Eric Dean <edean@gip.net> writes:
Our goal was to give better international Web performance to customers while also making the most intelligent use of the international resources by removing redundant information. Interestingly enough, we also have seen a reduction of 20% TCP retransmissions to less than 2% on the core.
This point is very, very important in most international ISP situations. The problem comes, in our experience, from customers with routinely saturated lines. The effect of "thousands of nibbling mice" (to paraphrase Sean Doran), meaning lots and lots of concurrent sessions from dialup or slow LAN users, means that normal TCP backoff doesn't work well. We can add CAR on the interface to maximize utilization, and save our router buffers, but the drops and retransmissions are still there. As expected, packets are lost at our border router facing such customers. However, for the data coming in from an international source (on an unsaturated international link), the retransmissions cause double traffic on the international line. Adding the cache effectively displaces the source of retransmissions from the (overseas) origin web server to the (local) cache server. We see traffic reductions due to both the caching effect, which can be significant, and due to the displacement in retransmissions. The customer still sees the same level of packet loss, since his line is still overloaded, but that traffic is served from the local cache and thus does not need to come over the expensive international link. -jem See http://www.data.com/issue/981107/crisis.html to learn more about Dacom BORANet