[C4Grey]

Скорее всего, ответ можной найти здесь: http://blog.leeburrows.com/2011/10/p...network-part1/
Если конкретнее:

private function setupGroup():void
{
	//create a GroupSpecifier object
	var groupspec:GroupSpecifier = new GroupSpecifier("myGroup");
	//enable posting (to entire group)
	groupspec.postingEnabled = true;
	//allow data to be exchanged on IP multicast sockets
	groupspec.ipMulticastMemberUpdatesEnabled = true;
	//set the IP adress and port to use
	groupspec.addIPMulticastAddress("225.225.0.1:30000");
	//create NetGroup with our NetConnection using GroupSpecifier details
	group = new NetGroup(netConn, groupspec.groupspecWithAuthorizations());
	//listen for result of setup
	group.addEventListener(NetStatusEvent.NET_STATUS, netHandler);
}

И дальше слушаем события уже экземпляра GroupSpecifier:

...
case "NetGroup.Neighbor.Connect":
    var peer:Object = new Object();
    peer.id = event.info.peerID.toString();
    peer.label = truncateString(event.info.peerID);
    peerList.addItem(peer);
    break;
...