Optimising network transfers to and from Queen Mary University of London, a large WLCG tier-2 grid site

Optimising network performance is key to high bandwidth data transfers required for a Tier-2 site. We describe the techniques we have used to obtain good performance. Monitoring plays a key part, as does the elimination of bottlenecks and tuning TCP window sizes. Multiple parallel transfers allowed us to saturate a l Gbit/s link for 24 hours - whilst still achieving acceptable download speeds. Source based routing and multiple data transfer servers allowed us to use an otherwise unused "resilient" link.