Quote:
However, their router is dropping packets, and not telling anybody about it, which means that the retry (I think) traffic is saturating the link, and our application isn't getting a realistic measure of the available bandwidth, which means it's not backing off properly.

Correct me if I'm wrong, but this is exactly what an IP router is supposed to do when it's overloaded. Sending "your packet was dropped" notices would effectively double traffic exactly when the network was trying to reduce traffic.

The TCP implementation is supposed to take the dropped packet as the sign to back off. This would appear to be RFC2988.

Matthew