[Asterisk-Users] Codec negotiation

[Tamas J]

Hello!

I would like to know wether it is possible to have end-to-end codec
negotiation in iax2?
What I mean is...

In case the user dials a number available through PSTN, let's force to
use alaw (the client is in LAN) to overcome unneeded transcoding:
iaxphone->1st asterisk -> PSTN

In case the same user dials a number available throug a chain of IAX2
peers (e.g. 2 peers), try to negotiate the codec end-to-end to consume
less resources for transcoding on asterisk servers (of course, in that
case we don't want to use g711, but ilbc, speex or gsm).
iaxphone->1st asterisk->2nd asterisk->PSTN
Or maybe:
iaxphone->1st asterisk->2nd asterisk->iaxpohone

Is there a way to do that? If yes, how?

Thanks in advance,
        TamasJ