[asterisk-users] Different codecs for reading and writing

[Tim Panton]

On 1 Aug 2009, at 22:26, Alex Balashov wrote:

> Elliot Murdock wrote:
>
>> Thank you...do you know if IAX can do this?
>>
>> The reason for doing is this is to get over the adsl upload/download
>> discrepancy.  While G711 gives terrific quality, it is not always  
>> that
>> feasible for the upload direction, which has much more limited
>> bandwidth.  Accordingly, it would be possible to use G729 for upload,
>> but keep the higher quality codec, G711, for download.
>
> I do not know a great deal about IAX so I will defer to the experts  
> for
> the definitive word on whether it is possible from the point of view  
> of
> its formal protocol mechanics.
>
> However, poking around the various configuration options for IAX peers
> on voip-info.org and a few other places suggests that there is no  
> option
> to do that with IAX, either.  It's not really something 99.9% of VoIP
> users want to do.  :-)



I think you will find that it may work with Asterisk's IAX  
implementation.

The protocol expects the 2 ends to agree a single symmetrical codec
as part of the connection setup, but it doesn't define what actually  
happens
if the codec specified in the first (full frame) voice packet isn't  
what was agreed.

I have a vague memory that if the codec is one that is allowed,  
asterisk does
'the right thing' issues a warning and uses what it was given.

But, as Alex says, there is no clear way to define this in the config  
files.

You would probably do better to use Speex in both directions, but set  
the encoding quality
(in codec.conf )
parameters to be different at the 2 ends. The speex decoder should at  
the far end
should be fine with that.

see http://www.voip-info.org/wiki/view/Asterisk+config+codecs.conf

Tim.


Tim Panton - Web/VoIP consultant and implementor
www.westhawk.co.uk



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