IAX2 limit number of calls

Hello, I have two servers with asterisk each one, they are conected with IAX2 in a limited bandwith link. I need to limit only 4 calls between the two PBXs, how can I do it?

Thank you

you can set incominglimit and outgoinglimit in iax.conf

But its parameters are not for iax2!!! Or yes?

http://voip-info.linuxsys.com/wiki/view/Asterisk+config+iax.html

andres