The biggest problem with UDP is NAT, since UDP is connectionless. Still, it is extensively used in all sorts of applications. The reason it's not used to much

The biggest problem with UDP is NAT, since UDP is connectionless. Still, it is extensively used in all sorts of applications. The reason it's not used to much in file transfer is because you basically need to re-implement everything you get for free with TCP for reliable transfer. Secondly, one of the big things that made TCP slow for large file transfer was that the way most TCP congestion control algorithms worked meant that transfer rates would drop quickly as latency increased. Google have come up with an algorithm that drastically improves this [1], and contributed it to the Linux kernel. I expect their strategy will be adopted by most operating systems. I believe Google is already using it, and I read something on Netflix's tech blog that they are at least trialing it. For small files, TCP slow-start is an issue but protocols like HTTP/2 can work around this by multiplexing multiple downloads through one connection. So I don't think there will be much advantage to UDP based file transfer for things that you want reliability for. 1. http://queue.acm.org/detail.cfm?id=3022184 http://queue.acm.org/detail.cfm?id=3022184