Re: Please Help!!! - CAsyncSocket::OnReceive Not Working for Microsoft UDP Application (msocudp)

"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp>
Thu, 15 May 2008 20:57:47 -0400
"Roshan" <> wrote in message

To Any Whom Can Answer,

Hello. I am using Microsoft's Visual C++ 6.0 UDP application
to retrieve packets from a device that is connected to our network.
The problem is the UDP application will not receive all the packets
from the device.

I even used Ethereal (packet sniffer) program to ensure the packets
arrive at my computer and they definitely do!

So I'm stumped as to why the OnReceive() callback function in the UDP
socket code doesn't get invoked for all the packets that arrive. For
example, for 10 packets that may be sent by the device, the UDP
application would only receive 9 packets (i.e. OnReceive() only gets
called 9 times instead of 10).

Please provide any help, if you know the answer.

The answer is that UDP is designed for speed, not reliability. It is
expected to lose some packets. (Yes, even if you see the packets with a
sniffer.) It is very difficult for an application program to keep up with
closely-spaced UDP packets. You can improve upon this somewhat by receiving
the packets in a high-priority thread that does very little else.

If you cannot afford to lose a few percent of the packets then you should
not use UDP.

Scott McPhillips [VC++ MVP]

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