How to voice codec work =?

[shezad]

Hi can someone take the time to explain how a voip adapter voice codec work with voxalot ?

Im trying to find a best solution for calls made in europe and asia. I use like betamax internetcalls to make calls out to landline and to ip i use sipbroker. Sometimes im getting the voice fine and sometimes not, i have to always change the voice codec. Sometimes they work fine with g729 and sometime with alaw and ulaw.

How can i get the best automatic voice system ?

In europe i know the best voice is to use alaw and it works fine, but the problem is when i want to use betamax internetcalls to call out to pakistan i think they use the voicecodec g729 to get the best voice quality to call there. Im not sure if anyone else know so please tell me.

How do my adapter and the voice codec at voxalot provider list know which one to use ? how do it pass to the next one ?

Im using linksys SPA1001 and grandstream 486 adapter.
regards shezad