I have to do a bittorrent application project in Java, and it require to transport data by UDP protocol, not TCP. In this project, the teacher asks me to assure the reliability in UDP protocol. So I have searched some solutions on the internet and found that in java, there are classes such as "ReliableSocket" and "ReliableServerSocket". So I'd like know that these classes can satisfy my project's requirement. And what are the differences between these two classes ?
Thanks a lot for your help
UDP is a a lossy unreliable protocol which runs on top of the IP protocol. Unlike TCP (which handles all aspects of reliable communication) it is up to the application layer to handle dropped packets and other aspects of a "reliable" transport protocol. As such it is likely that any implementation which requires reliability to similar extent as that given by TCP will occur additional overhead.
You could set aside two ports
port Aandport B. Each port is unidirectional unless there is a dropped packet.client 1 = port A = server 2server 1 = port B = client 2This keeps things simple. Server simply sends data and listens periodically but only receives messages if it's client drops a signal.
The client is the negation. It receives signals and only sends if it is missing a packet. An alternative implementation would be one in which the client/server pair could talk to each other, making the port truly unidirectional.
We get message reliability on both ports by using two packet index.
client index 1 = server index 2server index 1 = client index 2The index for each are single byte and incremented by the clients when they send a new message. Message delivery is assumed until reception of a special message which would be a UDP message for dropped packet. It would contane the signal for dropped message probably in it's most significant or least significant bit/byte depending on the endianness of the design as well as the index of the message. A queue also seems to be necessary but I have not worked the details of that out yet.