I am writing an application to measure UDP packet loss over...

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Question by lconklin
Submitted on 1/23/2004
Related FAQ: TCP/IP FAQ; Frequently Asked Questions (1999-09) Part 1 of 2
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I am writing an application to measure UDP packet loss over our IP network. What I am having a problem with is on the sending side of the equation. I am sending a UDP message every five seconds to 10 servers in different locations. When I run snoop on the sending side I occasionally see that the packet never leaves our server. I can tell this because snoop shows the last time between udp messages. So for most of my messages I see a time of either 4.99991 or 5.0014. But what I also see is a time of 10.0001 or 9.99987, some thing like that. I not getting any errors back on any of the socket calls. I know that when the message is placed on the IP stack socket calls won't return any errors messages since this is as far as they go on the OSI. We also see packets leave our server and never make it to the other servers which is acceptable since this is an actual udp packet loss. We have no congestion on our network so we are expecting a packet loss of .01 or lower. I have not been able to read anything that says why the sending udp packet message would not leave our server and be seen by snoop. One thing I did which seems to have helped this project I used setsockopt and increased the sending queue size to 65535. It has helped but has not solved the problem. Does anyone have any suggestions?

Answer by Yaniv
Submitted on 10/29/2006
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Notice that UDP packetloss on the sender side are a real cause for some packet loss. This of it this (simplified) way: if your application sends a UDP packet and it cannot be sent, it may be dropped (and lost). Setting the sending queue (for UDP) would not be very helpful. Suggestions: 1. Space out your packets. Rather than send out 10 packets to all servers every 5 seconds, send a packet every half-second. 2. Increase the thread priority of the sending thread 3. Try to ensure that the sending system is not overly busy - no excessive CPU usage, no competing packets being sent, no thrashing or unnecessary disk swapping Hope this helped, Yaniv - http://www.yanivpessach.com

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<< Back to: TCP/IP FAQ; Frequently Asked Questions (1999-09) Part 1 of 2

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Answer by anonymous
Submitted on 9/11/2006
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I encountered the same problem.

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