The managed service, which is claimed to be the first on the market to use Arbor's TMS (Threat Management System) technology, is billed as reducing response times to a DDoS attacks by up to two thirds.
What makes the BT service different (it says here) is that it create a unique profile of expected traffic for each client.
If the traffic levels rise for a BT-hosted Web site, then BT routes the traffic through a mitigation server that filters out attack traffic and allows genuine traffic to flow on to the Web site as normal.
Using a semi-automated approach to detecting DDoS attacks is claimed to allow BT to reduce its average response time to an attack from 30 minutes down to 10 minutes or less.
That isn't bad. I suspect the routing of traffic via an intermediary server when a DDoS attack has been detected will add a degree of latency to the connection, but that's a small price to pay for ensuring traffic can still flow to a site under DDoS attack...