 
	
	
	-----Original Message-----
	From: megaco-bounces at ietf.org [mailto:megaco-bounces
<mailto:megaco-bounces>  at ietf.org] On Behalf Of
	Troy Cauble
	Sent: Wednesday, December 01, 2004 12:46 PM
	To: megaco at ietf.org
	Subject: [Megaco] descriptor order and error descriptors

	
	Hi,

	I recently ran into the exchange below.
	I think it points out a weakness in the protocol w.r.t.
associating
	descriptor level errors with the appropriate descriptor.

	I could find nothing in the docs that say a response's
descriptors should be
	in the same order as the request's descriptors.

	I could find nothing in the docs that say the AuditValue's
response's
	descriptors should be in the same order as the request tokens.
In fact, the
	V2 doc has examples of AuditValue returning descriptors in an
order other
	than the request tokens.

	I didn't check to see if there are similar issues in the other
lists that an
	errorDescriptor can be used in.  It seems likely though.

	Forcing the order to be maintained and using that for context is
ugly, IMO.
	But it's probably the minimal change solution.
	The real problem is lack of info in the errorDescriptor.
	(Relying on the text of the error descriptor field would also be
a bad idea,
	IMO.)

	-troy

	
	

	
	MEGACO/1 [135.112.125.109]:55555
	    Transaction = 50007 {
	       Context = - {AuditValue = aaln/2 {
	          Audit{ Packages, Statistics , DigitMap, Signals,
Events, Media
	    }}}}

	MEGACO/1 [135.112.125.214]
	Reply = 50007 {
	   Context = - {
	     AuditValue = aaln/2 {
	       Media {
	         TerminationState {
	           Buffer = OFF},
	         Stream = 1 {
	           LocalControl {

	           }
	         }
	       },
	       Events = 2222 {
	         al/of
	       },
	       Error = 447 { "Descriptor not legal in this command" },
	       Error = 447 { "Descriptor not legal in this command" },
	       Packages {
	         g-1,
	         tonegen-1,
	         tonedet-1,
	         dg-1,
	         dd-1,
	         cg-1,
	         cd-1,
	         al-1,
	         ct-1,
	         rtp-1,
	         tdmc-1,
	         ftmd-1,
	         ctyp-1,
	         an-1,
	         bau-1,
	         aau-1,
	         xal-1

	       },
	       Error = 501 { "Not implemented" }
	     }
	   }
	}

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