Has anyone managed to restrict the number of concurrent calls on an openser box?

I'm using openser 1.1.1 and found on the web that this was needed.

I've included the dialog.so and avpops.so modules.

   if ( avp_check("$DLG_count", "gt/i:10") ) {
      sl_send_reply("403","no more calls accepted");
      exit;
   }

I'm not sure if I've configured the dialog.so module correctly, the documentation tells you what each function does, but not what the parameters mean (for example the documentation says dlg_flg default value is "none" and they give an example of it set to 4 - but what do these values mean?)

Has anyone got this working or does anyone know how I should be configuring the dialog.so module?

Thanks,

-Axel