Everyone with some basic knowledge on the TCP/IP protocol knows that TCP can cope with lost packets. The lost packet is retransmitted, the send-rate is throttled back a bit and on it goes. I just found this usenet-post by stanislav shalunov giving a formula to calculate just how much bandwidth remains after all that “throttling back”:

Standard TCP has throughput that’s limited by approximately MSS/(RTT*sqrt(loss)). Therefore, if your MSS is 1460B and RTT 70ms (typical for a cross-continent path), you need no more no more than 0.0003% packet loss to get 100Mb/s or 0.03% to get 10Mb/s. Note that, because of that square root, every doubling of required throughput means dividing permissible packet loss by four.