Re: [AVT] Sound Level Indicators

[Randell Jesup <rjesup at wgate.com>]

David R Oran <oran at cisco.com> writes:
>On Jun 19, 2009, at 12:08 PM, Alan Clark wrote:
>
>>
>> A parallel problem is the control (rather than indication) of volume
>> and noise suppression in VoIP calls.  911 operators find that
>> sometimes they do want noise suppression and sometimes they don't.
>> Noise suppression can be helpful when they are trying to understand a
>> caller in a noisy background environment however it can also suppress
>> background noises that can help to understand the emergency situation
>> (e.g. if they hearing kids laughing in the background the call may be
>> a prank (which does happen quite frequently) but other sounds may
>> indicate how serious a problem is or provide location information).
>>
>I would think the right mechanism for this would be CCM (Codec Control
>messages), not header extensions.

CCM seems more correct; header extensions aren't really designed/meant
for a control backchannel -- CCM is.  

The downside is that CCM requires AVPF, which because of how
capabilities work in SDP is a real pain.  Header extensions are easier
to just send and if the other side doesn't understand them, oh well.
Putting AVPF in a negotiation will 'break' attempts to talk to most SIP
equipment in the field.  (Some simply ignore the profile...)  Cap-neg
may make it possible to negotiate the profile, but again most things
don't support that, and needing it in order to use AVPF/CCM adds a
significant amount of additional complexity (plus I don't know if
cap-neg is near finalization).

So, it's a pain.  CCM is "right", but would require either major
compatibility pain OR would require implementing cap-neg, which is a
major pain.

-- 
Randell Jesup, Worldgate (developers of the Ojo videophone), ex-Amiga OS team
rjesup at wgate.com
"The fetters imposed on liberty at home have ever been forged out of the weapons
provided for defence against real, pretended, or imaginary dangers from abroad."
		- James Madison, 4th US president (1751-1836)