[Asterisk-Dev] changing codec during call

[Race Vanderdecken]

Tricky,

First turn on silence suppression. As a student you should know that you
only need 1/3 of the channel at any time for voice conversations. But
sadly silence suppression does not work with Asterisk due to timing
issues.

You could have the code start another call in the background and then
move the old calls to the new conversation and then drop the old calls,
sort of like a conference bridge.

Other wise you could create the code to dynamically adjust the jitter
buffers.

Not an easy thing to do with the current architecture of asterisk.

Race "The Tyrant" Vanderdecken

-----Original Message-----
From: asterisk-dev-bounces at lists.digium.com
[mailto:asterisk-dev-bounces at lists.digium.com] On Behalf Of Jesse Kaijen
Sent: Friday, February 25, 2005 9:40 AM
To: asterisk-dev at lists.digium.com
Subject: [Asterisk-Dev] changing codec during call

Hello I'm a student and for my bachelor-assignment I'm looking into
VoIP.
I'm researching if the audio perceptive of the end-user will get higher
if
during a call a switch of codec is made.
I was wondering if it's possible to switch codec's during a call with
IAX.
Can someone help me on that?

This is the idea:
During a call with ulaw (64kb) the available bandwidth drops from 80kb
(sufficient) to 40kb for a longer period. The losses are great and the
call-quality is horrible. At that point changing codec to GSM for
instance
may result in a better quality. When the bandwidth is restored change
the
codec back. A monitor must listen after a jitterbuffer and then decide
to
change codec. 

Picture:
                        +----*asterisk*-----+
UA--->---->|---->up---->|--jitbuf---decoder-|--PSTN
UA---jitbuf|<---down<---|-----------encoder-|--PSTN
   ^                    +-------------------+
   |
 point where the monitor must listen

My question is (if possible) which command do I have to send during a
call
to switch codecs? And can the current iax-clients handle a codec change?

Greetings

Jesse Kaijen
jesse at kayen.nl


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