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    <p>The differences have two sides, conceptually and practically. Many documentation regarding performance is from the '90s when CPU power was significantly faster than network speed and network adapters were quite basic.</p> <p>Consider, UDP can technically be faster due to less overheads but modern hardware is not fast enough to saturate even 1 GigE channels with smallest packet size. TCP is pretty much accelerated by any card from checksumming to segmentation through to full offload.</p> <p>Use UDP when you need multicast, i.e. distributing to say more than say a few recipients. Use UDP when TCP windowing and congestion control is not optimised, such as high latency, high bandwidth WAN links: see UDT and WAN accelerators for example.</p> <p>Find any performance documentation for 10 GigE NICs. The basic problem is that hardware is not fast enough to saturate the NIC, so many vendors provide total TCP/IP stack offload. Also consider file servers, such as NetApp et al, if software is used you may see tweaking the MTU to larger sizes to reduce the CPU overheads. This is popular with low end equipment such as SOHO NAS devices from ReadyNAS, Synology, etc. With high end equipment if you offload the entire stack then, if the hardware is capable, better latency can be achieved with normal Ethernet MTU sizes and Jumbograms become obsolete.</p> <p><code>iperf</code> is pretty much the one goto tool for network testing, but it will not always be the best on Windows platforms. You need to look at Microsoft's own tool NTttcp:</p> <p><a href="http://msdn.microsoft.com/en-us/windows/hardware/gg463264.aspx" rel="nofollow">http://msdn.microsoft.com/en-us/windows/hardware/gg463264.aspx</a></p> <p>Note these tools are more about testing the network and not application performance. Microsoft's tool goes to extremes with basically a large memory locked buffer queued up waiting for the NIC to send as fast as possible with no interactivity. The tool also includes a warm up session to make sure no mallocs are necessary during the test period. </p>
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    1. POUtility to benchmark udp and tcp performance for large data transfer
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    1. COthanks for reply Steve. There are some application level open source implementations such as UDT for large and reliable file transfers which rely on the same principle that udp is faster. I want to convince myself that UDP is X times faster than TCP in my network. If it is giving large performance benefit, then it is worth trying some reliable UDP implementations.
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    2. CO@atv I mentioned UDT in my answer, it is popular in WAN accelerators for high latency high bandwidth links.
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