Codec support

Hi All,

I am trying to increase the no of simultaneous outbound call with the Asterisk version 1.2.13.
Asterisk is been connected to 1Mbps line. Please guide me whether 1 mbps line would be enough to handle 30 simultaneous calls or do i need to use any compression algorithm for me to achieve 30 simultaneous calls. If so which codec would suit best?

Eagerly waiting for your reply