String protocol = url.substring(0, ix);
String server = url.substring(ix + PSEP.length());
Sender sender = _senders.get(protocol);
if (sender == null) {
if (protocol.equals(UDP)) {
sender = new UdpSender();
addSender(UDP, sender);
}
else {
throw new IllegalArgumentException("Unsupported protocol: " + protocol);
}