Re: Please help me with my lost UDP packets

From: Trevor (trevor_at_nospam.com)
Date: 04/02/04 

Date: Fri, 2 Apr 2004 10:11:42 -0500

"@ *SPAM* yahoo_com" <""jlindwall*NO*\"@ *SPAM* yahoo_com"> wrote in message
news:88CdnQbscvDvq_DdRVn-hQ@adelphia.com...
> I'm new to the Compact Framework and C# but have been programming for
> years, but not on small devices.
>
> I have written a program running on Dell Axim that receives UDP packets.
> that was converted from java using the tool provided by Microsoft. It
> creates a TextBox to display messages (like "packet received" etc) and a
> button. When the button is pressed the program listens for UDP packets
> on port 51800.
>
> On my desktop PC I then run a program that creates packets and sends
> them to the proper IP address/port. Early in my learning process I
> learned that I needed to disconnect the Axim from the cradle and use the
> wireless network for receiving network traffic. I *DO* receive some of
> the UDP packets, so my problem is not that I can't receive any data ---
> my problem is that delivery seems unreliable even by UDP standards.
>
> Out of 100 packets (each 10 bytes) sent (with a delay of 500 or 1000 ms
> between packets) my program receives 10-12 of them. I also tried 256
> byte packets and 1024 with similar disappointing results.
>
> Is this normal on these little devices? Am I expecting too much? I
> know that UDP is not guaranteed but this seems so bad that I can only
> assume my program is flawed.
>
> I can provide more code if needed. A UdpClient is used to receive the
> data. Here's the receive method if that helps.
>
> THANKS!
>
> public static void Receive(System.Net.Sockets.UdpClient tempClient,
> out PacketSupport packet)
> {
> System.Net.IPEndPoint remoteIpEndPoint =
> new System.Net.IPEndPoint(System.Net.IPAddress.Any, 0);
>
> PacketSupport tempPacket;
> try
> {
> byte[] data_in = tempClient.Receive(ref remoteIpEndPoint);
> tempPacket = new PacketSupport(data_in, data_in.Length);
> tempPacket.IPEndPoint = remoteIpEndPoint;
> }
> catch ( System.Exception e )
> {
> throw new System.Exception(e.Message);
> }
> packet = tempPacket;
> }

In general, if you are looking towards using UDP and packet loss is
unacceptable you have two solutions.

1) Build a "smarter" protocol on top of UDP which implements sequence
numbers, resends, acks, etc..
2) Switch to TCP which already has sequence numbers, resends, acks, etc...

Most people would choose #2 and be on their merry way. Plain old UDP is not
reliable. It really depends on the networks, routers, etc... I wouldn't
waste much time on this issue. It is the nature of the beast. The only
feasible situation for using plain old UDP is in a video game or something
like that where speed is more important than data integrity or where data
integrity is not important at all.