I'm sending very large (64000 bytes) datagrams. I realize that the MTU is much smaller than 64000 bytes (a typical value is around 1500 bytes, from my reading), but I would suspect that one of two things would happen - either no datagrams would make it through (everything greater than 1500 bytes would get silently dropped or cause an error/exception to be thrown) or the 64000 byte datagrams would get chunked into about 43 1500 byte messages and transmitted transparently.
Over a long run (2000+ 64000 byte datagrams), about 1% (which seems abnormally high for even a LAN) of the datagrams get dropped. I might expect this over a network, where datagrams can arrive out of order, get dropped, filtered, and so on. However, I did not expect this when running on localhost.
What is causing the inability to send/receive data locally? I realize UDP is unreliable, but I didn't expect it to be so unreliable on localhost. I'm wondering if it's just a timing issue since both the sending and receiving components are on the same machine.
For completeness, I've included the code to send/receive datagrams.
Sending:
DatagramSocket socket = new DatagramSocket(senderPort);
int valueToSend = 0;
while (valueToSend < valuesToSend || valuesToSend == -1) {
byte[] intBytes = intToBytes(valueToSend);
byte[] buffer = new byte[bufferSize - 4];
//this makes sure that the data is put into an array of the size we want to send
byte[] bytesToSend = concatAll(intBytes, buffer);
System.out.println("Sending " + valueToSend + " as " + bytesToSend.length + " bytes");
DatagramPacket packet = new DatagramPacket(bytesToSend,
bufferSize, receiverAddress, receiverPort);
socket.send(packet);
Thread.sleep(delay);
valueToSend++;
}
Receiving:
DatagramSocket socket = new DatagramSocket(receiverPort);
while (true) {
DatagramPacket packet = new DatagramPacket(
new byte[bufferSize], bufferSize);
System.out.println("Waiting for datagram...");
socket.receive(packet);
int receivedValue = bytesToInt(packet.getData(), 0);
System.out.println("Received: " + receivedValue
+ ". Expected: " + expectedValue);
if (receivedValue == expectedValue) {
receivedDatagrams++;
totalDatagrams++;
}
else {
droppedDatagrams++;
totalDatagrams++;
}
expectedValue = receivedValue + 1;
System.out.println("Expected Datagrams: " + totalDatagrams);
System.out.println("Received Datagrams: " + receivedDatagrams);
System.out.println("Dropped Datagrams: " + droppedDatagrams);
System.out.println("Received: "
+ ((double) receivedDatagrams / totalDatagrams));
System.out.println("Dropped: "
+ ((double) droppedDatagrams / totalDatagrams));
System.out.println();
}
