Modern data centers host operations as varied as flight planning, drug discovery, and Internet search running on thousands of machines. These services are often limited by the speed of the underlying network to coordinate parallel data access. In current data centers, network I/O remains a primary bottleneck and a significant fraction of capital expenditure ($10B/year). Compounding the problem are operational issues caused by interference between services, down times due to failures, and violations of performance requirements. This project will develop a hardware/software architecture with the following capabilities: i) non-blocking bandwidth to hundreds of thousands of hosts; ii) ``slicing'' across services with minimum bandwidth guarantees; iii) detecting fine-grained performance violations; iv) tolerating a range of failure scenarios; v) supporting end host virtualization and migration. Our goal is to enable modular deployment and management of networking infrastructure to keep pace with the burgeoning computation and storage explosion in data centers. This work will result in a prototype fully functional virtualizable data center network fabric to support higher-level services. Broader impacts include: i) outreach to under-represented minorities through the UCSD COSMOS program; ii) a public release of the data center communication workloads, protocols, and algorithms we develop; iii) working with our industrial partners and advisory board to address key performance and reliability issues in a critical portion of the national computation infrastructure. A significant outcome will be students trained in data center networking and cloud computing.