freeswitch/conf/vanilla/autoload_configs/opal.conf.xml

<configuration name="opal.conf" description="Opal Endpoints">
   <settings>
      <param name="trace-level" value="3"/>
      <param name="context" value="default"/>
      <param name="dialplan" value="XML"/>
      <param name="dtmf-type" value="signal"/>                   <!-- string, signal, rfc2833, in-band -->
      <param name="jitter-size" value="40,100"/>                 <!-- Jitter buffer min/max size, milliseconds -->
      <!-- <param name="codec-prefs" value="PCMU,PCMA"/> -->     <!-- list, and preferecnce order, of codecs -->
      <!-- <param name="disable-transcoding" value="true"/> -->  <!-- do not transcode, use source channel codec only -->
      <param name="gk-address" value=""/>                        <!-- empty to disable, "*" to search LAN -->
      <param name="gk-identifer" value=""/>                      <!-- optional name of gk -->
      <param name="gk-interface" value="$${local_ip_v4}"/>       <!-- optional listener interface name -->
   </settings>
   <listeners>
      <listener name="default">
         <param name="h323-ip" value="$${local_ip_v4}"/>
         <param name="h323-port" value="1720"/>
      </listener>
   </listeners>
</configuration>