Subject: [Megaco] Echo control question

From: András Kérdô (IJ/ETH)<[email-masked]>
Date: Thu, 18 Jan 2007 16:40:24 +0100

Dear All,

Please, imagine the following indication in a command request (Add/Modify) in the LocalControlDescriptor:

tdmc/ec = { on , off }

This indicates that turning on an echo suppressor resource is supposed, but it is also acceptable not doing that (when e.g. such resources are exhausted in the MG). Whether the echo suppressor resource is successfully turned on or not, could be indicated in the command reply with a fully specified value ('tdmc/ec=on' , or 'tdmc/ec=off'). 

The indication is following the syntax of 'alternativeValue' element that is introduced in H.248.1 ABNF. The 'alternativeValue' is a kind of overspecification on property values, so the H.248 rule that is introduced in H.248.1 v2 §7.1.1 is applicable:

"... Overspecified parameters have a list of potential values. The list order specifies the command initiator's order of preference of selection. The command responder chooses one value from the offered list and returns that value to the command initiator. ..."

So, what is your opinion? This interpretation seems to be correct, doesn't?

Regards,
Andras Kerdo
Ericsson Hungary Ltd., R&D
H-1037 Budapest, Laborc u. 1.
Tel.: +36 1 437 7575

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