code: function(data, sessionId, sendMessageCallback){
      console.log('incomingCallAnswer: ', data.from, data.answer);
      if (data.answer === 'accepted') {
        var userId = data.from;
        var callId = data.callId;
        console.log('PARTICIPANT ', userId, ': trying to join call ', callId);
  
        callManager.getCall(callId, function (error, call) {
          console.log('getCall:', call);
          if (call) {
            call.join(userId, sendMessageCallback, sessionId, userRegistry);
          }
        });
      }
    }
docs: /*
  onInviteUsers: function(data, currentUserId, invitees){
  console.log('inviteUsers: ', data.userIds);
  
  var currentUserId = socket.client.user._id;
  console.log('inviteUsers: currentUserId=', currentUserId, ' socketId=', socket.id);
  var length = data.userIds.length;
  for (var i = 0; i < length; i++) {
  var userId = data.userIds[i];
  var socks = authenticatedSockets[userId];
  if (socks) {
  console.log('inviteUsers: send incomingCall message', socks[0].id);
  socks[0].emit('incomingCall', { from: currentUserId, callId: data.callId } );
  } else {
  console.log('ERROR user not connected: userId=', userId);
  }
  }
  });