Subject: Re: [Megaco] Signals played on a TDM termination in H.248

From: "Stephen Mell" <[email-masked]>
Date: Mon, 12 Sep 2005 16:12:03 +0100

Hello List,

I was thinking about an earlier discussion concening subtraction of 
provisioned terminations.

The effect on event handling particularly seems significant.

H248.1 v2 states:

   "When a provisioned Termination is Subtracted from a Context, it 
property values shall revert to:

    * the default value, if specified for the property and not overridden 
by provisioning 

    * otherwise, the provisioned value."

this is then re-worded in H248.1 v3 to:

    "When a provisioned termination is Subtracted from a context, its 
descriptor values shall revert to: 

    * the default value, if specified for the descriptor and not 
overridden by provisioning;

    * otherwise, the provisioned value."

Surely that means that when I return a provisioned termination to the NULL 
context that I must enter a state (albeit briefly) where the MG is forced 
to discard and lose events. In effect an empty events descriptor must be 
applied (the default) and the bufferControl mode must bereturned to "Off". 
Even if the default EventBufferControl mode were "LockStep" rather than 
"Off" the MG would have to discard the first event after the subtract on 
that termination before entering event buffering, whilst I wait for a new 
events descriptor to arrive.

Even with a construct such as:

transaction = 1 { context = 1 { subtract = prov/1 }, 
                  context = - { modify = prov/1 { events = 1 { ... } } }

The window is still open a little, as I would expect normally to be able 
to process events occuring during the subtract on prov/1, as soon as the 
subtract is complete.

Steve 

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---

From: "Kevin Boyle" <[email-masked]>
Date: Mon, 12 Sep 2005 12:34:18 -0400

This assumes that the default or provisioned Events Descriptor is empty,
which may not necessarily be the case.
 
Given the command you have shown (a Subtract followed by a Modify in
NULL), the window for loss of event is remarkably small, unless there is
a processing problem on the MG.  Granted, because the window is
non-zero, there is a slight possibility that an event will be missed.
However, upon application of the new Events Descriptor, any events that
are not instantaneous in nature would be detected at that time and
reported (such as hook state transitions).
 
Kevin

________________________________

	From:  [email-masked] [mailto:[email-masked]]
On Behalf Of Stephen Mell
	Sent: Monday, September 12, 2005 11:12 AM
	To: [email-masked]
	Subject: Re: [Megaco] Signals played on a TDM termination in
H.248

	Hello List, 
	
	I was thinking about an earlier discussion concening subtraction
of provisioned terminations. 

	H248.1 v2 states: 
	
	   "When a provisioned Termination is Subtracted from a Context,
it property values shall revert to: 
	
	    * the default value, if specified for the property and not
overridden by provisioning 

	
	    "When a provisioned termination is Subtracted from a
context, its descriptor values shall revert to: 

	Surely that means that when I return a provisioned termination
to the NULL context that I must enter a state (albeit briefly) where the
MG is forced to discard and lose events. In effect an empty events
descriptor must be applied (the default) and the bufferControl mode must
bereturned to "Off". Even if the default EventBufferControl mode were
"LockStep" rather than "Off" the MG would have to discard the first
event after the subtract on that termination before entering event
buffering, whilst I wait for a new events descriptor to arrive. 

	transaction = 1 { context = 1 { subtract = prov/1 }, 
	                  context = - { modify = prov/1 { events = 1 {
... } } } 
	
	The window is still open a little, as I would expect normally to
be able to process events occuring during the subtract on prov/1, as
soon as the subtract is complete. 

	Steve

---

From: "Stephen Mell" <[email-masked]>
Date: Mon, 12 Sep 2005 19:55:55 +0100

Would it be fair to say then that any descriptor or property that can be 
assigned to a provisioned termination of a certain type and is meaningful 
whilst that termination is in the NULL context could be allowed to have 

a provisoned value for use in place of the default value?

These provisioned values can then be applied (a) when the termination is 
initially brought into service (b) when the termination is returned to the 
NULL context. 

Thanks,

Steve 

"Kevin Boyle" <[email-masked]>
12/09/2005 17:34

        To:     "Stephen Mell" <[email-masked]>, <[email-masked]>
        cc: 
        Subject:        RE: [Megaco] Signals played on a TDM termination in H.248

Given the command you have shown (a Subtract followed by a Modify in 
NULL), the window for loss of event is remarkably small, unless there is a 
processing problem on the MG.  Granted, because the window is non-zero, 
there is a slight possibility that an event will be missed.   However, 
upon application of the new Events Descriptor, any events that are not 
instantaneous in nature would be detected at that time and reported (such 
as hook state transitions).
 
Kevin

From:  [email-masked] [mailto:[email-masked]] On Behalf Of Stephen Mell
Sent: Monday, September 12, 2005 11:12 AM
To: [email-masked]
Subject: Re: [Megaco] Signals played on a TDM termination in H.248

Hello List, 

H248.1 v2 states: 

   * the default value, if specified for the descriptor and not overridden 
by provisioning;

Steve

---

From: "Kevin Boyle" <[email-masked]>
Date: Mon, 12 Sep 2005 17:45:36 -0400

Yes, that is exactly correct.
 
Kevin

	From: Stephen Mell [mailto:[email-masked]] 
	Sent: Monday, September 12, 2005 2:56 PM
	To: Boyle, Kevin [NCRTP:3Z40:EXCH]; [email-masked]
	Subject: RE: [Megaco] Signals played on a TDM termination in
H.248

	Would it be fair to say then that any descriptor or property
that can be assigned to a provisioned termination of a certain type and
is meaningful whilst that termination is in the NULL context could be
allowed to have 

	These provisioned values can then be applied (a) when the
termination is initially brought into service (b) when the termination
is returned to the NULL context. 

	Thanks, 
	
	Steve 

12/09/2005 17:34 

        To:        "Stephen Mell" <[email-masked]>,
<[email-masked]> 
        cc:         
        Subject:        RE: [Megaco] Signals played on a TDM termination
in H.248

	This assumes that the default or provisioned Events Descriptor
is empty, which may not necessarily be the case. 
	  
	Given the command you have shown (a Subtract followed by a
Modify in NULL), the window for loss of event is remarkably small,
unless there is a processing problem on the MG.  Granted, because the
window is non-zero, there is a slight possibility that an event will be
missed.   However, upon application of the new Events Descriptor, any
events that are not instantaneous in nature would be detected at that
time and reported (such as hook state transitions). 
	  
	Kevin 

	Hello List, 

	
	H248.1 v2 states: 

	

	   "When a provisioned termination is Subtracted from a context,
its descriptor values shall revert to: 

	

	Steve

---

From: "Joe Stone \(joestone\)" <[email-masked]>
Date: Tue, 13 Sep 2005 08:06:25 -0700

> Surely that means that when I return a provisioned termination to the
> NULL context that I must enter a state (albeit briefly) where the MG
> is forced to discard and lose events. 

This is a distinct disadvantage of the Megaco/H.248 approach. Note that
with MGCP the Call Agent must explicitly stop RequestedEvents and
SignalRequests associated with an endpoint in deleting a connection.
This gives the Call Agent the *flexibility* of determining whether
RequestedEvents and SignalRequests are stopped.

Joe