title: SIP multicast conference with parallel calls and confirmation
body: <p>When conferencing with SIP you usually have two options:</p>
  
  <ul>
  <li><a href="http://www.voip-info.org/wiki/view/Asterisk+cmd+Page" rel="nofollow">paging</a> all targets (in parallel) and putting them in a conference 
  <ul>
  <li>Pros: you get answer confirmation</li>
  <li>Cons: you need a conference bridge software go receive media and unicast it to each destination, which leads to synchronization problems and higher load</li>
  </ul></li>
  <li>making all receivers dumbly listen to a <a href="http://www.voip-info.org/wiki/view/Asterisk+MulticastRTP+channels" rel="nofollow">multicast</a> address and port for RTP audio
  <ul>
  <li>Pros: media is synchronized on all receiver</li>
  <li>Cons: you don't know who's really listening</li>
  </ul></li>
  </ul>
  
  <p>Is there a way of having all the pros by parallel calling all targets and sending them the multicast address and port they need to listen to? We're currently using Asterisk, but I was looking at FreeSWITCH or Kamailio/OpenSIPs, with little luck.</p>