Subject: [Megaco] Events Descriptor with KeepActive set and an Emebdded Signals Descriptor

From: "Dal Chohan" <[email-masked]>
Date: Mon, 2 Feb 2004 12:10:34 -0000

H.248v2 clause 7.1.9 states that ; "A media gateway controller shall not send EventsDescriptors with an event both marked KeepActive and containing an embedded SignalsDescriptor"
I think that this is unnecessarily too restrictive and unduly reduces the flexibility of H.248. The judicious use of the KA flag within the Embedded Signal descriptor itself can keep the Signal currently being applied active.

The following scenario describes a practical situation where the above rule is violate. Take the case where "Automatic Metering" is applied to an analogue line and automatic meter pulses are being generated  by the MG. Now the MG is monitoring for "On-Hook" and the KA (KeepActive) flag is sent against the "On-Hook" event. Upon detection of  "On-Hook" the event is reported to the MGC by the MG and the automatic metering still continues. 

Now the MGC sends a command requesting that the MG monitor for "Off-Hook" with the KA flag set, plus an Embedded signals/event descriptor indicating that "dial tone" should be played. In addition the KA flag is set for the "enable metering" signal to ensure that the automatic metering continues when the dial tone signal is applied , and the digit map descriptor is also enabled. Now this sequence clearly violates the rule stated above.

I would therefore recommend that the sentence above is deleted from the specification unless someone can think off a good reason for keeping it, because it is unnecessarily too restrictive and reduces the flexibility of the H.248 protocol.

Regards.

Dal Chohan