Re:Did some digging (Score 3, Informative)

Interestingly, that's not supposed to happen. The original design of the internet (specifically, the congestion control mechanism) doesn't account for the massive buffers routers carry nowadays, and relies on packet overflows resulting in packets being dropped immediately, rather than after some enormous buffer fills up. Those buffers completely screw over latency during large transfers, a symptom of which is the ping lag you mention - because the buffer slows the response to overflow, the congestion control on the big transfer thinks there's no congestion, and speeds up. When the buffer fills, it doesn't drain properly because as soon as it starts to drain the large transfer fills it up again. Meanwhile, the ping has to wait while the entirety of the buffer is flushed ahead of it; that can be on the order of 30 seconds, an eternity on the network. This is the main place that the idea that BitTorrent oversaturates the network comes from - these buffers are the real cause, not BitTorrent. Even FTP with large enough files will cause the same problem; there just weren't enough people doing large transfers for it to be visible before BitTorrent. Look up 'bufferbloat' and visit http://gettys.wordpress.com/ for more info.