Question

I am trying to send an image over UDP using JAVA. I have managed to implement the sender and receiver and it works for a small image (18KB in this case). When I try to send a larger image (2MB) the receiver seems to jam after sending a few hundred datagrams.

Here is the loop in my receiver which recieves each packet from the sender.

while(true) {
            packetCount++;
            System.out.println("PKT: " + packetCount);
            receievePacket = new DatagramPacket(recieveData, recieveData.length);

            try {
                receieveSocket.receive(receievePacket);
            } catch (IOException e) {
                System.out.println("Error receieving packet");
                e.printStackTrace();
            }

            bos.write(recieveData, 0, (int) DATAGRAM_MAX_SIZE);
            // Terminate loop if last packet received
            if (packetCount == packetNum) {
                break;
            }

        }

The code before this loop just receives the port number from the user, sets up the socket and recieves a single packet from the sender which specifies how many packets will be sent. This is stored in packetNum.

Can anyone think of a reason why it stalls when trying to send larger images?
Thanks

Answer 1

You mean “receiver seems to jam after receiving a few hundred datagrams,” not sending, right? If that’s the case, then you may possibly be the victim of the infamous UDP packet loss! 🙂 There are two options:

1. Slow down the transmission rate.
2. Implement reliable UDP.

The first one is easier to do and it should allow you to quickly determine if you’re experiencing packet loss. Run a few tests and see if you’re receiving the same number of bytes by varying the transmission rates (i.e. put a small sleep between sending out each packet). If you detect a difference in packet loss, then implement reliable UDP and request the re-transmission of out-of-sequence or missing packets.