Question

Since UDP is a connection less protocol so we know there is no guarantee that data will be received by a receiver. But if the datagram is received, is it possible that data is partly /fully corrupt ?

UDP header also contains CRC, so this makes me feel that in case datagram is received the data would be reliable ? Is that correct or not ?

To more elaborate the problem I send the data from Java udp server like

// Sending in Java
InetAddress group = InetAddress.getByName("230.0.0.1");
    //buf is a String.getBytes();
DatagramPacket packet = new DatagramPacket(buf, buf.length, group, 4446);
//socket is DatagramSocket in Java
socket.send(packet);

and get data in C# client like this

       // client  is UdpClient of C#
       Byte[] data = client.Receive(ref localEp);                        
       strData = Encoding.ASCII.GetString(data);

I am not manipulating CRC myself , at the receiver end I get the same data that was sent in buf, SO how do I check the CRC here, given I have an array of byte data.. ? or assume it would be correct (I can live with those extreme cases where CRC would match ie CRC and data are magically corrupt)

Answer 1

You can trust that the datagram is intact if its checksum (not technically a CRC) is correct, but that doesn’t mean you can trust the data. There’s nothing magic about the checksum formula, so a process that altered the data could merely recalculate the checksum and you’d never know.